EP2655526A2

EP2655526A2 - Pickering emulsion for producing electrically conductive coatings and process for producing a pickering emulsion

Info

Publication number: EP2655526A2
Application number: EP11797328.9A
Authority: EP
Inventors: Stefanie Eiden; Diana Dimova LANDEN; Daniel Gordon Duff; Daniel Rudhardt
Original assignee: Bayer Intellectual Property GmbH
Current assignee: Clariant International Ltd
Priority date: 2010-12-21
Filing date: 2011-12-19
Publication date: 2013-10-30
Also published as: US20130337158A1; WO2012084849A2; EP2468826A1; WO2012084849A3; TW201232566A; SG191736A1; JP2014505969A; BR112013018452A2; CN103429673A; CA2821844A1; KR20140007359A

Abstract

The present invention relates to a process for producing a Pickering emulsion, which contains water, a solvent which is immiscible with water and stabilized, preferably sterically stabilized, silver nanoparticles for producing conductive coatings. The invention further relates to a process for coating surfaces over the full area or part of the area, in particular with a Pickering emulsion according to the invention, where the coating obtained has, in particular, a high electrical conductivity and can advantageously also be transparent.

Description

Pickering emulsion for the production of electrically conductive coatings and process for the preparation of a Pickering emulsion

The present invention relates to a process for the preparation of a Pickering emulsion containing water, a water-immiscible solvent and, preferably sterically, stabilized syllable nianopartikel for the production of conductive coatings. The invention further relates to a process for the full or partial coating of surfaces, in particular with a Pickering emulsion according to the invention, wherein the coating obtained in particular has a high electrical conductivity and may advantageously additionally be transparent. Plastic components usually have good mechanical properties and sometimes also good optical properties, such as the transparency of polycarbonate. Most engineering plastics are electrical insulators.

The combination of mechanical properties such as stability, optical properties such as transparency and electrical properties such as electrical conductivity in transparent plastics is desirable for many applications and can bring enormous benefits.

Of particular note here is the transparency of components that should be as high as possible in many applications, for example, for windows in automotive or building, or for viewing windows in devices that are to be coupled with advanced electrical applications, such as electrical heating, shielding electromagnetic Radiation or dissipation of surface charge. At the same time, in most cases, the mechanical stability of the base material as well as the freedom of design with regard to the shape should be as high as possible. The use in the field of Soiarzellentechnik (photovoltaic systems) as hochieitfähiger electrical conductor is desirable.

In the processing of silver or other metals, it is known to disperse stabilized nanoparticles in organic solvents or in water and to subsequently apply and dry these formulations to substrates. However, comparatively high temperatures are usually needed to sinter the stabilized nanoparticles. However, this is not compatible with all substrates, especially not with many plastic substrates such as polycarbonate. Xia et al. in Adv. Mater., 2003, 15, No.9, 695-699 describe the preparation of stable aqueous dispersions of silver nanoparticles with Polv (vinylpyrrolidone) (PVP) and sodium citrate as stabilizers. Xia thus obtained monodisperse dispersions with silver nanoparticles with particle sizes below 10 μm and narrow particle size distribution. The use of PVP as a polymeric stabilizer leads to steric stabilization of the nanoparticles against aggregation. Such sterile polystyrene dispersion stabilizers may optionally reduce the direct contact of the particles with one another and thus the conductivity of the coating in the resulting conductive coatings by the surface coverage of the silver particles. According to Xia, it is not possible to obtain such stable monodisperse dispersions without the use of additional PVP as stabilizer.

EP 1493780 A I describes the production of conductive surface coatings comprising a liquid conductive composition comprising a binder and silver particles, wherein the aforementioned silver-containing particles may be silver oxide particles, silver carbonate particles or silver acetate particles, each of which may have a size of 10 .mu.m to 10 .mu.m. The binder is a polyvalent phenolic compound or one of several resins, so in any case at least one additional polyun component. According to EP 1 493 780 A1, a conductive layer is obtained from this composition after application to a surface with heating, the heating preferably being carried out at temperatures of 140 ° C. to 200 ° C. The according to EP I

493 780 A 1 are dispersions in a dispersion medium selected from among alcohols such as methanol, ethanol and propanol, isophorones, terpineols, triethylene glycol monobutyl ether acetate and triethylene glycol monobutyl ether acetate. It is pointed out in EP I 493 780 A I that the silver-containing particles in the dispersion medium are preferably to be protected from aggregation by addition of dispersion stabilizers such as hydroxypropylcellulose, polyvinylpyrrolidone and polyvinyl alcohol. These dispersion stabilizers are also polymeric components. The silver-containing particles are stabilized in the dispersant always steri sch by the aforementioned dispersion stabilizers and the binder as a dispersion stabilizer against aggregation.

A method for producing transparent leitfohigen metal nanoparticle-based Be laminations is disclosed in WO2006 / 13735 A2 and in US 7,566,360 B2. Here, first, a nano-metal powder with several additives, such as surface-active substances, binders. Polymers. Buffers, dispersing aids. and coupling reagents, processed in organic solvents to a homogeneous mixture. The nano-metal powders can also

To be silver anoparticcl. This homogeneous mixture is then mixed again with water or a water-miscible solvent to give a water-in-oil (W / O) emulsion. This emulsion is applied directly to the surface to be coated by spraying, printing, spin coating or dipping, the solvents are removed and the coating is sintered to give a conductive and transparent coating or structure. Also described is the formation of network-like structures by the metal nanoparticles.

A disadvantage of the abovementioned water-in-oil emulsions is, in particular, that they must be washed at least twice with water before they can be used, so that the desired transparent, conductive metal nanoparticle-based coatings can be produced from these.

The self-assembly of CNTs (carbon nanotubes) and SWNTs (single walled carbon nanotubes) into a honeycomb structure by emulsion technique has been described by N. Wakamatsu et al. in Ad. Funct. Mater. 2007, 19, 2535-2539.

The publication by Minzhi Rong, Polymer 40 (1999) 6169 describes the self-assembly of silver nanoparticles in polymeric systems.

There continues to be a need for alternative methods of coating surfaces with conductive coatings using dispersions containing silver manoparticles which have short drying and sintering times and / or low drying and sintering temperatures

Can be used, so that even temperature-sensitive plastic surfaces can be coated. In addition, it is also desirable to use alternative coating compositions for producing electrically highly conductive coatings which, in particular, may additionally have good transparency, and, in particular, cost-effective and simple processes for their preparation which make it possible, for example, to dispense with complicated washing or cleaning of the emulsion before its applicability ,

The invention therefore proposes a process for producing a Pickering emulsion for producing conductive coatings, wherein a) an aqueous dispersion containing, in particular sterically, stabilized silver manoparticles and water is mixed with at least one, water-immiscible solvent and then dispersed to form an emulsion , wherein the content of stabilized silver nanoparticles, based on the total weight of the emulsion obtained, is between 0.5 wt .-% and 7 wt .-%, and b) then during a service life, the emulsion obtained in (a) by a creaming in an upper concentrated emulsion phase and a lower, substantially aqueous, phase is separated, and c) the resulting upper concentrated emulsion phase is isolated, this emulsion phase having a content of Silbemanopartikeln up to 7% by weight, preferably up to 4.5 wt .-%, based on the total weight, having.

In other words, in the step (a) of the present invention, a source emulsion is stabilized from dispersed in aqueous dispersion media or aqueous dispersants

Silbemanopartikeln, for example, a silver manoparticle sol, water and a water-immiscible solvent produced. This parent emulsion may preferably be an O / W emulsion. The oil phase of the O / W emulsion in this case is formed by the solvent (s) which is not water-miscible. The silver nanoparticles occupy the surface of the oil droplets and stabilize the oil droplets in the emulsion. The stated content of silver particles in% by weight relates according to the invention to the content of stabilized silver mane particles, ie the silver nanoparticles which are coated with dispersion stabilizer on their surface.

The aqueous dispersant (s) is preferably water or mixtures containing water and organic, preferably water-soluble, solvents. The liquid dispersing agent (s) are particularly preferably water or mixtures of water with alcohols, aldehydes and / or ketones, more preferably water or mixtures of water with mono- or polyhydric alcohols having up to four carbon atoms, such as eg Methanol, ethanol, n-propanol, iso-propanol or ethylene glycol, aldehydes of up to four carbon atoms, e.g. Formaldehyde, and / or ketones of up to four carbon atoms, e.g. Acetone or methyl ethyl ketone. Very particularly preferred Dispersionsmittei is water.

For the purposes of the invention, silver particles are to be understood as meaning those having a d.sub.50 value of less than 100 nm, preferably less than 80 nm, measured by means of dynamic light scattering. For example, a ZetaPius Zeta Potential Analyzer from Brookhaven Instrument Corporation is suitable for the measurement by means of dynamic light scattering.

According to the invention, the stabilization of the silver nanoparticles in the aqueous dispersion of silver silipartan particles used, for example silver nanoparticle sol, is preferably carried out using a steric dispersing aid such as polyvinyl pyrrolidone, block copolyether and block copolyether with polystyro blocks, very preferably Disperbyk 190 (BYK-Chemie, Wesel).

By using a dispersing aid, the silver nanoparticle particles used to produce the Pickering emulsion according to the invention have a high colloid-chemical stability. The choice of the dispersing agent also makes it possible to optimally adjust the surface properties of the particles. For example, dispersing agent adhering to the particle surface can impart a positive or negative surface charge to the particles.

It is in principle also possible, but less preferred according to the invention, to stabilize the silver nanoparticles electrostatically. For electrostatic stabilization of the Siibernanopartikel at least one electrostatic dispersion stabilizer is added in the preparation of the dispersions. An electrostatic dispersion stabilizer in the context of the invention is to be understood as meaning one by whose presence the silver nanoparticles are provided with repulsive forces and, based on these repulsive forces, no longer tend to aggregate. Consequently, the presence and effect of the electrostatic dispersion stabilizer between the silver nanoparticles provides repelling electrostatic forces which counteract van der Waals forces acting on the aggregation of the silver nanoparticles.

Particularly preferred electrostatic dispersion stabilizers are citric acid and / or citrates, e.g. Lithium, sodium, potassium or tetramethylammonium citrate. In an aqueous

Dispersion, the salt-like electrostatic dispersion stabilizers are largely dissociated into their ions, the respective anions causing the electrostatic stabilization.

In step (b), the source emulsion of step (a) is subjected to creaming. In this case, during a service life, the original emulsion separates into an upper concentrated emulsion phase and into a lower, essentially aqueous, emulsion phase. The upper concentrated emulsion phase according to the invention is also referred to as cream phase or cream layer. In other words, the cream phase advantageously contains a higher concentration of drops of the oil phase, since the oil drops rise during the service life.

In step (c) of the process according to the invention, the cream phase is finally isolated. The cream phase may contain a content of stabilized silver nanoparticles of up to 7% by weight, preferably up to 4.5% by weight, based on the total weight of the isolated Pickering emulsion.

In other words, the Pickering emulsion according to the invention is formed by the cream phase. The oil drops in the cream phase are further occupied by the Siibernanopartikel on its surface, thereby advantageously a sufficient concentration of silver enters the cream phase. It can thus be ensured according to the invention that the resulting coating material is suitable for the production of conductive coatings. With comparatively low starting concentrations of silver nanoparticles in the original emulsion, the concentration of silver nanoparticles in the cream phase can advantageously also be increased according to the invention compared with the concentration in the original emulsion. This is particularly advantageous with regard to a cost-efficient coating process, since according to the invention it is possible to obtain suitable coating compositions for the production of conductive coatings with comparatively low use of silver nanoparticles.

The inventive method for the preparation of the coating composition, so the Pickering emulsion, is easy and inexpensive to perform. It has surprisingly been found that the Pickering emulsions provided by the method according to the invention are furthermore particularly stable and can be stored, for example, for several days. A further advantage of the method according to the invention is that the Pickering emulsion obtained in step (c) is outstandingly suitable as a coating agent for the production of electrically conductive, in particular also transparent, coatings on substrates. Furthermore, in the process according to the invention, it is advantageously possible to dispense with the use of additional additives, such as binders, dispersing aids and film formers, which slow down or even increase the drying and / or sintering of a surface coating obtained from a Pickering emulsion according to the invention from step (c) Temperature require until drying and / or sintering and thus a conductivity of the surface coating occurs by sintering of the silver particles.

In a preferred embodiment of the method, it is provided that the service life under (b) is 1 h to 5 d, preferably 6 h to 3 d, more preferably 12 h to 36 h, for example 24 h. These service lives have been found to be particularly suitable for the formation of stable Pickering emulsions with good properties for the production of conductive coatings. In a further preferred embodiment of the method, the content of the silver anopartikel of the original emulsion under (a), based on the total weight of the original emulsion obtained under (a), preferably between 0.7 wt .-% and 6.5 wt .-%, more preferably between 0.7 and 3.0 wt .-%. By adjusting the silver nanoparticle content in this preferred range, in subsequent steps (b) and (c), Pickering emulsions can be obtained and isolated which exhibit particularly advantageous properties for forming electrically conductive coatings. In particular, by adjusting the silver content in the parent emulsion in this preferred range after the application of the Pickering emulsion isolated as the coating agent in (c), self-assembly of the silver mani particles is also added promoted net-like structures, for example, the formation of W'abenstrukturen from these anoparticles in such a coating. In addition, it is possible that those from these inventively preferred. In addition, pectinergic emulsions obtained from emulsion emulsions are also enriched in silver nanoparticles and in that they may have a higher silver nanoparticle content than a parent emulsion.

With regard to further features of the method according to the invention, reference is hereby explicitly made to the explanations in connection with the inventive Pickering invention and the use according to the invention.

According to the invention, a Pickering emulsion for producing conductive coatings is furthermore proposed for achieving the object according to the invention, the emulsion being stabilized

Contains silver nanoparticles, water and at least one organic, not m water-soluble solvent, wherein the stabilized silver nanoparticles in an amount of 0.5 wt .-% to 7 parts by weight preferably 0.7 to 6.5 parts by weight %, more preferably up to 5 wt .-%, for example up to 3.5 wt .-%, based on the total weight of the emulsion, are included. The present invention provided Pickering emulsion. is suitable as a coating agent for the production of electrically conductive structures, in particular for the formation of reticulated honeycomb structures by Selbstorgani organization of silver nanoparticles and can also be used for the production of transparent electrically conductive structures, in particular of continuously connected transparent conductive networks. Advantages of the self-organization of Si l bernanopartikel ^{'abenstrukturen} to W are that kei n asc ändiger printing process or expensive technologies are required to obtain electrically conductive structures. Moreover, the honeycomb structures are transparent and / or help to improve the transparency of the formed structured coating.

As already explained in the description of the preparation process, the Pickering emulsion according to the invention preferably contains small sterically stabilized silver nanoparticles as coating agent. which have a dso of approximately 80 nm in the main and are colloidally stable in the silver nanoparticle sol used. The stabilized silver nanoparticles are having a low concentration according to the invention of from 0.5% by weight to 7% by weight, preferably from 0.5 to 5% by weight, particularly preferably up to 4.5% by weight, for example up to 3, 5 wt .-%, without additional dispersing agent in the Pickering emulsion. Presumably, even by this low concentration, a low after-treatment temperature of 140 ° C is sufficient to achieve surprisingly high conductivities of the formed structures after application and drying of the Pickering emulsion as a coating agent on egg nem substrate. In a preferred embodiment of the Pickering emulsion according to the invention, it is thus provided that it contains no additional surface-active compounds, binders, polymers, buffers, film formers or dispersants. Advantage haftcnvci sc the inventive Pickering emulsion is therefore free of additional substances which could reduce the conductivity of a coating produced therefrom.

This means that no additives, in particular no additional surface-active compounds, binders, polymers, buffers or dispersants have to be added in order to obtain a suitable for the production of electrically conductive coatings Pickering emulsion. Therefore, the Pickering emulsion according to the invention has the further advantage that it is not only less expensive, but also easier to prepare compared to coating compositions containing additional additives, such as surface-active compounds, other dispersing aids or polymers. It is also advantageous that steric hindrance of the silver particles is avoided by such additional additives and good conductivity of a coating produced from the Pickering emulsion according to the invention, in particular also comparatively low after-treatment temperatures, can be ensured.

In a preferred embodiment of the inventive Pickering emulsion, the organic solvent is at least one linear or branched alkane. an optionally alkyl-substituted cycloalkane, an alkyl acetate or a ketone, benzene or toluene. Examples of organic solvents suitable according to the invention! si nd cyclohexane, methylcyclohexane, n-hexane, octadecane, ethyl acetate, butyl acetate, acetophenone and cyclohexanone, this list is not exhaustive. With these solvents as the oil phase, stable Pickering emulsions could be produced according to the invention, which are particularly suitable as coating agents for producing electrically conductive structures, in particular for the formation of reticulated honeycomb structures by self-organization of the silver manopar particles.

In a further preferred embodiment of the Pickering emulsion according to the invention it is provided that the organic solvent and the water in the emulsion preferably in a ratio (in wt .-%) of 1: 4 to 1: 2, for example in a ratio of 1: 3, are included.

Within the scope of a preferred embodiment of the Pickering emulsion according to the invention, those in the Pickering emulsion are, for example, in the form of a silver nanoparticle sol. contributed

Silbemanopartikel sterically stabilized by a dispersing aid. The dispersing aid for the stable stabilizer is preferably selected from the series: polyvinylpyrrolidone, block copolymer and block copolyether with polystyrene blocks. Especially polyvinylpyrrolidone having a molecular weight of about 10000 amu (for example PVP K15 from Fluka) and polyvinylpyrrolidone having a molecular weight of about 360000 amu (for example PV K90 from Fluka) and more preferably block copolyether with polystyrene blocks having 62 are preferred Wt.% C: -Pol> ethcr. 23 wt ⁰ "CVPolvether and 15 wt ^0" polystyrene, based on the dried dispersion aids, with a ratio of the block lengths CVPolvether to CVPolvether of 7: 2

Units (eg Disperbyk 190 from BY K-Chemie, Wesel) used.

Preferably the dispersing aid in an amount of 10 wt .-% is up, preferably from 3 wt ⁰ "to 6 wt .-%, based on the silver content of the particles present. On the one hand, the selection of such a concentration range ensures that the particles are covered with dispersing assistant so far that the desired properties, such as stability of the emulsion, are ensured. On the other hand, according to the invention, this avoids excessive enclosure of the particles with the dispersing assistant. An unnecessary excess of dispersing agent could undesirably affect the properties of the Pickering emulsion to be produced and the coatings to be produced therefrom. Furthermore, an excess of dispersing aid may be detrimental to the colloidal stability of the particles and, if appropriate, hinders further processing. In addition, an excess of dispersing aids may lower the conductivity of the coatings produced from the Pickering coatings, or even cause insulation. All the above-mentioned disadvantages are advantageously avoided according to the invention. With regard to further features of the inventive Pickering emulsion, reference is hereby explicitly made to the explanations in connection with the process according to the invention and the use according to the invention.

The invention further relates to a method for fully or partially compliant Besch

Surfaces, wherein AA) a Pickering emulsion according to the invention is applied in full or in part to a surface,

AB) the surface thus coated is then covered with a cover so that water and solvent can escape.

AC) the thus covered, coated top surface is then dried to remove the water and the organic solvent at least at a temperature of less than 40 ° C, AD), the thus dried coating is then sintered in the presence or absence of the cover.

The application of the Pickering emulsion according to the invention in step (AA) can be carried out, for example, by spray coating, dipping. Floods or knife coating done. For example, the Pickering emulsion can also be applied by means of a pipette. When applying the inventive

Pickering Emulsion has surprisingly been found to retain the oil droplets coated with silver nanoparticles, which advantageously influences the separation of silver particles and the formation of honeycomb structures. A good self-leveling of the silver particles allows the formation of continuous structures, whereby costly printing processes or cost-intensive technologies for their production can advantageously be dispensed with.

By means of the cover, which is applied in step (AB) to the surface coated with the Pickering emulsion, it is possible, on the one hand, for the speed of the drying of the wet layer to be favorably favored, so that a continuous network of silver nanoparticles can be formed. On the other hand, it was surprisingly found that the cover also promotes the self-organization of the silver manopar particles, in particular to honeycomb structures of the silver particles. Due to the formation of honeycomb structures made of silver nanoparticles, according to the invention, in addition to a good conductivity, advantageously also a good transparency can be achieved. To remove the water and the organic solvent, drying is carried out at least at a temperature below 40 ° C. under step (AC). It has been found that particularly good conditions for the formation of the desired honeycomb structures by the silver particles could be achieved in these drying conditions, which in particular have little thermal stress, and the associated slow evaporation of the water and of the organic solvent. Furthermore, the drying conditions are also suitable for cooking sto ffsu b st rate.

Within the scope of a preferred embodiment of the process, it is provided that the drying takes place under (AC) at at least one temperature of less than 35 ° C., particularly preferably at room temperature. The drying step is thereby very gentle, and it has been advantageously the formation of consistently connected reticulated honeycomb structures by the

Silver nanoparticles. achieved.

In a further embodiment of the method, the drying under (AC) for a period of 15 minutes to 36 hours. In the context of a further preferred embodiment of the method, the cover can be a glass or plastic plate, a plastic film or a plastic or Tcxtih read, preferably a water and solvent-permeable cover.

If a cover is used which is not permeable to water and / or solvents, water and / or solvents can escape, for example, via the edge regions between substrate and cover. An example of this is the covering of a Pickering emulsion coated glass slide with another glass slide. If such a substrate cover arrangement is used, in accordance with the invention it is also referred to as a sandwich decay. A water and solvent-permeable cover may be preferred in accordance with the invention

Embodiment be a porous filter cloth. For example, a Monodur polyamide (PA) filter cloth (VERSEIDAG) can be used. This is commercially available with different mesh sizes and can be used depending on the solvent used. The advantage of such a filter cloth is that the drying over the surface of the substrate can be carried out more uniformly than with a transparent cover. In addition, the

Drying time can be shortened. Advantageously, equally good or even better results with regard to the self-assembly of the silver manoparticles into suitable mesh and honeycomb structures than in a sandwich method can be achieved. Furthermore, the silver particles are relatively less liable to such a cover, so that the risk of destruction of the formed, possibly not yet sintered, silver nanoparticle structures can be significantly reduced.

In another preferred embodiment of the method according to the invention for partial or full-surface coating, it is provided that the surface is the surface of a glass, metal. Ceramic or plastic substrates. For example, a plastic substrate may be made of polyimide (PI). Polycarbonate (PC) and / or polyethylene terephthalate (PET) polyurethane (PU), polypropylene (PP), which may optionally, for example, to ensure sufficient wettability, pretreated with the inventive Pickering emulsion and / or provided with a primer. Preferably, the substrate may also be transparent. In the context of a further preferred embodiment of the invention, the invention relates to a further embodiment of the invention

Coating may include sintering under (AD) at least at a temperature greater than 40 ° C, preferably at least at a temperature of from 80 ° C to 180 ° C, most preferably from 130 ° C to 160 ° C, for example at 140 ° C , respectively. First of all, it is through comparatively low aftertreatment temperatures also possible, the invention also for the production of transparent electrically conductive structures on temperature-sensitive substrates, such as Poiycarbonatfolien use. According to the invention, it is advantageously possible even under the low thermal load to obtain very well adhering, electronically conductive structures on substrates such as glass slides, but also polycarbonate foils. In this case, electrically conductive structures are in particular structures which have a resistance of less than 5000 Ω / m. In addition, the coatings obtained according to the invention can be transparent, which is particularly advantageous for various applications. Another object of the invention are electrically conductive coatings. get through

Processes according to the present invention, wherein these coatings have the additional advantage that they are transparent. Such electrically conductive transparent coatings can, for example, form conductor tracks, antenna elements, sensor elements or bond connections for contacting with semiconductor components. The transparent and conductive coatings according to the invention can be used, for example, as transparent electrodes for displays, screens and touch panels. are used as electroluminescent displays, as transparent electrodes for touch switches, as transparent shields for electrodes and auxiliary electrodes, for example for solar cells or in OLEDs, in applications for plastic spectacle lenses, as transparent electrodes for electrochromic layer systems or as transparent electromagnetic shielding. In this case, advantageously, the expensive layers and structures of tin-doped indium oxide (indium tin oxide, ITO) can be replaced or supplemented.

The following examples serve to exemplify the invention and are not intended to be

To understand limitation.

Examples

Equipment used to carry out the analysis

1. Determination of Ag concentration by solid scale: METTLER TOLEDO

HG53 halogen moi sture analyzer)

2. Determination of the theological properties and the stability of the cream layer:

Measuring device: MCR301 SN801 18503

Measuring system: CC 17-SN7448; d = 0 mm

Measuring profile: 21 measuring points;

Measuring point duration 30 ... 2 s log

25 ° C

d (gamma) / dt = 0, 1 ... 1E + 3 1 / s log; jSteigungj = 5 pts / dec

3. Determination of the Drop Size Distribution and Checking the Stability of the Emulsions by Light Microscopy

LEICA DMLB light microscope

4. Determination of the surface tension by means of a ring tensiometer: SerNr: 20002901 5. Dispersing device: ULTRA-TURRAX (IKA T 25 digital ULTRA-TURRAX)

6. Dispersing Device Ultrasonic Finger (G. Heinemann, Ultrasound and Laboratory Technology)

7. Measurement of resistance: Multimeter: METRA Hit 14A

8. UV-VIS spectrophotometer

HEWLETT 8452 A

PACKARD diode array spectrophotometer

Example 1 Preparation of a Silver Nanoparticle Sol (Nanosilver Dispersion)

A 0.054 molar silver nitrate solution was mixed with a mixture of 0.054 molar sodium hydroxide solution and the dispersing aid Disperbyk 190 (manufacturer BYK Chemie, Wesel) (1 g 1) in a volume ratio of 1: 1 and stirred for 10 m. To this reaction mixture A 4.6 molar aqueous Formaldehvd solution was added with stirring so that the ratio of Ag ^" to reducing agent was 1: 10. This mixture was heated to 60 ° C., kept at this temperature for 30 minutes and then cooled In a first step, diafiltration separated the unreacted educts, and the mixture was concentrated, using a membrane of 30,000 daltons to give a colloid-stable

Sol with a solids content of 2 1.2 wt .-% (silver particles and dispersing agent). According to elemental analysis after membrane filtration, the proportion of Disperbyk 190 was 6% by weight, based on the silver content. An investigation by means of laser correlation spectroscopy revealed an effective particle diameter of 78 nm. 2: Preparation of the Pickering emulsion

The silver nanoparticle sol of Example 1, water and organic solvent, were mixed and treated with the sonicator for 3 minutes at 50% amplitude and an O / W emulsion was prepared. After a service life of 24 h, the cream phase was characterized.

The droplet size distribution, the viscosity, the surface tension of the Pickering emulsion and the solids content of stabilized silver particles were determined. The results are summarized in Tab. 1.

Tab. I

Example 3: Coating of Substrates

Those from the parent emulsions. Pickering emulsions prepared in Example 2 were applied to a glass slide and the resulting wet layer was covered with a glass slide (sandwich method) or by applying a porous, water and solvent impermeable filter cloth and at temperatures less than Dried 35 ° C. It was the formation of honeycomb structures from the silver parts in the

Dry films detected. In order to achieve a conductivity of the coatings with the honeycomb structures, the dry films were sintered after removal of the cover 4-12 h at 140 ° C. The resistance of the resulting coating was measured on the honeycomb film with a multimeter between two approximately 0.3 cm wide and 1 cm long strips at a distance of 1 cm. The transmission was determined by UV-VIS spectrophotometer. Example 3.1

With the aid of an Eppendorf pipette, 500 μl of the cream phase were applied to a glass slide [25 mm / 75 mm / lmm (b / l / h)] and covered with a glass slide as cover glass (cover). Thereafter, the wet film covered with the coverslip was dried at RT overnight. The water and the organic solvent were able to escape through the edges of the glass slide sandwich formed. After removing the coverslip, the formed dry film was sintered at 140 ° C for 12 hours. The formation of a honeycomb structure could be observed by light microscopy.

The solids content of stabilized silver nanoparticles in the Pickering emulsion and the conductivity and transmission of the coating produced were determined:

The results are summarized in Tab. 2.

Tab. 2

Example 3.2

Using an Eppendorf pipette, 5000 μl of the frame phase were applied to a glass slide [100 mm / 200 mm / 4 mm b / l h] and covered with a glass slide as cover glass (cover). Thereafter, the wet film covered with the coverslip was dried at RT for five days. The water and the organic solvent were able to escape over the edges of the glass slide sandwich formed. After removing the coverslip, the formed dry film was sintered at 140 ° C for 12 hours. The formation of a honeycomb structure could with

Light microscopy are observed.

The results are summarized in Tab. 3. Table 3

Step Example! 3.3

With the help of an Eppendorf pipette 5000μ1 of the cream hare was applied to a glass slide [100mm / 200mm / 4mm b / l / h] and lapped with 200μηι wet layer. On the wet layer a filter cloth PA ΙΟΟμηι mesh size was launched. Thereafter, the wet film covered with the filter cloth was dried at RT for one hour. The water and the organic solvent were able to escape through the pores of the filter cloth. After removing the filter cloth, the dry film formed was sintered at 140 ° C for 12 h. The formation of a honeycomb structure could be observed by light microscopy.

The Feststoffgchalt of stabilized silver nanoparticles in the Pickering emulsion and the conductivity and transmission of the coating produced were determined.

The results are summarized in Tab.4.

Table 4

Example 3.4

With the aid of an Eppendorf pipette, ΙΟΟμΙ of the frame phase were pipetted onto a glass slide [25 mm / 75 mm / lmm (b / lh)] and knife-coated with a 50 μm wet layer. On the wet layer, apply a filter cloth PA ΙΟΟμιη machine ash. Thereafter, the wet film covered with the filter cloth was dried at RT for 30 minutes. The water and the organic solvent were able to escape through the pores of the filter cloth. After removing the filter cloth, the dry film formed was sintered at 140 ° C for 12 h.

This experiment was carried out once with cyclohexane and once with n-Hxxan as organic

Solvent to form the oil phase in the Pickering emulsion.

The formation of a honeycomb structure could be observed in each case with light microscopy. The solids content of stabilized silver particles in the Pickering emulsion and the conductivity and transmission of the coating produced were determined.

The results are summarized in Tab. 5.

Tab. 5

Example 3.5

Analogous coating experiments to the above examples by means of knife coating or spray coating on untreated polycarbonate film were unsuccessful due to poor wetting.

Example 3.6

With the aid of an Eppendorf pipette, ΙΟΟΟμϊ of the cream layer was applied to a polycarbonate film coated with TiOx [100 mm / 100 mm / O. 1 7mm (b / l / h)] applied and m i t Ι ΟΟμηι wet layer scrape, with a good wetting was achieved. On the wet layer a filter cloth PA ΙΟΟμιη mesh size was launched. Thereafter, the wet film covered with the filter cloth was dried at RT for one hour. The water and the organic solvent were able to escape through the pores of the filter cloth. After removing the filter cloth, the dry film formed was sintered at 140 ° C for 12 h. This experiment was repeated once with cyclohexane and once with methylcyclohexane as the organic solvent to form the oil phase in the Pickering

Emulsion performed. The formation of a honeycomb structure could be observed by light microscopy.

The solids content of stabilized silver particles in the Pickering emulsion and the conductivity and transmission of the coating produced were determined:

The results are summarized in Tab. 6.

Tab. 6

Example 4: Influence of silver concentration

The mixtures listed below were prepared as described in Example 2 and then applied as in Example 3, dried and sintered. The content of silver nanoparticles in the emulsion was determined. Then two silver points with one

Silver paste applied to the conductive coating at a distance of 1 cm, and the resistance determined. In addition, the drop size of the emulsion was determined with the light microscope. The results are summarized in Tab. 7. Tab. 7

Example 5 Analysis of the Silver Content in the Cream Phase (Pickering Emulsion)

First, an Ag sol was prepared analogously to Example 1, which indicates a solids content

Silver nanoparticles of 18.5%.

Then, in analogy to Example 2, the Pickering emulsions (ultrasonic fingers 3 m in at 50%

Amplitude) and the solids content of stabilized silver nanoparticles was determined after each 20 h and after five days. It could be shown that, especially at comparatively low starting concentrations of silica-solubilizing molecules, a concentration of stabilized silver nanoparticles in the cream phase can advantageously be obtained.

The results are summarized in Tab. 8.

Tab. 8

Ag Sol

water

(18.5%) cyclohexane solid halide the solids content solids content in

Cream layer after cream layer Source emulsion [g] [g]

[g] calculated 20h after 5 days (wt%)

72.0 4.0 24.0 1.33 1, 10 0.74

68.0 8.0 24.0 2.05 2.01 1.48

64.0 12.0 24.0 2.45 2.33 2.22

60.0 16.0 24.0 2.76 2.74 2.96

49.0 27.0 24.0 3.08 3.98 5.0

Claims

claims

1. A process for the preparation of a Pickering emulsion for the production of conductive coatings, characterized in that a) an aqueous dispersion containing, in particular sterically, stabilized silver nanoparticles and water mixed with at least one, not water-miscible, solvent and then dispersed to form an emulsion , wherein the content of stabilized silver nanoparticles, based on the total weight of the emulsion obtained, is between 0.5 wt .-% and 7 wt .-%, and b) then during a service life, the emulsion obtained in (a) by a creaming in an upper concentrated emulsion phase and a lower, substantially aqueous, phase is separated, and c) the resulting upper concentrated emulsion phase is isolated, this emulsion phase having a content of silver nanoparticles of up to 7% by weight, preferably up to 4.5% by weight. %, based on their total weight.

2. The method according to claim 1, characterized in that the service life under (b) is 1 hour to 5 days.

3. The method according to claim 1 or 2, characterized in that the content of silver nanoparticles of the emulsion under (a), based on the total weight of the emulsion obtained under (a), between 0.7 wt .-% and 6.5 wt. -% lies.

4. Pickering emulsion for the production of conductive coatings, in particular produced by a process according to any one of claims 1 to 3, characterized in that the emulsion contains stabilized silver nanoparticles, water and at least one organic water-immiscible solvent, wherein the stabilized silver nanoparticles in a Amount of 0.5 wt .-% to 7 wt .-%, based on the total weight of the emulsion contained.

5. Pickering emulsion according to claim 4, characterized in that it contains no additional surface-active compounds, binders, polymers, film formers, buffers or dispersants.

6. Pickering emulsion according to claim 4 or 5, characterized in that the organic solvent is at least one linear or branched alkane, an optionally alkyl-substituted cycloalkane, an alkyl acetate or a ketone, benzene or toluene.

7. Pickering emulsion according to at least one of claims 4 to 6, characterized in that the organic solvent and the water are contained in the emulsion in a volume ratio of 1: 4 to 1: 2 ,

8. Pickering emulsion according to at least one of claims 4 to 7, characterized in that the silver nanoparticles are sterically stabilized.

9. A process for the full or partial coating of surfaces, characterized in that

AA) a Pickering emulsion according to at least one of claims 4 to 7 is fully or partially applied to a surface,

AC) the coated surface thus covered is subsequently dried at at least a temperature of less than 40 ° C,

AD), the thus dried coating is then sintered in the presence or absence of the cover.

10. The method according to claim 9, characterized in that the drying under (AC) at least at a temperature of less than 35 ° C, preferably at room temperature, takes place.

1 1. A method according to claim 9 or 10, characterized in that the drying is carried out under (AC) for a period of 15 minutes to 36 hours.

12. The method according to claim 9, wherein the cover is a glass or plastic plate. a KunststoffYolic or a plastic or textile fleece, preferably a water and solvent-permeable cover is.

13. The process according to claim 9, wherein the surface is the surface of a glass, metal, ceramic or plastic substrate.

14. The method according to at least one of claims 9 to 13, characterized in that the sintering under (AD) at least at a temperature of more than 40 ° C, preferably at least one temperature in a range of 80 ° C to 180 ° C takes place ,

15. A conductive coating produced by a process according to any one of claims 9 to 14, characterized in that it is transparent.