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Controlling surface wettability and adhesive properties by laser marking approach
Optics and Laser Technology 115 (2019) 160–165
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Full length article
Controlling surface wettability and adhesive properties by laser marking approach
T
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Jing Lia, , Yingluo Zhoua, Fengyu Fana, Feng Dub, Huadong Yua a b
Department of Mechanical and Electric Engineering, Changchun University of Science and Technology, Changchun 130022, PR China Department of Mechanical Engineering, Changchun Institute of Engineering, Changchun 130117, PR China
H I GH L IG H T S
processing method is found to fabricate superhydrophobic surface. • AThelaser prepared microstructure is the main reason for changing the surface wettability. • Different laser scanning spacing results in different wettability and adhesion. •
A R T I C LE I N FO
A B S T R A C T
Keywords: Laser marking approach Microstructure Wettability Adhesion
We provide a special microstructure to fabricate superhydrophobicity surface of aluminum alloy by laser marking method. The morphologies and wettability of the fabricated aluminum alloy surface are investigated through scanning electron microscopy (SEM) and the contact angle meter. The results indicate that the fabricated surface with irregular protrusions and pits shows excellent superhydrophobicity/hydrophobic. The surface texture of this microstructure is characterized by a contact angle of up to 156.4° when the surface exhibits superhydrophobicity and a contact angle of up to 147.8° when the surface exhibits hydrophobicity. Because the unidirectional processing of the laser makes the surface anisotropic, we discuss the wettability in this area. Moreover, we discuss the effect of wettability and adhesion at different scales on the fabricated surface. A series of data shows differences in related properties due to different laser texture scales. Differences in performance of the material can be applied in different field conditions. The fabrication technique is a promising method to provide superhydrophobic surface with potential applications including fluid transfer, fluid power systems, stain-resistant and anti-fouling surfaces, anti-creeping of oils, anti-contamination, and oil transport. More importantly, this novel surface structure further extends the application of aluminum alloys in industry.
1. Introduction Superhydrophobic surfaces with a water contact angle of more than 150° and extremely low sliding angle (< 5°) have received the attention of a wide range of researchers these years because of its importance in essential research [1,2]. Preparation surfaces with different wettability have their own applications in various fields, such as corrosion resistance, anti-icing, self-cleaning, anti-attrition, etc. [3–9]. As is wellknown, lotus leave is a superhydrophobic surface and its superhydrophobicity comes from the specific microstructures besides the epicuticular waxes [10]. A superhydrophobic surface is usually achieved by changing the surface microstructure and reducing the surface energy [11]. Therefore, many researchers have used various methods to fabricate surface microstructures to obtain surfaces with
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superhydrophobic properties [12–14]. For example, Sun et al. fabricated superhydrophobic coating by casting the alkoxy polysiloxane copolymerization emulsioncontaining fumed silica and phenyltrimethoxysilane (PhTMS)/γ-(2,3-epoxypropoxy) propytrimethoxysilane (EPTMS) on the glass slide [15]. Hu et al. present a simple method for fabricating a microstructured Cu/Ni–W alloy coating by combining electroless and electro deposition [16]. Aluminum and its alloys are irreplaceable engineering materials owing to their easy accessibility, excellent machinability, high fatigue strength and low price. Accordingly, they have achieved extensive industrial applications, especially in the fields of shipbuilding, oceanography engineering, aerospace and machine manufacturing [17,18]. In order to improve the performance of aluminum alloys and expand the application of aluminum alloys, many superhydrophobic surfaces are
Corresponding author. E-mail address: [email protected] (J. Li).
https://doi.org/10.1016/j.optlastec.2019.02.023 Received 4 June 2018; Received in revised form 7 December 2018; Accepted 3 February 2019 0030-3992/ © 2019 Elsevier Ltd. All rights reserved.
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Fig. 1. The schematic process of the laser marking approach.
600–2000). Then they were cleaned ultrasonically with alcohol and deionized water respectively, and dried in air. (2) The process of laser processing: The polished samples were constructed roughness structure on the surface by a portable laser marking machine (fibre laser marking machine with putout power of 12 W, focal spot size of 0.05 mm). under processing parameters (lined grooves surface, scanning line spacing of 50, 100, 150, 200 μm, frequency of 20 kHz, scanning speed of 1100 mm/s, scanning times of 2 times).
prepared on aluminum alloys. For example, Yu et al. fabricated the submillimeter-scale structures by the high speed wire electrical discharge machining (HSWEDM) technology on the 5083 aluminum (Al) alloy substrates, the results showed that the V-shaped groove arrays with a hierarchical structure presented the good superamphiphobicity after a solution immersion [19]. Sooksaen et al. fabricated hydrophobic surfaces on Al-0.5Mg-0.5Mn aluminum alloy thick sheet. An electrochemical anodization process was carried out followed by silane treatment on the anodized surfaces [20]. So far, a large number of approaches have been successfully used to develop superhydrophobic surfaces, including chemical vapor deposition [21], chemical etching [22], sol-gel [23], solution immersion [24], hydrothermal synthesis [25] and laser fabrication [26,27]. For example, Li et al. have constructed superhydrophobic surface on stainless steel substrate by acid treatment and hydrophobic film deposition [28]. Zhao et al. have generated periodic micro–nano hole structures on superhydrophobic surface with a three-beam laser interference system [29]. Li et al. reported that bionic alumina samples were fabricated on convex dome type aluminum alloy substrate using hard anodizing technique [30]. The research group has long been devoted to the study of the functional properties of metal surfaces. It has been fabricated on the surfaces of aluminum alloys, carbon steels, stainless steels, and copper by electrodeposition of nickel [31], laser etching [32,33], and electrodeposition of copper [34] to obtain structures of different scales and morphologies. In this work, the laser marking approach was used to fabricate a superhydrophobic aluminum alloy surface, and the fabricated surface exhibited several properties. With this serving as context, the discussion below examines some of the theory and progress surrounding these properties.
2.3. Characterization The microstructures of the sample surface fabricated were observed via SEM (COXEM EM-30, Korea). The static contact angle (An OCA15 system from Dataphysics GmbH, Germany) was measured with 4 μL of distilled pure droplets at ambient temperature. The element composition of these samples surface was estimated with XRD.
3. Results and discussion 3.1. Preparation of a hydrophobic surface by a one-step method In Fig. 1, the schematic process of the laser marking approach is shown. In the process of the treatment, the laser beam rapidly heats and densely melts the surface of the aluminum alloy at a given speed on a set track. In the direction of y, by changing the size of the laser processing line spacing, the surface of the sample with different morphologies is manufactured; In the direction of x, under the action of the laser beam, a laser texture with a 50 μm diameter pit-like structure is uniformly and closely arranged. We use the laser impact force to make the pit-shaped molten pools on the surface of the material. A part of the molten material is evaporated due to the heat received. The remaining material, due to the impact force, accumulates in the form of a melt on the edge of the pit-like structure and after cooling, it fuses with the surface of the substrate. Compared with most of reported approached for fabricating superhydrophobic surfaces, the laser marking approach is low-cost, and high efficiency of treated surface. The process is very simple, and there is no requirement for area and thickness. It is suitable for large-scale processes and batch processing. It is a relatively convenient and effective laser processing method in the field of mechanical processing and manufacturing.
2. Experimental section 2.1. Materials 7075 series aluminum alloys, as experimental materials, were purchased from subsidiary company of Shanghai AoFeng metal products Co., Ltd. The sample size is 10 mm × 10 mm × 2 mm, which is gained by line cutting machine. 2.2. Preparation of the superhydrophobic surface (1) The process of the pre-treated: Aluminum alloy samples were sanded and polished with different grades of sandpaper (Nos. 161
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Fig. 2. Low-magnified SEM image of the morphology of surface treated by laser marking (lined pits surface, frequency of 20 kHz, scanning speed of 1100 mm/s) with textures spacing of (a) 50 μm, (b) 100 μm, (c) 150 μm, (d) 200 μm. The insets corresponding to their high-magnified SEM images.
3.2. Morphological analysis of as-prepared surfaces
Table 1 OCA results of laser processing surface.
In order to study the effect of laser processing surfaces on the microstructure of the treated surface, the textured surfaces with different spacings are investigated. After the aluminum alloy surfaces used in the experiment were fabricated by laser processing, the surface micro-topography can be obtained. As can be seen in Fig. 2, with the increase of laser texture line spacing (50, 100, 50 and 200 μm), the microstructure of the surface has changed. In the direction of the laser, they are all composed of tight pit-like structures. However, in the direction perpendicular to the laser, the microstructure of the protrusions and pits becomes more and more unique. It can be observed that because of the increase of line spacing, the structure of protrusions and pits are reduced in unit area and reach a minimum (texture spacing of 200 μm). Moreover, from high-magnified SEM image presented in the inset of Fig. 2(a–d), it can be found the size of the pit structure is unchanged. It is explained that the change in the surface properties of the material is mainly due to the area ratio of the microstructure in the unit area. There are not effects in molten metal of adjacent rows, but protrusions are manufactured independently.
Laser texture line spacing (μm)
The contact angle of x (°)
The contact angle of y (°)
Difference value (°)
50 100 150 200
156.4 154.6 147.8 138.9
155.7 151.5 137.4 111.2
0.7 3.1 10.4 27.7
line spacing and the maximum value is 27.7° (line spacing of 200 μm). The difference value from the minimum (line spacing of 50 μm) is 20°. Meanwhile, the laser processing surface is transformed from a superhydrophobic surface (line spacing of 100 μm, the contact angle is 154.6°on the x direction and 151.5° on the y direction) to a hydrophobic surface (line spacing of 150 μm, the contact angle is 147.8° on the x direction and 137.4° on the y direction). This shows that the laser processing line spacing directly affects the wettability of the surface. The larger the laser processing distance, the greater the effect on wettability and the poorer the wettability. As shown in Fig. 4a, whether viewed from the x direction or from the y direction, the contact angles are greatly reduced from laser texture line spacing of 50 μm to laser texture line spacing of 200 μm. This can be explained that the pit microstructure on the surface makes the smooth surface rough. When the water droplet contacts with the surface, a great number of air will be trapped into the space between the roughness structure and water droplet, and it will lead most of water to contact with air. However, from the results, the lower the roughness of the surface is, the smaller the contact angle of the surface will be. Therefore, the treated surfaces show superhydrophobicity and hydrophobicity, and the contact angle can be as high as about 156.4°. However, with larger line spacing, the pit microstructure leads to the decrease of roughness, and that causes the reduction of the contact angle.
3.3. Wettability 3.3.1. Wettability of the surfaces Due to the laser textured surface with anisotropic, contact angles in both directions (x, along the laser direction and y, vertical laser direction) were investigated. In Table 1, it is obvious that the contact angles of the surfaces with line spacing of 50, 100, 150 and 200 μm on the direction of x are 156.4°, 154.6°, 147.8° and 138.9° respectively. And on the direction of y are 155.7°, 151.5°, 137.4° and 111.2° respectively. It can be seen that the contact angle on the x direction is generally better than the contact angle on the y direction. This is because when the direction of the laser texture is uniform, the water droplets will also spread along the direction on the surface, resulting in a slight deformation. Moreover, The difference value between the x and y directions increases with the increase of the laser processing texture
3.3.2. Theoretical calculation of wettability Although the laser processing surface has anisotropy, from the data 162
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Fig. 3. The contact angle of the prepared surface and the number of days placed.
above, it is uniformly expressed that they have superhydrophobicity and hydrophobicity. Therefore, we only select the contact angle data in the x direction for analysis. With the different constructs on the aluminum surfaces, the aluminum surfaces exhibited the different wettability. So the static contact angles were respectively measured on the polished surface and laser marking surfaces. The wettability of the fabricated surfaces can be measured via contact angle meter at ambient temperature (22 ± 3 °C) and relative humidity (45 ± 8%). When the line spacing is 50 μm, the fabricated surface via laser marking exhibited a contact angle of 156.4°. By changing the line spacing (100, 150 and 200 μm) during laser beam irradiation, a contact angles of the fabricated surfaces via laser marking is different. The static contact angles of the surfaces exhibited the contact angles of 154.6°, 147.8°and 138.9° respectively. As shown in Fig. 3, there is no substantial change in the contact angle of the sample surface within 300 days of prepared sample, which indicates that the stability of this microstructure is strong. The relationship of surface wettability at heterogeneous surfaces was proposed by Cassie and Baxter’s [35,36] such as the equation:
cosθr = f1 cosθ − f2 = cosθ − f2 (cosθ + 1)
Fig. 4. The physical map of the sample and corresponding contact angle profiles (a), Cassie model (b) and structure model (c).
3.3.3. Effect of the surface structure to the surface wettability The wettability is an important property for the solid surfaces, and the static contact angle is used as describing the physical parameters of the water droplets. According to the Cassie theory [36], we believe the circular pit structures and the interval between one circular pit and another circular pit will store air, and the water droplets on the asprepared surface directly contact with the outside air. It can be supported by the storage air, which increases the contact angle. In this study, we mainly research the effect of structure to the surface wettability. We assume that when laser scanning distance is 50 µm, the water droplets on the surfaces are in a typical Cassie model state. Based on the hydrophobic model of the pit structure, we can calculate the biggest drop height of the water droplets in the surface. We study the relative references and combine with the as-prepared surface structure for modeling. As can be seen in Fig. 4c, h is the embedding depth of the water droplets. The formula of the circular pit structure mode is:
(1)
where f1 and f2 are the fractions of aluminum solid surface and air in composite surface respectively and f1 + f2 = 1. θr and θ are contact angles on rough aluminum and the bare surface (the contact angle is 79.2°), respectively. As shown in Table 2, when the line spacing is 50 μm, the f2 value of the micro- and nano-structure via laser marking approach was estimated to be 0.9295, and the low value of f1 shows that only about 7.050% of the water surface is in contact with the aluminum surface. By changing the line spacing (100, 150, 200 μm) during laser beam irradiation, the f2 value is 0.9186, 0.8704 and 0.7923 respectively and the low value of f1 is 8.14%, 12.96% and 20.76% respectively. This indicates that f2 (liquid projected area fraction in contact with air) plays an extremely important role in wettability. When f2 is larger, the wettability of the sample surface is better. Therefore, how to construct a structure that increases f2 becomes a problem to be solved.
cosθr =
The contact angle of X (°)
f1
f2
50 100 150 200
156.4 154.6 147.8 138.9
0.0705 0.0814 0.1296 0.2077
0.9295 0.9186 0.8704 0.7923
(2)
This formula evolved from the Cassie theory formula, and it can be used to understand the relationship between the circular pit structures and the surface wettability. The R and h are the radius of the circular pit structures and the drop height of the water droplets respectively. The a and b is the distance between two directions of the circular pit structures. The θr is the contact angle on the as-prepared surface. The θ0 (79.2°) is the contact angle on the polished surface. The measured values (a = 50 µm, b = 41 µm, Ra =21.05 µm, Rb =19.55 µm) is put into the (2) formula, and we can obtain the value that h is 1.36 µm. From the results above, we can see the drop height of the water droplets are less than the height of the surface shoulder and the depth of the pit. The water droplets are not fully immersed inside the pit. The more contact area of the water droplets is the surface shoulder structure. Therefore, the relationship between the surface contact state and the Cassie model is further verified. The area calculation formula can be
Table 2 The results obtained through Cassie and Baxter’s equation. Laser texture line spacing (μm)
2πRh (1 + cosθ0) a×b
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deduced from the shoulder structure of the surface:
fs =
π (Ra2 − Rb2 ) a×b
(3)
TheR a andR b are the outer wall and inner wall radius of the circular pit structures respectively. The measured values is put into the (3) formula and we can obtain the value that fs is 0.093, and the value r of the surface roughness is 1.653. Then the fa was put into the Cassie theory formula: cosθr = f (1 + rcosθ0) − 1
(4)
We can obtain the theoretical contact angle of θr and it is 151.4°. The contact angle is close to 156.4°of the actual measured contact angle (There are some errors between the theoretical model and the actual surface); So when the laser scanning line spacing is 50 µm, the existing form of water droplets on the as- prepared surface is similar with the Cassie state. The experimental results are consistent with the experimental hypothesis. Under the combination of the shoulder structure of the surface and the air, the water droplets have only a small drop height. It can be shown that this protrusions and pits structure cause the water droplets to come into contact with the air rather than the surface of the substrate, greatly improving the hydrophobicity of the material surface.
Fig. 5. The rolling characteristic profiles for (a), a series of photos were recorded before and after the water droplet contacting with the as-prepared surface under 50 µm, 100 µm, 150 µm, and 200 µm) (b).
platform on surface contact angle measurement is used to discuss the adhesion problem. At first, because of the water droplets’ surface tension, the water droplets are suspended on the front end of the needle. When the instrument platform drives the fabricated surface to rise slowly, and the surface starts to contact with the water drop (Fig. 5(b1)). During the rising of the contact angle platform, the water droplets are gradually deformed and produce a gradual deformation (Fig. 5(b3)). But the instrument platform rises from the bottom to the top, the instrument platform doesn’t seem to have much effect on the dynamic contact angle of the water droplets. Then the contact angle platform slowly began to decline, which causes the water droplet to slide along the needle, and the water droplet finally returns to the tip of the needle again (Fig. 5(b5)). In the process of the falling contact angle platform, because the water droplets have surface tension, the water droplets produce a gradual deformation. The surface tension finally causes the separation of water droplets and the platform of contact angle. When the water droplets are separated from the platform, the water droplets show a significant shaking. But in the process of the water droplets separating from the platform, the dynamic contact angle of water droplets do not change obviously. When the laser scanning line spacing is different, the difficulty degree of the separation process of the water droplets and the texture of sample surface is different. In Fig. 5(b6–b10), When the laser scanning line spacing is 100 μm (because the separation process of the water droplets of 150 μm, 200 μm is similar with 100 μm, the separation process of 100 μm represents 150 and 200 μm), the subsequent larger exposed area of the unprocessed Al alloy surface resulted in a decrease of the surface roughness, which changed the droplet's adhesion to the sample surface (Fig. 5(b10)). Additionally, the larger exposed area of the unprocessed Al alloy surface resulted in a stronger surface wettability, further increasing the solid-liquid contact area between the droplet and the unprocessed Al alloy surface, which can lead to a strong adsorption capacity with high adhesion. Through the observation of the above dynamic process, there were some differences in the adhesion of the samples to the water droplets with differences of the laser scanning line spacing.
3.4. Effect of high/low adhesion on surface The static contact angles of the water droplet on the surfaces cannot show its motion state on the inclined surfaces. It can only reflect the instantaneous static state of the water droplets. Sometimes the water droplets have a small contact angle on the prepared surface, but the water droplets on the aluminum alloy surfaces may also be prone to slide. On the contrary, although the contact angles on some sample surfaces have a great improvement, it's hard to slide. For example, the static contact angle of the rose petal surfaces has exceeded 150°, but the water droplets are tightly attached to the surface through small contact area between the water droplets and the rose petal surface. It’s difficult to slide. This is also the limitations of the static contact angle in the performance of hydrophobic. So the dynamic contact angle can further be used to discuss the wettability of the sample surfaces, and it can be measured by the method of the adding and subtracting water droplets. The size of the contact angle hysteresis theoretically represents the degree of the difficulty of the water droplets motion on the surface. In order to obtain low adhesion surface, we tend to need contact angle hysteresis as small as possible. The measured data on the sample surfaces under 50 μm can be 6.1°, the prepared superhydrophobic aluminum alloy surface has a smaller hysteresis contact angle, which shows the water droplets have the more possibility of motion. The measured data on the sample surfaces under 100, 150 and 200 μm can be 17.2°, 16.5°and 18.1°respectively. As can be seen in Fig. 5a, it shows that the sliding process of the water droplets on the inclined prepared superhydrophobic surface is under 50 μm. In Fig. 5a (1–3), under 50 μm, we can see the water droplets do not have the shaking or moving tendency. When the angle of inclined surface was about 2.3°, the water droplets on the surface begin to slide and instantaneous slide down from the inclined surface. The sliding speed of the water droplets is about 10.34 mm/s measured by Nano Measure software. The prepared surface under 50 μm shows a low adhesion to water droplets, and the water droplets is in the unstable state on the superhydrophobic surface. In Fig. 5(a4–a6), under 100 μm (because the rolling process of the water droplets of 150 μm, 200 μm is similar with 100 μm, the rolling process of 100 μm also represents 150 μm, 200 μm), the prepared aluminum alloy surfaces have high adhesion. When the prepared surfaces were inclined at about 90°, the water droplets on the surfaces do not appear the sliding tendency. As illustrated in Fig. 5b, in order to observe the dynamic behavior of the fabricated surface under the line spacing of 50 μm, the lifting
4. Conclusions In summary, we have fabricated two surfaces with different degrees of performance via a simple and low-cost laser marking approach. The morphology of the surface fabricated can have been slightly tuned, but it led to the different wettability of the surfaces as-prepared. The line spacing during laser beam irradiation was changed to achieve different 164
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sizes of the Al alloy surface. When the laser texture line spacing is 50 μm, the surface shows with excellent superhydrophobicity and antiadhesive property. When the laser texture line spacing is 100, 150, 200 μm, the surface shows with hydrophobicity and high adhesion property. Surfaces prepared with different processing spacings have different contact angles. The static contact angle of the prepared surface can be as high as 156.4° and the sliding angle was 2.3°. The small contact angle hysteresis can be shown on the superhydrophbic surface fabricated via laser marking approach. The prepared surface with high adhesion was of great significance for water collection and preservation. The area ratio between the microstructure and the unprocessed Al alloy surface played a key role in determining the wetting conditions of the sample surface.
[14]
[15]
[16]
[17]
[18]
[19]
Conflict of interest [20]
None. [21]
Acknowledgements [22]
The authors are grateful to the National Natural Science Foundation of China (Grant No. 51505039), the Postdoctoral Science Foundation of China (no. 2014 M551145), the Natural Science Foundation of Science and Technology Department of Jilin Province (Grant No. 20180101322JC), and the “111” Project of China (Grant No. D17017) for support of this work.
[23]
[24]
[25]
References [1] Y. Liu, J.D. Liu, S.Y. Li, Z.W. Han, S.R. Yu, L.Q. Ren, Fabrication of biomimetic super-hydrophobic surface on aluminum alloy, J. Mater. Sci. 49 (2014) 1624–1629. [2] Q. Ke, W. Fu, S. Wang, T. Tang, J. Zhang, ACS Appl. Mater. Interfaces 2 (2010) 2393–2398. [3] P. Wang, T. Yao, B. Sun, X.L. Fan, S.J. Dong, Y. Bai, Y. Shi, A cost-effective method for preparing mechanically stableanti-corrosive superhydrophobic coating based on electrochemicallyexfoliated graphene, Colloid. Surf. A 513 (2017) 396–401. [4] Y. Liu, S.Y. Li, J.J. Zhang, J.A. Liu, Z.W. Han, L.Q. Ren, Corrosion inhibition of biomimetic super-hydrophobic electrodeposition coatings on copper substrate, Corros. Sci. 94 (2015) 190–196. [5] R. Rahul, K. Marina, S. Konstantin, N. Michael, Anti-icing superhydrophobic surfaces: controlling entropic molecular interactions to design novel icephobic concrete, Entropy 18 (4) (2016) 1–26. [6] Y. Liu, X.L. Li, J.F. Jin, J.A. Liu, Y.Y. Yan, Z.W. Han, L.Q. Ren, Anti-icing property of bio-inspired micro-structure superhydrophobic surfaces and heat transfer model, Appl. Surf. Sci. 400 (2017) 498–505. [7] J. Li, Y. Wei, Z.Y. Huang, F.P. Wang, X.Z. Yan, Z.L. Wu, Electrohydrodynamic behavior of water droplets on a horizontal super hydrophobic surface and its selfcleaning application, Appl. Surf. Sci. 403 (2017) 133–140. [8] R. Blossey, Self-cleaning surfaces–virtual realities, Nat. Mater. 2 (2003) 301–306. [9] Q.G. Han, H.Z. Zhang, L. Fang, Y.Q. Wang, Tribological properties of nanocrystalline cu coatings produced by electroless plating under various lubrication conditions, Rare Met. Mater. Eng. 40 (2011) 356–359. [10] Y.T. Cheng, D.E. Rodak, C.A. Wong, Effects of micro-and nano-structures on the self-cleaning behaviour of lotus leaves, Nanotechnology 17 (2006) 1359–1362. [11] M.K. Tang, X.J. Huang, Z. Guo, J.G. Yu, X.W. Li, Q.X. Zhang, Fabrication of robust and stable superhydrophobic surface by aconvenient, low-cost and efficient laser marking approach, Colloids Surf. A: Physicochem. Eng. Aspects 484 (2015) 449–456. [12] I. Vilaró, J.L. Yagüe, S. Borrós, Superhydrophobic copper surfaces with anticorrosion properties fabricated by solventless CVD methods, ACS Appl. Mater. Interfaces 9 (2017) 1057–1065. [13] B. Mondal, M.M.G. Eain, Q.F. Xu, V.M. Egan, J. Punch, A.M. Lyons, Design and
[26]
[27]
[28]
[29]
[30] [31]
[32]
[33]
[34] [35]
[36]
165
fabrication of a hybrid superhydrophobic-hydrophilic surface that exhibits stable dropwise condensation, ACS Appl. Mater. Interfaces 7 (2015) 23575–23588. Z.X. Lian, J.K. Xu, Z.B. Wang, Z.C. Wang, Z.K. Weng, H.D. Yu, Fabrication and applications of two- and three-dimensional curved surfaces with robust underwater superoleophobic properties, J. Mater. Sci. 52 (2017) 1123–1136. Z.G. Sun, B. Liu, S.Q. Huang, J. Wu, Q.C. Zhang, Facile fabrication of superhydrophobic coating based on polysiloxane emulsion, Prog. Org. Coat. 102 (2017) 131–137. F.T. Hu, P.H. Xu, H.Z. Wang, U.B. Kang, A. Hu, M. Li, Superhydrophobic and anticorrosion Cu microcones/Ni–W alloy coating fabricated by electrochemical approaches, RSC Adv. 5 (2015) 103863–103868. E.M. Sherif, H.R. Ammar, K.A. Khalil, Effects of copper and titanium on the corrosion behavior of newly fabricated nanocrystalline aluminum in natural seawater, Appl. Surf. Sci. 301 (2014) 142–148. Y.S. Huang, T.S. Shih, J.H. Chou, Electrochemical behavior of anodized AA 7075–T73 alloys as affected by the matrix structure, Appl. Surf. Sci. 283 (2013) 249–257. H.D. Yua, Z.X. Lian, Y.L. Wan, Z.K. Weng, J.K. Xua, Z.J. Yu, Fabrication of durable superamphiphobic aluminum alloy surfaces with anisotropic sliding by HS-WEDM and solution immersion processes, Surf. Coat. Technol. 275 (2015) 112–119. P. Sooksaen, O. Chulasinont, P. Janmat, W. Thovasaku, Chemical treat ment on aluminum alloy for hydrophobic surfaces, Mater. Today 4 (2017) 6528–6533. J. Yu, L. Qin, Y. Hao, S. Kuang, X. Bai, Y.M. Chong, W. Zhang, E. Wang, Vertically aligned boron nitride nanosheets: chemical vapor synthesis, ultraviolet light emission, and superhydrophobicity, ACS Nano 4 (2010) 414–422. B.T. Qian, Z.Q. Shen, Fabrication of superhydrophobic surfaces by dislocation-selectivechemical etching on aluminum, copper, and zinc substrates, Langmuir 21 (2005) 9007–9009. A.V. Rao, S.S. Latthe, S.A. Mahadik, C. Kappenstein, Mechanically stable and corrosion resistant superhydrophobic sol–gel coatings on copper substrate, Appl. Surf. Sci. 257 (2011) 5772–5776. A. Chaudhary, H.C. Barshilia, Nanometric multiscale rough CuO/Cu(OH)2 superhydrophobic surfaces prepared by a facile one-step solution-immersion process: transition to superhydrophilicity with oxygen plasma treatment, J. Phys. Chem. C. 115 (2011) 18213–18220. J. Li, Z.J. Jing, Y.X. Yang, Q.T. Wang, Z.Q. Lei, From Cassie state to Gecko state: a facile hydrothermal process for the fabrication of superhydrophobic surfaces with controlled sliding angles on zinc substrates, Surf. Coat. Technol. 258 (2014) 973–978. C.D. Dong, Y. Gu, M.L. Zhong, L. Li, K. Sezer, M. Ma, W.J. Liu, Fabrication of superhydrophobic Cu surfaces with tunable regular micro and random nano-scale structures by hybrid laser texture and chemical etching, J. Mater. Process. Technol. 211 (2011) 1234–1240. Z. Yang, Y.L. Tian, C.J. Yang, F.J. Wang, X.P. Liu, Modification of wetting property of Inconel 718 surface by nanosecond laser texturing, Appl. Surf. Sci. 414 (2017) 313–324. L. Li, V. Breedveld, D.W. Hess, Creation of superhydrophobic stainless steel surfaces by acid treatments and hydrophobic film deposition, ACS Appl. Mater. Inter. 4 (2012) 4549–4556. L. Zhao, Z. Wang, J. Zhang, L. Cao, L. Li, Y. Yue, D. Li, Antireflection silicon structures with hydrophobic property fabricated by three-beam laser interference, Appl. Surf. Sci. 346 (2015) 574–579. J. Li, F. Du, X.L. Liu, Z.H. Jiang, L.Q. Ren, Superhydrophobicity of bionic alumina surfaces fabricated by hard anodizing, J. Bionic. Eng. 8 (2011) 369–374. J. Li, H. Li, F. Du, Y.H. Zhao, H.D. Yu, Fabricated composite structure with hydrophobicity and anti-corrosion by sandblasting and electro-brush plating, Chin. Sci. Bull. 62 (2017) 1307–1314. J. Li, S.C. Zhao, F. Du, Y.L. Zhou, H.D. Yu, One-step fabrication of superhydrophobic surfaces with different adhesion via laser processing, J. Alloy. Compd. 739 (2018) 489–498. J. Li, F.Y. Fan, Y.H. Zhao, Y.L. Zhou, H. Li, H.D. Yu, Influence of laser surface texturing on a low-adhesion and superhydrophobic aluminium alloy surface, Micro Nano Lett. 13 (3) (2018) 389–392. X.L. Liu, Z.H. Jiang, J. Li, Z.H. Zhang, L.Q. Ren, Super-hydrophobic property of nano-sized cupric oxide films, Surf. Coat. Technol. 204 (20) (2010) 3200–3204. F.Z. Zhang, L.L. Zhao, H.Y. Chen, S.L. Xu, D.G. Evans, X. Duan, Corrosion resistance of superhydrophobic layered double hydroxide films on aluminum, Angew. Chem. (Int. Ed.) 47 (2008) 2466–2469. A.B.D. Cassie, S. Baxter, Wettability of porous surface, Trans. Faraday Soc. 40 (1994) 546–550.
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Optics and Laser Technology journal homepage: www.elsevier.com/locate/optlastec
Full length article
Controlling surface wettability and adhesive properties by laser marking approach
T
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Jing Lia, , Yingluo Zhoua, Fengyu Fana, Feng Dub, Huadong Yua a b
Department of Mechanical and Electric Engineering, Changchun University of Science and Technology, Changchun 130022, PR China Department of Mechanical Engineering, Changchun Institute of Engineering, Changchun 130117, PR China
H I GH L IG H T S
processing method is found to fabricate superhydrophobic surface. • AThelaser prepared microstructure is the main reason for changing the surface wettability. • Different laser scanning spacing results in different wettability and adhesion. •
A R T I C LE I N FO
A B S T R A C T
Keywords: Laser marking approach Microstructure Wettability Adhesion
We provide a special microstructure to fabricate superhydrophobicity surface of aluminum alloy by laser marking method. The morphologies and wettability of the fabricated aluminum alloy surface are investigated through scanning electron microscopy (SEM) and the contact angle meter. The results indicate that the fabricated surface with irregular protrusions and pits shows excellent superhydrophobicity/hydrophobic. The surface texture of this microstructure is characterized by a contact angle of up to 156.4° when the surface exhibits superhydrophobicity and a contact angle of up to 147.8° when the surface exhibits hydrophobicity. Because the unidirectional processing of the laser makes the surface anisotropic, we discuss the wettability in this area. Moreover, we discuss the effect of wettability and adhesion at different scales on the fabricated surface. A series of data shows differences in related properties due to different laser texture scales. Differences in performance of the material can be applied in different field conditions. The fabrication technique is a promising method to provide superhydrophobic surface with potential applications including fluid transfer, fluid power systems, stain-resistant and anti-fouling surfaces, anti-creeping of oils, anti-contamination, and oil transport. More importantly, this novel surface structure further extends the application of aluminum alloys in industry.
1. Introduction Superhydrophobic surfaces with a water contact angle of more than 150° and extremely low sliding angle (< 5°) have received the attention of a wide range of researchers these years because of its importance in essential research [1,2]. Preparation surfaces with different wettability have their own applications in various fields, such as corrosion resistance, anti-icing, self-cleaning, anti-attrition, etc. [3–9]. As is wellknown, lotus leave is a superhydrophobic surface and its superhydrophobicity comes from the specific microstructures besides the epicuticular waxes [10]. A superhydrophobic surface is usually achieved by changing the surface microstructure and reducing the surface energy [11]. Therefore, many researchers have used various methods to fabricate surface microstructures to obtain surfaces with
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superhydrophobic properties [12–14]. For example, Sun et al. fabricated superhydrophobic coating by casting the alkoxy polysiloxane copolymerization emulsioncontaining fumed silica and phenyltrimethoxysilane (PhTMS)/γ-(2,3-epoxypropoxy) propytrimethoxysilane (EPTMS) on the glass slide [15]. Hu et al. present a simple method for fabricating a microstructured Cu/Ni–W alloy coating by combining electroless and electro deposition [16]. Aluminum and its alloys are irreplaceable engineering materials owing to their easy accessibility, excellent machinability, high fatigue strength and low price. Accordingly, they have achieved extensive industrial applications, especially in the fields of shipbuilding, oceanography engineering, aerospace and machine manufacturing [17,18]. In order to improve the performance of aluminum alloys and expand the application of aluminum alloys, many superhydrophobic surfaces are
Corresponding author. E-mail address: [email protected] (J. Li).
https://doi.org/10.1016/j.optlastec.2019.02.023 Received 4 June 2018; Received in revised form 7 December 2018; Accepted 3 February 2019 0030-3992/ © 2019 Elsevier Ltd. All rights reserved.
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Fig. 1. The schematic process of the laser marking approach.
600–2000). Then they were cleaned ultrasonically with alcohol and deionized water respectively, and dried in air. (2) The process of laser processing: The polished samples were constructed roughness structure on the surface by a portable laser marking machine (fibre laser marking machine with putout power of 12 W, focal spot size of 0.05 mm). under processing parameters (lined grooves surface, scanning line spacing of 50, 100, 150, 200 μm, frequency of 20 kHz, scanning speed of 1100 mm/s, scanning times of 2 times).
prepared on aluminum alloys. For example, Yu et al. fabricated the submillimeter-scale structures by the high speed wire electrical discharge machining (HSWEDM) technology on the 5083 aluminum (Al) alloy substrates, the results showed that the V-shaped groove arrays with a hierarchical structure presented the good superamphiphobicity after a solution immersion [19]. Sooksaen et al. fabricated hydrophobic surfaces on Al-0.5Mg-0.5Mn aluminum alloy thick sheet. An electrochemical anodization process was carried out followed by silane treatment on the anodized surfaces [20]. So far, a large number of approaches have been successfully used to develop superhydrophobic surfaces, including chemical vapor deposition [21], chemical etching [22], sol-gel [23], solution immersion [24], hydrothermal synthesis [25] and laser fabrication [26,27]. For example, Li et al. have constructed superhydrophobic surface on stainless steel substrate by acid treatment and hydrophobic film deposition [28]. Zhao et al. have generated periodic micro–nano hole structures on superhydrophobic surface with a three-beam laser interference system [29]. Li et al. reported that bionic alumina samples were fabricated on convex dome type aluminum alloy substrate using hard anodizing technique [30]. The research group has long been devoted to the study of the functional properties of metal surfaces. It has been fabricated on the surfaces of aluminum alloys, carbon steels, stainless steels, and copper by electrodeposition of nickel [31], laser etching [32,33], and electrodeposition of copper [34] to obtain structures of different scales and morphologies. In this work, the laser marking approach was used to fabricate a superhydrophobic aluminum alloy surface, and the fabricated surface exhibited several properties. With this serving as context, the discussion below examines some of the theory and progress surrounding these properties.
2.3. Characterization The microstructures of the sample surface fabricated were observed via SEM (COXEM EM-30, Korea). The static contact angle (An OCA15 system from Dataphysics GmbH, Germany) was measured with 4 μL of distilled pure droplets at ambient temperature. The element composition of these samples surface was estimated with XRD.
3. Results and discussion 3.1. Preparation of a hydrophobic surface by a one-step method In Fig. 1, the schematic process of the laser marking approach is shown. In the process of the treatment, the laser beam rapidly heats and densely melts the surface of the aluminum alloy at a given speed on a set track. In the direction of y, by changing the size of the laser processing line spacing, the surface of the sample with different morphologies is manufactured; In the direction of x, under the action of the laser beam, a laser texture with a 50 μm diameter pit-like structure is uniformly and closely arranged. We use the laser impact force to make the pit-shaped molten pools on the surface of the material. A part of the molten material is evaporated due to the heat received. The remaining material, due to the impact force, accumulates in the form of a melt on the edge of the pit-like structure and after cooling, it fuses with the surface of the substrate. Compared with most of reported approached for fabricating superhydrophobic surfaces, the laser marking approach is low-cost, and high efficiency of treated surface. The process is very simple, and there is no requirement for area and thickness. It is suitable for large-scale processes and batch processing. It is a relatively convenient and effective laser processing method in the field of mechanical processing and manufacturing.
2. Experimental section 2.1. Materials 7075 series aluminum alloys, as experimental materials, were purchased from subsidiary company of Shanghai AoFeng metal products Co., Ltd. The sample size is 10 mm × 10 mm × 2 mm, which is gained by line cutting machine. 2.2. Preparation of the superhydrophobic surface (1) The process of the pre-treated: Aluminum alloy samples were sanded and polished with different grades of sandpaper (Nos. 161
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Fig. 2. Low-magnified SEM image of the morphology of surface treated by laser marking (lined pits surface, frequency of 20 kHz, scanning speed of 1100 mm/s) with textures spacing of (a) 50 μm, (b) 100 μm, (c) 150 μm, (d) 200 μm. The insets corresponding to their high-magnified SEM images.
3.2. Morphological analysis of as-prepared surfaces
Table 1 OCA results of laser processing surface.
In order to study the effect of laser processing surfaces on the microstructure of the treated surface, the textured surfaces with different spacings are investigated. After the aluminum alloy surfaces used in the experiment were fabricated by laser processing, the surface micro-topography can be obtained. As can be seen in Fig. 2, with the increase of laser texture line spacing (50, 100, 50 and 200 μm), the microstructure of the surface has changed. In the direction of the laser, they are all composed of tight pit-like structures. However, in the direction perpendicular to the laser, the microstructure of the protrusions and pits becomes more and more unique. It can be observed that because of the increase of line spacing, the structure of protrusions and pits are reduced in unit area and reach a minimum (texture spacing of 200 μm). Moreover, from high-magnified SEM image presented in the inset of Fig. 2(a–d), it can be found the size of the pit structure is unchanged. It is explained that the change in the surface properties of the material is mainly due to the area ratio of the microstructure in the unit area. There are not effects in molten metal of adjacent rows, but protrusions are manufactured independently.
Laser texture line spacing (μm)
The contact angle of x (°)
The contact angle of y (°)
Difference value (°)
50 100 150 200
156.4 154.6 147.8 138.9
155.7 151.5 137.4 111.2
0.7 3.1 10.4 27.7
line spacing and the maximum value is 27.7° (line spacing of 200 μm). The difference value from the minimum (line spacing of 50 μm) is 20°. Meanwhile, the laser processing surface is transformed from a superhydrophobic surface (line spacing of 100 μm, the contact angle is 154.6°on the x direction and 151.5° on the y direction) to a hydrophobic surface (line spacing of 150 μm, the contact angle is 147.8° on the x direction and 137.4° on the y direction). This shows that the laser processing line spacing directly affects the wettability of the surface. The larger the laser processing distance, the greater the effect on wettability and the poorer the wettability. As shown in Fig. 4a, whether viewed from the x direction or from the y direction, the contact angles are greatly reduced from laser texture line spacing of 50 μm to laser texture line spacing of 200 μm. This can be explained that the pit microstructure on the surface makes the smooth surface rough. When the water droplet contacts with the surface, a great number of air will be trapped into the space between the roughness structure and water droplet, and it will lead most of water to contact with air. However, from the results, the lower the roughness of the surface is, the smaller the contact angle of the surface will be. Therefore, the treated surfaces show superhydrophobicity and hydrophobicity, and the contact angle can be as high as about 156.4°. However, with larger line spacing, the pit microstructure leads to the decrease of roughness, and that causes the reduction of the contact angle.
3.3. Wettability 3.3.1. Wettability of the surfaces Due to the laser textured surface with anisotropic, contact angles in both directions (x, along the laser direction and y, vertical laser direction) were investigated. In Table 1, it is obvious that the contact angles of the surfaces with line spacing of 50, 100, 150 and 200 μm on the direction of x are 156.4°, 154.6°, 147.8° and 138.9° respectively. And on the direction of y are 155.7°, 151.5°, 137.4° and 111.2° respectively. It can be seen that the contact angle on the x direction is generally better than the contact angle on the y direction. This is because when the direction of the laser texture is uniform, the water droplets will also spread along the direction on the surface, resulting in a slight deformation. Moreover, The difference value between the x and y directions increases with the increase of the laser processing texture
3.3.2. Theoretical calculation of wettability Although the laser processing surface has anisotropy, from the data 162
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Fig. 3. The contact angle of the prepared surface and the number of days placed.
above, it is uniformly expressed that they have superhydrophobicity and hydrophobicity. Therefore, we only select the contact angle data in the x direction for analysis. With the different constructs on the aluminum surfaces, the aluminum surfaces exhibited the different wettability. So the static contact angles were respectively measured on the polished surface and laser marking surfaces. The wettability of the fabricated surfaces can be measured via contact angle meter at ambient temperature (22 ± 3 °C) and relative humidity (45 ± 8%). When the line spacing is 50 μm, the fabricated surface via laser marking exhibited a contact angle of 156.4°. By changing the line spacing (100, 150 and 200 μm) during laser beam irradiation, a contact angles of the fabricated surfaces via laser marking is different. The static contact angles of the surfaces exhibited the contact angles of 154.6°, 147.8°and 138.9° respectively. As shown in Fig. 3, there is no substantial change in the contact angle of the sample surface within 300 days of prepared sample, which indicates that the stability of this microstructure is strong. The relationship of surface wettability at heterogeneous surfaces was proposed by Cassie and Baxter’s [35,36] such as the equation:
cosθr = f1 cosθ − f2 = cosθ − f2 (cosθ + 1)
Fig. 4. The physical map of the sample and corresponding contact angle profiles (a), Cassie model (b) and structure model (c).
3.3.3. Effect of the surface structure to the surface wettability The wettability is an important property for the solid surfaces, and the static contact angle is used as describing the physical parameters of the water droplets. According to the Cassie theory [36], we believe the circular pit structures and the interval between one circular pit and another circular pit will store air, and the water droplets on the asprepared surface directly contact with the outside air. It can be supported by the storage air, which increases the contact angle. In this study, we mainly research the effect of structure to the surface wettability. We assume that when laser scanning distance is 50 µm, the water droplets on the surfaces are in a typical Cassie model state. Based on the hydrophobic model of the pit structure, we can calculate the biggest drop height of the water droplets in the surface. We study the relative references and combine with the as-prepared surface structure for modeling. As can be seen in Fig. 4c, h is the embedding depth of the water droplets. The formula of the circular pit structure mode is:
(1)
where f1 and f2 are the fractions of aluminum solid surface and air in composite surface respectively and f1 + f2 = 1. θr and θ are contact angles on rough aluminum and the bare surface (the contact angle is 79.2°), respectively. As shown in Table 2, when the line spacing is 50 μm, the f2 value of the micro- and nano-structure via laser marking approach was estimated to be 0.9295, and the low value of f1 shows that only about 7.050% of the water surface is in contact with the aluminum surface. By changing the line spacing (100, 150, 200 μm) during laser beam irradiation, the f2 value is 0.9186, 0.8704 and 0.7923 respectively and the low value of f1 is 8.14%, 12.96% and 20.76% respectively. This indicates that f2 (liquid projected area fraction in contact with air) plays an extremely important role in wettability. When f2 is larger, the wettability of the sample surface is better. Therefore, how to construct a structure that increases f2 becomes a problem to be solved.
cosθr =
The contact angle of X (°)
f1
f2
50 100 150 200
156.4 154.6 147.8 138.9
0.0705 0.0814 0.1296 0.2077
0.9295 0.9186 0.8704 0.7923
(2)
This formula evolved from the Cassie theory formula, and it can be used to understand the relationship between the circular pit structures and the surface wettability. The R and h are the radius of the circular pit structures and the drop height of the water droplets respectively. The a and b is the distance between two directions of the circular pit structures. The θr is the contact angle on the as-prepared surface. The θ0 (79.2°) is the contact angle on the polished surface. The measured values (a = 50 µm, b = 41 µm, Ra =21.05 µm, Rb =19.55 µm) is put into the (2) formula, and we can obtain the value that h is 1.36 µm. From the results above, we can see the drop height of the water droplets are less than the height of the surface shoulder and the depth of the pit. The water droplets are not fully immersed inside the pit. The more contact area of the water droplets is the surface shoulder structure. Therefore, the relationship between the surface contact state and the Cassie model is further verified. The area calculation formula can be
Table 2 The results obtained through Cassie and Baxter’s equation. Laser texture line spacing (μm)
2πRh (1 + cosθ0) a×b
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deduced from the shoulder structure of the surface:
fs =
π (Ra2 − Rb2 ) a×b
(3)
TheR a andR b are the outer wall and inner wall radius of the circular pit structures respectively. The measured values is put into the (3) formula and we can obtain the value that fs is 0.093, and the value r of the surface roughness is 1.653. Then the fa was put into the Cassie theory formula: cosθr = f (1 + rcosθ0) − 1
(4)
We can obtain the theoretical contact angle of θr and it is 151.4°. The contact angle is close to 156.4°of the actual measured contact angle (There are some errors between the theoretical model and the actual surface); So when the laser scanning line spacing is 50 µm, the existing form of water droplets on the as- prepared surface is similar with the Cassie state. The experimental results are consistent with the experimental hypothesis. Under the combination of the shoulder structure of the surface and the air, the water droplets have only a small drop height. It can be shown that this protrusions and pits structure cause the water droplets to come into contact with the air rather than the surface of the substrate, greatly improving the hydrophobicity of the material surface.
Fig. 5. The rolling characteristic profiles for (a), a series of photos were recorded before and after the water droplet contacting with the as-prepared surface under 50 µm, 100 µm, 150 µm, and 200 µm) (b).
platform on surface contact angle measurement is used to discuss the adhesion problem. At first, because of the water droplets’ surface tension, the water droplets are suspended on the front end of the needle. When the instrument platform drives the fabricated surface to rise slowly, and the surface starts to contact with the water drop (Fig. 5(b1)). During the rising of the contact angle platform, the water droplets are gradually deformed and produce a gradual deformation (Fig. 5(b3)). But the instrument platform rises from the bottom to the top, the instrument platform doesn’t seem to have much effect on the dynamic contact angle of the water droplets. Then the contact angle platform slowly began to decline, which causes the water droplet to slide along the needle, and the water droplet finally returns to the tip of the needle again (Fig. 5(b5)). In the process of the falling contact angle platform, because the water droplets have surface tension, the water droplets produce a gradual deformation. The surface tension finally causes the separation of water droplets and the platform of contact angle. When the water droplets are separated from the platform, the water droplets show a significant shaking. But in the process of the water droplets separating from the platform, the dynamic contact angle of water droplets do not change obviously. When the laser scanning line spacing is different, the difficulty degree of the separation process of the water droplets and the texture of sample surface is different. In Fig. 5(b6–b10), When the laser scanning line spacing is 100 μm (because the separation process of the water droplets of 150 μm, 200 μm is similar with 100 μm, the separation process of 100 μm represents 150 and 200 μm), the subsequent larger exposed area of the unprocessed Al alloy surface resulted in a decrease of the surface roughness, which changed the droplet's adhesion to the sample surface (Fig. 5(b10)). Additionally, the larger exposed area of the unprocessed Al alloy surface resulted in a stronger surface wettability, further increasing the solid-liquid contact area between the droplet and the unprocessed Al alloy surface, which can lead to a strong adsorption capacity with high adhesion. Through the observation of the above dynamic process, there were some differences in the adhesion of the samples to the water droplets with differences of the laser scanning line spacing.
3.4. Effect of high/low adhesion on surface The static contact angles of the water droplet on the surfaces cannot show its motion state on the inclined surfaces. It can only reflect the instantaneous static state of the water droplets. Sometimes the water droplets have a small contact angle on the prepared surface, but the water droplets on the aluminum alloy surfaces may also be prone to slide. On the contrary, although the contact angles on some sample surfaces have a great improvement, it's hard to slide. For example, the static contact angle of the rose petal surfaces has exceeded 150°, but the water droplets are tightly attached to the surface through small contact area between the water droplets and the rose petal surface. It’s difficult to slide. This is also the limitations of the static contact angle in the performance of hydrophobic. So the dynamic contact angle can further be used to discuss the wettability of the sample surfaces, and it can be measured by the method of the adding and subtracting water droplets. The size of the contact angle hysteresis theoretically represents the degree of the difficulty of the water droplets motion on the surface. In order to obtain low adhesion surface, we tend to need contact angle hysteresis as small as possible. The measured data on the sample surfaces under 50 μm can be 6.1°, the prepared superhydrophobic aluminum alloy surface has a smaller hysteresis contact angle, which shows the water droplets have the more possibility of motion. The measured data on the sample surfaces under 100, 150 and 200 μm can be 17.2°, 16.5°and 18.1°respectively. As can be seen in Fig. 5a, it shows that the sliding process of the water droplets on the inclined prepared superhydrophobic surface is under 50 μm. In Fig. 5a (1–3), under 50 μm, we can see the water droplets do not have the shaking or moving tendency. When the angle of inclined surface was about 2.3°, the water droplets on the surface begin to slide and instantaneous slide down from the inclined surface. The sliding speed of the water droplets is about 10.34 mm/s measured by Nano Measure software. The prepared surface under 50 μm shows a low adhesion to water droplets, and the water droplets is in the unstable state on the superhydrophobic surface. In Fig. 5(a4–a6), under 100 μm (because the rolling process of the water droplets of 150 μm, 200 μm is similar with 100 μm, the rolling process of 100 μm also represents 150 μm, 200 μm), the prepared aluminum alloy surfaces have high adhesion. When the prepared surfaces were inclined at about 90°, the water droplets on the surfaces do not appear the sliding tendency. As illustrated in Fig. 5b, in order to observe the dynamic behavior of the fabricated surface under the line spacing of 50 μm, the lifting
4. Conclusions In summary, we have fabricated two surfaces with different degrees of performance via a simple and low-cost laser marking approach. The morphology of the surface fabricated can have been slightly tuned, but it led to the different wettability of the surfaces as-prepared. The line spacing during laser beam irradiation was changed to achieve different 164
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sizes of the Al alloy surface. When the laser texture line spacing is 50 μm, the surface shows with excellent superhydrophobicity and antiadhesive property. When the laser texture line spacing is 100, 150, 200 μm, the surface shows with hydrophobicity and high adhesion property. Surfaces prepared with different processing spacings have different contact angles. The static contact angle of the prepared surface can be as high as 156.4° and the sliding angle was 2.3°. The small contact angle hysteresis can be shown on the superhydrophbic surface fabricated via laser marking approach. The prepared surface with high adhesion was of great significance for water collection and preservation. The area ratio between the microstructure and the unprocessed Al alloy surface played a key role in determining the wetting conditions of the sample surface.
[14]
[15]
[16]
[17]
[18]
[19]
Conflict of interest [20]
None. [21]
Acknowledgements [22]
The authors are grateful to the National Natural Science Foundation of China (Grant No. 51505039), the Postdoctoral Science Foundation of China (no. 2014 M551145), the Natural Science Foundation of Science and Technology Department of Jilin Province (Grant No. 20180101322JC), and the “111” Project of China (Grant No. D17017) for support of this work.
[23]
[24]
[25]
References [1] Y. Liu, J.D. Liu, S.Y. Li, Z.W. Han, S.R. Yu, L.Q. Ren, Fabrication of biomimetic super-hydrophobic surface on aluminum alloy, J. Mater. Sci. 49 (2014) 1624–1629. [2] Q. Ke, W. Fu, S. Wang, T. Tang, J. Zhang, ACS Appl. Mater. Interfaces 2 (2010) 2393–2398. [3] P. Wang, T. Yao, B. Sun, X.L. Fan, S.J. Dong, Y. Bai, Y. Shi, A cost-effective method for preparing mechanically stableanti-corrosive superhydrophobic coating based on electrochemicallyexfoliated graphene, Colloid. Surf. A 513 (2017) 396–401. [4] Y. Liu, S.Y. Li, J.J. Zhang, J.A. Liu, Z.W. Han, L.Q. Ren, Corrosion inhibition of biomimetic super-hydrophobic electrodeposition coatings on copper substrate, Corros. Sci. 94 (2015) 190–196. [5] R. Rahul, K. Marina, S. Konstantin, N. Michael, Anti-icing superhydrophobic surfaces: controlling entropic molecular interactions to design novel icephobic concrete, Entropy 18 (4) (2016) 1–26. [6] Y. Liu, X.L. Li, J.F. Jin, J.A. Liu, Y.Y. Yan, Z.W. Han, L.Q. Ren, Anti-icing property of bio-inspired micro-structure superhydrophobic surfaces and heat transfer model, Appl. Surf. Sci. 400 (2017) 498–505. [7] J. Li, Y. Wei, Z.Y. Huang, F.P. Wang, X.Z. Yan, Z.L. Wu, Electrohydrodynamic behavior of water droplets on a horizontal super hydrophobic surface and its selfcleaning application, Appl. Surf. Sci. 403 (2017) 133–140. [8] R. Blossey, Self-cleaning surfaces–virtual realities, Nat. Mater. 2 (2003) 301–306. [9] Q.G. Han, H.Z. Zhang, L. Fang, Y.Q. Wang, Tribological properties of nanocrystalline cu coatings produced by electroless plating under various lubrication conditions, Rare Met. Mater. Eng. 40 (2011) 356–359. [10] Y.T. Cheng, D.E. Rodak, C.A. Wong, Effects of micro-and nano-structures on the self-cleaning behaviour of lotus leaves, Nanotechnology 17 (2006) 1359–1362. [11] M.K. Tang, X.J. Huang, Z. Guo, J.G. Yu, X.W. Li, Q.X. Zhang, Fabrication of robust and stable superhydrophobic surface by aconvenient, low-cost and efficient laser marking approach, Colloids Surf. A: Physicochem. Eng. Aspects 484 (2015) 449–456. [12] I. Vilaró, J.L. Yagüe, S. Borrós, Superhydrophobic copper surfaces with anticorrosion properties fabricated by solventless CVD methods, ACS Appl. Mater. Interfaces 9 (2017) 1057–1065. [13] B. Mondal, M.M.G. Eain, Q.F. Xu, V.M. Egan, J. Punch, A.M. Lyons, Design and
[26]
[27]
[28]
[29]
[30] [31]
[32]
[33]
[34] [35]
[36]
165
fabrication of a hybrid superhydrophobic-hydrophilic surface that exhibits stable dropwise condensation, ACS Appl. Mater. Interfaces 7 (2015) 23575–23588. Z.X. Lian, J.K. Xu, Z.B. Wang, Z.C. Wang, Z.K. Weng, H.D. Yu, Fabrication and applications of two- and three-dimensional curved surfaces with robust underwater superoleophobic properties, J. Mater. Sci. 52 (2017) 1123–1136. Z.G. Sun, B. Liu, S.Q. Huang, J. Wu, Q.C. Zhang, Facile fabrication of superhydrophobic coating based on polysiloxane emulsion, Prog. Org. Coat. 102 (2017) 131–137. F.T. Hu, P.H. Xu, H.Z. Wang, U.B. Kang, A. Hu, M. Li, Superhydrophobic and anticorrosion Cu microcones/Ni–W alloy coating fabricated by electrochemical approaches, RSC Adv. 5 (2015) 103863–103868. E.M. Sherif, H.R. Ammar, K.A. Khalil, Effects of copper and titanium on the corrosion behavior of newly fabricated nanocrystalline aluminum in natural seawater, Appl. Surf. Sci. 301 (2014) 142–148. Y.S. Huang, T.S. Shih, J.H. Chou, Electrochemical behavior of anodized AA 7075–T73 alloys as affected by the matrix structure, Appl. Surf. Sci. 283 (2013) 249–257. H.D. Yua, Z.X. Lian, Y.L. Wan, Z.K. Weng, J.K. Xua, Z.J. Yu, Fabrication of durable superamphiphobic aluminum alloy surfaces with anisotropic sliding by HS-WEDM and solution immersion processes, Surf. Coat. Technol. 275 (2015) 112–119. P. Sooksaen, O. Chulasinont, P. Janmat, W. Thovasaku, Chemical treat ment on aluminum alloy for hydrophobic surfaces, Mater. Today 4 (2017) 6528–6533. J. Yu, L. Qin, Y. Hao, S. Kuang, X. Bai, Y.M. Chong, W. Zhang, E. Wang, Vertically aligned boron nitride nanosheets: chemical vapor synthesis, ultraviolet light emission, and superhydrophobicity, ACS Nano 4 (2010) 414–422. B.T. Qian, Z.Q. Shen, Fabrication of superhydrophobic surfaces by dislocation-selectivechemical etching on aluminum, copper, and zinc substrates, Langmuir 21 (2005) 9007–9009. A.V. Rao, S.S. Latthe, S.A. Mahadik, C. Kappenstein, Mechanically stable and corrosion resistant superhydrophobic sol–gel coatings on copper substrate, Appl. Surf. Sci. 257 (2011) 5772–5776. A. Chaudhary, H.C. Barshilia, Nanometric multiscale rough CuO/Cu(OH)2 superhydrophobic surfaces prepared by a facile one-step solution-immersion process: transition to superhydrophilicity with oxygen plasma treatment, J. Phys. Chem. C. 115 (2011) 18213–18220. J. Li, Z.J. Jing, Y.X. Yang, Q.T. Wang, Z.Q. Lei, From Cassie state to Gecko state: a facile hydrothermal process for the fabrication of superhydrophobic surfaces with controlled sliding angles on zinc substrates, Surf. Coat. Technol. 258 (2014) 973–978. C.D. Dong, Y. Gu, M.L. Zhong, L. Li, K. Sezer, M. Ma, W.J. Liu, Fabrication of superhydrophobic Cu surfaces with tunable regular micro and random nano-scale structures by hybrid laser texture and chemical etching, J. Mater. Process. Technol. 211 (2011) 1234–1240. Z. Yang, Y.L. Tian, C.J. Yang, F.J. Wang, X.P. Liu, Modification of wetting property of Inconel 718 surface by nanosecond laser texturing, Appl. Surf. Sci. 414 (2017) 313–324. L. Li, V. Breedveld, D.W. Hess, Creation of superhydrophobic stainless steel surfaces by acid treatments and hydrophobic film deposition, ACS Appl. Mater. Inter. 4 (2012) 4549–4556. L. Zhao, Z. Wang, J. Zhang, L. Cao, L. Li, Y. Yue, D. Li, Antireflection silicon structures with hydrophobic property fabricated by three-beam laser interference, Appl. Surf. Sci. 346 (2015) 574–579. J. Li, F. Du, X.L. Liu, Z.H. Jiang, L.Q. Ren, Superhydrophobicity of bionic alumina surfaces fabricated by hard anodizing, J. Bionic. Eng. 8 (2011) 369–374. J. Li, H. Li, F. Du, Y.H. Zhao, H.D. Yu, Fabricated composite structure with hydrophobicity and anti-corrosion by sandblasting and electro-brush plating, Chin. Sci. Bull. 62 (2017) 1307–1314. J. Li, S.C. Zhao, F. Du, Y.L. Zhou, H.D. Yu, One-step fabrication of superhydrophobic surfaces with different adhesion via laser processing, J. Alloy. Compd. 739 (2018) 489–498. J. Li, F.Y. Fan, Y.H. Zhao, Y.L. Zhou, H. Li, H.D. Yu, Influence of laser surface texturing on a low-adhesion and superhydrophobic aluminium alloy surface, Micro Nano Lett. 13 (3) (2018) 389–392. X.L. Liu, Z.H. Jiang, J. Li, Z.H. Zhang, L.Q. Ren, Super-hydrophobic property of nano-sized cupric oxide films, Surf. Coat. Technol. 204 (20) (2010) 3200–3204. F.Z. Zhang, L.L. Zhao, H.Y. Chen, S.L. Xu, D.G. Evans, X. Duan, Corrosion resistance of superhydrophobic layered double hydroxide films on aluminum, Angew. Chem. (Int. Ed.) 47 (2008) 2466–2469. A.B.D. Cassie, S. Baxter, Wettability of porous surface, Trans. Faraday Soc. 40 (1994) 546–550.