WO2015138143A1

WO2015138143A1 - Process for preparing high % solids inorganic hollow particle dispersions using an interfacial miniemulsion sol-gel reaction

Info

Publication number: WO2015138143A1
Application number: PCT/US2015/017808
Authority: WO
Inventors: Hau-Nan LEE; Stephanie A. BERNARD
Original assignee: E I Du Pont De Nemours And Company
Priority date: 2014-03-11
Filing date: 2015-02-26
Publication date: 2015-09-17

Abstract

The disclosure provides a process for making an inorganic hollow particle dispersion at a solids concentration of at least 2 wt% solids through interfacial miniemulsion sol-gel reaction comprising: forming an oil-in-water or water-in-oil minemulsion by high energy shearing at least one non-reactive solvent; at least one solvent-based silica precursor; and at least one surfactant; at an energy density of at least 10^6 J/m^3; wherein the concentration of silica precursor is about 2 to about 10 weight (wt) %; in the absence of a catalyst or alcohol cosolvent; and wherein the silica precursor to non-reactive solvent ratio is about 0.1 to about 6; and oil to water or water to oil ratio is about 0.01 to 0.55; and surfactant concentration is about 0.001 wt % to about 5 wt%; and initiating a one-step sol-gel reaction, or to allow the silica precursor to diffuse to the oil/water interface, where it hydrolyzes and condenses to form a silica shell resulting in silica hollow particles having a particle size of less than about 400 nm being formed.

Description

TITLE

PROCESS FOR PREPARING HIGH % SOLIDS INORGANIC HOLLOW PARTICLE DISPERSIONS USING AN INTERFACIAL MINIEMULSION

SOL-GEL REACTION

BACKGROUND OF THE DISCLOSURE

Field of the Disclosure

The present disclosure relates to a process for preparing high % solids inorganic hollow particle dispersions, more particularly to a process for preparing high % solids inorganic hollow particle dispersions using an interfacial miniemulsion sol-gel reaction; and use of the high % solids inorganic hollow particle dispersions in coating compositions.

Description of the Related Art

Nanospheres are submicroscopic colloidal systems composed of a solid or liquid core surrounded by a thin polymer or inorganic shell. This solid or liquid core is removed to form hollow nanospheres. Such core- shell systems may be prepared from micro or miniemulsions via

polymerization reaction at the interface of the droplets, the so-called interfacial polymerization reaction. Interfacial polymerization occurs at the interface of two immiscible phases, for example, oil and water, and a thin shell is formed. In the formation of the shell, the monomers are in either oil or water phase to participate in the reaction. Typically, for the preparation of core-shell nanocapsules via interfacial polymerization, a microemulsion or miniemulsion is first prepared, either water in oil or oil in water, wherein in the former nanocapsules with an aqueous core suspended in oil are formed and in the latter nanocapsules with an oily core suspended in water are formed. Existing processes for the preparation of high % solids inorganic hollow particle dispersions do not produce hollow particle at a solid concentration higher than 2 wt%, or often produce unwanted large-size aggregation in addition to hollow particles.

A need exists for a process for preparing high % solids inorganic hollow particle dispersions using an interfacial miniemulsion sol-gel reaction. SUMMARY OF THE DISCLOSURE

In a first aspect, the disclosure provides a process for making an inorganic hollow particle dispersion at a solids concentration of at least 2 wt% solids through an interfacial miniemulsion sol-gel reaction comprising: a) providing a mixture of an oil phase comprising at least one non- reactive solvent and at least one solvent-based silica precursor, and a water phase comprising water and at least one surfactant; b) forming an oil-in-water or water-in-oil minemulsion by high energy shearing the mixture from step (a) at an energy density of at least 10^Λ6 J/m^A3, in the absence of a catalyst or alcohol cosolvent, and wherein the concentration of silica precursor is about 2 to about 10 wt %, the silica precursor to non-reactive solvent ratio is about 0.1 to about 6, oil to water or water to oil ratio is about 0.01 to 0.55, and surfactant concentration is about 0.001 wt % to about 5 wt %; and

c) initiating a one-step sol-gel reaction to form silica hollow particles having a particle size of less than about 400 nm.

In the first aspect, the one-step sol-gel reaction is initiated at room temperature, more typically about 20°C- to about 90°C.

By non-reactive solvent we mean that the solvent does not

substantially react, more typically does not react, with any of the other components added to the reaction. The non-reactive solvent is compatible with the solvent-based silica precursor.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is the structure of the resulting particles from Example 1 that was analyzed using transmission electron microscopy.

Figure 2 is the structure of the resulting particles from Example 2 that was analyzed using transmission electron microscopy.

Figure 3 is the structure of the resulting particles from Example 3 that was analyzed using transmission electron microscopy. Figure 4 is the structure of the resulting particles from Example 4 that was analyzed using transmission electron microscopy.

Figure 5 is the structure of the resulting particles from Example 5 that was analyzed using transmission electron microscopy.

Figure 6 is the structure of the resulting particles from Example 6 that was analyzed using transmission electron microscopy.

Figure 7 is the structure of the resulting particles from Example 7 that was analyzed using transmission electron microscopy.

Figure 8 is the structure of the resulting particles from Example 8 that was analyzed using transmission electron microscopy.

Figure 9 is the structure of the resulting particles from Example 9 that was analyzed using transmission electron microscopy.

Figure 10 is the structure of the resulting particles from Example 10 that was analyzed using transmission electron microscopy.

DETAILED DESCRIPTION OF THE DISCLOSURE

In this disclosure "comprising" is to be interpreted as specifying the presence of the stated features, integers, steps, or components as referred to, but does not preclude the presence or addition of one or more features, integers, steps, or components, or groups thereof. Additionally, the term "comprising" is intended to include examples encompassed by the terms "consisting essentially of and "consisting of." Similarly, the term "consisting essentially of is intended to include examples encompassed by the term "consisting of."

In this disclosure, when an amount, concentration, or other value or parameter is given as either a range, typical range, or a list of upper typical values and lower typical values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or typical value and any lower range limit or typical value, regardless of whether ranges are separately disclosed. Where a range of numerical values is recited herein, unless otherwise stated, the range is intended to include the endpoints thereof, and all integers and fractions within the range. It is not intended that the scope of the disclosure be limited to the specific values recited when defining a range.

In this disclosure, terms in the singular and the singular forms "a," "an," and "the," for example, include plural referents unless the content clearly dictates otherwise. Thus, for example, reference to "inorganic hollow particle dispersion", "the inorganic hollow particle dispersion", or "a inorganic hollow particle dispersion" also includes a plurality of inorganic hollow particle dispersions.

The disclosure provides a process for preparing an inorganic hollow particle dispersion at a solids concentration of at least 2 wt% solids, more typically about 2 wt% to about 7 wt%, still more typically about 2 wt% to about 5 wt%. These inorganic hollow particle dispersions are useful as hiding or opacifying agents in coating and molding compositions. They are also useful as drug delivery systems in the pharmaceutical and medical industries; in food, personal care and cosmetics; and agriculture.

These nanospheres have a particle size of less than about 400nm, more typically about 5 nm to about 400 nm, still more typically about 50 nm to about 300 nm, and most typically about 100 nm to about 250 nm.

The disclosure provides a process for making an inorganic hollow particle dispersion at a solids concentration of at least 2 wt% solids through an interfacial miniemulsion sol-gel reaction comprising:

a) providing a mixture of an oil phase comprising at least one non- reactive solvent and at least one solvent-based silica precursor, and a water phase comprising water and at least one surfactant; b) forming an oil-in-water or water-in-oil minemulsion by high energy shearing the mixture from step (a) at an energy density of at least 10^Λ6 J/m^A3, in the absence of a catalyst or alcohol cosolvent, and wherein the concentration of silica precursor is about 2 to about 10 wt %, the silica precursor to non-reactive solvent ratio is about 0.1 to about 6, oil to water or water to oil ratio is about 0.01 to

0.55, and surfactant concentration is about 0.001 wt% to about 5 wt%; and c) initiating a one-step sol-gel reaction to form silica hollow particles having a particle size of less than about 400 nm.

The oil phase comprises at least one non-reactive solvent and at least one solvent based silica precursor.

The non-reactive solvent may be an alkane, a hydrocarbon oil, aromatic hydrocarbon or halogenated hydrocarbon liquid, more typically alkane or hydrocarbon oil.

The solvent based silica precursor is tetraethyl orthosilicate (TEOS), tetramethyl orthosilicate (TMOS) tertrapropyl orthosilicate (TPOS), tetrabutyl orthosilicate (TBOS), tetrahexyl orthosilicate,

diethoxydimethylsilane, ethoxytrimethylsilane, methoxytrimethylsilane, trimethoxy(octyl)silane, triethoxy(octyl)silane,

methoxy(dimethyl)octylsilane, or 3-aminopropyl-(diethoxy)methylsilane; more typically tetraethyl orthosilicate (TEOS) or tertrapropyl orthosilicate (TPOS). The concentration of silica precursor is about 2 to about 10 wt%, more typically about 2 to about 7 wt%, still more typically about 2 to about 5 wt%.

The water phase comprises water and at least one surfactant. Some suitable surfactants include cetyltrimethylammonium bromide (CTAB), lauryltrimethylammonium bromide, dodecyltrimethylammonium bromide, octyltrimethylammonium bromide, sodium dodecyl sulfate (SDS), sodium dodecylbenzene sulfonate (SDBS), or dioctylsulfosuccinate , nonionic surfactants such as alkylphenol polyoxyethylene, polyoxyethylene glycol alkyl ethers, polyoxypropylene glycol alkyl ethers, octylphenol ethoxylates orpoloxamers, more typically SDS, SDBS or CTAB. Some useful commercially available surfactants series include Triton X^® manufactured by The Dow Chemical Company, Brij^® manufactured by Croda

International PLC, or Pluoronic^® manufactured by BASF.

The silica precursor to non-reactive solvent ratio is about 0.1 to about 6, more typically about 0.5 to about 3, still more typically about 1 to about 2; oil to water or water to oil ratio is about 0.01 to about 0.55, more typically about 0.05 to about 0.25; and surfactant concentration is about 0.001 wt% to about 5 wt%, more typically about 0.1 wt% to about 2 wt%, based on the total weight of all components. It is important because the combination of silica precursor to non-reactive solvent ratio, oil to water ratio and surfactant level determine the particle size, hollow or non-hollow particle structure, and allow high % solid hollow silica synthesis. The process is carried out in the absence of a catalyst or alcohol cosolvent.

The mixture in step (a) may be prepared in any glass container or stainless steel reaction vessel.

The mixture of the water phase and oil phase components is then sheared at an energy density of at least 10^Λ6 J/m^A3, more typically about 10^Λ7 J/m^A3 to about 5^*10^Λ8 J/m^A3, to form a mini-emulsion. Some useful means for shearing include an ultrasonic disruptor, high speed blender, high pressure homogenizer, high shear disperser, membrane

homogenizer or colloid mill, more typically an ultrasonic disruptor, high speed blender, or a high pressure homogenizer. Typically shearing occurs for a period of about 5 to about 120 minutes depending on amount of emulsion needed to be prepared and desired emulsion size range, more typically about 30 minutes to about 60 minutes. Typically, shearing is accomplished at room temperature. Optionally, a defoamer may be needed to avoid foaming during emulsifying. Some suitable defoamers include BASF's Foamaster®, Dow Corning® 71 and 74 Antifoams.

A sol gel reaction or process is a method used for fabrication of solid metal oxides materials, especially the oxides of silicon and titanium, from small molecules. The process involves conversion of monomers

(precursors) into a colloidal solution that later on turns into an integrated network (or gel) of particles or network polymers.

A one-step sol-gel reaction of this disclosure is initiated using the mini- emulsion formed in step (b), by holding it at room temperature or about 20°C to about 90°C, more typically about 20°C to about 70°C, with or without stirring for several hours to allow the silica precursors to diffuse to the oil/water interface, where they hydrolyze and condense to form a silica shell resulting in silica hollow particles having a particle size of less than about 400 nm being formed. The pH may be typically adjusted to between 4 and 10 prior to initiation of the one step sol gel process.

Typically the miniemulsion is held for several hours, more typically at least 4 hours to form, in one step, a fluorinated hollow silica nanosphere having a particle size of less than about 400nm. Heating may be accomplished using hot plate, heating mantle or any other heating method.

A one-step sol-gel reaction is then initiated using the mini-emulsion formed in step (b), by allowing the silica precursors to diffuse to the oil/water interface, where they hydrolyze and condense to form a silica shell resulting in silica hollow particles having a particle size of less than about 400 nm being formed. The one-step sol-gel reaction may be initiated at room temperature, more typically about 20 °C to about 90 °C, and still more typically about 20 °C to about 70 °C. Heating may be

accomplished using hot plate, heating mantle or any other heating method.

Applications:

These inorganic hollow particle dispersions are useful as hiding or opacifying agents in coating and molding compositions. They are also useful as drug delivery systems in the pharmaceutical and medical industries; in food, personal care and cosmetics; and agriculture.

EXAMPLES

Glossary:

AIBN 2,2'-azobisisobutyronitrile

TEOS tetraethyl orthosilicate

TBOS tetrabutyl orthosilicate

TMSPM 3-(Trimethoxysilyl)propyl methacrylate

CTAB cetyltrimethylammonium bromide

SDS sodium dodecyl sulfate Example 1 :

An oily mixture containing 0.5 g of hexane and 0.5 g of TEOS was first prepared, and added to a water solution which contains 100.0 g of water and 0.1 g of CTAB. Miniemulsification was achieved by ultrasonicating the mixture for 120 s with a Branson sonifier W150 at 100% amplitude and then stopping for 30 s. This cycle was repeated 5 times. To avoid polymerization due to heating, the mixture was cooled in an ice-bath during homogenization. After forming a stable miniemulsion, the polymerization was started by heating to 80°C for at least 6 hours. The structure of the resulting particles was analyzed using transmission electron microscopy and shown in Figure 1 . The particle size of the resulting hollow particles is 10-15 nm.

Example 2:

An oily mixture containing 3.0 g of hexadecane and 3.0 g of TEOS was first prepared, and added to a water solution which contains 60.0 g of water, and 0.6 g of CTAB. Miniemulsification was achieved by

ultrasonicating the mixture for 60 s with a Branson sonifier W150 at 100% amplitude and then stopped for 30 s; and repeating this cycle 10 times. To avoid polymerization due to heating, the mixture was cooled in an ice-bath during homogenization. After forming a stable miniemulsion, the

polymerization was started by heating to 80°C for at least 6 hours. The structure of the resulting particles was analyzed using transmission electron microscopy as shown in Figure 2. The average particle size of the resulting hollow particles determined by dynamic light scattering is 174.3 nm with a polydispersity of 0.270.

Example 3:

An oily mixture containing 9.0 g of hexadecane and 3.0 g of TEOS was first prepared, and added to a water solution which contains 60.0 g of water, 0.6 g of CTAB. Miniemulsification was achieved by ultrasonicating the mixture for 60 s with a Branson sonifier W150 at 100% amplitude and then stopping for 30 s; and repeating this cycle 10 times. To avoid polymerization due to heating, the mixture was cooled in an ice-bath during homogenization. After forming a stable miniemulsion, the polymerization was started by heating to 80°C for at least 6 hours. The structure of the resulting particles was analyzed using transmission electron microscopy as shown in Figure 3. The average particle size of the resulting hollow particles determined by dynamic light scattering is 244.8 nm with a polydispersity of 0.193.

Example 4:

An oily mixture which contained 12.0 g of hexadecane and 6.0 g of TEOS was first prepared, and added to a water solution which contains 60.0 g of water, and 1 .2 g of CTAB. Miniemulsification was achieved by ultrasonicating the mixture for 60 s with a Branson sonifier W150 at 100% amplitude and then stopping for 30 s; and repeating this cycle 10 times. To avoid polymerization due to heating, the mixture was cooled in an ice-bath during homogenization. After forming a stable miniemulsion, the polymerization was started by heating to 80°C for at least 6 hours. The structure of the resulting particles was analyzed using transmission electron microscopy as shown in Figure 4. The average particle size of the resulting hollow particles determined by dynamic light scattering is 244.8 nm with a polydispersity of 0.193.

Example 5:

An oily mixture which contained 0.6 g of hexadecane, 2.4 g of hexane and 3.0 g of TEOS was first prepared, and added to a water solution which contains 60.0 g of water and 0.6 g of CTAB. Miniemulsification was achieved by ultrasonicating the mixture for 60 s with a Branson sonifier W150 at 100% amplitude and then stopping for 30 s; and repeating this cycle 10 times. To avoid polymerization due to heating, the mixture was cooled in an ice-bath during homogenization. After forming a stable miniemulsion, the polymerization was started by heating to 80°C for at least 6 hours. The structure of the resulting particles was analyzed using transmission electron microscopy as shown in Figure 5. The average particle size of the resulting hollow particles determined by dynamic light scattering is 182.6 nm with a polydispersity of 0.163. Example 6:

An oily mixture which contained 13.6 g of hexadecane, 47.6 g of octane, 20.9 g of TEOS and 0.5 g of TMSPM was first prepared, and added to a water solution which contains 408.0 g of water, 4.08 g of Pluronic F-127 nonionic surfactant and 0.5 g of defoamer (Foamaster® 1 1 1 , BASF). Miniemulsification was achieved by shearing the mixture for 30 minutes with a high speed blender at 9500 rpm. After forming a stable miniemulsion, the polymerization was started by heating to 70°C for at least 16 hours. The structure of the resulting particles was analyzed using transmission electron microscopy and shown in Figure 6. The average particle size of the resulting hollow particles determined by dynamic light scattering is 384.5 nm with a polydispersity of 0.257.

Example 7:

An oily mixture which contained 4.2 g of hexadecane, 16.8 g of hexane, and 21 .0 g of TEOS was first prepared, and added to a water solution which contains 420.0 g of water, 4.2 g of CTAB and 0.5 g of defoamer (Foamaster® 1 1 1 , BASF). Miniemulsification was achieved by shearing the mixture for 30 minutes with a high speed blender at 9500 rpm. After forming a stable miniemulsion, the polymerization was started by heating to 80°C for at least 16 hours. The structure of the resulting particles was analyzed using transmission electron microscopy and shown in Figure 7. The average particle size of the resulting hollow particles determined by dynamic light scattering is 144.9 nm with a polydispersity of 0.1 14. Example 8:

An oily mixture which contained 4.2 g of hexadecane, 16.8 g of octane, and 21 .0 g of TEOS was first prepared, and added to a water solution which contains 420.0 g of water, 4.2 g of CTAB and 0.5 g of defoamer (Foamaster® 1 1 1 , BASF). Miniemulsification was achieved by shearing the mixture for 30 minutes with a high speed blender at 9500 rpm. After forming a stable miniemulsion, the polymerization was started by heating to 80°C for at least 12 hours. The structure of the resulting particles was analyzed using transmission electron microscopy and shown in Figure 8. The average particle size of the resulting hollow particles determined by dynamic light scattering is 253.5 nm with a polydispersity of 0.171 .

Example 9:

An oily mixture which contained 1 .2 g of hexadecane, 4.8 g of octane, and 36.0 g of TEOS was first prepared, and added to a water solution which contains 420.0 g of water, 4.2 g of CTAB and 0.5 g of defoamer (Foamaster® 1 1 1 , BASF). Miniemulsification was achieved by shearing the mixture for 30 minutes with a high speed blender at 9500 rpm. After forming a stable miniemulsion, the polymerization was started by heating to 80°C for at least 12 hours. The structure of the resulting particles was analyzed using transmission electron microscopy and shown in Figure 9. The average particle size of the resulting hollow particles determined by dynamic light scattering is 167.9 nm with a polydispersity of 0.174. Example 10:

An oily mixture which contained 4.2 g of hexadecane, 16.8 g octane and 321 .0 g TEOS was first prepared, and added to a water solution which contains 420.0 g of water, 0.5 g G1640 defoamer and 4.2 g of CTAB. Emulsification was achieved by high-speed mixer, stirred at 9,500 rpm for 30 min. After obtaining a stable emulsion, the mixture was left sit at room temperature overnight, and hollow particle formed. The structure of the resulting particles was analyzed using transmission electron microscopy and shown in Figure 10. The average particle size of the resulting hollow particles determined by dynamic light scattering is 195.9 nm with a polydispersity of 0.153.

Example 1 1 : Hiding power performance of selected examples in coatings formulations

Some of the hollow silica particles shown in the Examples above were tested in an acrylic latex paint formulation. Three formulations were prepared (Table 1 ), one without any hollow silica (control), two with 5 wt% of materials from Examples 8 and 10, respectively. Thin coating films were made from the three formulations, and they were compared for hiding power (Scoat), using standard protocols of Kubelka-Munk theory of reflectance (Table 2). It is evident that addition of hollow silica particles provides films with superior hiding power. The hollow particles described above are thus seen as good additives for hiding power improvement.

Table 1 .

Composition of Paint Formulations

with and without Hollow Silica Particles.

Table 2.

Dry film PVC and hiding power data from formulations in Table 2.

*PVC=pigment volume concentration.

Claims

CLAIMS What is claimed is:

1 . A process for making an inorganic hollow particle dispersion at a

solids concentration of at least 2 wt% solids through an interfacial miniemulsion sol-gel reaction comprising:

a) providing a mixture of an oil phase comprising at least one non- reactive solvent and at least one solvent-based silica precursor, and a water phase comprising water and at least one surfactant; b) forming an oil-in-water or water-in-oil minemulsion by high energy shearing the mixture from step (a) at an energy density of at least 10^Λ6 J/m^A3, in the absence of a catalyst or alcohol cosolvent, and wherein the concentration of silica precursor is about 2 to about 10 wt%, the silica precursor to non-reactive solvent ratio is about 0.1 to about 6, oil to water or water to oil ratio is about 0.01 to 0.55, and surfactant concentration is about 0.001 wt% to about

5 wt%; and

2. The process of claim 1 wherein the one-step sol-gel reaction is

initiated at room temperature.

3. The process of claim 2 wherein the one-step sol-gel reaction is

initiated at a temperature of about 20°C to about 90°C.

4. The process of claim 1 wherein the the silica precursor to non-reactive solvent ratio is about 0.5 to about 3.

5. The process of claim 1 wherein the oil to water or water to oil ratio is 0.05 to 0.25.

6. The process of claim 1 wherein the oil to water or water to oil ratio is about 1 to about 2.

7. The process of claim 1 wherein the concentration of silica precursor is about 2 wt% to about 10 wt%.

8. The process of claim 1 wherein the surfactant concentration is about 0.1 wt% to about 2 wt%.

9. The process of claim 1 wherein the non-reactive solvent is an alkane, a hydrocarbon oil, aromatic hydrocarbon or halogenated hydrocarbon liquid.

10. The process of claim 9 wherein the non-reactive solvent is alkane or hydrocarbon oil.

1 1 . The process of claim 1 wherein the solvent based silica precursor is tetraethyl orthosilicate (TEOS), tetramethyl orthosilicate (TMOS) tertrapropyl orthosilicate (TPOS), tetrabutyl orthosilicate (TBOS), tetrahexyl orthosilicate, diethoxydimethylsilane, ethoxytrimethylsilane, methoxytrimethylsilane, trimethoxy(octyl)silane, triethoxy(octyl)silane, methoxy(dimethyl)octylsilane, or 3-aminopropyl- (diethoxy)methylsilane.

12. The process of claim 1 1 wherein the solvent based silica precursor is tetraethyl orthosilicate (TEOS) or tertrapropyl orthosilicate (TPOS).

13. The process of claim 1 wherein the surfactant is

cetyltrimethylammonium bromide (CTAB), lauryltrimethylammonium bromide, dodecyltrimethylammonium bromide,

octyltrimethylammonium bromide, sodium dodecyl sulfate (SDS), sodium dodecylbenzene sulfonate (SDBS), or dioctylsulfosuccinate, nonionic surfactants, octylphenol ethoxylates, or poloxamers.

14. The process of claim 13 wherein the surfactant is SDS, SDBS or CTAB.

15. The process of claim 1 wherein the mixture of the above components is then sheared at an energy density of about 10^Λ7 J/m^A3 to about 5^*10^Λ8 J/m^A3 form a mini-emulsion.

16. The process of claim 1 wherein the shearing means is an ultrasonic disruptor, high speed blender, high pressure homogenizer, high shear disperser, membrane homogenizer or colloid mill.