Passive anti-icing and self-cleaning functional surface structures

Abstract

This invention relates to a passive anti-icing and self-cleaning functional surface structure, comprising a base with a plurality of bowl-shaped entities on its surface. Each bowl-shaped entity is an axisymmetric entity formed by rotating a generatrix around an axis of symmetry perpendicular to the base surface. The generatrix consists of a quarter-circular arc and a straight line segment, with the arc tangent to the straight line segment. This results in a flat top for each axisymmetric entity and an outwardly convex lateral surface between the top and bottom. The bottom of each bowl-shaped entity is connected to the base. This invention causes droplets to continuously move in opposite directions from the bottom to the top of the bowl-shaped entities, and then remove them through droplet merging, jumping, or gravity. In cold environments, this effectively prevents water vapor from condensing into ice on the surface, thus preventing damage to equipment performance, and in humid environments, it possesses a self-cleaning function.

Description

Technical Field

[0001] This invention relates to the field of surface device technology, and in particular to a functional surface structure that provides passive anti-icing and self-cleaning properties. Background Technology

[0002] Oriented and spontaneous droplet transport on solid surfaces is crucial in numerous applications and fields, including liquid collection, anti-icing, anti-fogging, self-cleaning, and enhanced heat transfer. Droplets can be passively propelled by surface curvature gradients, which are reusable and feasible for large-scale manufacturing, making their application in these areas very broad. In existing technologies, curvature gradients are typically modeled after cactus spines and implemented using conical solids. This structure only allows droplets to move from the tip to the bottom of the cone, and after traveling a certain distance, the driving force gradually decreases as the cone diameter increases, eventually causing the droplet to stop moving. Furthermore, the limited transport distance and lack of control over droplet movement hinder further applications of this structure. For example, in anti-icing or self-cleaning applications, rapid droplet removal from the surface is required. Typically, micrometer-scale structures, such as tiny cylinders, are incorporated into functional surfaces. This increases the liquid-gas contact area to enhance hydrophobicity and decreases the liquid-solid contact area to reduce adhesion at the liquid-solid interface, thus enabling the surface to perform anti-icing and self-cleaning functions. However, when these surfaces are exposed to a humid environment, tiny droplets can nucleate and grow around the tiny cylinders, leading to a wetting state in the Wenzel and thus compromising the surface's superhydrophobicity. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a passive anti-icing and self-cleaning functional surface structure. The purpose is to control the continuous reverse movement of droplets from bottom to top, and then remove them through droplet merging, jumping, or gravity, thereby achieving the anti-icing and self-cleaning functions of the surface structure.

[0004] The technical solution adopted in this invention is as follows:

[0005] A passive anti-icing and self-cleaning functional surface structure includes a base. The base surface has a plurality of bowl-shaped entities. The bowl-shaped entities are axisymmetric entities formed by rotating a generatrix around an axis of symmetry, which is perpendicular to the base surface. The generatrix consists of a quarter-circular arc and a straight line segment, and the arc and the straight line segment are tangent, such that the top of the axisymmetric entity forms a plane, and the circumferential side between the bottom and the top is an outwardly convex curved surface. The bottom of the bowl-shaped entities is connected to the base.

[0006] The further technical solution is as follows:

[0007] The surface of the base is provided with a superhydrophobic layer.

[0008] The surface of the bowl-shaped entity is coated with a hydrophobic coating.

[0009] The radius of the 1 / 4 arc is 4.5-9.5 nm, and the length of the straight line segment and the perpendicular distance between the point of tangency between the arc and the straight line segment and the axis of symmetry are equal, which is 3-4 nm.

[0010] The several bowl-shaped entities are evenly distributed on the surface of the base with a gap of 30-80nm.

[0011] The bowl-shaped entity is formed on the surface of the base using micro-nano fabrication methods.

[0012] The base is placed at an angle.

[0013] The beneficial effects of this invention are as follows:

[0014] This invention achieves spontaneous and continuous reverse transport of droplets from the bottom to the top of a bowl-shaped solid by adjusting the surface geometry at the micro-nano scale and utilizing a bowl-shaped axisymmetric surface, thus avoiding surface icing and dust accumulation.

[0015] The bowl-shaped entity of this invention has a convex curved surface on its circumferential side and a small flat section at the top. Compared with conventional conical structures, this allows droplets to move spontaneously and continuously towards the top. The small flat section at the top promotes droplet merging and aggregation, while also facilitating droplet sliding, thus more effectively preventing the formation of large-area ice layers and frost on the surface. This solves the technical problem in the prior art where, after the droplet has moved a certain distance, the driving force gradually decreases as the cone diameter increases, causing the droplet to gradually stop moving, resulting in slow droplet removal speed and poor effect.

[0016] This invention can prevent damage caused by water vapor condensing into ice on the surface in cold and humid environments. For example, in cold environments, it can effectively prevent water vapor from condensing into ice on the surface and damaging the performance of the instrument, while in humid environments, it has a self-cleaning function.

[0017] The bowl-shaped entity in this invention can be formed on the surface of the base using micro-nano fabrication methods. The entire device does not contain complex parts, making the surface structure not only simple in structure and highly stable, but also easy to replace. It is also very convenient to process, maintain and clean, with low maintenance costs. Moreover, it does not require the transmission of external energy during operation, thus having good practicality and broad application prospects.

[0018] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description

[0019] Figure 1This is a three-dimensional structural diagram of an embodiment of the present invention.

[0020] Figure 2 This is a schematic diagram of the geometric structure of the bowl-shaped entity according to an embodiment of the present invention.

[0021] Figure 3 This is a schematic diagram of the molecular dynamics model of the bowl-shaped entity according to an embodiment of the present invention.

[0022] Figure 4 This is a graph showing the relationship between the position and time of a water droplet as it spontaneously moves from the bottom to the top of a bowl-shaped object during the application of an embodiment of the present invention.

[0023] Figure 5 This diagram illustrates the relationship between the radius of the arc in the busbar and the average speed of the water droplet moving on the bowl-shaped entity during the application of this embodiment of the invention.

[0024] Figure 6 This is a graph showing the relationship between the contact angle between a water droplet and a bowl-shaped entity and the average speed of the water droplet moving on the curved surface during the application of an embodiment of the present invention.

[0025] In the diagram: 1. Base; 2. Bowl-shaped solid; 21. Convex curved surface; 22. Plane. Detailed Implementation

[0026] The specific embodiments of the present invention are described below with reference to the accompanying drawings.

[0027] Droplets can spontaneously orient themselves via surface curvature gradients, a technique employed by organisms such as cacti and algae, particularly suitable for applications like anti-icing, self-cleaning, and water collection, all without requiring external energy. However, droplet-directed transport is limited by short transport distances and low operability; droplets can only migrate towards relatively flat areas and gradually cease movement. The applicant believes that creating a fixed structure to regulate droplet motion would greatly facilitate its application in various fields. The applicant's research revealed that the spontaneous motion of droplets on solid surfaces can be regulated by altering surface geometry. Molecular dynamics simulations show that droplets on a typical bowl-shaped axisymmetric surface can achieve reverse motion from bottom to top, continuously moving to the top at an almost constant speed. This bowl-shaped structure enables reverse droplet transport without the need for external energy. The technical solution of this application is further described below with specific embodiments.

[0028] like Figure 1 As shown, the passive anti-icing and self-cleaning functional surface structure of this embodiment includes a base 1 and a bowl-shaped entity 2, with the bowl-shaped entity 2 evenly distributed on the base 1.

[0029] like Figure 2As shown, the bowl-shaped entity 2 is an axisymmetric entity formed by rotating a generatrix around an axis of symmetry, which is perpendicular to the surface of the base 1. The generatrix consists of a quarter-circular arc of radius R and a straight line segment of length d, where the arc and the straight line segment are tangent, and the perpendicular distance (length of the straight line segment) from the point of tangency to the axis of symmetry is d. This results in the bowl-shaped entity 2 having a plane 22 at the top and a convex circumferential side surface (named convex surface 21) located between the top plane and the bottom. The bottom of the bowl-shaped entity 2 is connected to the base 1. It can be understood that... Figure 2 In the diagram, the long dashed line at the center represents the axis of symmetry of the axially symmetric entity.

[0030] During operation, water vapor continuously accumulates on the surface of the bowl-shaped entity 2, forming water droplets that adhere to the convex curved surface 21 of the bowl-shaped entity 2. The convex shape allows the water droplets to spontaneously and continuously move in opposite directions from bottom to top. (See attached diagram for direction of movement.) Figure 2 As indicated by the middle arrow.

[0031] The bowl-shaped entity 2 can be formed on the surface of the base 1 using micro-nano fabrication methods. Specifically, a layer of photoresist can be spin-coated onto the base 1 first, and then the bowl-shaped entity 2 can be fabricated using photolithography, reactive ion etching, or ion beam etching.

[0032] The bowl-shaped entity 2 is preferably evenly distributed on the upper surface of the base 1 with a gap of 30-80nm, which can prevent water droplets from forming ice or frost on the surface of the base 1.

[0033] In this embodiment, a hydrophobic coating is preferably provided on the surface of the bowl-shaped entity 2. The hydrophobic coating allows condensed water droplets to be transported in reverse more quickly on the surface of the bowl-shaped entity 2, and water vapor will condense more easily on the bowl-shaped entity 2 in a humid environment, and then be removed by the jumping caused by the merging of droplets or by gravity.

[0034] In this embodiment, a superhydrophobic layer is preferably provided on the surface of the base 1. The surface of the superhydrophobic layer facilitates the sliding of water droplets and can reduce the adhesion of water droplets on the surface in cold and humid environments, thereby achieving self-cleaning of the surface.

[0035] Both the superhydrophobic layer and the hydrophobic coating can be achieved through surface treatment processes.

[0036] The working principle of the passive anti-icing and self-cleaning functional surface structure in this embodiment is as follows:

[0037] The different transport properties of droplets on different axisymmetric surfaces are caused by the different driving forces. By analyzing the internal pressure gradient of the droplet caused by the curvature gradient, the driving force formula for droplets on general axisymmetric surfaces can be derived as follows:

[0038]

[0039] Can be combined Figure 3 Understanding the meaning of each symbol in equation (1): F is the driving force of the droplet on the axisymmetric surface, r d Let be the radius of the droplet, θ be the inherent contact angle between the droplet and the solid surface, γ be the surface tension of water, H be the droplet height, and α be the droplet height. z R represents the tangential angle of the projection of the droplet's center of mass onto the axisymmetric surface. C and R S These are the two principal radii of curvature in mutually perpendicular directions at the projection point of the droplet's center of mass onto the convex surface. For example... Figure 3 As shown, when the curved surface of the bowl-shaped solid convexes outward, R S If negative, R S =-R.

[0040] From equation (1), it can be seen that the direction of the driving force F depends only on (1+R) C / R S The sign of ) is used because all other terms take positive values.

[0041] The applicant establishes such Figure 3 The molecular dynamics model shown Figure 3 The circular shape in the middle represents a water droplet, the circumferential side of the bowl-shaped entity 2 is convex, and d represents the perpendicular distance from the point of tangency between the straight line segment and the arc in the generatrix to the axis of symmetry (i.e., as shown in the figure). Figure 2 (The length of the straight segment in the middle), when d is positive, the axisymmetric entity formed by the generatrix around the axis of symmetry is bowl-shaped; when d is negative, the axisymmetric entity formed by the generatrix around the axis of symmetry tends to be cone-shaped. Molecular dynamics simulations have confirmed that the specific convex surface of this embodiment can realize the spontaneous continuous transport of droplets from bottom to top, with high transport efficiency.

[0042] The following simulation study further illustrates the technical effects of the passive anti-icing and self-cleaning functional surface structure of this embodiment.

[0043] Based on the aforementioned driving force formula and related theories, the applicant studied d = 4nm, θ = 92°, R S The motion of a droplet on a bowl-shaped axisymmetric surface at -7.5 nm is shown in the results. Figure 4 . Figure 4 The middle vertical coordinate z m It is the coordinate of the center of mass of the water droplet in the Z direction (vertical direction), and the Z-axis is the axis of symmetry of the bowl-shaped solid. m When the time interval is 0, the center of mass of the water droplet is located at the top end face of the bowl-shaped solid, i.e., the plane. The horizontal axis t represents time. Figure 4 It can be seen that the bowl-shaped entity in this embodiment enables the nanodroplets to move spontaneously from its bottom to its top end face, and as z... mAs the driving force gradually increases, the droplet's speed increases, enabling it to move continuously and without stopping to the top of the bowl-shaped object. This effectively solves the technical problem in existing technologies where, after moving a certain distance, the driving force gradually decreases as the cone diameter increases, causing the droplet to gradually stop moving.

[0044] In order to study different R S The applicant conducted a quantitative comparison of the effect on droplet velocity, and the results are shown in [link to results]. Figure 5 . Figure 5 The middle vertical axis V ave The x-axis represents the average velocity of the droplet motion, |R|. S | represents the radius R of the quarter-circle arc in the generatrix of the axisymmetric solid. As shown in the figure, with other parameters remaining constant, |R S |It varies in the range of 4.5nm to 9.5nm, as |R S As the velocity of the droplet decreases, the average velocity of the droplet increases.

[0045] To further improve the reverse transport velocity of the droplets, d = 4 nm was chosen, R S The motion of a water droplet on an axisymmetric surface at -7.5 nm was analyzed when the contact angle θ was 109°, 100°, and 92°. The results are as follows: Figure 6 As shown, the results indicate that the larger the contact angle between the water droplet and the bowl-shaped axisymmetric surface, the faster the droplet's reverse motion. Therefore, optimizing the contact angle between the water droplet and the bowl-shaped axisymmetric surface by adjusting the wettability of the solid surface can positively influence the driving force of the nanodroplets. Thus, in this embodiment, a hydrophobic coating is applied to the surface of the bowl-shaped solid, enabling the accumulated water droplets to be transported more quickly from bottom to top in the reverse direction. Therefore, d = 4 nm, R... S =-7.5nm is the preferred setting for the bowl-shaped entity in this embodiment.

[0046] In summary, this embodiment, due to the uniform distribution of the bowl-shaped solid structure, enables spontaneous and continuous transport of water droplets from bottom to top, effectively preventing water droplets from solidifying on the base surface to form ice or frost. In cold and humid environments, it prevents water vapor condensing on the surface from forming ice or frost that could damage the surface. Because the base surface of this embodiment is superhydrophobic, water droplets are difficult to balance on the base surface and can slide off the surface under gravity, carrying away accumulated dust and achieving a self-cleaning function. To facilitate rapid water droplet removal, in practical applications, the entire device can be tilted at a certain angle to ensure that water droplets collected on the superhydrophobic surface of the base can slide off. This embodiment requires no external energy supply, enabling spontaneous and continuous transport of droplets from bottom to top, and possesses anti-icing and self-cleaning functions.

[0047] It will be understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A functional surface structure for passive anti-icing and self-cleaning, characterized in that, Includes a base (1), on the surface of which are a plurality of bowl-shaped entities (2), the bowl-shaped entities (2) are axisymmetric entities formed by rotating a generatrix around an axis of symmetry, the axis of symmetry being perpendicular to the surface of the base (1), the generatrix being composed of a 1 / 4 circular arc and a straight line segment, and the circular arc being tangent to the straight line segment, such that the top of the axisymmetric entity forms a plane (22), and the circumferential side surface between the bottom and the top is an outwardly convex curved surface (21), the bottom of the bowl-shaped entities (2) being connected to the base (1); The surface of the base (1) is provided with a superhydrophobic layer; The surface of the bowl-shaped entity (2) is provided with a hydrophobic coating; The radius of the 1 / 4 arc is 4.5-9.5 nm, and the length of the straight line segment and the perpendicular distance between the point of tangency between the arc and the straight line segment and the axis of symmetry are equal, which is 3-4 nm.

2. The functional surface structure for passive anti-icing and self-cleaning as described in claim 1, characterized in that, The plurality of bowl-shaped entities (2) are evenly distributed on the surface of the base (1) with a gap of 30-80nm.

3. The functional surface structure for passive anti-icing and self-cleaning as described in claim 1, characterized in that, The bowl-shaped entity (2) is formed on the surface of the base (1) by micro-nano processing.

4. The functional surface structure for passive anti-icing and self-cleaning as described in claim 1, characterized in that, The base (1) is placed at an angle.

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