U.S. patent application number 11/660814 was filed with the patent office on 2008-09-11 for surface with an anti-adhesion microstructure and method for producing same.
This patent application is currently assigned to SIEMENS AKTIENGESELLSCHAFT. Invention is credited to Christian Doye, Ursus Kruger, Manuela Schneider.
Application Number | 20080217180 11/660814 |
Document ID | / |
Family ID | 35445971 |
Filed Date | 2008-09-11 |
United States Patent
Application |
20080217180 |
Kind Code |
A1 |
Doye; Christian ; et
al. |
September 11, 2008 |
Surface with an Anti-Adhesion Microstructure and Method for
Producing Same
Abstract
The invention relates to a surface comprising a microstructure
that reduces adhesion and to a method for producing said
microstructure. Microstructures of this type that reduce adhesion
are known and are used, for example, to configure self-cleaning
surfaces that us the Lotus effect. According to the invention, the
surface is produced electrochemically by means of reverse pulse
plating, the known microstructure being first produced and a
nanostructure that is overlaid on the microstructure is produced at
the same time or in a subsequent step. To achieve this for example,
the pulse length of the current pulse that is used during the
reverse pulse plating lies in the millisecond range and has a pulse
length ratio greater than 1:3. The microstructure that has been
produced, consisting of peaks and troughs is then overlaid with
peaks and troughs of a smaller size order belonging to the
nanostructure.
Inventors: |
Doye; Christian; (Berling,
DE) ; Kruger; Ursus; (Berlin, DE) ; Schneider;
Manuela; (Berlin, DE) |
Correspondence
Address: |
SIEMENS CORPORATION;INTELLECTUAL PROPERTY DEPARTMENT
170 WOOD AVENUE SOUTH
ISELIN
NJ
08830
US
|
Assignee: |
SIEMENS AKTIENGESELLSCHAFT
MUENCHEN
DE
|
Family ID: |
35445971 |
Appl. No.: |
11/660814 |
Filed: |
August 8, 2005 |
PCT Filed: |
August 8, 2005 |
PCT NO: |
PCT/EP05/53902 |
371 Date: |
February 22, 2007 |
Current U.S.
Class: |
205/50 ;
205/103 |
Current CPC
Class: |
C25D 5/18 20130101; C25D
5/16 20130101 |
Class at
Publication: |
205/50 ;
205/103 |
International
Class: |
C25D 5/18 20060101
C25D005/18; C25D 7/00 20060101 C25D007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 26, 2004 |
DE |
10 2004 041 813.6 |
Claims
1.-9. (canceled)
10. A method for electrochemically producing a surface with an
anti-adhesion microstructure, comprising: providing a
macrostructure; arranging a microstructure on the macrostructure by
electrochemical pulse plating; and arranging a nanostructure on the
microstructure by reverse pulse plating.
11. The method as claimed in claim 10, wherein the reverse pulse
plating pulse length for producing the nanostructure is less than
500 ms.
12. The method as claimed in claim 11, wherein a cathodic pulse is
at least three times as long as an anodic pulse for reverse pulse
plating.
13. The method as claimed in claim 12, wherein the cathodic pulse
is implemented with a higher current density than the anodic pulse
for reverse pulse plating.
14. The method as claimed in claim 13, wherein the pulse length for
an upstream process step for producing the microstructure is at
least one second.
15. A surface with an anti-adhesion microstructure, comprising:
providing a microstructure; and superimposing a nanostructure on
the microstructure by pulse plating to produce the surface.
16. The surface as claimed in claim 15, wherein the surface is
superhydrophobic.
17. The surface as claimed in claim 16, wherein a macrostructure is
superimposed on the microstructure and the nanostructure.
18. The surface as claimed in claim 17, wherein a pulse plating
pulse length for producing the nanostructure is less than 500 ms.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is the US National Stage of International
Application No. PCT/EP2005/053902, filed Aug. 8, 2005 and claims
the benefit thereof. The International Application claims the
benefits of German application No. 10 2004 041 813.6 filed Aug. 26,
2004, both of the applications are incorporated by reference herein
in their entirety.
FIELD OF INVENTION
[0002] The invention relates to a surface with an anti-adhesion
microstructure and a method for electrochemically producing such a
surface.
BACKGROUND OF THE INVENTION
[0003] Anti-adhesion surfaces of the abovementioned type are used
e.g. as so-called lotus-effect surfaces and are described, for
example, in DE 100 15 855 A1. According to this publication, such
surfaces are characterized by a microstructure which can be
obtained by film deposition from solutions, but also by
electrolytic deposition. This mimics an effect observed on the
leaves of the lotus plant, according to which the resulting
micropatterning, which for this purpose must have peaks and valleys
with a radius of 5 to 100 .mu.m, reduces the adhesion of water and
dirt particles. This enables contamination of the corresponding
surface to be counteracted. The formation of limescale, for
example, can also be prevented.
SUMMARY OF INVENTION
[0004] The object of the invention is to specify a surface with an
anti-adhesion microstructure and a production method for said
surface, the adhesion-reducing effect being comparatively strongly
marked.
[0005] This object is achieved according to the invention by a
method in which the surface is produced by electrochemical pulse
plating, a nanostructure overlying the microstructure being created
by reverse pulse plating. According to the invention, the
nanostructure is overlaid on the microstructure by producing, on
the surface topology having surface profile bending radii in the
micrometer range (microstructure), a surface topology whose bending
radii are preferably in the range of a few nanometers to 100
nanometers (nanostructure). The formation of the nanostructure on
the microstructure is achieved by reverse pulse plating using
current pulses whose length is in the millisecond range. The
microstructure can be produced simultaneously or separately
depending on the process parameters such as pulse length and
deposition density.
[0006] The surface's nanostructure in conjunction with the
microstructure advantageously improves the effect of reducing the
adhesion of substances to the surface, thereby advantageously
improving the surface's lotus effect.
[0007] Although U.S. Pat. No. 5,853,897 discloses a method of
electrodepositing films with a rough surface by means of pulse
plating, the films produced according to this document are designed
solely for optical applications, as they have excellent light
absorbing properties in a wide optical wavelength range. For this
purpose it merely suffices to create a dendritic microstructure
without having to overlay same with a nanostructure.
[0008] Advantageously the pulse length for the process step of
producing the nanostructure is less than 500 ms. This means that,
during this step, favorable deposition parameters can be set on the
surface to be produced, so that the resulting nanostructure differs
sufficiently in its dimensions from the microstructure created.
[0009] The current pulses for reverse pulse plating are generated
by reversing the polarity of the deposition current so that a
significant time differential for the charge transfers at the
surface can be advantageously achieved. In respect of their length,
the individual current pulses are advantageously in the range
between 10 and 250 milliseconds. It has been shown that
advantageously, for the parameters specified, the surface's
nanostructure is particularly pronounced.
[0010] It is particularly advantageous if during reverse pulse
plating the cathodic pulses are at least three times as long as the
anodic pulses. For the purposes of the invention, cathodic pulses
are taken to mean those pulses resulting in deposition on the
surface, whereas the anodic pulses produce dissolution of the
surface. For the specified ratio between cathodic and anodic pulses
it has been found that the needle-like basic elements of the
nanostructure are advantageously produced with a high density on
the microstructure, to the benefit the lotus effect to be
achieved.
[0011] Another advantageous possibility is that, for reverse pulse
plating, the cathodic pulses are implemented with a higher current
density than the anodic pulses. This also increases the deposition
rate of the cathodic pulses compared to the erosion rate of the
anodic pulses so that nanopatterning layer growth is advantageously
produced. Self-evidently, the measures of modifying the pulse
duration and varying the current density can be combined together,
an optimum having to be found for the material to be deposited by
adjusting the specified parameters.
[0012] According to one embodiment of the method it is provided
that the pulse length is at least one second for an upstream
microstructure producing step. With pulse lengths in the seconds
range, the surface's required microstructure can be advantageously
produced time-efficiently by electrochemical means if it is not
produced, or not with sufficient markedness, in the nanostructure
producing step.
[0013] According to another embodiment of the method, the surface
is additionally produced with a macrostructure superimposed on the
microstructure. The macrostructure can be produced
electrochemically or by other means, e.g. mechanically. The term
macrostructure is to be understood here as a surface topology whose
elementary structural components' geometrical dimensions are at
least an order of magnitude greater than those of the
microstructure. In the case of a wavy macrostructure, this would
mean e.g. for the radius of the waves that said radius is greater
to a corresponding degree than the radii of the peaks and valleys
of the microstructure. The macrostructure advantageously allows the
anti-adhesion properties of the surface to be increased still
further. In addition, the surface's macrostructure can
advantageously assume additional functions such as improving the
flow characteristics of the surface.
[0014] The surface according to the invention achieves its stated
object by a nanostructure created by pulse plating being overlaid
on the microstructure. This inventive surface composition enables
the already mentioned advantages to be achieved, in particular
improving the anti-adhesion properties of the surface.
[0015] According to a particular embodiment of the surface, same is
superhydrophobic. This means that the adhesion of water or other
hydrophilic substances is particularly greatly reduced. The
superhydrophobic properties in particular cause poor wettability of
the surface for water, so that water present on the surface forms
individual droplets which, because of the surface's contact angle
of more than 140.degree., readily roll off and possibly also
entrain dirt particles present on the surface with them. Surfaces
with superhydrophobic properties are therefore particularly
suitable for making the surface a lotus-effect surface.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Further details of the invention will now be described with
reference to the accompanying drawings in which the same or
corresponding elements are provided with the same reference
numerals and will only be explained more than once where they
differ from drawing to drawing.
[0017] FIG. 1 schematically illustrates an embodiment of the
surface according to the invention in schematic cross section,
[0018] FIG. 2 shows the surface profile of a lotus-effect surface
as an example of the inventive surface in cross section and
[0019] FIG. 3 shows perspective views of the lotus-effect surface
according to FIG. 2.
DETAILED DESCRIPTION OF INVENTION
[0020] FIG. 1 shows a body 11 having a surface with reduced
adhesion properties. The surface 12 can be schematically described
by an overlaying of a macrostructure 12 with a microstructure 13
and a nanostructure 14. The microstructure creates surface
waviness. The microstructure is indicated by hemispherical peaks on
the wavy macrostructure 12. The nanostructure 14 is represented in
FIG. 1 by bumps on the hemispherical peaks (microstructure) and in
the parts of the macrostructure 12 located between the peaks and
forming the valleys of the microstructure 13.
[0021] The anti-adhesion properties of the surface formed by the
superimposition of the macrostructure 12, the microstructure 13 and
the nanostructure 14 are indicated by a water droplet 15 which form
a pearl of water 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, there is formed between the water droplet 15
and the surface a relatively large contact angle .gamma. which is
defined by an angle leg 16a running parallel to the surface and an
angle leg 16b forming a tangent to the skin of the water droplet,
said tangent running through the edge of the contact area of the
water droplet 15 with the surface (or more precisely the angle leg
16a). FIG. 1 shows a contact angle .gamma. of more than 140.degree.
so that the schematically represented surface is superhydrophobic
surface.
[0022] As part of an experiment, reverse pulse plating has been
used to produce a lotus-effect surface by depositing copper on a
surface smoothed by electroplating, the following process
parameters having been selected:
[0023] Production of the nanostructure in a process step:
Pulse length (reverse pulses): 240 ms at 10 A/dm.sup.2 cathodic, 40
ms at 8 A/dm.sup.2 anodic Electrolyte contains 50 g/l Cu, 20 g/l
free cyanide, 5 g/l KOH
[0024] The electrochemically produced surface was then examined
using an SPM (Scanning Probe Microscope--also known as AFM or
Atomic Force Microscope). An SPM enables surface structures down to
the nanometer range to be identified and displayed. A segment of
the surface produced is shown in cross section in FIG. 2 as an SPM
test result, the profile being exaggerated. Relative to a zero line
17, there is drawn in FIG. 2 a waveform 18 making clear the
macrostructure superimposed on the surface structure. Because of
the exaggeration, the microstructure 13 is identifiable as a
succession of peaks 19 and valleys 20. In addition, there can be
identified, in particular regions, the nanostructure 14 resulting
from a close succession of peaks and valleys which cannot be
resolved further at the scale shown in FIG. 2 and are therefore
only identifiable as a thickening of the profile line of the
surface profile.
[0025] Further details may be obtained from FIG. 3a which provides
a perspective view of the SPM recording of the copper surface. A
region 100.times.1100 .mu.m square was selected as the extracted
segment, the needle-like peaks 19 determining the microstructure 13
being clearly visible. The resulting image has the appearance of a
"coniferous forest", with interspaces between the "conifers" (peaks
19) forming the valleys 20. The surface as shown in FIG. 3a is also
represented in exaggerated form in order to make clear the peaks 19
and valleys 20 of the microstructure 13.
[0026] As can be seen from the perspective view of the surface
according to 3b which constitutes a segment enlargement of the
representation according to FIG. 3a, a nanostructure 14 is
additionally superimposed on the microstructure 13. In the less
exaggerated representation according to FIG. 3b, the peaks 19 and
valleys 20 look more like a waviness of the surface (which,
however, because of the different scale must not be confused with
the waviness according to FIG. 2). Additionally superimposed on
this waviness are very small peaks 19n and valleys 20n
characterizing the nanostructure of the surface. These are again
reminiscent in terms of their structure of a coniferous forest
already explained in connection with FIG. 3a, their geometrical
dimensions turning out to be about two orders of magnitude smaller,
i.e. totally imperceptible at the scale selected in FIG. 3a.
[0027] In order to make the size relationships clear, the
macrostructure 12, the microstructure 13, and the nanostructure 14
are each marked with a bracket in FIGS. 2 and 3. The bracket in
each case encloses only one segment of the relevant structure,
which contains a peak and a valley, so that, among one another, the
brackets within a Figure allow the orders of magnitude of the
structures in relation to one another to be compared. In the
example shown, the contact angle measured for a water droplet was
152.degree.. The superhydrophobic properties of the copper coating
shown, which produce a lotus effect, are achieved by an interplay
of at least the microstructure 13 and the nanostructure 14, the
overlaying of a macrostructure 12 improving the observed effects
still further. By selecting suitable process parameters, such
lotus-effect surfaces can be produced for different coating
materials (silver coatings have been successfully tested, for
example) and for liquids with different wetting behaviors.
* * * * *