Patent Application
20120258283
This application claims priority under 35 U.S.C. §119 to Korean Patent Application No. 10-2011-0031284, filed on Apr. 5, 2011 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field
The present disclosure relates to hydrophobic surfaces and, more particularly, to super-hydrophobic surfaces having increased durability.
2. Description of the Related Art
Super-hydrophobicity refers to a physical property of a surface on which wetting is relatively difficult. For example, the leaves of plants, wings of insects, or wings of birds allow certain contaminants to be removed therefrom without requiring any particular removing action or prevention of contamination from the start. This is because the leaves of plants, wings of insects, or wings of birds have super-hydrophobic properties.
An object having a super-hydrophobic surface may have water-proof and anti-contamination characteristics. Therefore, a technology of forming a super-hydrophobic surface may be useful when applied to various industries.
A method of forming a super-hydrophobic surface may be a chemical method or a structural method.
The chemical method of forming a super-hydrophobic surface may be a method of coating a hydrophobic chemical material on a material surface. However, there are limitations in reducing the surface energy of a material using only a chemical treatment.
The structural method of forming a super-hydrophobic surface may be a method of increasing a contact angle between a surface of a solid material and a liquid by increasing the roughness of the surface of the solid material. A super-hydrophobic surface may be realized by taking advantage of a property of a material surface where hydrophobicity increases as the roughness of a surface increases by patterning the material surface. However, when a contact angle is increased by performing protrusion patterning, a relatively complicated pattern or a pattern having a relatively high slenderness ratio is necessary. Thus, a pattern may be relatively easily damaged, thereby reducing practicability.
Various example embodiments relate to super-hydrophobic surfaces having higher hydrophobicity and higher durability.
According to a non-limiting embodiment of the present invention, a super-hydrophobic surface may have a structure having at least dual sink patterns. The super-hydrophobic surface may include a base having a first sink pattern and a second sink pattern. The first sink pattern may include first sink grooves extending below a surface of the base (e.g. a solid). The second sink pattern may include second sink grooves which have a size smaller than that of the first sink grooves. The second sink grooves may extend below the surface of the base (which may be an upper surface of a wall of the first sink pattern).
The first sink grooves of the first sink pattern may be disposed in a triangular array.
The first sink grooves of the first sink pattern may be disposed on a center and vertexes of a hexagon formed by disposing the first sink grooves in a regular triangular array.
The second sink grooves of the second sink pattern may be disposed in an overall triangular array.
The second sink grooves of the second sink pattern may be disposed on a center and vertexes of a hexagon formed by disposing the second sink grooves in a regular triangular array.
The surface of the base may further include protruded columns or particles so as to make the surface rougher.
When a size of the first sink grooves or the second sink grooves is d, a gap between adjacent first sink grooves or second sink grooves is p, and a pattern radius λ is λ=d/p, the first sink pattern and the second sink pattern may be formed to satisfy an equation below,
cos θ*=φL(φS cos θE+(φS−1))+(φL−1) <Equation>
where θ* is a contact angle on the surface of the base on which the first and second sink patterns are formed, θE is contact angle on the surface of the base before the first and second sink patterns are formed, and φL and φS satisfy φ=1−(π/2√{square root over (3)})λ2.
A super-hydrophobic structure according to another non-limiting embodiment may include a base having a first surface and an opposing second surface; a plurality of first sink grooves extending from the first surface into the base; and a plurality of second sink grooves disposed between the plurality of first sink grooves, the plurality of second sink grooves extending from the first surface into the base, the plurality of second sink grooves being smaller than the plurality of first sink grooves.
The super-hydrophobic surface according to a non-limiting embodiment of the present invention may have a sink structure on a surface thereof, may have super-hydrophobicity since the sink structure having a relatively small size is formed on the wall that forms the sink structure to increase an area where aft present between a droplet and a solid surface is collected, and may have a relatively strong durability against, for example, scratches since the sink structure increases a surface strength. Also, a dual sink structure may be formed by forming a relatively small sink structure on the relatively large sink structure. Thus, when the small sink structure is damaged, the basic super-hydrophobic structure may still be maintained by the large sink structure, thereby maintaining the relatively high durability of the super-hydrophobic surface.
The above and/or other aspects will become more apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
It will be understood that when an element or layer is referred to as being “on,” “connected to,” “coupled to,” or “covering” another element or layer, it may be directly on, connected to, coupled to, or covering the other element or layer or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly connected to,” or “directly coupled to” another element or layer, there are no intervening elements or layers present. Like numbers refer to like elements throughout the specification. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
It will be understood that, although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers, and/or sections, these elements, components, regions, layers, and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer, or section from another element, component, region, layer, or section. Thus, a first element, component, region, layer, or section discussed below could be termed a second element, component, region, layer, or section without departing from the teachings of example embodiments.
Spatially relative terms, e.g., “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the term “below” may encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.
The terminology used herein is for the purpose of describing various embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms, “comprises,” “comprising,” “includes,” and/or “including,” if used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
Example embodiments are described herein with reference to cross-sectional illustrations that are schematic illustrations of idealized embodiments (and intermediate structures) of example embodiments. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, example embodiments should not be construed as limited to the shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art. It will be further understood that terms, including those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
A super-hydrophobic surface according to a non-limiting embodiment of the present invention may have a structure having two or more sink patterns (e.g., dual sink patterns). As a result, the super-hydrophobic surface may have a relatively high hydrophobicity and durability. The super-hydrophobic surface may be applied in situations where self-cleaning, anti-water drop wetting, and/or low drag force is necessary or desired.
The super-hydrophobic surface may be applied to places where self-cleaning with rain or other water sources is necessary. For example, the super-hydrophobic surface may be applied to the surfaces of solar cells or solar power generators, electronic products (such as outdoor electronic displays), external wars and building glass, and automobile windows and body surfaces. Also, the super-hydrophobic surface may be applied to places where there is a need or desire to secure a clear view by preventing or reducing water drop wetting. For example, the super-hydrophobic surface may be applied to the windows of airplanes and vehicles, rear mirrors of vehicles, and outdoor electronic displays. Also, the super-hydrophobic surface may be applied to places where energy can be saved by reducing friction with water for water transportation and traffic means such as vessels. Also, the super-hydrophobic surface may be applied to places where a hydrophobic surface is required or desired for display processes and to a micro-fluid device that uses micro-fluid engineering.
When a contact area between a droplet that contacts a solid and air present below the droplet is increased, since a surface energy of the droplet contacted with air is relatively high at an interface between the droplet and air, the droplet tends to reduce its total surface energy by becoming rounder, thereby increasing a contact angle with the solid. Accordingly, in order to increase hydrophobicity of a solid, it may be desirable to form as many air pockets as possible below the droplets by, for example, patterning a surface of the solid to increase a distance from a non-contact bottom surface to the solid, and thus, to maintain a relatively large number of air pockets below the droplets even when there are external disturbances.
A principle of generating hydrophobicity by way of a structure will now be described in further detail.
A contact angle θE of the droplet 5 before texturing may be determined by Young's Equation shown in the following equation 1:
cos θE=(γSV−γSL)/γ [Equation 1]
where γSV is an interfacial tension between a solid and a gas, γSL is an interfacial tension between a solid and a liquid, and γ is an interfacial tension between a liquid and a gas.
An increase in the contact angle θE* of the droplet 5 after texturing is increased as shown in the following Equation 2:
cos θE*=−1+φA(cos θE+1) [Equation 2]
where φA is an area fraction of a solid that contacts a liquid droplet
At this point, so as not to wet a textured area, the droplet 5 needs to satisfy the following condition:
where γ is a ratio between a protruded area and an actual area. The actual area corresponds to a spread area of a protruded structure.
Studies have been conducted to manufacture a solid structure that has a capability of self-cleaning, preventing or reducing formation of water drops, or relatively low drag force through increasing a contact angle according to the above principle. As depicted in
A super-hydrophobic surface according to a non-limiting embodiment of the present invention is configured to maintain super-hydrophobicity and to overcome a low durability problem of a general super-hydrophobic surface.
Referring to
The first sink pattern 40 includes first sink grooves 41 formed by sinking from the upper surface 45a of the solid. The second sink pattern 50 includes second sink grooves 51 that are formed by sinking from the upper surface 45a of the wall 45 of the first sink pattern 40. The second sink grooves 51 have a size that is smaller than that of the first sink grooves 41. For instance the width and/or depth of the second sink grooves 51 may be less than that of the first sink grooves 41.
As depicted in
The second sink pattern 50 is formed in a sink structure by sinking from the upper surface 45a of the wall 45 of the first sink pattern 40, that is, from the surface of the super-hydrophobic surface 30. The second sink pattern 50 may be arranged such that, for example, the second sink grooves 51 of the second sink pattern 50 are arranged to form an overall triangular arrangement, for example, an overall regular triangular arrangement. The second sink grooves 51 may not be formed on sink regions where the first sink grooves 41 are formed. For instance, the second sink grooves 51 may be formed in an overall triangular arrangement (e.g., an overall regular triangular arrangement) in regions other than where the first sink grooves 41 are formed, that is, on the upper surface 45a of the wall 45 that surrounds the first sink grooves 41. When the second sink grooves 51 are disposed to form an overall regular triangular arrangement, the second sink pattern 50 may form an overall arrangement structure in which the second sink grooves 51 are disposed on a center and vertexes of a hexagon. In this way, the second sink pattern 50 may be arranged to have a structure in which the second sink grooves 51 are closely arranged in a hexagon.
As depicted in
As shown in
cos θ*=φL(φS cos θE+(φS−1))+(φL−1)
where θ* is a contact angle of a droplet on a surface of a solid on which the first sink pattern 40 and the second sink pattern 50 are formed, and θE is a contact angle of the droplet on a surface of a solid before the first sink pattern 40 and the second sink pattern 50 are formed, and φL and φS satisfy φ=1−(π/2√{square root over (3)})λ2.
For example, when a size of the first sink grooves 41 is dL and a gap is pL, a pattern radius λL is λL=dL/pL and φL is φL=1−(π/2√{square root over (3)})λL2. When a size of the second sink grooves 51 is dS and a gap is pS, a pattern radius λS is λS=dS/pS and φS is φS=1−(π/2√{square root over (3)})λS2. cos θE may be obtained from Equation 1.
A process of obtaining Equation 4, which shows an example of the super-hydrophobic surface 30 having a dual sink pattern structure of the first sink pattern 40 having a relatively a large periodicity and the second sink pattern 50 having a relatively small periodicity will now be described.
The Equation 1 and Equation 5, which are related to energy change per unit (dE), are considered.
dE=(w+v(1−w))γ+(1−v)(1−w)(γSL−γSV)+γ cos θ* [Equation 5]
When dE=0, energy change is minimized, and when substituted into Equation 5, Equation 6 is obtained:
cos θ*=(1−w)((1−v)cos θE−v)−w [Equation 6]
The variable w is a fraction of a droplet/gas interface of large air pockets and small air pockets on a surface of a solid below a droplet. The large air pockets may be represented by the relatively large first sink grooves 41, and the small air pockets may be represented by the relatively small second sink grooves 51.
Accordingly, a fraction of a solid/liquid interface of the large air pockets is 1−w, and a fraction of a solid/liquid interface of the small air pockets is 1−v, and thus, φL=1−w and φS=1−v. When φL=1−w and φS=1−v are substituted into Equation 6, Equation 4 is obtained.
If the first sink grooves 41 and the second sink grooves 51 have the same size, w=v, and when it is assumed that φ=1−w, by substituting this into Equation 6, Equation 7 is obtained.
cos θ*=φ2(cos θE+1)−1 [Equation 7]
Table 1 shows a design example of a dual sink pattern structure of the first sink pattern 40 that has the relatively large first sink grooves 41 having a relatively large pitch and the second sink pattern 50 that has the relatively small second sink grooves 51 having a relatively large pitch.
Pattern radii λL and λS with respect to the first and second sink grooves 41 and 51 denote ratios between a size (diameter) of a sink groove and a pitch of the sink groove, and, as may be seen from the above description, are values obtained from λL=dL/pL and λS=dS/pS. φL is a value obtained from an equation φS=1−(π/2√{square root over (3)}))λL2, and φS is a value obtained from an equation φS=1−(π/2√{square root over (3)})λS2.
As it may be seen from the design of Table 1, a contact angle θ of a droplet with respect to a solid surface having no sink grooves is 110°. However, it is seen that a contact angle θ of the droplet with respect to the solid surface on which the dual sink groove patterns of the first sink pattern 40 and the second sink pattern 50 having a sink groove size different from that of the first sink pattern 40 is formed may be greatly increased to 166°.
The super-hydrophobic surface 30 according to a non-limiting embodiment of the present invention may have a sink structure on a surface thereof. As a result, super-hydrophobicity may be attained since a sink structure having a relatively small size is formed on the wall 45, which forms a sink structure, to increase an area where air is present between a droplet and a solid surface. The super-hydrophobic surface 30 may have relatively strong durability against, for example, scratches since the sink structure increases a surface strength. Also, a dual sink structure is formed by forming a small sink structure on the large sink structure. Thus, when the small sink structure is damaged, a basic super-hydrophobic structure may be maintained by the large sink structure, thereby maintaining a relatively high durability of the super-hydrophobic surface 30.
Also, according to the super-hydrophobic surface 30, a pattern having a lower slenderness ratio when compared to a single structure may be used by configuring the sink structure in a dual sink pattern or above, thereby making the process easier. The super-hydrophobic surface 30 may be manufactured with a relatively high productivity process such as a nano-imprint process.
As described above, a case where the super-hydrophobic surface 30 according to a non-limiting embodiment of the present invention may have a sink structure having two or more sink patterns on a solid surface is depicted and described. However, as depicted in
It should be understood that the example embodiments described therein should be considered in a descriptive sense only and not for purposes of limitation. The descriptions of features or aspects within each non-limiting embodiment should typically be considered as available for other similar features or aspects in other embodiments.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2011-0031284 | Apr 2011 | KR | national |
