EP1846593A1

EP1846593A1 - Surface with a wettability-reducing microstructure and method for the production thereof

Info

Publication number: EP1846593A1
Application number: EP06707914A
Authority: EP
Inventors: Christian Hansen; Ursus KRÜGER; Manuela Schneider
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2005-02-04
Filing date: 2006-01-31
Publication date: 2007-10-24
Also published as: WO2006082179A1

Abstract

The invention relates to a surface with an adhesion-reducing microstructure and to a method for the production thereof. Adhesion-reducing microstructures of this type exist in order to form, for example, self-cleaning surfaces while utilizing the so-called lotus effect. The invention provides that during an electrochemical production of the layer, particles (21n) having an oligophobic surface are added to the electrolyte whereby forming a suspension with the electrolyte, and/or molecules (21m) having oligophobic properties are added whereby dissolving in the electrolyte, so that the particles or molecules are incorporated in the layer that forms the surface. The produced microstructure of the inventive surface having oligophilic and oligophobic surface areas consisting of elevations (19) and depressions (20) can be superimposed by smaller dimension elevations (19n) and depressions (20n) of a nanostructure whereby enabling the lotus effect obtained by the surface to be advantageously improved. The surfaces can be used, for example, in building components such as façades or also in machine parts, which are exposed to the earth's atmosphere, where both hydrophilic as well as oligophilic substances come in contact with the surface.

Description

description

Surface with a wettability reducing micro ^¬ structure and method for their preparation

The invention relates to a surface having an adhesion-reducing microstructure and to a process for the electrochemical production of such a surface.

Adhesion-(d. E., The wettability with flues sigkei ^¬ th diminishing) z surfaces of the type mentioned come. B. are used as so-called lotus effect surfaces and are described, for example, in DE 100 15 855 ^A1 . According to this document, such surfaces are characterized by a microstructure which can be obtained by a layer deposition from solutions, but also by an electrolytic deposition. This mimics an effect observed on the leaves of the lotus flower, according to which the microstructure produced, which for this purpose has elevations and depressions with a radius of 5 to 100 μm, reduces the adhesion of water and dirt particles. As a result, contamination of the corresponding surface can be counteracted. Furthermore, z. B. also avoid limescale deposits.

The object of the invention is to provide a surface with an adhesion reducing microstructure or. specify a production method for this surface, wherein the effect of reducing the adhesion of the surface should also be pronounced in olophophilic substances. According to the invention, the object is achieved by the method mentioned in the introduction by adding to the electrolyte particles having an oligophobic surface which form a suspension with the electrolyte and / or adding molecules having oligophobic properties which dissolve in the electrolyte, such that the particles or molecules are incorporated into the surface-forming layer. This advantageously ensures that the Molecule ^¬ le or particles constituting the oligophoben properties also a part of the surface, so that these areas have a repellent action for oligophile substances. Further prevents the microstructure in the surface be per se known manner ^¬, the s particular What ^¬ ser easily adhere hydrophilic substances, on the surface. The surface according to the invention is thus advantageous in a special way to ge ^¬ suitable to be exposed to the environmental influences of the earth's atmosphere. Can raindrops difficult to wet the surface so that they roll off and ^¬ zen debris rei with it. Due to the oligophobic properties of subregions of the surface, it is further ensured that the dirt particles, which are often oligophilic, can not accumulate on the surface, so that the bead-dropping water droplets can tear these contaminants with them. The property of reduced wettability of the surface similar to that observed in the leaves of lotus flowers effect over longer periods of use of the surface is guaranteed because a tendency to fouling of the surface is effectively prevented with oligophilic substances.

According to another embodiment of the invention it is provided that particular molecules as a fluorinated wetting agents, insbeson ^¬ Ancor F ® is used as a commercially available substance. These Agents are added in electrochemical processes to increase the deposition rate of the layers. In the process, they are also incorporated into the layer, with the fluoride groups of the wetting agent being in the form of strong dipoles and therefore having strong oligophobic properties. By uniform incorporation of the wetting agent in the e- lektrochemisch generated layer therefore an oligophobic overall character of the surface is achieved on the surface by the fluoride groups. The addition of a wetting agent is based upon the intended function of this substance has the advantage that the surface of the invention ausbil ^¬ Dende layer may be deposited with a shortened sdauer Prozes addition.

It is advantageous if the surface by elektrochemi ^¬ ULTRASONIC pulse plating is prepared, wherein a micro ^¬ structure overlying nanostructure by Reverse Pulse Pla ^¬ ting is generated. The superposition of the microstructure by a nano-structure is accordance with the invention, the s is formed on the surface topology with radii of curvature of the surface profile in the micrometer range (microstructure) a surface topology, whose radii of curvature before ^¬ Trains t in the range of a few nanometers to 100 nanometers (nano-structure). The formation of the nanostructure on the microstructure is assisted by reverse pulse plating

Current pulses of a length in the millisecond range achieved. Depending on the choice of process parameters such as pulse length and deposition current density, the microstructure can be produced simultaneously or separately. When forming a micro structure overlying nanostructure it is particularly advantageous, well let nanoparticles to be used, as these rer due ih ^¬ dimen solutions especially in the nanostructure of the surface installed. The nanostructure of the surface in combination with the microstructure advantageously improves the effect of reducing the adhesion of substances on the surface. This advantageously improves the lotus effect of the surface.

It is known indeed from US 5, 853, 897, galvanically len layers with a rough surface by means of pulse plating herzustel ^¬, but this document produced in accordance layers only optical applications are intended, since it swallow in a wide wave line spectrum of light excellent light Have properties. Again, just be ^¬ already the formation of a so-called dendritic microstructure without the s advertising superimposed on this a nanostructure to have to.

Advantageously, the pulse length in the method step for producing the nanostructure is less than 500 ms. In this way, favorable deposition parameters can be set on the surface to be produced in this method step, so that the nanostructure produced differs sufficiently in its dimensions from the microstructure produced.

The current pulses during reverse pulse plating, the current pulses are generated by respective reversal of the polarity of Abschei ^¬ destromes, so that advantageously a strong temporal gradient in the charge shifts on the surface can be achieved. Advantageously, the individual current pulses are in the range between 10 and 250 milliseconds in terms of their length. It has been shown that the nanostructure of the surface is advantageously particularly pronounced in the case of the parameters mentioned. It is particularly advantageous if, during reverse pulse plating, the cathodic pulses have at least three times the length of the a nodonic pulses. As cathodic pulses within the meaning of He-making ^¬ The ones pulses are perceived, at which there is egg ner deposition on the surface, while the Anodi ^¬ rule pulses cause a dissolution of the surface. For the specified ratio between cathodic and Anodi ^¬ rule pulses it has been shown that the needle-like basic elements of the nanostructure advantageously be generated with a high density on the microstructure, which favors the Lotus effect to be achieved.

Another possibility is advantageously that the reverse pulse plating, the cathodic pulses with a higher current density are performed rule as the Anodi ^¬ pulses. Also by this measure, the deposition rate of the cathodic pulses is increased in comparison to the removal rate of the anodic pulses, so that advantageously a layer ^¬ growth of the nanostructuring is generated. Of course, the measures of a modification of the pulse duration and the variation of the current density can be combined with each other. In each case, an optimum is to be found by setting the parameters mentioned for the material to be ^deposited .

According to one embodiment of the method it is provided that the pulse length is at least one second in an upstream process step for producing the microstructure. With pulse lengths in the range of seconds, the required micro- can advantageously low time on electro ^¬ chemical means are produced in the structure of the surface if it does not, or not crossed with sufficient expression in the method is produced for producing the nanostructure. According to an additional embodiment of the method, the surface is additionally produced with a macrostructure which superimposes the microstructure. The macrostructure can be electrochemically or by other means z. B. be made mechanically. A topography of the surface of a macrostructure this logy understood whose geometrical dimensions than the microstructure of the elementary structural components greater by at least ei ^¬ ne magnitude. For a wavy macrostructure, this would mean for the radius of the waves, for example, that it is correspondingly larger than the radii of the elevations or. Recesses of the microstructure. The macrostructure advantageously permits an additional increase in the adhesion-reducing properties of the surface. Furthermore, the macrostructure of the surface can advantageously have additional functions, such. B. ei ^¬ ner improve the flow characteristics of the surface take over.

The aforementioned object is also achieved by a top surface with an ^adhesion-¬ microstructure rial in accordance with the invention in that the surface forming Mate ^¬ particles, especially nanoparticles with a oligophoben surface and / or molecules with oligophoben Eigenschaf- th are incorporated, which form part of the surface. With such a surface, the advantages described in connection with the method according to the invention of a simultaneously hydrophobic and oligophobic character of the surface can be achieved.

Advantageously, it can be provided that the microstructure is superimposed on a nanostructure produced by pulse plating. Leave with this surface structure according to the invention the advantages already mentioned, in particular a Ver ^¬ improvement achieve the adhesion-properties of the surface.

According to a particular embodiment of the surface, this is superhydrophobic. This means that the adhesion of water or other hydrophilic substances is greatly reduced. The superhydrophobic properties cause, in particular, poor wettability of the surface for water, so that water present on the surface forms individual droplets which, owing to a contact angle to the surface of more than 140 °, easily bead off and thereby possibly precipitate. Also on the surface befindliches dirt particles with ^¬ tear. Therefore, surfaces with superhydrophobic properties are particularly suitable for forming the surface as a lotus effect surface.

Further details of the invention are described below with reference to the drawing. In the individual figures, identical or corresponding drawing elements are each provided with ^¬ weils the same reference numerals, and these will only be explained more than once, such as differences arise between the figures. Show it

Figure 1 shows the schematic structure of an embodiment of the surface according to the invention in the schematic

Cut,

Figure 2 shows the surface profile of a lotus effect surface as an embodiment of the surface according to the invention in section, Figure 3 perspective views of the lotus effect surface according to Figure 2 and Figure 4 shows the structural formula of the wetting agent Ankor F® In Figure 1, a body 11 is shown with a surface whose adhesion properties is reduced. The surface 12 can be described schematically by a superimposition of a macrostructure 12 having a microstructure 13 and a nanostructure 14. The microstructure produces a

Waviness of the surface. The microstructure is indicated by semi-spherical protrusions on the wavelength ^¬ macrostructure 12th The nanostructure 14 is represented in FIG. 1 by nubs which are located on the hemispherical elevations (microstructure) and in the parts located between the elevations of the macrostructure 12 which form the depressions of the microstructure 13.

The adhesion-reducing properties of the surface formed by the superimposition of the macrostructure 12, the microstructure 13 and the nanostructure 14 become clear on the basis of a water droplet 15 which forms a water ^pearl on the surface. Due to the low wettability of the surface on the one hand and the surface tension of the water droplet on the other hand, formed between the water droplet 15 and the surface of a relatively large contact angle γ, which is defined by an angle leg 16a, which runs paral ^¬ lel to the surface, and an angle leg 16b, which forms a tangent to the skin of the water droplet which passes through the edge of the contact surface of the water droplet 15 with the surface (or more precisely the angle leg 16a). FIG. 1 shows a contact angle γ of more than 140 °, so that the surface shown schematically is a superhydrophobic surface.

In the context of an experiment, Reverse Pulse Platings has a lotus effect surface by deposition of copper a surface polished by electropolishing has been produced. The following process parameters were chosen.

Generation of the nanostructure in one process step: Pulse length (reverse pulses): 240 ms at 10 A / dm ² cathodic, 40 ms at 8 A / dm ² anodic

Electrolyte contained 50 g / l Cu, 20 g / l free cyanide, 5 g / l KOH

The surface is electrochemically generated in the following with ^¬ means of an SPM (Scanning Probe Microscope - AFM or also called A- Tomic Force Microscope) has been studied. With an SPM, surface structures down to the nanometer range can be determined and displayed. A section of the surface produced is shown in section in FIG. 2 as a measurement result of the SPM in section, with the profile being excessively elevated. With reference to a zero line 17, a waveform 18 is entered in FIG. 2, which illustrates the macrostructure superimposed on the surface structure. The microstructure 13 can be recognized as a succession of needle-like elevations 19 and depressions 20 as a result of the elevation. Furthermore, in certain areas, the nanostructure 14 can be recognized, which results from a narrow sequence of elevations and depressions, which are no longer to be resolved in the scale shown in FIG. 2 and can therefore only be seen as a thickening of the profile line of the surface profile.

Further details can be read from the figure 3, which contains a perspective view of the copper surface. A square area of 100 × 100 μm has been selected as a cutout, the needle-like elevations 19 determining the microstructure 13 being clearly recognizable. The resulting image reminds the viewer of a "naive" delwald ", wherein the spaces between the" conifers "(elevations 19) form the recesses 20. The surface according to FIG. 3 is also shown elevated in order to illustrate the elevations 19 and the depressions 20 of the microstructure 13.

As can be seen from the perspective view of the surface according to FIG. 4, which shows an enlarged detail of the illustration according to FIG. 3, the microstructure 13 is furthermore superimposed on a nanostructure 14. In less excessive representation according to Figure 4, the elevations 19 and depressions 20 appear more like a waviness of the surface (but not ness of Figure 2 may be confused due to the different scale with the wavy ^¬). These ripples are superimposed on the smallest increases 19n and

Wells 2On, which characterize the nanostructure of the surface. These also recall in their construction of the already explained to Figure 3 expression of a "coniferous forest" whose geometric dimensions by about two orders of magnitude lower fall, so at the selected scale in Figure 3 is not visible.

In the section according to FIG. 4, furthermore, molecules 21m with strongly oligophobic properties are indicated, which are not shown to scale. These molecules can be found in the

Electrolyte to produce the surface to be solved. In ^¬ play, the known under the name Ankor F® Sub ^¬ can be punched as a wetting agent and at the same area for installation in the upper ^¬ be added. The substance Ankor F® (tetraetylammonium perfluorooctanesulfonate) is shown in FIG. 4 as a structural formula. To illustrate the size relationships are shown in Figu ^¬ ren each characterized by a clamp 2 and 3, the macrostructure 12, the microstructure 13 and the nanostructure fourteenth The bracket always comprises only a section of the respective structure, which contains an elevation and a depression, so that the brackets allow one another in each case within a figure a comparison of the magnitudes of the structures in relation to each other. In the illustrated embodiment, the contact angle measured for a drop of water was 152 °. The superhydrophobic properties of the copper layer shown, which act a lotus effect be ^¬ is achieved by a combination of at least the micro ^¬ structure 13 and the nanostructure 14, wherein the superposition of a macrostructure 12 further improves the observed effects. By selecting suitable process parameters, it is possible to produce such lotus effect surfaces for different layer materials (for example, silver layers have also been successfully tested) and for liquids with different wetting behavior.

Claims

claims

1. A process for electrochemically producing a surface having an adhesion-reducing microstructure (13) in an electrolyte, characterized in that particles (2 In) having an oligophobic surface which form a suspension with the electrolyte are added to the electrolyte and / or molecules (21m) having oligophobic properties which dissolve in the electrolyte such that the particles or molecules are incorporated into the surface forming layer.

2. The method according to claim 1, characterized in that are used as particles nanoparticles (2In).

3. The method according to any one of the preceding claims, characterized in that the particles (2In) are supplied to the electrolyte as a suspension.

4. The method according to claim 1, characterized in that as molecules a fluorinated wetting agent, in particular Ankor F®, is used.

5. The method according to any one of the preceding claims, characterized in that the surface is produced by electrochemical pulse plating, wherein the microstructure (13) überla ^¬ like nanostructure (14) is generated by reverse pulse plating.

6. The method according to any one of the preceding claims, characterized in that the pulse length in the step of producing the nanostructure is less than 500 ms.

7. The method according to any one of the preceding claims, characterized in that the reverse pulse plating, the cathodic pulses have at least three times the duration of the anodic pulses.

8. The method according to any one of the preceding claims, characterized in that the reverse pulse plating, the cathodic pulses are carried out with a higher current density, as the anodic ^¬ 's pulses.

9. The method according to any one of the preceding claims, characterized in that the pulse length at an upstream process step for producing the microstructure is at least one second.

10. The method according to any one of the preceding claims, characterized in that the surface is additionally produced with a macrostructure (12) which superimposes the microstructure (13).

11. surface with an adhesion-microstructure (13), characterized in that in the surface-forming material particles, in particular ^¬ sondere nanoparticles (2In) having a surface oligophoben and / or molecules with oligophobic properties are incorporated which form part of the surface.

12. Surface according to claim 11, characterized in that the microstructure (13) is overlaid with a nanostructure (14) produced by pulse plating.

13. Surface according to any one of claims 11 or 12, characterized in that the surface is superhydrophobic.

14. Surface according to one of claims 11 to 13, characterized in that the microstructure (13) and the nanostructure (14) is superimposed on a macrostructure (12).