GB2467780A - Liquid Composite Materials - Google Patents

Abstract

A self-supporting construct or "liquid marble" comprises a body of liquid and a hydrophobic coating material entirely surrounding the liquid. At least one property of the coating material changes on application of an external stimulus to the construct. Preferably the coating material is a polymeric material including functional groups (Z) which change in response to the external stimulus applied to the construct, thereby changing a property of the coating material. An example of the external stimulus is a change in pH of the environment in which the construct is located.

Description

Liquid Composite Materials The present disclosure relates to so-called "liquid marbles", and in particular to liquid marbles which are responsive to an external stimulus. More especially the liquid marbles comprise a coating of a particulate sterically stabilised latex material. The present disclosure further relates to the preparation of the sterically stabilised latex materials typically by a process of emulsion or dispersion polymerisation, more especially by aqueous emulsion polymerisation or non-aqueous dispersion polymerisation.

BACKGROUND

Liquid marbles have been prepared primarily using inorganic materials such as hydrophobised (fluorinated) lycopodium powder or hydrophobically modified silica as the coating material. The term liquid marbles was coined by Pascale Ausillous and Davide Quéré in an article in Nature (2001, 411, 924) to refer to a new construct comprising a droplet of water coated in lycopodium powder. The lycopodium powder migrated to the surface of the water droplet, thereby preventing the water from interacting with any external surface. These liquid marbles can be made to roll around on a surface without "leaking" the water contained within and may be rested on the surface of a body of water. Thus the use of "marble" is an allusion to a small hard ball, usually of glass, used in children's games. The term "liquid marble" is now applied to similar coated liquid droplet constructs and is not restricted to water-lycopodium powder combinations. For example, liquid marbles comprising a modified silica coating have been described, as has the use of glycerol as the coated liquid. Gao and McCarthy in Langmuir 23 (21) 10445-10447 (2007) describe liquid marbles comprising an ionic liquid and a coating of chemically inert periluoroalkyl particles, such as of PTFE.

BRIEF SUMMARY OF THE DISCLOSURE

The present disclosure is concerned with liquid marble-type constructs (hereinafter "liquid marbles") which are responsive to an external stimulus. Examples of an external stimulus can include: changes in the environment in which the liquid marble is located, or exposure of the liquid marble to a new environment, such as by movement of the liquid marble from a first location having environmental conditions of a first type to a second location having environmental conditions of a second type.

In particularly preferred forms of the liquid marbles of the present disclosure, the external stimulus is a change in pH, that is, for example, changes in pH of an environment or substance in which the liquid marble is located, with which it is in contact or by which it is otherwise influenced by virtue of, for example, its proximity. In one embodiment, the external stimulus is a change in the pH of a liquid with which the external surface of the liquid marble is in contact.

The liquid marbles of the present disclosure comprise a liquid droplet (more especially an aqueous liquid droplet) having an external layer or coating of a coating material which is most preferably a polymeric material. The coating of the polymeric material may comprise multiple layers of the polymeric material. The coating surrounds the liquid droplet with no gaps or discontinuities, so that the liquid is wholly contained within the coating and no part of the liquid is directly exposed to the environment external to the liquid marble. The coating of polymeric material prevents the liquid from contacting any surfaces which the liquid marble encounters and renders the liquid marble perfectly non-wetting when located on, for example, a glass plate or the surface of liquid water.

The external layer or coating is generally not monolithic, typically being a granular or pulverulent (powdered or powdery) material. The polymeric material most preferably includes functional groups which are responsive to an external stimulus, in particular a chemical stimulus such as a change in pH. That is, the functional groups undergo a change in properties or chemical state, chemical composition or the like in response to such external stimulus, notably in response to changes in ambient pH. Thus, the liquid marbles of the present disclosure can be constructed to be stable in the absence of the external stimulus (such as at one given ambient pH) and to be, or to become, unstable (and therefore, for example, to disintegrate) when the stimulus is applied (such as by changing to another given ambient pH).

Transitioning of the liquid marble may be from a situation in which a stimulus is absent to a situation in which a stimulus is present or may involve physical transfer of the liquid marble from a first environment where the stimulus is absent to a second environment where the stimulus is present. For example, the first and second environments may be at different ambient pH. Alternatively transitioning of the liquid marble from the absence to the presence of a stimulus may involve a change in the environment in which the liquid marble is located, such as by changing the ambient pH of the environment.

The polymeric coating is thus configured such that the body of liquid within the marble is retained within the liquid marble in the absence of the external stimulus (e.g. at the first pH) and is released when the stimulus is applied (e.g. at the second pH). In one preferred form, the surface properties of the polymeric material are hydrophobic in the absence of the external stimulus, (hydrophobicity being a pre-requisite for the formation of stable water-containing liquid marbles) and become less hydrophobic, or become hydrophilic, when the stimulus is applied. Thus the degree of hydrophobicity is "tuneable" by varying the pH of the environment of the polymeric coating.

In one preferred form, the polymer includes basic groups and the degree of protonation of the basic groups increases (and hence the hydrophobicity decreases) as the polymer coating is transitioned from a first environment to a relatively more acidic second environment, for example from a basic environment to an acidic environment or from a substantially neutral environment to an acidic environment or from a more basic environment to a less basic environment. Thus in these examples the stimulus is a reduction in the ambient pH to an extent sufficient to render the liquid marble unstable, attributable to decreasing hydrophobicity of the coating material.

In another preferred form, the polymer includes acidic groups and the degree of protonation of the acidic groups decreases as the polymer is transitioned from a first environment to a relatively more basic second environment, for example from an acidic environment to a basic environment or from a substantially neutral environment to a basic environment or from a more acidic environment to a less acidic environment.

Thus in these examples the stimulus is an increase in the ambient pH to an extent sufficient to render the liquid marble unstable, due to the reduced hydrophobicity of the coating material.

In one embodiment, the liquid marbles of the present disclosure thus provide a means of targeted delivery of a liquid contained or encapsulated within the liquid marble. That is, at a first ambient pH the liquid marble is stable and self supporting and retains the liquid within the coating. When the liquid marble is delivered to a target location at which location the ambient pH is, or is changed to, a second pH at which second pH the liquid marble becomes unstable, the encapsulated liquid is released. In this context, the liquid may contain an active ingredient, such as a pharmaceutically active ingredient, or an ingredient used in cleaning or personal care products, and the liquid marble provides a means of delivering that active ingredient to a desired location.

The present disclosure is also concerned with the synthesis of coating materials suitable for preparing stimulus-responsive liquid marbles. More especially, the present disclosure is concerned with aqueous emulsion polymerisation techniques and with non-aqueous dispersion polymerisation techniques for preparing materials suitable for providing the coating of liquid marbles.

According to a first aspect of the present disclosure there is provided a self-supporting construct comprising a body of liquid and a hydrophobic coating material entirely surrounding the liquid, wherein at least one property of the coating material changes on application of an external stimulus to the construct.

In preferred embodiments, the coating material is a polymeric material including functional groups (Z) which change in response to the external stimulus applied to the construct, thereby changing a property of the coating material.

In further preferred embodiments the coating material includes units of the formula (1) (Q2)(MZ))( Q2)q (1) where p and q are integers, either p or q may be 0 and (p+q) is from about 10 to about 1000, preferably 20 to 100, more preferably 40 to 50; (Q2) and (Q2)q represent polymeric residues of the polymerisation of a monomer moiety Q2'; and M(Z) represents (i) a residue of a macromonomer including the functional groups (Z) which macromonomer is co-polymerised with Q2, or, (ii) a polymer including the functional groups (Z).

Preferably either p or q is 0.

A second aspect of the disclosure provides a self-supporting construct comprising a body of liquid and a coating material entirely surrounding the liquid, wherein the coating material includes units of the formula (1) (Q2)(M(Z))( Q2)q where p and q are integers, either p or q may be 0 and (p+q) is from about 10 to about 1000, preferably 20 to 100, more preferably 40 to 50; (Q2) and (Q2)q represent polymeric residues of the polymerisation of a monomer moiety Q2'; and M(Z) represents (iii) a residue of a macromonomer including functional groups (Z) which macromonomer is co-polymerised with Q2, or, (iv) a polymer including functional groups (Z) which functional groups (Z) change in response to an external stimulus applied to the construct, thereby changing a property of the coating material.

Preferably either p or q is 0.

In some preferred embodiments M(Z) represents a homopolymer. In these embodiments preferably the polymer is chemically grafted to one or more residues (Q2) or is physically adsorbed on the residues (Q2).

In other preferred embodiments preferably M(Z) comprises moieties selected from the group comprising moieties (a), (b), (c) and (d) Qia Q1C L:rd1 L:1d1 (a) (b) (C) (d) where moieties (c) and (d) are terminal groups and moieties (a) and (b) are constituents of the polymer backbone of M(Z); Q1 and Q1C represent a functional group by means of which M(Z), when a macromonomer, is polymerisable with Q2 and Q1 and Qic may be the same or different; A represents a residue of a moiety A' comprising or including a polymerisable functional group by means of which A_(Rd)1_Z is polymerised on formation of M(Z); Rda, Rdb, Rdc, and R may be the same or different and each independently represents a straight chain or branched, substituted or unsubstituted alkyl chain including from 1 to carbon atoms and wherein optionally the carbon chain is interrupted by one or more moieties selected from secondary or tertiary amine moieties, -0-, -S-, -CO-, -COO H, amide (-CONR"-), and ester (-000R"-) where R" represents H or alkyl; ra, rb, rc and rd is each independently 0 or 1, (preferably 1); and Za, Zb, Z, and Zd may be the same or different and each independently represents a functional group which is changed in response to the external stimulus applied to the construct.

In some preferred embodiments M(Z) is a homopolymer comprising groups (b) and (d).

In other preferred embodiments M(Z) is a macromonomer residue comprising at least one of groups (a) and (c).

In some preferred embodiments the external stimulus is a chemical stimulus.

In some preferred embodiments the external stimulus is a change in, or of, the environment in which the construct is located and in particularly preferred embodiments the change in the said environment is a chemical change. Preferably the change in the said environment is a change in environmental pH.

In preferred forms the construct is rendered unstable when the environmental pH is changed beyond a given threshold pH value.

In some preferred embodiments the coating material comprises a plurality of basic functional groups, at least some of which groups, or a greater proportion of which groups, become protonated when the environmental pH is changed from a relatively higher pH value to a relatively lower pH value.

Preferably at least some of the groups represented by Z become, or a greater proportion of the groups represented by Z become, protonated when the environmental pH is changed from a relatively higher pH value to a relatively lower pH value.

In some embodiments preferably the coating material comprises a plurality of acidic functional groups, at least some of which groups, or a greater proportion of which groups, become de-protonated when the environmental pH is changed from a relatively lower pH value to a relatively higher pH value.

Preferably at least some of the groups represented by Z become, or a greater proportion of the groups represented by Z become, de-protonated when the environmental pH is changed from a relatively lower pH value to a relatively higher pH value.

In some preferred embodiments the external stimulus is a physical stimulus.

The external stimulus may be a change in, or of, the environment in which the construct is located. The change in or of the said environment may preferably be a physical change.

In some preferred embodiments the external stimulus is a physical change in or of the environment in which the construct is located.

Preferably the external stimulus causes a change in at least one property of the coating material selected from the group comprising: solubility of the coating material in a fluid present in the environment in which the construct is located; degree or extent of solvation of the coating material, or of constituent functional groups thereof, by a fluid present in the environment in which the construct is located; hydrophobicity of the coating material, degree or extent of ionisation of constituent functional groups of the coating material; and degree or extent of protonation of constituent functional groups of the coating material.

In particularly preferred embodiments Z is a group of the formula

N

Re" Rb where Ra and R may be the same or different and are selected from H or Ci to 08 alkyl, preferably C, 02, 03 or 04 alkyl.

In other preferred embodiments Z includes an organic acid group, preferably carboxylic acid group, a phenol group or a sulphonic acid group.

In preferred embodiments Q1 and/or Q1' is, or includes, a vinyl moiety.

Q1 and/or Q1C may preferably be selected from: x where X is 0 or N; methacrylate; acrylate; vinyl acetate; vinyl ether and allylic pendent groups.

In preferred embodiments Q2 is a hydrophobic moiety.

Preferably Q2' is, or includes, a vinyl moiety. More preferably Q2' is an aromatic vinyl monomer and in particular Q2' is a substituted or unsubstituted styrene moiety.

In some preferred embodiments the coating material includes units of the formula: - iq Qia [ tta] where Q2, Q1, p, q, A, Rda, ra and Zaare as defined above and n is an integer.

In particularly preferred embodiments Q2 comprises a moiety of the formula where Rs is present or absent and where present represents one, two, three, four or five substituent groups of the aromatic ring.

Preferably A represents a residue of an acrylate or methacrylate group.

In preferred embodiments the construct is stable in the absence of the external stimulus and is, or becomes, unstable when subject to said external stimulus.

In preferred embodiments the coating material is a sterically stabilised latex.

In most preferred embodiments the coating material is in particulate form, in particular in granular or powder form.

Preferably the body of liquid has a volume in the range of from about lOpI to about 500p1.

Preferably the coating material is substantially or entirely non-wettable by the body of liquid.

Preferably the body of liquid is aqueous.

For a better understanding of the invention and to show how the same may be carried into effect, reference will be made, by way of example only, to the following Figures, in which: Figure 1 is a schematic illustration of the formation of a polymer latex according to

Examples 1 and 2.1 of the present disclosure;

Figure 2 is a scanning electron micrograph of a PDEA-PS latex (entry I in Table 1 below) after drying from aqueous solution (pH 4) at ambient temperature. The scale bar is 100 nm.

Figures 3a and 3b are images of individual 10 iL liquid marbles prepared using PDEA-PS latex (entry 1 in Table 1; dried at pH 10) deposited onto (a) a glass slide and (b) the surface of liquid water (in a Petri dish); Figure 4 shows the time required for destabilisation of 10 pL liquid marbles placed on liquid water on varying the solution pH using a series of aqueous buffers; Figure 5 shows XPS survey spectra recorded for: (a) the PDEA50-St macromonomer, (b) charge-stabilised bare polystyrene latex prepared using the AIBA initiator (entry 4 in Table 1), (c) the PDEA-PS latex (entry 1 in Table 1) Figure 6 shows the variation of mean hydrodynamic diameter and zeta potential with solution pH for a 0.01 wt. % aqueous solution of PDEA-PS latex (entry 1 in Table 1) in the presence of 0.00 1 M KCI; Figure 7 shows the relationship between the mass of PDEA-PS latex and the mean surface area of 10-150 pL water droplets used to prepare liquid marbles; Figure 8 shows confocal laser microscope images of a) rhodamine dye-labelled PDEA- PS latex particles (Entry 1 in Table 1) at the air-water interface of a 10 p1 droplet of de- ionised water and b) PDEA-PS latex (Entry 1 in Table 1) stabilised 10 p1 droplet of de-ionised water containing a water-soluble dye; Figure 9 shows still frames from a video clip showing the complete disintegration of the liquid marbles encapsulating deionised water containing 0.01 wt.% of Alizarin blue on the surface of liquid water by addition of concentrated HCI to pH 2 with a glass pipette.

Note the release of dyed water on disintegration of the liquid marbles (image(b)) due to the solvation and re-dispersion of the latex particles in contact with the acidic water surface; Figure 10 is a scanning electron micrograph of the PDPA42St-PS latex of Example 2.1 (entry 1 in Table 2 below) after drying from aqueous solution (pH 4) at ambient temperature. The scale bar is 200 nm; Figures 11 a and 11 b show images of individual 10 pL liquid marbles prepared using PDPA42St-PS latex of Example 2.1 (entry 1 in Table 2; dried at pH 10) deposited onto (a) a glass slide and (b) the surface of liquid water (in a Petri dish); Figure 12 shows the time required for destabilisation of 10 pL liquid marbles prepared using a PDPA42St-PS latex of Example 2.1 placed on liquid water on varying the solution pH using a series of aqueous buffers; Figure 13 shows XPS survey spectra recorded for: (a) the PDPA42St macromonomer, (b) charge-stabilised polystyrene control latex prepared using the AIBA initiator (entry 4 in Table 2), (c) the PDPA42St-PS latex of example 2.1 (entry 1 in Table 2); Figure 14 shows the variation of mean hydrodynamic diameter and zeta potential with solution pH for a 0.01 wt. % aqueous solution of PDPA42St-PS latex of Example 2.1 (entry 1 in Table 2) in the presence of 0.00 1 M KCI; Figure 15 shows stills taken from a video clip showing the complete disintegration of the liquid marble prepared using the PDPA42St-PS latex of Example 2.1 (and containing deionised water) on the surface of liquid water after addition of concentrated HCI using a glass pipette; Figure 16 is a schematic illustration of the formation of a PDPA42St-PS latex according

to Example 2.2 of the present disclosure;

Figure 17 is a scanning electron micrograph of the PDPA42St-PS latex of Example 2.2 after drying from aqueous solution (pH 4) at ambient temperature. The scale bar is 2 pm; Figures 18a and 18b show images of an individual 10 pL liquid marble prepared using PDPA42St-PS latex of Example 2.2 (dried at pH 10) deposited onto (a) a flat substrate and (b) the surface of liquid water (in a Petri dish); Figure 19 shows XPS survey spectra recorded for: (a) the PDPA42St macromonomer, (b) charge-stabilised polystyrene control latex prepared using the AIBN initiator, (c)the PDPA42St-PS latex of Example 2.2; Figure 20 shows the variation of mean hydrodynamic diameter and zeta potential with solution pH for a 0.01 wt. % aqueous solution of PDPA42St-PS latex of Example 2.2 in the presence of 0.001 M KCI; Figure 21 shows stills from a video clip showing the complete disintegration of the liquid marble prepared using PDPA42St-PS latex of Example 2.2 (and containing deionised water) placed on the surface of liquid water by addition of concentrated HCI with a glass pipette; Figure 22 is a schematic representation of the formation of a PSAHPMA30-PS latex prepared by emulsion polymerisation initiated by AIBA at pH 6.5 and 6000 (Example 3); Figure 23 is a scanning electron micrograph of the PSAHPMA30-PS latex of Example 3 after drying from aqueous solution (pH 8) at ambient temperature. The scale bar is 100 nm; Figure 24 shows digital images of individual 10 pL liquid marbles prepared using PSAHPMA30-PS latex of Example 3 (dried at pH 3) deposited onto (a) a flat substrate and (b) the surface of liquid water at pH 3 (in a Petri dish); Figure 25 shows XPS survey spectra recorded for: (a) the PSAHPMA30-St macromonomer, (b) charge-stabilised polystyrene control latex prepared using the AIBA initiator, (c)the PSAHPMA30-PS latex of example 3 (the Ols signal in the latter spectrum confirms the presence of the macromonomer chains at the latex surface); Figure 26 shows the variation of mean hydrodynamic diameter and zeta potential with solution pH for a 0.01 wt. % aqueous solution of PSAHPMA30-PS latex in the presence of 0.001 M KCI; Figure 27 shows still frames from a video clip showing the complete disintegration of a liquid marble prepared using PSAHPMA30-PS latex by addition of concentrated NaOH with a glass pipette to raise the solution pH to pH 7. The liquid marble (comprising deionised water containing 0.01 wt.% of alizarin blue dye) was initially placed on the surface of the liquid water; Figure 28 is a schematic representation of the preparation of PDEA homopolymer by aqueous emulsion polymerisation (solution pH > 9) at 10 % solids initiated by APS at 70 Figure 29 is a schematic representation of the preparation of PS latex particles by aqueous emulsion polymerisation (10 % solids) at a solution pH of 6.5 in the presence of PDEA homopolymer at 60 °C; Figure 30 shows SEM images of polystyrene latexes prepared in the presence of PDEA homopolymer that was previously synthesised by: (a) free radical solution polymerisation in IPA and (b) by aqueous emulsion polymerisation; Figure 31 shows XPS survey spectra recorded for: PDEA homopolymer, a charge-stabilised polystyrene latex prepared using the AIBA initiator, PDEA-PS latex (entry 1 in

Table 4);

Figure 32 shows a comparison of the variation of zeta potential with solution pH for a 0.01 wt. % aqueous solution of PDEA-PS latex (entry 1 in Table 4) with a charge-stabilised polystyrene latex in the presence of 0.00 1 M KCI; and Figure 33 shows digital images of an individual 10 pL liquid marble prepared using (left-hand side picture) PDEA-PS latex (entry 1 in Table 4; dried at pH 10) and (right-hand side picture) PDEA-PS latex (entry 2 in Table 4; dried at pH 10) deposited onto black paper (for contrast).

Examples

The following Examples are illustrative, but not limitative, of the invention.

In some preferred embodiments of the disclosure the polymer latex is prepared by reacting a chosen monomer with a macromonomer having a terminal functional group capable of undergoing copolymerisation with the chosen monomer. In the resulting polymer latex the macromonomer chains act to sterically stabilise the polymer latex.

Examples 1 and 2-Liquid Marbles using PDEA-PS and PDPA-PS latexes Polymer Preparation Macromonomer preparation The macromonomer is preferably prepared following the protocol described in Lascelles, S. F.; Malet, F.; Mayada, R.; Billingham, N. C.; Armes, S. P. Macromolecules, 1999, 32, 2462-2472. More especially, poly(tertiary amine methacrylate)-based macromonomers were prepared by the route shown in Scheme 1 which shows the oxyanion-initiated polymerisation of 2-(dialkylamino)ethyl methacrylate [alkyl is ethyl (DEA) or propyl (DPA)] using the potassium salt of 4-vinylbenzyl alcohol [potassium (4-vinylphenyl) methanolate] in dry THF at 50°C, according to the protocol reported in the above reference. The resulting styrene-functionalised macromonomer (which is conveniently denoted PDEA50-St) was purified by precipitation and characterised by 1H NMR spectroscopy and gel permeation chromatography. Its mean degree of polymerisation was estimated to be approximately 50 and its polydispersity was around 1.25. The respective PKa5 of these PDEA-St and PDPA-St macromonomers were 7.0 -7.5 and 6.3.

As can be seen from Scheme 1, both PDEA-St and PDPA-St have a terminal styrene group which provides vinyl functionality for subsequent reaction, in particular copolymerisation with styrene, to form the desired sterically stabilised polystyrene latex.

OH O-K

KH 0oc

n{ DEA or DPA DryTHF, 5000 \ //() Scheme I R/N\R Note to Scheme 1: In the above scheme, either R is typically lower alkyl such as CH2CH3 [giving styrene functionalised poly[2-(diethylamino)ethyl methacrylate] (PDEA-St)] or CH(CH3)2 [giving styrene functionalised poly[2-(diisopropylamino)ethyl methacrylate] (PDPA-St)].

Example I -PDEA Latex Polymer formation Formation of the desired polymer in one preferred method is schematically illustrated in Figure 1. In accordance with this method, PDEA50-St macromonomer (0.50 g) was dissolved in 10 g de-ionised water adjusted to pH 5 by addition of concentrated HCI in a ml single-necked round-bottomed flask. Styrene monomer (5.00 g) was then added to this solution and the solution pH was adjusted to pH 5.0-6.9 by addition of an aqueous NaOH solution. De-ionised water (adjusted to the same desired pH) was added to produce a 45.0 g aqueous emulsion in the flask, which was sealed with a rubber septum. This reaction mixture was degassed at ambient temperature using five vacuum/nitrogen cycles, stirred at 250 rpm using a magnetic stirrer, heated at 60°C with the aid of an oil bath and then the AIBA initiator solution (0.050 g AIBA dissolved in 5.0 g de-ionised water, adjusted to the reaction pH using either HCI or NaOH) was added after 20 minutes. The polymerising solution turned milky-white within 15 minutes and stirring was continued at 250 rpm for 24 h at 60°C. The resulting milky-white latex was purified by repeated centrifugation-redispersion cycles [15,000 rpm for2 h; each supernatant was carefully decanted, discarded and replaced with mildly acidic de-ion ised water (adjusted to pH 4 using H Cl)] to remove excess styrene monomer and any unreacted macromonomer.

Polymer characterisation The resulting dispersion is conveniently referred to as PDEA-PS latex and was characterised by scanning electron microscopy, X-ray photoelectron spectroscopy, dynamic light scattering, aqueous electrophoresis and 1H NMR spectroscopy. An SEM image of the sub-micrometer sized latex particles can be seen in Figure 2.

Figure 5 depicts x-ray photoelectron spectra recorded for the PDEA-PS latex (entry 1 in Table 1, spectrum c), the PDEA50-St macromonomer (spectrum b) and the charge-stabilised polystyrene (PS) latex (entry 4 in Table 1; spectrum a). Each spectrum exhibits a nitrogen signal at around 400 eV. The additional signal at 530 eV observed in the PDEA-PS latex spectrum, which is not present in the PS latex spectrum, is assigned to the two oxygen atoms (C=Q and C-Q) of the chemically grafted PDEA stabilizer. This is consistent with the observation of a weak carbonyl feature at 289 eV in the Cis core-line spectrum obtained for the PDEA-PS latex (spectrum not shown).

Curve-fitting analysis of the Ols core-line spectrum supports this assignment, since the two sub-peaks due to the C=O oxygen (at 532 eV) and the C-O oxygen (at 534 eV) are of roughly equal intensity (spectrum not shown). Given that the typical XPS sampling depth is only 2-5 nm, these observations provide good evidence that the grafted PDEA stabiliser is present at the surface of the PDEA-PS latex particles, as expected.

Combined aqueous electrophoresis and DLS studies were conducted as a function of solution pH. The results are shown in Figure 6. The PDEA-PS latex exhibits an IEP at approximately pH 8.8. Substantial flocculation occurs above approximately pH 8 since the PDEA stabiliser chains (PKa = 7.0 -7.5) become substantially deprotonated (and hence hydrophobic) under these conditions. Conversely, protonation of the PDEA chains below pH 7 led to strongly cationic latex particles with very high degrees of dispersion. Thus this PDEA-PS latex can exist in two states in aqueous solution, that is, as a colloidally stable latex with protonated, highly cationic PDEA chains below pH 7 or as a flocculated latex with neutral PDEA chains in either neutral or alkaline solution.

Formation of stable latex The pH of the initial reaction solution was varied and the results are shown in Table 1.

Table 1 also includes as a comparison the formation of polymer in the absence of any macromonomer.

Table I

Initial pH Number-Intensity-Poly-Amount of Entry of Macro-averagea average dispersity coagulum Number reaction monomer diameter dlameterb index' (wt. %) solution (nm) (nm) 1 6.9 PDEA50-St 120 160 0.08 0 2 6.0 PDEA50-St 150 170 0.04 3 3 5.0 PDEA50-St 160 180 0.05 5 4 6.5 none 1050 1190 0.07 20 a. Estimated by scanning electron microscopy; b. Measured by dynamic light scattering at 25°C From Table 1, it can be seen that that control initial solution pH has a significant effect on the efficient formation of colloidally stable latexes. The pKa of the PDEA50-St macromonomer is approximately pH 7.0-7.5. Whereas it might initially be expected that full protonation of the macromonomer chains would be desirable for latex syntheses, under such conditions the cationic charge density may be so high that the surface concentration of stabilizer chains (the macromonomer residues) on the latex surface becomes relatively low.

Significant levels of coagulum were observed at both pH 6.0 and 5.0 (entries 2 and 3 in Table 1). On the other hand, relatively stable latexes were prepared at pH 6.9 with essentially zero coagulum. Under these conditions, the PDEA macromonomer is more than 50 % protonated and hence fairly hydrophilic. Hence, a significant degree of protonation of the basic groups is desirable for achieving a stable latex.

Preparation of Liquid Marbles De-ionised water at pH 6.5 was dispensed as 10 pL droplets using a 10-1 00 pL Eppendorf micropipette and mixed with the dried PDEA-PS latex (entry 1 in Tablel).

The latex powder spontaneously coated the water droplet, which then behaved as a perfectly non-wetting liquid marble'.

Figure 3 shows digital photographs of liquid marbles prepared by initially rolling a 10 iL droplet of de-ionised water over PDEA-PS latex powder (entry 1 in Table 1) previously dried at pH 10, followed by transferring these droplets to either a glass slide (Figure 3a) or to the surface of liquid water in a Petri dish (Figure 3b). The latex powder immediately coats the water droplet and renders it both hydrophobic and non-wetting.

These liquid marbles remain stable for several hours, typically until water evaporation through the latex coating occurs, leading to partial buckling and collapse of the droplet.

However, such water evaporation can be substantially delayed if concentrated salt solutions are used instead of water.

The images shown in Figure 3 indicate that these liquid marbles have significant surface roughness, which suggests that they are coated with latex multilayers, rather than just a monolayer. In order to further examine the nature of the latex coating, the variation in the latex mass of the liquid marbles (determined gravimetrically after oven drying) with the droplet surface area was determined. An approximately linear relationship was obtained, as expected (see Figure 7). From the gradient of this line, it is estimated that, on average, the liquid marble coating comprises 40-50 latex particles, which corresponds to an estimated thickness of 3-4 pm. A confocal laser microscope study of a Rhodamine dyed PDEA-PS latex (see Figure 8) confirms the surface roughness of the liquid marbles. Particle layers varying from 20 pm to a few microns can be observed, suggesting that the 3-4 pm coating thickness determined from Figure 7 is a crude estimate.

Response to stimulus -pH stability of liquid marbles Water droplets of 10 pL were used to prepare liquid marbles, which were deposited onto the surface of various aqueous buffer solutions ranging from pH 2 to pH 10. The characteristic time required for either catastrophic destruction of each liquid marble or its partial deformation due to water evaporation was determined. The results are summarised in Figure 4. The longer times observed above pH 8 refer to partial dehydration (i.e. buckling or collapse) of the liquid marbles due to slow evaporation of water (see the inset picture in Figure 4), whereas the much shorter times observed at lower pH indicate catastrophic destruction of the liquid marbles (see the inset picture in Figure 4). Clearly, the minimum pH required for long-term stability of the liquid marbles correlates quite closely with the critical solution pH observed for the loss of colloidal stability of the PDEA-PS latex.

The pH-responsive character of liquid marbles was further assessed by depositing stable liquid marbles onto de-ionised water at pH 6.5 and then carefully adding concentrated HCI using a glass pipette to lower the solution pH to around 2. Whereas individual liquid marbles remained stable for several hours after being placed on the surface of de-ionised water, the addition of a few drops of concentrated HCI to the de-ionised water via pipette led to immediate disintegration of the liquid marbles as shown in Figure 9. Figures 9a and 9b show the release of the water containing 0.01 wt% of Alizarin Blue, as dye, before complete disintegration of the liquid marble (Figure 9d).

This is attributed to protonation of the PDEA chains, which results in the corresponding partial dissolution of the latex particles.

Example 2.1 -PDPA-PS latex -emulsion polymerisation Synthesis of PDPA42St-stabiised polystyrene (PS) latex Formation of PDPA-PS latex in one preferred method is schematically illustrated in Figure 1. In accordance with this method, PDPA42St macromonomer (0.50 g) was dissolved in 10 g deionised water adjusted to pH 3.5 by addition of concentrated HCI in a 100 ml single-necked round-bottomed flask. Styrene monomer (5.00 g) was then added to this solution and the solution pH was adjusted to pH 4.5-6 by addition of an aqueous NaOH solution. Deionised water (adjusted to the same desired pH) was added to produce a 45.0 g aqueous emulsion in the flask, which was sealed with a rubber septum. This reaction mixture was degassed at ambient temperature using five vacuum/nitrogen cycles, stirred at 250 rpm using a magnetic stirrer and heated at 60°C with the aid of an oil bath. AIBA initiator solution (0.050 g AIBA dissolved in 5.0 g deionised water, adjusted to the desired reaction pH using either HCI or NaOH) was added after 20 minutes. The polymerising solution turned milky-white within 15 minutes and stirring was continued at 250 rpm for 24 h at 60°C. The resulting milky-white latex was purified by repeated centrifugation-redispersion cycles [20,000 rpm for 3 h; each supernatant was carefully decanted, discarded and replaced with mildly acidic deionised water (adjusted to pH 4 using H Cl)] to remove excess styrene monomer and any unreacted macromonomer.

Polymer latex characterisation The resulting dispersion is conveniently referred to as PDPA42St-PS latex and was characterised by scanning electron microscopy, x-ray photoelectron spectroscopy, dynamic light scattering, aqueous electrophoresis and 1H NMR spectroscopy. An SEM image of the latex particles can be observed in Figure 10.

Figure 13 depicts x-ray photoelectron spectra recorded for the PDPA42St-PS latex (entry 1 in Table 2, spectrum c), a charge-stabilised polystyrene control latex (entry 4 in Table 2; spectrum b) and the PDPA42St macromonomer (spectrum a)). Each spectrum exhibits a nitrogen signal at around 400 eV. The additional signal at 530 eV observed in the PDPA42St-PS latex spectrum, which is not present in the PS latex spectrum, is assigned to the two oxygen atoms (C=Q and C-Q) of the chemically grafted PDPA42St stabiliser. This is consistent with the observation of a weak carbonyl feature at 289 eV in the Cis core-line spectrum obtained for the PDPA42St-PS latex (spectrum not shown). Curve-fitting analysis of the Ols core-line spectrum supports this assignment, since the two sub-peaks due to the 0=0 oxygen (at 532 eV) and the 0-0 oxygen (at 534 eV) are of roughly equal intensity (spectrum not shown). Given that the typical XPS sampling depth is only 2-5 nm, these observations provide good evidence that the grafted PDPA42St stabiliser is present at the surface of the polystyrene latex particles, as expected.

Combined aqueous electrophoresis and DLS studies were conducted as a function of solution pH. The results are shown in Figure 14. The PDPA42St-PS latex exhibits an IEP at approximately pH 7.6 (see Fig 14). Substantial flocculation occurs above approximately pH 7 since the PDPA42St stabiliser chains (PKa = 6.3-6.5) become substantially deprotonated (and hence hydrophobic) under these conditions.

Conversely, protonation of the PDPA42St chains below pH 6.3 led to strongly cationic latex particles with very high degrees of dispersion. Thus this PDPA42St-PS latex can exist in two states in aqueous solution, that is, either as a colloidally stable latex with protonated, highly cationic PDPA chains below pH 6.3 or as a flocculated latex with neutral PDPA42St chains in either neutral or alkaline solution.

Formation of stable latex The pH of the initial reaction solution was varied and the results are shown in Table 2.

Table 2 also includes as a comparison the formation of charge-stabilised polystyrene latex prepared in the absence of any macromonomer (see entry 4).

Table 2

Initial pH Number-Intensity-PDPA42St Poly-Amount of Entry of averagea average concn. dispersity coagulum Number reaction diameter dlameterb gIL index' (wt. %) solution (nm) (nm) 1 6.0 10 140 170 0.04 10 2 5.5 10 100 110 0.03 15 3 4.5 10 90 120 0.02 21 4 6.5 Zero 1050 1190 0.07 20 a. Estimated by scanning electron microscopy; b. Measured by dynamic light scattering at 25°C From Table 2, it is clear that the initial solution pH has a significant effect on the efficient formation of colloidally stable latexes. The pKa of the PDPA42St macromonomer is approximately pH 6.3. Whereas it might initially be expected that full protonation of the macromonomer chains (i.e. maximum hydrophilic character) would be desirable for latex syntheses, under such conditions the cationic charge density may be so high that the surface concentration of macromonomer stabiliser chains on the latex surface becomes relatively low, which may not be desirable for subsequent liquid marble formation.

Significant levels of coagulum were observed at all pH. However, relatively stable latexes were prepared at pH 6.0 with least coagulum, that is, around 10 wt.%. Under these conditions, the PDPA42St macromonomer is more than 50 % protonated and hence fairly hydrophilic. Hence a significant degree of protonation of the tertiary amine groups is desirable for achieving a stable latex in aqueous solution.

Preparation of Liquid Marbles Deionised water at pH 6.5 was dispensed as 10 pL droplets using a 10-1 00 pL Eppendorf micropipette and mixed with the dried PDPA42St-PS latex (entry 1 in Table 2). The latex powder spontaneously coated each water droplet, which then behaved as a perfectly non-wetting liquid marble'.

Figure 11 shows digital images recorded for liquid marbles prepared by initially rolling a 10 iL droplet of deionised water over PDPA42St-PS latex powder (entry 1 in Table 2) previously dried at pH 10, followed by carefully transferring these liquid marbles to either a glass slide (Figure 1 la) or to the surface of liquid water in a Petri dish (Figure 11 b). The latex powder immediately coats the water droplet and renders it both hydrophobic and non-wetting. These liquid marbles remain stable for several hours until water evaporation through the latex coating occurs, leading to partial buckling and collapse of the droplet. However, such water evaporation can be substantially delayed if concentrated salt solutions are used instead of water.

The images shown in Figure 11 indicate that these liquid marbles have significant surface roughness, which suggests that they are coated with latex multilayers, rather than just a single monolayer.

Response to stimulus -pH-responsive behaviour of liquid marbles Water droplets of 10 pL were used to prepare liquid marbles, which were deposited onto the surface of various aqueous buffer solutions ranging from pH 2 to pH 10. The characteristic time required for either catastrophic disintegration of each liquid marble or its partial deformation due to water evaporation was determined. The results are summarised in Figure 12 showing that the liquid marble is rendered unstable at pH values less than about pH 4. The longer times observed above pH 4.0 refer to partial dehydration (i.e. buckling or collapse) of the liquid marbles due to slow evaporation of water, whereas the much shorter times observed at lower pH indicate catastrophic destruction of the liquid marbles. Clearly, the minimum pH required for long-term stability of the liquid marbles correlates quite closely with the critical solution pH observed for the loss of colloidal stability of the PDPA42St-PS latex.

The pH-responsive character of liquid marbles was further assessed by depositing stable liquid marbles onto deionised water at pH 6.5 and then carefully adding concentrated HCI using a glass pipette to lower the solution pH to around 2. Individual liquid marbles remained stable for several hours after being placed on the surface of deionised water, but the addition of a few drops of concentrated HCI to the aqueous phase via pipette led to immediate catastrophic disintegration of the liquid marbles as shown in Figure 14. This is attributed to protonation of the PDPA42St chains, which also results in the corresponding partial dispersion of the latex particles.

Example 2.2 -PDPA-PS latex -dispersion polymerisation Polymer formation Formation of the desired polymer in a preferred method is schematically illustrated in Figure 16. In accordance with this method, PDPA42St macromonomer (0.50 g) was dissolved in 44.5 g of IPA in a 100 ml single-necked round-bottomed flask. Styrene monomer (4.00 g) was then added to this solution and the flask was fitted with a condenser and heated at 70°C with the aid of an oil bath. Styrene monomer (5.00 g) containing AIBN initiator solution (0.050 g AIBN) was added after 20 minutes. The polymerising solution turned milky-white within 15 minutes and stirring was continued at 250 rpm for 24 h at 70°C. The resulting milky-white latex was purified by repeated centrifugation-redispersion cycles [4,000 rpm for 20 mm; each supernatant was carefully decanted, discarded and replaced with mildly acidic deionised water (adjusted to pH 4 using HCI)] to remove excess styrene monomer and any unreacted macromonomer.

Polymer characterisation The resulting dispersion is conveniently referred to as PDPA42St-PS latex and was characterised by scanning electron microscopy, x-ray photoelectron spectroscopy, dynamic light scattering, aqueous electrophoresis and 1H NMR spectroscopy. An SEM image of this latex is shown in Figure 2.

Figure 19 depicts x-ray photoelectron spectra recorded for the PDPA42St-PS latex (entry 1 in Table 2, spectrum c)), a charge-stabilised polystyrene control latex (entry 4 in Table 2; spectrum b) and the PDPA42St macromonomer (spectrum a)). Each spectrum exhibits a nitrogen signal at around 400 eV. The additional signal at 530 eV observed in the PDPA42St-PS latex spectrum, which is not present in the PS latex spectrum, is assigned to the two oxygen atoms (C=Q and C-Q) of the chemically grafted PDPA42St stabiliser. This is consistent with the observation of a weak carbonyl feature at 289 eV in the Cis core-line spectrum obtained for the PDPA42St-PS latex (spectrum not shown). Curve-fitting analysis of the Ols core-line spectrum supports this assignment, since the two sub-peaks due to the 0=0 oxygen (at 532 eV) and the 0-0 oxygen (at 534 eV) are of roughly equal intensity (spectrum not shown). Given that the typical XPS sampling depth is only 2-5 nm, these observations provide good evidence that the grafted PDPA42St stabiliser is present at the surface of the PDPA42St-PS latex particles, as expected.

Combined aqueous electrophoresis and DLS studies were conducted as a function of solution pH. The results are shown in Figure 20. The PDPA42St-PS latex exhibits an IEP at approximately pH 7.9. Substantial flocculation occurs above approximately pH 6.5 since the PDPA42St stabiliser chains (PKa = 6.3) become substantially deprotonated (and hence hydrophobic) under these conditions. Conversely, protonation of the PDPA42St chains below pH 6.5 led to strongly cationic latex particles with very high degrees of dispersion. Thus this PDPA42St-PS latex can exist in two states in aqueous solution, that is, either as a colloidally stable latex with protonated, highly cationic PDPA42St chains below pH 6.3 or as a flocculated latex with neutral PDPA42St chains in either neutral or alkaline solution.

Formation of stable PDPA42St-PS latex PDPA42St-PS latexes can be easily prepared by dispersion polymerisation in IPA initiated by AIBN at 70°C. The particle diameter was measured to be around 2 pm by dynamic light scattering in acidic aqueous solution.

No coagulum was observed at the end of the reaction and the conversion was determined to be more than 95 % by gravimetry. After purification by centrifugation, the latex dispersion was freeze-dried at a solution pH of 10 to ensure complete deprotonation of the PDPA42St stabiliser.

Preparation of Liquid Marbles Deionised water at pH 6.5 was dispensed as 10 pL droplets using a 10-1 00 pL Eppendorf micropipette and mixed with the dried PDPA42St-PS latex. The latex powder spontaneously coated the water droplet, which then behaved as a perfectly non-wetting liquid marble'.

Figure 18 shows digital photographs of liquid marbles prepared by initially rolling a 10 iL droplet of deionised water over PDPA42St-PS latex powder previously dried at pH 10, followed by transferring these droplets to either a glass slide (Figure 1 8a) or to the surface of liquid water in a Petri dish (Figure 1 8b). The latex powder immediately coats the water droplet and renders it both hydrophobic and non-wetting. These liquid marbles remain stable for several hours until water evaporation through the latex coating occurs, leading to partial buckling and collapse of the droplet.

The images shown in Figure 18 indicate that these liquid marbles have significant surface roughness, which suggests that they are coated with latex multilayers, rather than just a monolayer. It was also observed that a large excess of particles was required to make the liquid marbles, compared to those prepared with either PDEA50St-PS latex or PDPA42St-PS latex prepared by emulsion polymerisation. This is probably a reflection of the much lower surface area of the micrometer-sized PDPA42St-PS latex prepared by dispersion polymerisation.

Response to stimulus -pH-responsive behaviour of liquid marbles The pH-responsive character of liquid marbles formed from PDPA42St-PS latex prepared by dispersion polymerisation was assessed by depositing stable liquid marbles onto deionised water at pH 6.5 and then carefully adding concentrated HCI using a glass pipette to lower the solution pH to around pH 2. Whereas individual liquid marbles remained stable for several hours after being placed on the surface of deionised water, the addition of a few drops of concentrated HCI to the aqueous phase via pipette led to catastrophic disintegration of the liquid marbles, as shown in Figure 21. This is attributed to protonation of the PDPA chains, which results in the corresponding partial dispersion of the latex particles.

Example 3-PSAHPMA30-PS latex Synthesis of N-(dimethylamino)ethyl-2-bromoisobutyrylamide (amide initiator) NH2 + Br NEt3 Scheme 2 THF + NHEt Br N,N'-Dimethylethylenediamine (6.0 g, 0.068 mol), triethylamine (27.5 g, 0.272 mol) and THF (120 ml) were placed in a 1 L three-necked round-bottomed flask and purged with nitrogen for 30 mm. On addition of 2-bromoisobutyryl bromide (IUPAC: 2-bromo-2-methylpropanoyl bromide) (15.65 g, 0.068 mol) to this solution, a white precipitate of triethylammonium bromide formed immediately. The reaction mixture was stirred for a further 5 h prior to removal of the precipitate by filtration. The solution was washed three times with 200 ml NaHCO3 solution and dried with anhydrous MgSO4. The solvent was removed under reduced pressure to give a pale brown liquid (yield 11.5 g, 72 %).

1H NMR spectroscopy: 2.0 (s, 6H, (OH3)2 -C-Br), 2.4 (s, 6H, (CH3)2N), 2.6 (t, 2H, (CH3)2-N-CH2CH2-), 3.4 (m, 2H, N-CH2CH2-NH).

Homopolymerisation of HPMA via Atom Transfer Radical Polymerization (A TRP): Br + X Scheme 3 Cu(I)CI, bpy CH3OH or IPA, 20°C or 50°C Amide initiator (0.55 g, 2.31 mmol), bpy (2,2'-bipyridine) (0.72 g, 4.62 mmol) and 2-hydroxypropyl methacrylate (HPMA) (10.0 g, 69.3 mmol) monomer were weighed into a ml round-bottomed flask and degassed. IPA (11.0 ml) was degassed and transferred into the reaction solution under nitrogen. Cu(l)Cl catalyst (0.23 g, 2.31 mmol) was added to the stirred solution, maintained at 50 00 in an oil bath. The reaction solution immediately turned brown and an increase in solution viscosity was observed, indicating the onset of polymerisation. After 24 h, the reaction solution was diluted with methanol and passed through a silica column to remove the spent Cu(ll) catalyst. The product was then dried on a vacuum line overnight to afford a white powder. The purified polymer was characterised by 1H NMR and GPO.

Quaternisation of tertiary amine-functionalised PHPMA3O precursor with excess 4-vinylbenzyl chloride + * Cl Methanol Scheme 4 10* Quaternisation of the tertiary amine-functionalised PHPMA3O homopolymer was conducted as follows, in accordance with Scheme 4. The PHPMA3O precursor (9.0 g, 1.97 mmol) was dissolved in methanol (27 ml). 4-Vinylbenzyl chloride (0.67 g, 3.94 mmol) was added to this solution and stirred for 3 days at 2000. Excess unreacted 4-vinylbenzyl chloride was removed by repeated precipitation from a minimum amount of methanol into excess cyclohexane. The resulting macromonomer was dried under vacuum overnight to give a white powder.

Preparation of succinic anhydride-esterified PHPMA3O macromonomer (PSAHPMA30-St) Esterification of the styrene-fu nctional ised poly(2-hydroxypropyl methacrylate) (PHPMA30) macromonomer was conducted using two equivalents of succinic anhydride per HPMA residue. PHPMA3O (2.5 g, 18.6 mmol OH residues) was dissolved in anhydrous pyridine (30.0 mL) at room temperature in a 100 mL round-bottomed flask.

Succinic anhydride (3.72 g, 37.2 mmol) was then added and esterification was allowed to proceed at 20 °C for 48 h. At the end of the reaction, the reaction mixture was precipitated into 200 mL diethyl ether. The recovered solid polymer was redissolved in mL of THF and reprecipitated into a further 200 mL diethyl ether. This clean-up procedure was repeated three times. Finally, the off-white solid was dried for 48 h in a vacuum dessicator.

Preparation of PS latex particles via aqueous emulsion polymerisation using succinic anhydride-esterified PHPMA macromonomer (PSAHPMA30-St) Succinic anhydride-esterified PSAHPMA30-St macromonomer (0.50 g) was dissolved in 10.0 g de-ionised water adjusted to pH 9 by addition of concentrated NaOH in a 100 ml single-necked round-bottomed flask. Styrene monomer (5.00 g) was then added to this solution and the solution pH was adjusted to pH 6.5 by addition of an aqueous NaOH solution. De-ionised water (adjusted to the same desired pH) was added to produce a 45.0 g aqueous emulsion in the flask, which was sealed with a rubber septum. This reaction mixture was degassed at ambient temperature using five vacuum/nitrogen cycles, stirred at 250 rpm using a magnetic stirrer, heated at 60°C with the aid of an oil bath and then the AIBA initiator solution (0.050 g AIBA dissolved in 5.0 g de-ionised water, adjusted to the reaction pH using either HCI or NaOH) was added after 20 minutes. The polymerising solution turned milky-white within 15 minutes and stirring was continued at 250 rpm for 24 h at 60°C. The resulting milky-white latex was purified by repeated centrifugation-redispersion cycles [20,000 rpm for 4 h; each supernatant was carefully decanted, discarded and replaced with mildly alkaline de-ionised water (adjusted to pH 9 using NaOH)] to remove excess styrene monomer and any unreacted macrom on om er.

Polymer characterisation The resulting dispersion is conveniently denoted as PSAHPMA30-PS latex and was characterised by scanning electron microscopy, x-ray photoelectron spectroscopy, dynamic light scattering, aqueous electrophoresis and 1H NMR spectroscopy. An SEM image of the dried latex particles is shown in Figure 23.

Figure 25 depicts x-ray photoelectron spectra recorded for the PSAHPMA30-PS latex (spectrum c)), a charge-stabilised polystyrene control latex (spectrum b)) and the PSAHPMA30-St macromonomer (spectrum a)). The additional signal at 530 eV observed in the PSAHPMA30-PS latex spectrum, which is not present in the PS latex spectrum, is assigned to the two oxygen atoms (0=0 and 0-0) of the chemically grafted PSAHPMA3O stabiliser. This is also consistent with the observation of a weak carbonyl feature at 289 eV in the Cis core-line spectrum obtained for the PSAHPMA30-PS latex (spectrum not shown). Curve-fitting analysis of the Ols core-line spectrum supports this assignment, since the two sub-peaks due to the 0=0 oxygen (at 532 eV) and the 0-0 oxygen (at 534 eV) are of roughly equal intensity (spectrum not shown).

Given that the typical XPS sampling depth is only 2-5 nm, these observations provide good evidence that the grafted PSAHPMA30 stabiliser is present at the surface of the polystyrene latex particles, as expected.

Combined aqueous electrophoresis and DLS studies were conducted as a function of solution pH. The results are shown in Figure 26. The PSAHPMA30-PS latex exhibits an IEP at approximately pH 3.5. Substantial flocculation occurs below approximately pH 4 since the PSAHPMA30 stabiliser chains become substantially neutral (and hence hydrophobic) under these conditions. Conversely, deprotonation of the PSAHPMA30 chains above pH 4 led to strongly anionic latex particles with very high degrees of dispersion. Thus this PSAHPMA30-PS latex can exist in two states in aqueous solution, that is, either as a colloidally stable latex with deprotonated, highly anionic PSAHPMA30 chains above pH 4 or as flocculated latex with neutral PSAHPMA30 chains in acidic solution.

Preparation of Liquid Marbles Deionised water at pH 2.5 was dispensed as 10 pL droplets using a 10-1 00 pL Eppendorf micropipette and mixed with the dried PSAHPMA30-PS latex. The latex powder spontaneously coated the water droplet, which then behaved as a perfectly non-wetting liquid marble'.

Figure 24 shows digital photographs of liquid marbles prepared by initially rolling a 30 iL droplet of de-ionised water over PSAHPMA30-PS latex powder previously dried at pH 2, followed by transferring these droplets to either a flat substrate (Figure 24a) or to the surface of liquid water at pH 2.5 in a Petri dish (Figure 24b). The latex powder immediately coats the water droplet and renders it both hydrophobic and non-wetting.

These liquid marbles remain stable for several hours until water evaporation through the latex coating occurs, leading to partial buckling and collapse of the droplet. However, such water evaporation can be substantially delayed if a concentrated salt solution is used instead of water.

The images shown in Figure 24 indicate that these liquid marbles have significant surface roughness, which suggests that they are coated with latex multilayers, rather than just a monolayer.

Response to stimulus -pH stability of liquid marbles The pH-responsive character of liquid marbles was assessed by depositing individual stable liquid marbles onto deionised water at pH 2.5 and then carefully adding concentrated NaOH aqueous solution using a glass pipette to increase the solution pH to around 9. Individual liquid marbles remained stable for several hours after being placed on the surface of deionised water, but the addition of a few drops of concentrated NaOH to the aqueous phase via pipette led to catastrophic disintegration of the liquid marbles within 1 second, as shown in Figure 27. This is attributed to the ionisation of the PSAHPMA3O chains, which results in the concomitant partial redispersion of the latex particles in the alkaline deionised water.

Example 4

Preparation of PDEA homopolymer Preparation of PDEA homopolymer by free radical polymerisation in IPA PDEA homopolymer was prepared in accordance with Scheme 5.

AIBN(70°C) Isopropanol, N2 N Scheme 5 N 14.0 g DEA monomer was added to a 100 mL two-necked round-bottomed flask. After addition of isopropanol (IPA) (35 g), the flask was equipped with a water condenser, was placed in an oil bath at 70 °C and the solution was stirred at 250 rpm with a magnetic stirrer and purged with N2 for 20 mm. Then 1.0 g DEA monomer containing 0.15 g AIBN initiator was added to the reaction mixture via a syringe. The reaction was stirred at 250 rpm and allowed to proceed for 24 h at 70 °C. At the end of the reaction, PDEA homopolymer was characterised by THF GPO and 1H NMR (see Table 3).

Preparation of PDEA homopolymer by aqueous emulsion polymerisation PDEA homopolymer was prepared in accordance with the scheme shown in Figure 28.

5.0 g DEA monomer was added to a 100 mL two-necked round-bottomed flask. After addition of deionised water (40 g), the flask was equipped with a water condenser, was placed in an oil bath at 70 °O and the emulsion was stirred at 250 rpm with a magnetic stirrer and purged with N2 for 20 mm. The initiator solution (0.10 g ammonium persulfate dissolved in 5.0 g water) was added after 20 minutes. The copolymerising solution turned milky-white within 20 minutes and stirring was continued for 24 h at 70 °O. PDEA homopolymer was characterised by THF GPO and 1H NMR (see Table 3).

Table 3 confirms that these two PDEA homopolymers prepared by free radical solution polymerisation and aqueous emulsion polymerisation are relatively polydisperse ( M,/M >> 1.5).

Table 3. Summary of the PDEA homopolymers prepared by free radical solution polymerisation in IPA or aqueous emulsion polymerisation, respectively.

Solid Solvent Initiator Conversion M M M/M content % (%) IPA AIBN 99 39,700 77,300 1.95 Water APS 90 68,700 176,100 2.56 Emulsion polymerisation of styrene in the presence of PDEA homo polymer In a 100 ml single-neck round-bottomed flask, PDEA homopolymer (0.50 g), prepared as described above by either free radical polymerisation or emulsion polymerisation, was dissolved in 10 g deionised water adjusted to pH 5 by addition of concentrated HCI.

Styrene monomer (5.00 g) was then added to this solution and the solution pH was adjusted to pH 5.0-6.9 by addition of aqueous NaOH solution. De-ionised water (adjusted to the same desired pH) was added to produce a 45.0 g aqueous emulsion in the flask, and the flask was then sealed with a rubber septum. This reaction mixture was degassed at ambient temperature using five vacuum/nitrogen cycles, stirred at 250 rpm using a magnetic stirrer, heated at 60 °C with the aid of an oil bath and then the AIBA initiator solution (0.050 g AIBA dissolved in 5.0 g de-ionised water, adjusted to the reaction pH using either HCI or NaOH) was added after 20 minutes. The polymerising solution turned milky-white within 15 minutes and stirring was continued at 250 rpm for 24 h at 60 °C. The resulting milky-white latex was purified by repeated centrifugation-redispersion cycles [15,000 rpm for 2 h; each supernatant was carefully decanted, discarded and replaced with mildly acidic de-ionised water (adjusted to pH 4 using HCI)] to remove excess styrene monomer and any non-grafted PDEA homopolymer.

The resulting dispersions are conveniently referred to as PDEA-PS latex and were characterised by scanning electron microscopy, x-ray photoelectron spectroscopy, aqueous electrophoresis and 1H NMR spectroscopy.

Table 4. Summary of the preparation of polystyrene latex by emulsion polymerisation initiated by AIBA at 60 °C in the presence of PDEA homopolymer stabiliser prepared by either free radical solution polymerisation in IPA or by aqueous emulsion polymerisation (see Table 1). Reaction pH was adjusted to pH 6.5.

Origin of Conversion PDEA Hydrodynamic Polydispersity PDEA (%) content diameter (nm) index homopolymer (%) Free radical 95 4 340 0.09 solution polymerisation Emulsion 95 8 210 0.08 polymerisation An SEM image of the latex particles is shown in Figure 30. Figure 30a) shows PDEA-PS latex prepared with the PDEA homopolymer synthesised by free radical polymerization (Entry 1 in Table 4) and Figure 30b) is an SEM image of the PDEA-PS latex prepared using the PDEA homopolymer produced by emulsion polymerization

(Entry 2 in Table 4)

Figure 31 depicts x-ray photoelectron spectra recorded for the PDEA-PS latex (entry 1 in Table 4), a charge-stabilised polystyrene control latex and the PDEA homopolymer prepared by free radical polymerisation (entry 1 in Table 3). Each spectrum exhibits a nitrogen signal at around 400 eV. The additional signal at 530 eV observed in the PDEA-PS latex spectrum, which is not present in the PS latex spectrum, is assigned to the two oxygen atoms (CO and C-O) of the chemically-grafted PDEA stabiliser.

Aqueous electrophoresis studies were conducted as a function of solution pH. The results are shown in Figure 32. The PDEA-PS latex exhibits an IEP at approximately pH 8. This latex can exist in two states in aqueous solution: as a colloidally stable cationic latex with protonated PDEA chains below pH 7 or as a flocculated latex with neutral PDEA chains in either neutral or alkaline solution.

Preparation of Liquid Marbles Deionised water at pH 6.5 was dispensed as 10 pL droplets using a 10-100 pL Eppendorf micropipette and mixed with the dried PDEA-PS latex (entry 1 and 2 in Table 4). The latex powder spontaneously coated the water droplet, which then behaved as a perfectly non-wetting liquid marble'.

Figure 33 shows digital photographs of liquid marbles prepared by initially rolling a 10 pL droplet of deionised water over PDEA-PS latex in its dry powder form after drying at pH 10 (Figure 33a corresponds to entry 1 in Table 4 and Figure 33b corresponds to entry 2 in Table 4). The latex powder immediately coats the water droplet and renders it both hydrophobic and non-wetting.

The images shown in Figure 33 also indicate that these liquid marbles have significant surface roughness, which suggests that they are coated with latex multilayers, rather than just a monolayer.

Comparative Examples

Comparative Example 1 -Charge-stabilised polystyrene latex.

Charge-stabilised PS latex could not be used to prepare liquid marbles. Liquid droplets initially remained spherical when placed on the dried latex powder. After gently shaking the Petri dish to coat the droplet surface, the contact angle between the droplet and the powder decreased and complete wetting of the particles occurred.

Comparative Example 2 -PEGMA-stabilised polystyrene latex The same result was achieved as for the charge-stabilised PS latex, except that complete wetting occurred more quickly (within a couple of seconds).

Comparative Example 3-PHPMA-stabilised polystyrene latex PHPMA-PS latex was prepared by non-aqueous dispersion polymerisation in alcoholic media but liquid marbles could not be formed. The inventors suggest that this may be because the PHPMA stabiliser chains are insufficiently hydrophobic.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of the words, for example "comprising" and "comprises", means "including but not limited to", and is not intended to (and does not) exclude other moieties, additives, components, integers or steps.

Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.

Claims (40)

1. CLAIMS1. A self-supporting construct comprising a body of liquid and a hydrophobic coating material entirely surrounding the liquid, wherein at least one property of the coating material changes on application of an external stimulus to the construct.
2. 2. A self-supporting construct as claimed in claim 1 wherein the coating material is a polymeric material including functional groups (Z) which change in response to the external stimulus applied to the construct, thereby changing a property of the coating material.
3. 3. A self-supporting construct as claimed in claim 2 wherein the coating material includes units of the formula (1) (Q2)(MZ)( Q2)q where p and q are integers, either p or q may be 0 and (p+q) is from about 10 to about 1000, preferably 20 to 100, more preferably 40 to 50; (Q2) and (Q2)q represent polymeric residues of the polymerisation of a monomer moiety Q2'; and M(Z) represents (v) a residue of a macromonomer including the functional groups (Z) which macromonomer is co-polymerised with Q2, or, (vi) a polymer including the functional groups (Z).
4. 4. A self-supporting construct comprising a body of liquid and a coating material entirely surrounding the liquid, wherein the coating material includes units of the formula (1) (Q2)(MZ)( Q2)q where p and q are integers, either p or q may be 0 and (p+q) is from about 10 to about 1000, preferably 20 to 100, more preferably 40 to 50; (Q2) and (Q2)q represent polymeric residues of the polymerisation of a monomer moiety Q2'; and M(Z) represents (vii) a residue of a macromonomer including functional groups (Z) which macromonomer is co-polymerised with Q2', or, (viii) a polymer including functional groups (Z) which functional groups (Z) change in response to an external stimulus applied to the construct, thereby changing a property of the coating material.
5. 5. A self-supporting construct as claimed in claim 3 or 4 wherein M(Z) represents a homopolymer.
6. 6. A self-supporting construct as claimed in claim 3, 4 or 5 wherein the polymer is chemically grafted to one or more residues (Q2) or is physically adsorbed on the residues (Q2).
7. 7. A self-supporting construct as claimed in claim 3 or 4 wherein M(Z) comprises moieties selected from the group comprising moieties (a), (b), (c) and (d) Qia Q1C L:rd1 L:1d1 (a) (b) (C) (d) where moieties (c) and (d) are terminal groups and moieties (a) and (b) are constituents of the polymer backbone of M(Z); Qia and Q1C represent a functional group by means of which M(Z), when a macromonomer, is polymerisable with Q2 and Q1 and Q1C may be the same or different; A represents a residue of a moiety A' comprising or including a polymerisable functional group by means of which A_(Rd)1_Z is polymerised on formation of M(Z); Rda, Rdb, RdC, and R may be the same or different and each independently represents a straight chain or branched, substituted or unsubstituted alkyl chain including from ito 10 carbon atoms and wherein optionally the carbon chain is interrupted by one or more moieties selected from secondary or tertiary amine moieties, -0-, -S-, -00-, -000H, amide (-CONR"-), and ester (-000R"-) where R" represents H or alkyl; ra, rb, rc and rd is each independently 0 or 1, (preferably 1); and Za, Zb, Z and Zd may be the same or different and each independently represents a functional group which is changed in response to the external stimulus applied to the construct.
8. 8. A self-supporting construct as claimed in claim 7 wherein M(Z) is a homopolymer comprising groups (b) and (d).
9. 9. A self-supporting construct as claimed in claim 7 wherein M(Z) is a macromonomer residue comprising at least one of groups (a) and (c).
10. 10. A self-supporting construct as claimed in any of claims 1 to 9 wherein the external stimulus is a chemical stimulus.
11. 11. A self-supporting construct as claimed in any of claims 1 to 10 wherein the external stimulus is a change in, or of, the environment in which the construct is located.
12. 12. A self-supporting construct as claimed in claim 11 wherein the change in the said environment is a chemical change.
13. 13. A self-supporting construct as claimed in claim 12 wherein the change in the said environment is a change in environmental pH.
14. 14. A self-supporting construct as claimed in claim 13 wherein the construct is rendered unstable when the environmental pH is changed beyond a given threshold pH value.
15. 15. A self-supporting construct as claimed in claim 13 or 14 wherein the coating material comprises a plurality of basic functional groups, at least some of which groups, or a greater proportion of which groups, become protonated when the environmental pH is changed from a relatively higher pH value to a relatively lower pH value.
16. 16. A self-supporting construct as claimed in 13, 14 or 15 wherein at least some of the groups represented by Z become, or a greater proportion of the groups represented by Z become, protonated when the environmental pH is changed from a relatively higher pH value to a relatively lower pH value.
17. 17. A self-supporting construct as claimed in claim 13 or 14 wherein the coating material comprises a plurality of acidic functional groups, at least some of which groups, or a greater proportion of which groups, become deprotonated when the environmental pH is changed from a relatively lower pH value to a relatively higher pH value.
18. 18. A self-supporting construct as claimed in 13, 14 or 17 wherein at least some of the groups represented by Z become, or a greater proportion of the groups represented by Z become, de-protonated when the environmental pH is changed from a relatively lower pH value to a relatively higher pH value.
19. 19. A self-supporting construct as claimed in any of claims 1 to 9 wherein the external stimulus is a physical stimulus.
20. 20. A self-supporting construct as claimed in claim 19 wherein the external stimulus is a change in, or of, the environment in which the construct is located.
21. 21. A self-supporting construct as claimed in claim 20 wherein the change in or of the said environment is a physical change.
22. 22. A self-supporting construct as claimed in any of claims 1 to 9 wherein the external stimulus is a physical change in or of the environment in which the construct is located.
23. 23. A self-supporting construct as claimed in any of claims 1 to 22 wherein the external stimulus causes a change in at least one property of the coating material selected from the group comprising: solubility of the coating material in a fluid present in the environment in which the construct is located; degree or extent of solvation of the coating material, or of constituent functional groups thereof, by a fluid present in the environment in which the construct is located; hydrophobicity of the coating material, degree or extent of ionisation of constituent functional groups of the coating material; and degree or extent of protonation of constituent functional groups of the coating material.
24. 24. A self-supporting construct as claimed in claim 2, 3 or 4 or any of claims 5 to 16 when dependent on claim 2, 3 or 4 wherein Z is a group of the formulaNRe" Rb where Ra and Rb may be the same or different and are selected from H or Ci to 08 alkyl, preferably C, 02, 03 or 04 alkyl.
25. 25. A self-supporting construct as claimed in claim 17 or 18 wherein Z includes an organic acid group, preferably carboxylic acid group, a phenol group or a sulphonic acid group.
26. 26. A self-supporting construct as claimed in claim 7 or any of claims 8 to 25 when dependent on claim 7 wherein Qia and/or Q1C is, or includes, a vinyl moiety.
27. 27. A self-supporting construct as claimed in claim 26 wherein Q1 and/or Q1C is (are) selected from: x where X is 0 or N; methacrylate; acrylate; vinyl acetate; vinyl ether and allylic pendent groups.
28. 28. A self-supporting construct as claimed in claim 3 or 4 or any of claims 4 to 27 when dependent on claim 3 or 4, wherein Q2 is a hydrophobic moiety.
29. 29. A self-supporting construct as claimed in claim 3 or 4 or any of claims 5 to 28 when dependent on claim 3 or claim 4, wherein Q2' is, or includes, a vinyl moiety.
30. 30. A self-supporting construct as claimed in claim 29 wherein Q2' is an aromatic vinyl monomer.
31. 31. A self-supporting construct as claimed in claim 30 wherein Q2' is a substituted or
32. 32. A self-supporting construct as claimed in claim 3 or 4 or any preceding claim when directly or indirectly dependent on claim 3 or 4 wherein the coating material includes units of the formula: - iq Qia [ tta] where Q2, Q1, p, q, A, Rda, ra and Zaare as defined above and n is an integer.
33. 33. A self-supporting construct as claimed in claim 3 or 4 or any preceding claim when directly or indirectly dependent on claim 3 or 4 wherein Q2 comprises a moiety of the formula where Rs is present or absent and where present represents one, two, three, four or five substituent groups of the aromatic ring.
34. 34. A self-supporting construct as claimed in claim 7 or any preceding claim when directly or indirectly dependent on claim 7 wherein A represents a residue of an acrylate or methacrylate group.
35. 35. A self-supporting construct as claimed in preceding claim wherein the construct is stable in the absence of the external stimulus and is, or becomes, unstable when subject to said external stimulus.
36. 36. A self-supporting construct as claimed in any preceding claim wherein the coating material is a sterically stabilised latex.
37. 37. A self-supporting construct as claimed in any preceding claim wherein the coating material is in particulate form, in particular in granular or powder form.
38. 38. A self-supporting construct as claimed in any preceding claim wherein the body of liquid has a volume in the range of from about 1 OpI to about 500p1.
39. 39. A self-supporting liquid construct as claimed in any preceding claim wherein the coating material is substantially or entirely non-wettable by the body of liquid.
40. 40. A self-supporting construct as claimed in any preceding claim wherein the body of liquid is aqueous.