Super Antiwetting Surfaces for Mitigating Drag-Out of Deep Eutectic

Jun 25, 2018 - This website uses cookies to improve your user experience. By continuing to use the site, you are accepting our use of cookies. Read th...
0 downloads 0 Views 7MB Size
Download PDF
Research Article Cite This: ACS Appl. Mater. Interfaces 2018, 10, 24209−24216

www.acsami.org

Super Antiwetting Surfaces for Mitigating Drag-Out of Deep Eutectic Solvents C. D. Gu,*,†,‡ X. Q. Wang,†,‡ J. L. Zhang,†,‡ and J. P. Tu†,‡ †

Downloaded via UNIV OF CALIFORNIA SANTA BARBARA on August 1, 2018 at 04:10:26 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

School of Materials Science and Engineering, State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou 310027, People’s Republic of China ‡ Key Laboratory of Advanced Materials and Applications for Batteries of Zhejiang Province, Zhejiang University, Hangzhou 310027, People’s Republic of China S Supporting Information *

ABSTRACT: Deep eutectic solvents (DESs) are, at room temperature, about dozens to hundreds of times more viscous than water, which brings pretty thick residues on solid surfaces, for example, causing drag-out and weight loss in the transfer process. Unfortunately, until now little work had been done for solving this knotty problem. In this study, the super antiwetting surface, i.e., super-DESphobic surface (defined as DES contact angle > 150°) is proposed and fabricated successfully by a facile coating technique. Hierarchical silver dendrites on copper foam substrate provide effective dual-roughness surfaces showing stable superDESphobicity. The superDESphobic surface can repel the DESs and their derived solutions even under elevated temperature of about 120 °C and the impact attack of drops. It is also found that the superDESphobic surface can significantly delay the DESs freezing and reduce the adhesion strength of the frozen DESs. Interestingly, the superDESphobic surface can be applied as an effective tool for gauging the density of DES using an ∼2 μL droplet in virtue of its super antiwetting property. The super antiwetting surfaces show promise for potential applications in DES self-cleaning and antifreezing. KEYWORDS: deep eutectic solvent, droplet impinging, drag-out, antiwetting, antifreezing interactions.10 The number of possible combinations of components forming DESs is extremely high, and many have been reported to date.1,11,12 Some typical and well-studied DES examples are listed in Table 1, including mixtures of choline chloride (ChCl) with urea, ethylene glycol (EG), glycerol, and CrCl3·6H2O, usually in a 1:2 molar ratio.1 Obviously, the viscosity of DESs is about dozens to hundreds of times higher than that of water or organic solvents as a result of the strong electrostatic and other interaction forces.1,13 The pretty thick DESs are very susceptible to being attached to solid surfaces, which causes drag-out and weight loss when delivering them from one container to others. Strong adhesion of DESs on solid surfaces would bring significant experimental deviations if smaller droplets were adopted. Wettability and adhesion of solid surfaces by a liquid droplet are quite important for both fundamental research and practical applications.14−16 Taking inspiration from nature, various bionic superwettable surfaces with tunable wettability and adhesion have been designed by simulating typical structures of plant surface and considering chemical composition simultaneously.17−22 Compared to superwettable surfaces by water, the research into superILphobic surfaces (defined as IL contact

1. INTRODUCTION Deep eutectic solvents (DESs) are now widely acknowledged as a new class of ionic liquid analogues with similar characteristics to ionic liquids (ILs) but with additional advantages, such as being less expensive, more synthetically accessible, nontoxic, and biodegradable.1,2 A great deal of research work has been focused on DESs as alternative media for metals and functional materials that are traditionally difficult to process or involves environmentally hazardous processes.1,3−9 However, DESs are more viscous than water, which brings pretty thick residues on solid surfaces, for example, causing drag-out and weight loss in the transfer process. Here, through careful study, for the first time, we have prepared the super antiwetting surface, i.e., super-DESphobic surface (defined as DES contact angle > 150°) to mitigating drag-out of DESs. The surface chemistry and substrate structure are emphasized to achieve stable nonwetting surfaces. The capability of the super antiwetting surface is thoroughly evaluated against the impact attack of DES drops and high temperature of about 120 °C. It is also found that the antiwetting surface can significantly delay the DES freezing and reduce the adhesion strength of the frozen DESs. We also demonstrate the application of the superDESphobic surface to measure the density of DES using an ∼2 μL droplet. DESs can be facilely prepared by mixing a quaternary ammonium salt with a metal salt or hydrogen bond donor (HBD) which forms a liquid driven by strong hydrogen-bond © 2018 American Chemical Society

Received: May 11, 2018 Accepted: June 25, 2018 Published: June 25, 2018 24209

DOI: 10.1021/acsami.8b07769 ACS Appl. Mater. Interfaces 2018, 10, 24209−24216

Research Article

ACS Applied Materials & Interfaces Table 1. Physical Properties of the Used DESs and Derived Solutions at Room Temperature (about 298 K)b abbreviation DES-1 DES-2 DES-3 DES-4 Solution-1 Solution-2 Solution-3

salt (mol equiv)

HBD (mol equiv)

ChCl (1)

ethylene glycol (2) ChCl (1) urea (2) ChCl (1) glycerol (2) ChCl (1) CrCl3·6H2O (2) NiCl2·6H2O (1 M) in DES-1 FeCl3·6H2O (1 M) in DES-1 H2O (50% vt.) in DES-1

surface tension, (±0.60) mN·m−1

density, (±2%) g·cm−3 (hydrometer)

density (superDESphobic surfaces), (±4%) g·cm−3

36

49.48

1.10

1.14

632 376 2346 / / /

54.32 59.10 80.80 56.70 58.40 67.70

1.19 1.15 1.50 1.12 1.16 1.04

1.21 1.16 1.48 1.12 1.18 1.07

viscosity,a cP

a Viscosity data taken from ref 1. bDensities of the DES-based solutions are obtained from a hydrometer and the SuperDESphobic surfaces, respectively.

Silver coating was facilely deposited on the copper substrates by using galvanic exchange reactions between silver ion and Cu. Briefly, the copper substrate (2 cm × 5 cm) was first dipped in a 1 M HCl solution for 5 min to remove the possible surface oxide layer. After being rinsed with deionized water, the copper (sheet or foam) was immersed into a solution with 0.05 M silver nitrate aqueous solution, maintained for 1 min, and then flushed by deionized water. Such a dipping process was repeated five times, followed by blow-drying. In this case, the galvanic exchange reaction was rapid. Some deposits with low adhension to the substrate would be removed in the following rinsing step. Therefore, the dipping process was repeated several times in order to obtain the stable silver coatings on the copper substrate. The Ag dendritic crystal was formed in the copper plate and copper foam substrate, which were referred to as Ag-CuP and Ag-CuF, respectively. The as-prepared Ag/Cu samples were modified by immersing the surfaces in an ethanol solution of n-dodecanethiol (∼1 wt %) for about 12 h, then washed with ethanol and water, and finally dried with air. The above superDESphobic surfaces were referred to as Ag-CuP/M (copper plate) and Ag-CuF/M (copper foam), respectively. Structural Characterization and Wettability. A field emission scanning electron microscope (FE-SEM, Hitachi SU-70) was employed to observe the surface morphology. The crystal structure was characterized by powder X-ray diffraction (XRD, XPert Pro-MPD with Cu Kα radiation, λ = 0.15406 nm). Contact angle (CA) and sliding angle (SA) were determined by a contact angle meter (SL200B, Solon Tech.) based on a sessile drop measuring method with a DES droplet volume of about 4 μL. The surface and interfacial tensions were calculated from the profile of a pendant drop. High-Temperature Resistance Characterization and Impacting Experiments on the SuperDESphobic Surfaces. To investigate the high-temperature resistance of the superDESphobic surfaces, the coating samples were placed on a heating stage which is associated with the contact angle meter. CAs were measured as the temperature is increased from room temperature to about 120 °C. The dynamic impact process of DES droplets on the superDESphobic surfaces was recorded with a high-speed camera (PCO: pco.dimax HD) operated at 8000 frames/s. The initial impact velocity of a water droplet was adjusted and calculated by the droplet release height. The dynamic impact behavior was analyzed with the images. Antifreezing performance of the superDESphobic surfaces. The adhesion strength of frozen DESs (DES-1 and DES-2) on Ag-CuF/M and Ag-CuP/M surfaces, respectively, was determined by a homemade apparatus (see Figure S9), which is set up according to the previous work.28,29 Freezing processes of DES droplets were observed through an optical microscope (Navitar Zoom 6000) on a cooling stage connected with a cryostat. The environment temperature and air humidity were 25 ± 2 °C and 65 ± 5%, respectively. All of the measurements were repeated at least three times to ensure the reproducibility.

angle > 150°) is in its infancy, let alone superDESphobic surfaces (defined as DES contact angle > 150°). Prior work on the superILphobic surfaces has been done by Jiang’s research group.23,24 It was reported that a series of surfaces with tunable wettability by three kinds of ILs (the surface tension is ranging from 32.7 to 64.8 mN/m2) have been designed through rationally controlling surface chemistries and structures.25 Based on the promising application of DESs in material science, it is urgent to take efforts to develop the superDESphobic surfaces, aiming to mitigate the strong adhesion of DESs on solids wherein wettability and adhesion between DESs and correlated surfaces are crucial. In this paper, we prepare the super antiwetting surface, i.e., super-DES-phobic surface (defined as DES contact angle > 150°) to mitigate drag-out of DESs. The surface chemistry and substrate structure are emphasized to achieve stable antiwetting surfaces. The capability of the super antiwetting surface is thoroughly evaluated against the impact attack of DES drops and high temperature of about 120 °C. It is also found that the fabricated surface can significantly delay the DESs freezing and reduce the adhesion strength of the frozen DESs. We also demonstrate the application of superDESphobic surface to measure the density of DESs.

2. EXPERIMENTAL SECTION Materials. Cu foam with a thickness of about 2.0 mm and copper sheet with a thickness of about 0.1 mm (Keliyuan in Changsha, Beige New Materials & Technology) were used as the substrates for depositing Ag coatings. All chemical reagents including choline chloride (ChCl), ethylene glycol (EG), glycerol, urea, chromium chloride hexahydrate (CrCl3·6H2O), nickel chloride hexahydrate (NiCl2· 6H2O), iron chloride hexahydrate (FeCl3·6H2O), and n-dodecanethiol were analytical grade and used without further purification. Three kinds of 1-alkyl-3-methylimidazolium hexafluorophosphate ionic liquids (ILs) with different chain lengths ([CnmIm][PF6], n = 4 ([BmIm][PF6]), n = 6 ([HMIm]PF6), n = 8 ([OmIm][PF6])) were purchased from the Center for Green Chemistry and Catalysis (CGCC, CAS) and used as received. Preparation of DESs. ChCl was mixed with ethylene glycol (EG), glycerol, urea, and CrCl3·6H2O with a molar ratio of 1:2, respectively, to get various DESs (abbreviated by DES-1, DES-2, DES-3, and DES-4 as listed in Table 1). NiCl2·6H2O and FeCl3·6H2O were dissolved into the DES-1 in 1 M to get two DES-derived solutions (Solution-1 and Solution-2), respectively. Deionized (DI) water was added into DES-1 with a volume ratio 1:1 to get Solution-3. All the eutectic mixtures were formed by heating and stirring two components at 60 °C until a transparent, homogeneous liquid was formed. All of them and their physical properties are showed in Table 1. Preparation of SuperDESphobic Surfaces. The fabrication of the superDESphobic surface involves a two-step coating technique and has a similar flow process to that of superhydrophobic surfaces.26,27

3. RESULTS AND DISCUSSION Drag-out usually refers to electrolyte losses in the surface finishing processes (electroplating or electropolishing) caused by adhering to workpieces when they are removed from the 24210

DOI: 10.1021/acsami.8b07769 ACS Appl. Mater. Interfaces 2018, 10, 24209−24216

Research Article

ACS Applied Materials & Interfaces

Figure 1. (a) DES droplets (from left to right: Solution-2, DES-4, Solution-1, and DES-1) leaving obvious drag-out traces when the slide glass was tilted at about 80°. (b) Deposited as spherical on the superDESphobic surface constructed by Ag-CuF/M. Photograph of various DESs droplets (from left to right: DES-1, Solution-2, Solution-1, DES-2, DES-3, and DES-4) on the fabricated superDESphobic surface.

Table 2. Wetting Properties (CA and SA values) of DESs on the Silver Coating/Copper Substrate with and without Surface Modification DESs

Ag-CuP (CA), ±2°

Ag-CuP/M (CA), ±3°

Ag-CuP/M (SA), ±2°

Ag-CuF (CA), ±2°

Ag-CuF/M (CA), ±3°

Ag-CuF/M (SA), ±1°

DES-1 DES-2 DES-3 DES-4 Solution-1 Solution-2 Water

6 8 12 10 9 7 14

130 156 157 148 142 147 158

a 7 6 a a 18 1

0 0 0 0 0 0 0

155 156 156 156 155 156 156

5 4 4 5 5 4 1

a

The DES drop pins on the surface and cannot slide off the surface.

plating bath.30 The high viscosity would result in enhanced mechanical loss through drag-out.30 As demonstrated in Figure 1, when the slide glass was tilted, the DES droplets predeposited on the surface cannot easily slide away, leaving a large wetting footprint. Therefore, loss of DESs must occur during the transfer process because of the strong adhesion on the vessels. On the contrary, a variety of DESs form spherical shapes on the as-fabricated superDESphobic surface (Ag-CuF/M), showing nonwetting property. The contact angle (CA) values of these DESs and derived solutions (as listed in Table 1) are all larger than 150°. More significantly, the sliding angles (SAs) of the DESs are all lower than about 5°, as shown in Figure 3, Table 2, and Figures S1−S5, which indicates that the superDESphobic surface possesses super antiwetting property without drag-out of DESs. The fabrication of the superDESphobic surface is facile, which involves a two-step coating technique and has similar flow process of superhydrophobic surfaces.26,27,31 The commercial Cu plate (CuP) and foam (CuF) were chosen as the substrates due to their good ductility and easy forming. Micro-/ nanostructure silver films were facilely deposited on the copper substrates by using galvanic exchange reactions between silver ion and Cu. The Ag film is formed by the microscale dendrite with coral-like aggregates, as shown in Figure 2. Figure 2a gives the surface morphology of Cu foam covered by Ag film. It can be seen that the ligament of the porous Cu is about 100 μm in width, leaving pores with a size range of about 50−500 μm. From the close view of the ligament region (Figure 2b and inset), it can be seen that the ligament of Cu foam was covered by plenty of silver dendrites and particles. The silver dendrites possess remarkable hierarchical structure sprawling to several generations with apparent self-similarity, which is due to a nonequilibrium and anisotropic growth mode.26 The similar morphology of the deposits can also be found on the sample of

the Cu plate (Figure 2c). Figure 2d gives the XRD patterns of micro-/nanostructure Ag/Cu sample composed by dendrite silver on the Cu foam substrate, which indicates the coating is identified by pure Ag (JCPDS 04-0783). The Cu peaks (JCPDS 03-1005) in the XRD patterns originates from the substrate. It is worth noting that the surface modification of n-dodecanethiol will not change the morphology and phase of the silver deposit. The wetting behavior of the as-prepared rough Ag film on Cu substrate by DES droplets were characterized by contact angle (CA) and sliding angle (SA), which is shown in Figures 3 and S1−S5 and summarized in Table 2. The Ag/Cu samples with and without the surface modification of n-dodecanethiol were compared. It can be found that the modification with n-dodecanethiol will affect wettability of DESs. Without the surface modification, the rough surfaces exhibit DESphilic behavior with a CA value less than 10°. Significantly, the sample of Ag on Cu foam without modification of n-dodecanethiol (Ag-CuF) has the superDESphilic surface with a CA of 0. However, after the surface modification of n-dodecanethiol, all Ag/Cu samples (Ag-CuP/M and Ag-CuF/M) show DESphobicity. Therefore, it can be concluded that both low-energy-material (n-dodecanethiol) and appropriate surface roughness (dendritic Ag and porous substrate) are necessary for the achievement of superDESphobicity. The superDESphobic surface with CA value larger than 150° and SA less than 5° was obtained on the Ag-CuF/M. The Ag-CuF/M exhibits excellent super antiwetting property to a series of DESbased solutions with various surface tensions (the surface tension is ranging from 49.5 to 80.8 mN/m2), as listed in Tables 1 and 2. It is also found that the superDESphobicity of the Ag-CuF/M surface is effective for some typical ILs, such as [OMIm]PF6, [HMIm]PF6, and [BMIm]PF6 (the surface tension is ranging from 35.7 to 42.2 mN/m2), showing the CA > 120° (see Table S1). The SA of the DES-droplets on Ag-CuP/M is larger than that on Ag-CuF/M. The droplets (DES-1, DES-4, 24211

DOI: 10.1021/acsami.8b07769 ACS Appl. Mater. Interfaces 2018, 10, 24209−24216

Research Article

ACS Applied Materials & Interfaces

Figure 2. Surface morphology of the superDESphobic surface on the Cu foam (a, b) and sheet (c) substrates. The magnified images (b) and (c) indicate the silver nanostructures with dendrites and particles are formed on the Cu substrates. (d) XRD patterns of the superDESphobic coating composed by dendrite coral-like silver on Cu foam substrate, which are identified by Ag (JCPDS 04-0783). The Cu peaks (JCPDS 03-1005) are originated from the substrate.

most such surfaces would lose their repellency to hot (e.g., >55 °C) water35,36 due to the transition of the wetting state from the Cassie−Baxter state to the Wenzel state.35,37−40 Therefore, it is indispensable to evaluate the thermal stability of the superDESphobic surfaces for potential applications. The temperature dependent CA values of DESs on the superDESphobic surface (Ag-CuF/M) were evaluated, and the corresponding results are shown in Figure 3g. The CA values were recorded when the substrate temperature was stabilized. It can be seen that in the temperature region from room temperature to about 120 °C, the CA values of the studied DESs on Ag-CuF/M were little changed and still greater than 150°, which indicates that the superDESphobic surface maintains its stable antiwetting property and can repel hot DESs. At above 120 °C, some DESs will slightly volatilize. The superDESphobicity of the surface is mainly determined by the C−H bands derived from n-dodecanethiol (low surface energy) and the micro-/nanobinary structures. The n-dodecanethiol cannot be desorbed when the temperature is increased to 120 °C. It is also found that the surface morphology of the superDESphobic sample after thermal treatments was little changed compared with Figure 2 and without cracks, which further guarantees the super antiwetting property of the surface at high temperatures. When a water droplet impacts on a solid surface, its bouncing behavior depends on the surface hydrophobic property. Accordingly, the superDESphobic property can also be characterized by the bouncing behavior of DES drops, which sheds light on the capability of the hierarchical Ag/Cu sample against the impact attack of DESs. The dimensionless Weber number, We = ρV2R/γ, compares the kinetic and surface energies of the drop, where V, ρ, and γ are the impinging velocity, liquid density, and surface

and Solution-1) on the Ag-CuP/M surface appear spherical in shape. However, they cannot roll off even when the surface is turned upside down (see Figure 3c). This phenomenon had been defined as the “petal effect”,32 exhibiting important superDESphobic Cassie impregnating wetting state. In the Cassie impregnating wetting state, grooves of the solid are wetted with liquid and solid plateaus are dry.32 In the Cassie impregnating wetting regime as sketched in Figure 4a, the DES liquid impregnates the texture; however, there will always remain islands that emerge above the “absorbed” liquid film.32 The surface of Ag-CuP/M is still repellent to water with a water CA larger than 150° and a SA of ∼2°, due to the higher surface tension of water, which is in agreement with previous reports.26 The superior DESphobic property of the Ag-CuF/M with the Cassie state should be attributed to the adopted Cu foam substrate, which possesses robust pore structure in microscale providing the second-order roughness for the superDESphobic surfaces as sketched in Figure 4b. As for the Cu plate sample, there is only the first-order roughness of the dendritic Ag on the surface, which cannot form stable air pockets to support the DES-droplets. Some grooves of the dendritic Ag on the Cu plate may be wetted with DES droplet according to the Cassie impregnating wetting state. The low-energy-material of n-dodecanethiol associated with dual roughness structures, i.e., the dendritic and the porous structures, in the Ag-CuF/M is suggested to be responsible for their superDESphobicity with high CA and lower SA. Due to the high thermal stability and nonvolatility property of DESs, they are usually handled at elevated temperatures to achieve higher ion conductivity or lower viscosity.8,33 Superhydrophobic surfaces are susceptible to be destroyed under higher temperature due to their fragile nanostructures.34 Moreover, 24212

DOI: 10.1021/acsami.8b07769 ACS Appl. Mater. Interfaces 2018, 10, 24209−24216

Research Article

ACS Applied Materials & Interfaces

Figure 3. Contact angles (a−e) and sliding angles (f) of the typical DES (DES-1) on the dendrite Ag coating on the Cu flat plates (a: Ag-CuP; b: Ag-CuP/M) and Cu foams (d: Ag-CuF; e and f: Ag-CuF/M) before and after modification with n-dodecanethiol. DES-1 droplets with each having a volume of about 4 μL were used in the tests. (c) The shape of a DES-1 drop on the Ag-CuP/M surface when it is turned upside down, indicating the “petal effect”. (g) The temperature dependent contact angles of various DESs on the superDESphobic surface (i.e., the Ag-CuF/M).

tension, respectively.41 The greater the value of We, the larger are the deformations of drop that occur during the impact.41 The impinging test of typical DES drops was performed on the samples of Ag-CuP/M and Ag-CuF/M, which is presented as in Figure 5, Supporting Information Figures S6−S8, and Movies S1−S3. Figure 5 shows the successive snapshots of DES drops free-falling on the surfaces of Ag-CuP/M and the Ag-CuF/M samples, respectively. Time 0 has been taken as the time before the drop impinging the surfaces. When ∼6 μL DES-1 drop impacts the Ag-CuF/M surface with a velocity of about 0.61 m·s−1, that corresponds to a Weber number of We = 7.4, and the drop bounces back as indicated by an arrow (see Figure 5a and Supporting Information Movie S1). However, when impacting the Ag-CuP/M surface with the similar velocity of about 0.55 m·s−1 and We = 6.5, the drop of DES-1 vibrates slightly but there is no bouncing (see Figure 5b and Supporting Information Movie S2). The above comparison indicates the superior superDESphobic property of the Ag-CuF/M surface (i.e., the dendritic silver on copper foam substrate) over the Ag-CuP/M sample. Moreover, when the water was added into the DESs up to a critical concentration, both Ag-CuF/M and Ag-CuP/M samples exhibit

repellency to the water−DES mixtures (see Figure S7). The water usually acts as the additive into the DESs. As the volume ratio of water/DES-1 is increased to about 1:5, the mixture droplet impinging on the Ag-CuP/M with a velocity of about 0.54 m·s−1 can bounce back (see Figure S8). The recovered bounce behavior on the Ag-CuP/M should be attributed to the increased surface tension of the mixtures due to the addition of water. It is also found that the drop of DES-3 does not detach the Ag-CuF/M suface after impinging with a velocity of about 0.65 m·s−1 (We = 12.5), which may be attributed to the transfer of the kinetic energy into the drop vibration and overcoming the gravity (see Figure S6c). However, it should be noted that the DES-3 droplet after impinging on the Ag-CuF/M surface can easily roll down when the surface tilts, which implies that the super antiwetting surface can resist more severe DESs impinging. Solution-1 is a typical DES-based electrolyte for electroplating Ni coatings in the surface finishing processes. It is found that the drop of Solution-1 can also bounce back when it hits the Ag-CuF/M surface with a velocity of about 0.65 m·s−1 (We = 12.7) (see Figure S6d). Therefore, the present super antiwetting surface should be valid for various DESs and their derived solutions. 24213

DOI: 10.1021/acsami.8b07769 ACS Appl. Mater. Interfaces 2018, 10, 24209−24216

Research Article

ACS Applied Materials & Interfaces

Figure 4. Schematic illustrations of a drop of DES in contact with the Ag-CuF/M (a: the Cassie impregnating wetting state) and Ag-CuP/M surfaces (b: the Cassie’s state).

Figure 5. Selected time sequence of snapshots of DES droplets free-falling on the surfaces of Ag-CuP/M and Ag-CuF/M samples. The impinging velocity (V) and the Weber number (We) of the droplet on the surface are shown in the brackets. (a) ∼6 μL DES-1 on Ag-CuF/M (V = 0.61 m s−1; We = 7.4); (b) ∼6 μL DES-1 on Ag-CuP/M (V = 0.55 m s−1; We = 6.5); (c) snapshots of the DES-1 droplet (∼5 μL) impacting on the Ag-CuF/M with a tilted angle of about 25°. The release height of the droplet was about 24 mm. The impacting position on the surface is marked by an arrow in the figure.

Figure 5c gives a selected time sequence of snapshots of the DES-1 droplet (∼12 μL) impacting on the Ag-CuF/M with a tilted angle of about 25°. The release height of the droplet was about 24 mm. The droplet impacts the surface with a speed of about 0.69 m s−1 that corresponds to a Weber number of We = 12.6. The drop hitting position on the surface was marked by an arrow in Figure 5c. As shown in Figure 5c, the liquid ball (DES-1) becomes a thin pie with a thickness of about 0.9 mm (snapshot at 3.9 ms) after hitting the Ag-CuF/M surface. Then the drop becomes highly elongated with severe vibrations but no bouncing, which should be due to the dissipation of kinetic energy by large vibrating of liquid. After contacting the surface, the droplet begins rolling with slight vibrations on the tilted surface. From the obvious trajectories of a number of air bubble shadows in the DES droplet reveal that the drop rolls rather than slips across the surface (see Supporting Information Movie S3). The melting point of DESs is dependent upon the interaction between the two component mixtures. Due to the strong hydrogen bond interactions between two different chemicals, the freezing points of most DESs are down to ambient conditions, however usually larger than the freezing point of water. Therefore, antifreezing on the superDESphobic surfaces is also important

for engineering materials for handling DESs at subfreezing temperatures. Table S2 exhibits the adhesion strength of frozen DESs (DES-1 and DES-2) on Ag-CuF/M and Ag-CuP/M surfaces, respectively, which was determined by a homemade apparatus (see Figure S9). The adhesion strengths of the frozen DES-1 and DES-2 on Ag-CuF/M were measured to be about 754.95 and 707.77 Pa, respectively, which are much lower than those on Ag-CuP/M (about 7863.49 and 6605.33 Pa). The results indicate the super antiwetting surface can effectively avoid the adhesion of frozen DESs. Furthermore, the antifreezing behavior of the modified Ag/Cu surfaces was also expressed by visual inspection. A DES-2 droplet (about 2 μL) was deposited on the Ag/Cu surface which was placed on the cold stage of −5 °C, and the drop freezing process was recorded by a camera accessary to the optical microscope. The optical images corresponding to the DES-2 droplet after cooling for about 15 min are shown in Figure S10. It can be seen that the droplet has been fully frozen on the Ag-CuP/M surface. However, there are only some flocculent frozen solids in the droplet on the Ag-CuF/M, which indicates the superDESphobic surface can effectively delay the freezing of DESs. The super antiwetting surface exhibits excellent repellency to DESs, which guarantees the transfer of DESs without loss 24214

DOI: 10.1021/acsami.8b07769 ACS Appl. Mater. Interfaces 2018, 10, 24209−24216

ACS Applied Materials & Interfaces (see Supporting Information Movie S4). A demonstration on the application of the superDESphobic surface is proposed to measure the density of the DESs. Mathematically, density (ρ) is defined as mass (m) divided by volume (V). Since the sphere can be formed when a DES droplet is sitting on the superDESphobic surface, the droplet volume can be easily calculated by

V=

4π 3

3

( d2 )

where the diameter (d) is directly measured by

ACKNOWLEDGMENTS

■

REFERENCES

(1) Smith, E. L.; Abbott, A. P.; Ryder, K. S. Deep Eutectic Solvents (DESs) and Their Applications. Chem. Rev. 2014, 114, 11060−11082. (2) Tomé, L. I. N.; Baião, V.; da Silva, W.; Brett, C. M. A. Deep Eutectic Solvents for the Production and Application of New Materials. Appl. Mater. Today 2018, 10, 30−50. (3) Ge, X.; Gu, C.; Wang, X.; Tu, J. Deep Eutectic Solvents (DESs)derived Advanced Functional Materials for Energy and Environmental Applications: Challenges, Opportunities, and Future Vision. J. Mater. Chem. A 2017, 5, 8209−8229. (4) Cooper, E. R.; Andrews, C. D.; Wheatley, P. S.; Webb, P. B.; Wormald, P.; Morris, R. E. Ionic Liquids and Eutectic Mixtures as Solvent and Template in Synthesis of Zeolite Analogues. Nature 2004, 430, 1012−1016. (5) Tang, B.; Row, K. H. Recent Developments in Deep Eutectic Solvents in Chemical Sciences. Monatsh. Chem. 2013, 144 (10), 1427− 1454. (6) Sze, L. L.; Pandey, S.; Ravula, S.; Pandey, S.; Zhao, H.; Baker, G. A.; Baker, S. N. Ternary Deep Eutectic Solvents Tasked for Carbon Dioxide Capture. ACS Sustainable Chem. Eng. 2014, 2, 2117−2123. (7) del Monte, F.; Carriazo, D.; Serrano, M. C.; Gutiérrez, M. C.; Ferrer, M. L. Deep Eutectic Solvents in Polymerizations: A Greener Alternative to Conventional Syntheses. ChemSusChem 2014, 7, 999− 1009. (8) Gu, C.; Tu, J. One-Step Fabrication of Nanostructured Ni Film with Lotus Effect from Deep Eutectic Solvent. Langmuir 2011, 27, 10132−10140. (9) Gu, C. D.; Yan, W.; Zhang, J. L.; Tu, J. P. Corrosion Resistance of AZ31B Magnesium Alloy with a Conversion Coating Produced from a Choline Chloride-Urea Based Deep Eutectic Solvent. Corros. Sci. 2016, 106, 108−116. (10) Abbott, A. P. Application of Hole Theory to the Viscosity of Ionic and Molecular Liquids. ChemPhysChem 2004, 5, 1242−1246. (11) Tome, L. I. N.; Baiao, V.; da Silva, W.; Brett, C. M. A. Deep Eutectic Solvents for the Production and Application of New Materials. Appl. Mater. Today 2018, 10, 30−50. (12) Wagle, D. V.; Zhao, H.; Baker, G. A. Deep Eutectic Solvents: Sustainable Media for Nanoscale and Functional Materials. Acc. Chem. Res. 2014, 47, 2299−2308. (13) Welton, T. Electrodeposition from Ionic Liquids. Angew. Chem., Int. Ed. 2008, 47, 4468−4468. (14) Guo, Z. G.; Liu, W. M.; Su, B. L. Superhydrophobic surfaces: From Natural to Biomimetic to Functional. J. Colloid Interface Sci. 2011, 353, 335−355. (15) Liu, Y. H.; Moevius, L.; Xu, X. P.; Qian, T. Z.; Yeomans, J. M.; Wang, Z. K. Pancake Bouncing on Superhydrophobic Surfaces. Nat. Phys. 2014, 10, 515−519. (16) Zang, D. M.; Yi, H.; Gu, Z. D.; Chen, L.; Han, D.; Guo, X. L.; Wang, S. T.; Liu, M. J.; Jiang, L. Interfacial Engineering of Hierarchically Porous NiTi/Hydrogels Nanocomposites with Exceptional Antibiofouling Surfaces. Adv. Mater. 2017, 29, 1602869. (17) Zhang, P. F.; Zhang, L. W.; Chen, H. W.; Dong, Z. C.; Zhang, D. Y. Surfaces Inspired by the Nepenthes Peristome for Unidirectional Liquid Transport. Adv. Mater. 2017, 29, 1702995. (18) Park, K. C.; Kim, P.; Grinthal, A.; He, N.; Fox, D.; Weaver, J. C.; Aizenberg, J. Condensation on Slippery Asymmetric Bumps. Nature 2016, 531, 78−82. (19) Peng, C. Y.; Chen, Z. Y.; Tiwari, M. K. All-organic Superhydrophobic Coatings with Mechanochemical Robustness and Liquid Impalement Resistance. Nat. Mater. 2018, 17, 355−360.

4. CONCLUSIONS A novel nonwetting surface with repellency to DESs was fabricated by a facile two-step method. Both low-energy-material (n-dodecanethiol) and appropriate surface roughness (dendritic Ag and porous substrate) are necessary for the achievement of superDESphobicity. The CA and SA values of a series of DESs and their derived solutions on the superDESphobic surface are all larger than 150° and lower than 5°, respectively. The super antiwetting surface can also repel DESs at high-temperature (∼120 °C) or external impact. Moreover, the superDESphobic surface can significantly delay DES freezing and reduce the adhesion strength of the frozen DESs on the surface. It is demonstrated that the superDESphobic surface is an effective tool to measure the density of DESs in virtue of its super antiwetting property. The present study opens a new avenue in search of superDESphobic surfaces, which show promise for potential applications in self-cleaning and antifreezing of DESs. ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.8b07769. Tables S1 and S2 and Figures S1−S10 (PDF) Movie S1 (AVI) Movie S2 (AVI) Movie S3 (AVI) Movie S4 (AVI)

■

■

This work was supported by the National Key Research and Development Program of China (2016YFF0204300) and the National Natural Science Foundation of China (51271169). The authors thank Prof. H. Bai for help in the dynamic impact tests of water droplets.

optical microscopy. The mass of the droplet, m, is determined by an electronic balance. It is worthy to note that the gravity will strongly affect the droplet shape, making it harder to calculate the drop volume precisely. Therefore, the droplet volume should be as small as possible. In our case, the DES droplet with a volume of about 2 μL was adopted for the demonstration of density measurement. The density values of the DES-based liquids obtained by the superDESphobic surface are listed in Table 1. For reference, the density of the DES-based liquids was also confirmed by hydrometer. It is amazing that the density deduced from the super-antiwetting surface is very close to the result from the hydrometer, which proves the density measurement by the superDESphobic surface is effective. It is the superDESphobic surfaces that ensure the delivering of tiny DES droplets without losses in weighing and diameter gauging. The present demonstration may open a new avenue for determining the density of liquid drops.

■

Research Article

AUTHOR INFORMATION

Corresponding Author

*(C.D.G.) E-mail: [email protected] ORCID

C. D. Gu: 0000-0001-8286-263X Notes

The authors declare no competing financial interest. 24215

DOI: 10.1021/acsami.8b07769 ACS Appl. Mater. Interfaces 2018, 10, 24209−24216

Research Article

ACS Applied Materials & Interfaces (20) Li, J. Q.; Zhou, X. F.; Li, J.; Che, L. F.; Yao, J.; McHale, G.; Chaudhury, M. K.; Wang, Z. K. Topological Liquid Diode. Sci. Adv. 2017, 3, eaao3530. (21) Chen, X. M.; Wu, J.; Ma, R. Y.; Hua, M.; Koratkar, N.; Yao, S. H.; Wang, Z. K. Nanograssed Micropyramidal Architectures for Continuous Dropwise Condensation. Adv. Funct. Mater. 2011, 21, 4617− 4623. (22) Yao, X.; Chen, L.; Ju, J.; Li, C. H.; Tian, Y.; Jiang, L.; Liu, M. J. Superhydrophobic Diffusion Barriers for Hydrogels via Confined Interfacial Modification. Adv. Mater. 2016, 28, 7383−7389. (23) Liu, H. L.; Jiang, L. Wettability by Ionic Liquids. Small 2016, 12, 9−15. (24) Liu, H.; Ding, Y.; Ao, Z.; Zhou, Y.; Wang, S.; Jiang, L. Fabricating Surfaces with Tunable Wettability and Adhesion by Ionic Liquids in a Wide Range. Small 2015, 11, 1782−1786. (25) Hou, J.; Zhang, H.; Yang, Q.; Li, M.; Jiang, L.; Song, Y. Hydrophilic−Hydrophobic Patterned Molecularly Imprinted Photonic Crystal Sensors for High-Sensitive Colorimetric Detection of Tetracycline. Small 2015, 11, 2738−2742. (26) Gu, C. D.; Ren, H.; Tu, J. P.; Zhang, T. Y. Micro/Nanobinary Structure of Silver Films on Copper Alloys with Stable Water-Repellent Property under Dynamic Conditions. Langmuir 2009, 25, 12299− 12307. (27) Gu, C. D.; Zhang, T. Y. Electrochemical Synthesis of Silver Polyhedrons and Dendritic Films with Superhydrophobic Surfaces. Langmuir 2008, 24, 12010−12016. (28) Zhang, J. L.; Gu, C. D.; Tu, J. P. Robust Slippery Coating with Superior Corrosion Resistance and Anti-Icing Performance for AZ31B Mg Alloy Protection. ACS Appl. Mater. Interfaces 2017, 9, 11247− 11257. (29) Meuler, A. J.; Smith, J. D.; Varanasi, K. K.; Mabry, J. M.; McKinley, G. H.; Cohen, R. E. Relationships between Water Wettability and Ice Adhesion. ACS Appl. Mater. Interfaces 2010, 2, 3100−3110. (30) Abbott, A. P.; Frisch, G.; Ryder, K. S. Electroplating Using Ionic Liquids. Annu. Rev. Mater. Res. 2013, 43, 335−358. (31) Zhang, M.; Wang, P.; Sun, H.; Wang, Z. Superhydrophobic Surface with Hierarchical Architecture and Bimetallic Composition for Enhanced Antibacterial Activity. ACS Appl. Mater. Interfaces 2014, 6, 22108−22115. (32) Feng, L.; Zhang, Y. A.; Xi, J. M.; Zhu, Y.; Wang, N.; Xia, F.; Jiang, L. Petal effect: A Superhydrophobic State with High Adhesive Force. Langmuir 2008, 24, 4114−4119. (33) Okoturo, O. O.; VanderNoot, T. J. Temperature Dependence of Viscosity for Room Temperature Ionic Liquids. J. Electroanal. Chem. 2004, 568, 167−181. (34) Wang, X. Q.; Gu, C. D.; Wang, L. Y.; Zhang, J. L.; Tu, J. P. Ionic Liquids-infused Slippery Surfaces for Condensation and Hot Water Repellency. Chem. Eng. J. 2018, 343, 561−571. (35) Zhang, P.; Chen, H.; Zhang, L.; Zhang, Y.; Zhang, D.; Jiang, L. Stable Slippery Liquid-infused Anti-wetting Surface at High Temperatures. J. Mater. Chem. A 2016, 4, 12212−12220. (36) Liu, Y.; Chen, X.; Xin, J. H. Can Superhydrophobic Surfaces Repel Hot Water? J. Mater. Chem. 2009, 19, 5602−5611. (37) Whyman, G.; Bormashenko, E.; Stein, T. The Rigorous Derivation of Young, Cassie−Baxter and Wenzel Equations and the Analysis of the Contact Angle hysteresis Phenomenon. Chem. Phys. Lett. 2008, 450, 355−359. (38) Bormashenko, E.; Bormashenko, Y.; Stein, T.; Whyman, G.; Bormashenko, E. Why do Pigeon Feathers Repel Water? Hydrophobicity of Pennae, Cassie−Baxter Wetting Hypothesis and Cassie− Wenzel Capillarity-induced Wetting Transition. J. Colloid Interface Sci. 2007, 311, 212−216. (39) Daniel, D.; Mankin, M. N.; Belisle, R. A.; Wong, T.-S.; Aizenberg, J. Lubricant-infused Micro/nano-structured Surfaces with Tunable Dynamic Omniphobicity at High Temperatures. Appl. Phys. Lett. 2013, 102, 231603.

(40) Urata, C.; Masheder, B.; Cheng, D. F.; Hozumi, A. A Thermally Stable, Durable and Temperature-dependent Oleophobic Surface of a Polymethylsilsesquioxane Film. Chem. Commun. 2013, 49, 3318−3320. (41) Richard, D.; Clanet, C.; Quere, D. Surface Phenomena - Contact Time of a Bouncing Drop. Nature 2002, 417, 811−811.

24216

DOI: 10.1021/acsami.8b07769 ACS Appl. Mater. Interfaces 2018, 10, 24209−24216