Method for producing patterned metallic coatings

Abstract

A method for producing patterned metallic coatings includes an initiator composition having at least one active substance being added to a substrate. A precursor composition including at least one precursor compound for a metallic layer is applied to the initiator composition coating. A metallic layer is then deposited by the active substance. At least one composition is applied as an emulsion in order to obtain a patterning of the resultant metallic layer.

Claims

1. A method for producing structured metallic coatings, comprising the following steps: a) application of an initiator composition comprising at least one active substance to a substrate, wherein the initiator composition comprises a Pickering emulsion; b) application of a precursor composition comprising at least one precursor compound for a metal layer to the substrate; and c) deposition of a metal layer of the precursor composition by the active substance of the initiator composition; wherein at least one of the compositions in step a) and/or step b) comprises an emulsion.

2. The method as claimed in claim 1, the active substance comprises reducing groups or precursors thereof or a photo catalytically active inorganic substance.

3. The method as claimed in claim 1, wherein the active substance comprises ZnO or TiO.sub.2.

4. The method as claimed in claim 3, wherein the active substance comprises nanoscale particles of ZnO or TiO.sub.2.

5. The method as claimed in claim 4, wherein the particles are surface-modified.

6. The method as claimed in claim 1, wherein a content of nanoparticles in the initiator composition is more than 0.1% by weight.

7. The method as claimed in claim 1, further comprising a drying carried out between step a) and step b).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a) diagrammatic representation of the method according to the invention; b) diagrammatic representation of the resulting network;

(2) FIG. 2 shows a photomicrograph of emulsion 7 h on a substrate under a cover glass (20 C.);

(3) FIG. 3 shows a photomicrograph of emulsion 7 k on a substrate under a cover glass (20 C.);

(4) FIG. 4 shows a photomicrograph of a titanium dioxide nanoparticle emulsion (sample 7 h) before metallization. The scale is 10 m;

(5) FIG. 5 shows a photomicrograph of a titanium dioxide nanoparticle emulsion (sample 7 h) after metallization.

(6) The scale is 10 m;

(7) FIG. 6 shows photomicrographs of emulsions; a) emulsion 8a directly after application; b) the same emulsion 15 minutes later; c) emulsion 8g after application; d) the same emulsion 15 minutes later;

(8) FIG. 7 shows a photomicrograph of the dried emulsion (8a) at 90 C. with incident light; grey areas are uncoated;

(9) FIG. 8 shows a section from FIG. 7;

(10) FIG. 9 shows a photomicrograph of the silver-coated emulsion (8a) with incident light;

(11) FIG. 10 shows DLS measurements of a dispersion with 2% by weight TiO.sub.2 at 20 C.;

(12) FIG. 11 shows DLS measurements of a diluted solution of TiO.sub.2 particles modified with acetylsalicylic acid at 20 C.;

(13) FIG. 12 shows DLS measurement of a dilute solution of TiO.sub.2 particles modified with salicylic acid at 20 C.

DETAILED DESCRIPTION OF THE INVENTION

(14) FIG. 1a shows a diagrammatic representation of a preferred embodiment of the method. Firstly, an emulsion of an initiator composition comprising two phases 2, 3, which comprises nanoparticles 1, is applied to a substrate 4. It is preferably a Pickering emulsion which is stabilized by the nanoparticles 1. The applied emulsion is dried on the surface of the substrate (step 10). This results in the concentration of the nanoparticles at the phase interfaces of the emulsion on the surface (step 11). This gives rise to the formation of thin grid-like structures of the nanoparticles 5. Then (step 12), a metal 6 is deposited on the nanoparticles. This gives a grid-like metalized structure. An idealized representation of the resulting structure is shown in FIG. 1b.

(15) FIG. 2 shows a photomicrograph of an emulsion with unmodified titanium dioxide particles. The emulsion exhibits a droplet size between 30 and 140 m on the substrate. FIG. 3 shows the influence of the addition of butanol as weak emulsifier. It leads to a considerable reduction in droplet size.

(16) FIG. 4 shows an emulsion with unmodified titanium dioxide particles after drying which, in FIG. 5, has been metalized in the next step with silver. The images show that the metal deposition takes place very selectively only on the titanium dioxide. However, the size of the droplets is relatively small, meaning that the sample does not appear transparent after the metallization.

(17) FIG. 6 shows the aging of emulsions at room temperature of two emulsions with surface-modified particles. It can be seen clearly that larger droplets are formed from the surface. A monolayer of relatively large drops is formed here. After 10 minutes, dynamics are no longer to be observed and the solvents slowly evaporate.

(18) FIGS. 7 and 8 show a dried emulsion with surface-modified titanium dioxide particles. It is possible to clearly see the formed webs of titanium dioxide which form a honeycomb-like pattern.

(19) As shown in FIG. 9, this structure can be metalized with silver in a simple manner.

WORKING EXAMPLES

(20) For transmission electron microscopy (TEM), a Philips CM200 FEG (200 kV accelerating voltage) was used.

(21) The photomicrographs were recorded using an Olympus BH2 Series System Microscope with transmitted light or incident light.

(22) Dynamic light scattering (DLS) for measuring the hydrodynamic radius was carried out using a Microtrac Nanotrac Ultra.

(23) 1. Synthesis of TiO.sub.2 Nanoparticles (Anatase)

(24) 97.07 g (342 mmol) of titanium isopropoxide in 105.45 g (1745 mmol) of 1-propanol are charged to a 250 ml round-bottomed flask and intensively stirred. 6.69 g (68 mmol) of 37% strength hydrochloric acid are added to 20.00 g (333 mmol) of 1-propanol and this solution is slowly added dropwise to the reaction mixture after 2 minutes. After 30 minutes, a mixture of 8.05 g (447 mmol) of water and 40.00 g (666 mmol) of 1-propanol is added dropwise.

(25) The mixture is stirred for a further 20 minutes and the sol produced in this way is placed in equal parts into two Teflon containers and brought to 225 C. in the autoclave over the course of 30 minutes and held at this temperature for 120 minutes. After cooling, the solvent is decanted off and discarded, the sediment is dried almost completely on a rotary evaporator at a maximum of 40 C. The anatase nanoparticles are obtained as white powder. FIG. 10 shows the size distribution measured with DLS.

(26) Characterization: BET: 11.14 nm; DLS: 1st maximum: 10.52 nm (S=0.31), 2nd maximum: 21.04 nm (S=0.77); Raman: E.sub.G: 146 cm.sup.1, B.sub.1G: 399 cm.sup.1, A.sub.1G: 639 cm.sup., E.sub.G: 639 cm.sup.1.

(27) 2. Surface Modification with Acetylsalicylic Acid (ASA)

(28) 0.18 g of acetylsalicylic acid (1 mmol) is suspended in 45 g of water and the resulting suspension is filtered in order to separate off excess acetylsalicylic acid from the saturated solution.

(29) With vigorous stirring, a dispersion of 10 g of water with 2.50 g (31 mmol) of titanium dioxide particles (anatase) is added dropwise very slowly. The mixture is mixed intensively for a further 10 minutes. By adding 7.03 g (71 mmol) of 37% strength hydrochloric acid, acetic acid is eliminated from acetylsalicylic acid and the reaction mixture becomes intense yellow in color. The resulting particles are centrifuged, and the supernatant is decanted off and discarded. The residue is redispersed in 40.00 g of water. This gives a clear, yellow dispersion.

(30) FIG. 11 shows DLS measurements of several samples which have been produced by the same method. The diluted dispersion obtained was measured.

(31) 3. Surface Modification with Salicylic Acid (SA)

(32) 0.14 g (1 mmol) of salicylic acid is suspended in 40 g of water and the excess salicylic acid is separated off by filtration. With vigorous stirring, a dispersion of 20 g of water and 3.58 g (44 mmol) of titanium dioxide is slowly added dropwise. The mixture is stirred intensively for a further 30 minutes. A slightly cloudy, yellow dispersion is obtained.

(33) FIG. 12 shows DLS measurements of several samples which have been produced by the same method. The diluted dispersion obtained was measured.

(34) 4. Producing Titanium Dioxide Pickering Emulsions

(35) In accordance with table E1, various emulsions are synthesized in a 250 ml flask which differ in the ratios of toluene, water, butanol and titanium dioxide nanoparticles. In principle, water and titanium dioxide nanoparticles are introduced and then homogenized using an IKA T25 Ultra Turrax at 25 000 rpm for two minutes. Then, the organic solvents are added and the mixture is homogenized with cooling for a further three minutes at 25 000 rpm.

(36) TABLE-US-00001 TABLE E1 Toluene/water emulsions with TiO.sub.2 nanoparticles (unmodified) Emulsion Water [g] Toluene [g] Butanol [g] TiO.sub.2 [g] 7a 100.04 87.03 1.0 7b 100.03 86.79 1.5 7c 99.97 86.80 2.0 7d 75.04 130.15 1.0 7e 74.89 130.24 1.5 7f 75.01 130.12 2.0 7g 150.03 52.02 1.0 7h 150.07 52.06 1.5 7i 150.12 52.07 2.0 7j 150.10 51.96 5 1.5 7k 149.97 51.97 10 1.5 7l 150.03 52.04 15 1.5

(37) The emulsions with butanol as weak emulsifier exhibit a considerably reduced droplet size. On account of the free OH groups on the surface of the titanium dioxide particles used, these stabilize preferably O/W emulsions. As expected, the W/O emulsions 7d, 7e, 7f are not stabilized by these titanium dioxide particles. In all other cases, emulsions are formed.

(38) 5. Producing Titanium Dioxide Pickering Emulsions with Surface-modified Particles

(39) In accordance with table E2 and E3, various emulsions are synthesized in a 20 ml glass vessel. 0.06 g (1 mmol) of sodium chloride and 10.00 g of water are used to prepare an NaCl solution.

(40) The dispersions from example 2 (TiO.sub.2 with ASA) or example 3 (TiO.sub.2 with SA) are initially introduced, and the NaCl solution is added. After adding the organic phase, hydrochloric acid (37%) is added and the mixture is emulsified using a vibration mixer (Heidolph Reax Control) at 25 000 rpm. In the first minutes, creaming may result, depending on the solvent. In this case, the upper phase after the creaming is used as emulsion and referred to as emulsion. Tables E2 and E3 show the prepared emulsions.

(41) TABLE-US-00002 TABLE E2 Emulsions based on toluene TiO.sub.2 NaCl with ASA TiO.sub.2 with SA Toluene Water HCl solution Name [g] [g] [g] [g] [g] [g] 8a 1.03 4.33 10.01 1.01 0.14 8b 2.01 4.32 9.00 1.00 0.10 8c 3.00 4.33 8.03 1.00 0.13 8d 1.00 4.33 10.00 1.01 0.10 8e 1.98 4.28 9.00 1.00 0.10 8f 3.01 4.28 7.98 0.99 0.12

(42) TABLE-US-00003 TABLE E3 Emulsions based on cyclohexane TiO.sub.2 NaCl TiO.sub.2 with with SA Cyclo-hexane Water HCl solution Name ASA [g] [g] [g] [g] [g] [g] 8g 1.02 4.67 10.00 1.00 0.12 8h 1.98 4.67 9.00 1.00 0.14 8i 3.00 4.66 7.97 1.00 0.12 8j 1.00 4.67 10.00 1.01 0.13 8k 1.99 4.65 9.04 1.00 0.11 8l 2.99 4.68 8.06 0.99 0.12

(43) 6. Application of the Initiator Composition without Surface Modification 200 l of emulsion 7h were placed onto a glass slide. The samples are prepared in three different ways: (1) they are covered with a second slide; (2) they are dried without covering; (3) they are covered with a filter cloth. After drying, the slides were washed thoroughly with distilled water in order to separate off excess titanium dioxide.

(44) FIG. 7 shows sample 7h after drying at 20 C. for 26 hours.

(45) 7. Application of the Initiator Composition with Surface Modification:

(46) In each case 200 l of the prepared emulsions 8a to 8l were placed onto glass slides and dried without covering. Table E4 shows the drying conditions of the emulsions. Then, any excess titanium dioxide and sodium chloride were rinsed off from the slides using distilled water and the samples were dried using compressed air.

(47) TABLE-US-00004 TABLE E4 Temperature [ C.] Time [min] 30 60 40 20 50 7 60 7 70 5 80 5 90 3 100 3

(48) In all cases, a self-organization, i.e. the formation of a grid-like structure was observed.

(49) FIGS. 7 and 8 show photomicrographs of the dried structure of emulsion 8a at 90 C. and 3 minutes.

(50) The surface-modified particles are localized at the interface of the two phases of the emulsion on account of their salicylic acid modification. They arrange themselves in the course of drying between the drops and this produces a network. Whereas the width of the titanium oxide ribs varies in the range from 1 m to 3 m, large, uncoated ranges from 40 m to 90 m diameter are obtained. The smaller droplets present in the images prior to drying have disappeared during drying due to coalescence and aging of the emulsion.

(51) Only the few evident broadenings of the ribs make the coating on the slides partially visible. In areas in which these miscoatings are not present or at least barely present, the dried sample appears optically transparent.

(52) 8. Producing a precursor composition (Ag-TRIS)

(53) With vigorous stirring, a solution of 1.69 g (10 mmol) of silver nitrate in 20 g of water was slowly added dropwise to a solution of 2.57 g of tris(hydroxymethyl)aminomethane (9 mmol) in 20 g of water.

(54) 9. Application of the Precursor Composition

(55) The dried samples were flooded with Ag-TRIS and then exposed to an Hg-Xe lamp (1000 watts) for 10 to 30 seconds. Silver is deposited only at the titanium dioxide ribs.

(56) FIG. 5 shows an exposed sample (30 seconds; Hg-Xe lamp; 1000 watts) of an emulsion with non-surface-modified titanium dioxide particles. A distribution of round non-silvered areas is evident. Silvered ribs are approx. 6 m wide. Consequently, although the sample is uniformly selectively metalized, the sample is not transparent.

(57) FIG. 9 shows an exposed sample (15 seconds Hg-Xe lamp; 1000 watts) of an emulsion with surface-modified titanium dioxide particles. This sample too was only silvered in the area coated with titanium dioxide particles. The optical transparency does not change since the ribs are considerably thinner.

CITED LITERATURE

(58) WO 2012/084849 A2 US 2009/0269510 A1 WO 93/21127 DE 4212633 WO 96/31572