Fabrication of multifunctional wax infused porous PVDF film with switchable temperature response surface and anti corrosion property

G Model JIEC 4821 No. of Pages 9

Journal of Industrial and Engineering Chemistry xxx (2019) xxx–xxx

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Fabrication of multifunctional wax infused porous PVDF film with switchable temperature response surface and anti corrosion property Arni M. Pornea, John Marc C. Puguan, Virendrakumar G. Deonikar, Hern Kim* Department of Energy Science and Technology, Smart Living Innovation Technology Center, Myongji University, Yongin, Gyeonggi-do 17058, Republic of Korea

A R T I C L E I N F O

A B S T R A C T

Article history: Received 18 July 2019 Received in revised form 7 October 2019 Accepted 11 October 2019 Available online xxx

The discovery of the lubricant infused surface (LIS) embarked a promising approach on the active surface applications. Demonstrated here is an intricately designed multifunctional film influenced by bottom-up approach, utilizing the underlying features of the compounding materials to provide greater functionalities and opportunities for various applications. Through facile fabrication method, a porous film was generated by incorporating ZnO nanoparticle as a porogen onto PDVF polymer prior casting followed by simple acid washing for the removal of ZnO. Wax was used to lubricate the porous thin film; the design was inspired by the advantageous property of the wax that will enhance surface wetting properties, exhibiting the surface with thermal responsiveness, anticorrosion protection and robust structure. By taking advantage onto the lubricant’s rheological property, droplet motion control in response with the temperature variation was explored. Surface responses on different kinds of liquids were also studied. The multifunctional film manifested anticorrosion protection, which is supported by electrochemical measurement technique. The film’s stability was explored through exposure on harsh condition that successfully preserve its robust architecture. © 2019 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.

Keywords: Slippery infused surface Temperature responsive surface Multifunctional film Anticorrosion Self-healing

Introduction Scientific and technological advancement towards the development of interfacial surfaces offers great opportunities in various fields [1–3]. And due to its domination on various applications, such as self-cleaning coatings [4–7], anticorrosion [8], anti-icing [9], anti-fogging and adhesion-drag reduction in microfluidics [4,5,10], anti-wetting substrates have received tremendous attention in the previous decade [11,12]. Various methods have been rapidly developed in the progression of interfacial technology by applying the lessons we learned from nature, these surface structures were termed as ‘natureinspired materials’ which exhibits effective repellence to overcome severe environments. Due to its simplistic approach that addresses scientific and technological issues in numerous applications, the progress of natured-inspired materials was stimulated. Particularly, the classic lotus leaf inspired or Cassie
Baxter surfaces that had influenced a lot of anti-wetting substrates which are mostly identified as superhydrophobic surfaces (SHS). The super hydrophobicity of SHS surfaces owes it to the trapped air in the

* Corresponding author. E-mail address: [email protected] (H. Kim).

nanotextured architecture of the surface when it contacts with water droplet. This air trapping phenomenon caused the inconsistent contact of the three phases (solid/air/water) in the surface plane that resulted in the low adhesive interaction. Although the surface configuration offers high water repellence, the surface cavities makes it vulnerable under harsh operating conditions. These problems were resolved by the introduction of a new breed of functional material, the interface influenced by nepenthes pitcher plant termed as liquid infused surfaces (LIS). Governed by the concept of applying liquid to oppose immiscible contacting liquid, this practical scheme was cited on designing numerous repellent substrates and coatings that addresses the limitations of SHS. The thin layer of lubricant retained in the porous network established a smooth, constant and chemically uniform over layer, which demonstrates resistance, low adhesion and anti-wetting capability on wide range of liquids [13–15], that provides stability under extreme temperature and pressure exposure [16]. Due to its great concept that considers the initial condition and basic properties of the compounding components, “bottom up approach” has influenced structural and mechanistic design across diverse fields. This approach is necessary to innovate materials that permits the potential of new conceptual design and maximizes its advantageous properties. “Bottom” was cited as the architecture and mechanics of the structure’s system makeup, while “up” was

https://doi.org/10.1016/j.jiec.2019.10.015 1226-086X/© 2019 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.

Please cite this article in press as: A.M. Pornea, et al., Fabrication of multifunctional wax infused porous PVDF film with switchable temperature response surface and anti corrosion property, J. Ind. Eng. Chem. (2019), https://doi.org/10.1016/j.jiec.2019.10.015

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defined as construction not toward a specific end structure but towards a responsive variable. This can be expounded as the capability of the material to respond on temperature and pressure gradient and other stimuli, it can also indicate the ability not to resonate onto distinct impulse, such as shear or gravity and miscellaneous contaminants [17]. In the present work, a robust multifunctional film slippery surface was fabricated influenced by “bottom-up approach”. At the core of the processing and structural design, a facile fabrication of porous scaffold surface has been demonstrated with beneficial contribution on lubricant absorption stability. PVDF was selected because of its outstanding chemical stability because of its ability to resist degradation upon exposure on corrosive solvents including acids [18], and it is tunable wettability through crystallinity improvement assisted by crystal seeds or porogen. The polymer’s crystallinity or its molecular orientation can affect its interfacial property (hydrophobicity or oleophilicity), which can be correlated to its effective lubricant absorbance and incorporation stability [19]. PVDF have four semi crystalline phases (α, β, g, and d), although the non-polar α phase is the most common phase available on the commercially produced films, phase can be induced accordingly depending on the application requirement [20,21]. The ZnO particles was introduced to the PVDF solution to serve as a porogen to generate interconnected pores in the film, and to induce partial charges in the PVDF interface that will initiate the β-phase nucleation or the surface exposure of C
F polar bonds [22]. Additionally, ZnO has been selected due to its several advantages such as; reasonable cost, non-toxicity, good scalability and simple removal by acid etching [18]. The fabrication of the porous film follows a simplistic two step procedure. (1) Casting of PVDF solution mixed with ZnO particles to generate a uniform film. (2) Removal of ZnO through acid etching to produce a porous structure. Wax on the other hand had been utilized as an infusing lubricant and was specifically chosen due to its ability to respond on designated changes in temperature [23]. Yao et al. infused PDMS polymer block with wax to generate thermal responsive surface, but this engineered structure suffers from swelling that might hinder its operational application [24]. Wang et al. lubricated a freeze dried polystyrene scaffold with wax to produce a temperature responsive surface, although it demonstrated great contribution there’s still limitations in regards with the scaffolding flexibility support requirement and its tedious preparation [25]. Recent publications has successfully managed to diversify the potential of LIS for assorted dynamic applications such as; superhydrophobic surfaces [17], anti corrosion and stimulusresponsive materials fabricated to respond onto mechanical, electrical, chemical, strain, light, temperature and other types of stimuli [24,26–29]. Nevertheless, with the aim to provide a facile and economical thermal responsive surface and to explore the wax protective capability, demonstrated here is the fabrication of multifunctional active surface inspired by “bottom up approach”. The fabrication of the dynamic surface was revolutionized to manifest temperature stimuli responsiveness, effective shielding effect onto corrosive environment and robust stability under harsh treatment which expands its field of application [2,30,31]. It should be noted that, even though wax can resist harsh environments and offers a great potential as a protective film, wax infused film had never been explored in anticorrosion application, which is dominated with inorganic based materials that is commonly prepared through electrochemical processing [32,33]. The fundamental design encores a sophisticated function manipulation that constitutes on the interaction mechanism of the supporting scaffold and the lubricating material, which is a viable property for the effectivity of the composite structure. Hence, the surface protection, anti corrosion applications and the asymmetric surface were anticipated to be utilize into various interfacial applications

in microreactors, biochips, and biomedical systems in which fluid or droplet transport manipulation is important [26,27,32,34–36]. Experimental Materials Poly vinylidene fluoride (PVDF), N,N-dimethylformamide (DMF, 99%) and ZnO (
350 Mesh Powder) were purchased from Alfa Aesar. Hydrochloric Acid (HCl, 37%) were purchased from Acros Organics. Paraffin wax were obtained from Aldrich Chemistry. Tetrabutylammonium Acetate were acquired from Tokyo Chemical Industry Co., LTD. Ammonia Water were bought Duksan Pure Chemical Co., LTD. Sulfuric acid were acquired from Matsuneon Chemicals Ltd. Fabrication of wax-PVDF WIS film First, PVDF dope solution was formulated by mixing PVDF powder to DMF and heating it at 65  C. Temperature applied is beyond the critical dissolution temperature of 40  C to ensure thermodynamic equilibrium. Then, varied amount of ZnO particles (10%, 20% and 30%) were added onto the PVDF solution to fabricate different porous film. The mixture was sonicated for 30 min to homogeneously mix the PVDF-ZnO mixture. Then the mixture was casted onto a petri dish. To prepare the porous PVDF film, the casted film was subjected to acid etching process wherein the ZnO will be dissolved by acid to produce a porous film. Various ZnO concentrations were generated to check its effect to the film porosity. Certain amount of wax lubricant was heated at 80  C above its melting point (Tm), the porous PVDF film was then submerged on the liquefied wax for 4 h to ensure complete penetration. Characterization Field emission scanning electron micrographs (FE-SEM) were used to identify the morphological configuration of the fabricated film, and to determine elemental mapping energy dispersive X-ray spectrometer and EDX (Hitachi, S-3500N) 5B to 92U were used. SITA, Capillary Flow Porometer (CFP-1200-AE), Functional groups of the structured porous film were detected with the aid of Fouriertransform infrared (FTIR) spectrum (Thermo Scientific, Nicolet iS5), with a scanning window value of 32 in the 4000–400 cm
1 and a resolution of 8 cm
1. Crystalline phase of the generated porous membrane was investigated via X-ray diffraction (XRD) using X’pert MPD diffract meter with Bragg angle ranging from 10 to 90 to record the XRD patterns (Cu-K radiation = 1.540 Å). Surface tensions of the wax lubricant and testing liquids was determined via SITA Messtechnik maximum GmbH bubble pressure tensiometer (SITA online t60) whereas the interfacial tension was measured using capillary tube method. The contact angles of the surfaces were evaluated using SCALAR video loupe (VL-11S) and measurement determination was assisted with ImageJ software. Surface temperature response characteristics of the slippery infused surface were investigated with the aid of an automatic heating plate an IRtec Miniray 100 was used to check the accuracy of the plate temperature as exposed in Fig. S5. The corrosion protection performance was examined by obtaining electrochemical impedance spectroscopy (EIS) and potensiodynamic polarization curves (Tafel) using electrochemical plot set-up (SIVE SP1) with 3.5% NaCl serving as an electrolyte at room temperature operating condition. Prior testing specimen were dipped into the NaCl solution for 15 min to stabilize open circuit potential (OCP). The measurement was conducted with a conventional electrode system that consist three components, Ag/

Please cite this article in press as: A.M. Pornea, et al., Fabrication of multifunctional wax infused porous PVDF film with switchable temperature response surface and anti corrosion property, J. Ind. Eng. Chem. (2019), https://doi.org/10.1016/j.jiec.2019.10.015

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Scheme 1. Systematic projection of preparation of multifunctional wax-infused film.

AgCl electrode which stands as the reference electrode that is submerged in KCl solution, platinum (Pt) that serves as the counter electrode and a testing sample with 1 cm2 exposed area as a working electrode. Tafel plots were gauge with a scanning rate of 1 mV s
1. The EIS quantification at OCP with 10
2–105 Hz of frequency range. Results and discussion Porous PVDF film characterization In this communication, a porous PVDF film was formed via casting method, PVDF and ZnO particles mixture were cast on a petri dish followed by acid etching to dissolve the ZnO particles as shown on Scheme 1. The ZnO nanoparticles was used as a porgen or crystal seed to manipulate the polymer’s crystallinity and generate β-phase lattice formation. PVDF possesses four semi crystalline phases (α, β, g, and d), relying on the preparation conditions. Normally the β-phase crystallite is attained during tensile orientation which contributes interfacial attributes (hydrophobicity or oleophilicity). The dissolution of ZnO resulted on pore matrix formation. Morphological trait was observed through scanning electron microscopy (SEM) images. Porosity is a significant characteristic for the lubricant absorbance and its incorporation stability. The porous structure of the PVDF membrane after acid etching of different ZnO concentration, 10 wt%, 20 wt% and 30 wt% (termed as Z10, Z20 and Z30) were projected on Fig. 1. It can be observed that as the ZnO concentration increases the porosity of the membrane increases as well. This can be accounted on to the spaces that ZnO particles previously occupy prior particles elimination. The higher the amount of ZnO particles, the higher volume it occupies, the higher pore volume for lubricant occupancy. This can also be correlated to the incremental increase on the porous membrane thickness as the ZnO concentration escalates. Shown on Fig. 2a is the film thickness relationship towards the increase in the ZnO

concentration, as observed the thickness of the film increases with the increase in the ZnO concentration which lowers the film density and gives the film more room for the lubricant. Pore size diameter was also investigated using capillary flow pressure (CFP) measurement, as shown on Fig. 2b and supported by Fig. S1, it can be observed that the pore size diameter incrementally increases upon increase in ZnO concentration. The interconnection of the ZnO particles allows its complete removal through acid etching. These measurements signify that length scales of the porous PVDF membrane were much smaller than the capillary length of the PFPE lubricant (1 mm under Earth’s gravity). Therefore, the generated membrane will support a stable incorporation of lubricant. The formation of the porous membrane is driven by the particle rearrangement matrix for porgen complete elimination. In case of the lower ZnO concentration, Due to lower concentration, particles didn’t form an enough pore interconnectivity matrix that will elucidate the particle accessibility. To explore the underlying mechanism of the PVDF porous substrate in compliance to lubricant absorbing ability in molecular scale. Insights on how molecules where oriented on the surface and its interactions with the lubricant to channel effective lubricant absorption were provided. PVDF polymer contains four types of atoms, consisting F, H, C connected to F and C connected to H. Which is supported by X-ray spectroscopy (EDX), only C and F elements were perceived as shown on Fig. S2a–c. These elements possesses various charges that leads to the polymer’s different electrostatic interactions which can be correlated on the interaction of fluid on to the polymer surface [37]. Fourier transform infrared (FTIR) spectra confirmed the presence of PVDF’s two crystal phase as shown on Fig. 2e [38,39]. The characteristic peaks of α-phase at 762 and 1072 cm
1 were observed, a sudden reduction or disappearance of these peaks upon the increase on the ZnO content can be notice. Corresponding peaks of β-phase were clearly discerned at 773, 840, 975, 1276 and 1431 cm
1 on all the PVDF films, on the other hand 441, 481, 508 β-phase peaks appears after the inclusion of the ZnO on the PVDF which showcase

Fig. 1. Porous PVDF thin film fabricated from a ZnO-PVDF mixture with different ZnO mass fraction. ((Z0) 0%, (Z10) 10%, (Z20) 20%, and (ZnO) 30%).

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Fig. 2. Porous PVDF membrane (a) thickness, (b) pore diameter, (c)wax loading capacity, (d) contact angle of different ZnO concentration membrane at 25  C and 55  C temperature, (e) FTIR spectra of porous and non-porous PVDF thin film, (d) and its corresponding XRD reading.

its β-phase nurturing effect. The surface of ZnO crystals are dominated with Zn cations which makes the particle positively charged, on the other hand the surface that terminated with O anions exhibit negative charge. The appearance of the PVDF βphase can be ascribe to the interactions between the PVDF dipoles and surface charges of the ZnO particle. The intrinsic polarity of the ZnO particle might interact on either CF2 or CH2 groups which possesses negative and positive charges that initiated the nucleation of the β-phase [40,41]. Regarding the effective removal of ZnO and to support its influence on the crystalline structure formation of the porous membrane, X-ray diffraction analysis were discerned in Fig. 2f. The existence of β-phase in the generated porous membranes were confirmed through the presence of diffraction peaks located at 2Q of 20.2 which are indexed to (332) crystal planes, it was identified that Z30 possesses the highest β-phase peak concentration. A sudden decrease in the peak intensity can be observe upon decrease in ZnO concentration, this constitutes to the effectiveness

of the ZnO on yielding β-phase orientation. Moreover, complete removal of ZnO can be proved due to the absence of ZnO peaks in Z30 and Z20, this may be accounted on the interconnected matrix of ZnO on the higher concentration that makes every particle susceptible on the acid treatment. On the other hand, strong peaks ZnO on Z10 were identified at 2Q of 18.40 , 31.76 , 34.41, 36.24 , 47.67, 56.75 , 62.85 , 66.36 and 76.95 which are indexed to (100), (002), (101), (102), (110), (104), (112) and (202) crystal planes. Wax lubrication stability on the porous PVDF film To explore the lubrication stability of the PVDF porous substrate and its wax absorbing effectiveness, absorbance ability of different concentration membrane was observed. As projected in Fig. 2c, an incremental increase in the wax absorbance was observed in regards with the increase in the ZnO concentration which greatly support the porosity increment in relation with increase in ZnO

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amount. As previously discussed, as the ZnO concentration increases the porosity of the membrane increases, this is due to the higher pore volume that the ZnO particles occupies prior particle removal, which contributed on higher lubricant occupancy. In correspondence to the ZnO concentration impact on lubrication quantity and interfacial behaviour, contact angle in regards with the concentration was identified. There is no observable difference with the WIS film CA at 55  C which signifies the uniform wax distribution onto the surface of the porous PVDF membrane. On the other hand, minimal difference was observed onto the interfacial characteristics (CA) of the WIS film with different ZnO concentration at 55  C, this is due to the uneven wax distribution onto the surfaces of the porous PVDF film. In contrast, with the effect of the phase transition of wax from solid to liquid which is initiated by exposing the WIS films at Tm. The contact angle tends to be lower with lower concentration as shown on Fig. 2d and Fig. S3, this may be due to the wax lubrication quantity. For the lower ZnO concentration, the infused wax does not implement a uniform wax interface. The film prepared with lower concentration tend to have less porous architecture and could not hold enough wax for SLIPS application, corresponding on the space that the particle previously occupied. To confirm lubricant infusion stability, shear stability tests were done on the WIS samples with the aid of water stirring bath at 55  C as shown on Fig. S4a. Samples were exposed in continuous shear by immersing in the water bath stirred at 500 rpm. As illustrated in Fig. S4b, weight loss of the sample due to wax leaching were measured, all the samples showed a decrease in mass indicating the loss of the lubricating wax, leaching percentile were also provided to assess the wax leaching performance. Likewise, Z30 demonstrated the lease wax leaching due to porous structure that assisted the lubricant incorporation stability through capillary action and its better lubricant compatibility. In consideration on the optimum lubrication advantage, porous Z30 PVDF film was chosen as the representative sample for the corresponding tests and qualifications. Computational methodology was done to explore the compatibility of the lubricant and the porous substrate. Slippery surface was fabricated by infusing liquefied paraffin wax onto porous PVDF film, wherein wax act as a lubricating liquid at T > Tm condition. Moreover, liquid drops were suspended on the lubricated surface to determine if the incorporation of wax into the porous PVDF film satisfy the criteria of the material lubrication [24,25,42].

DE1 = R (g L2 cosu

L2 –

g

L1 cos

DE2 = R (g L2 cosu

L2


u

L1)


g

L1 L2 > 0

(1)

g

L1 cos

u

L1) +

g

L2


g

(2)

L1 > 0

where DE1 and DE2 designated as the parameter set up to maintain lubrication on the porous structure, g stands for surface tension of the interfaces, with specific subscript designation L1 (liquid drop) and L2 (lubricating wax), and u L1 and u L2 are the contact angles of the liquid drop and lubricant on the surface of the porous PVDF film. The factor of roughness is constituted as R, which is the surface area ratio of the porous film and a flat surface and can be calculated from the contact angle of the porous surface and the flat surface [24,25,42]. R¼

cosuL1 cosu

ð3Þ

where u L1 = 131.14 of the porous PVDF film, and u = 128.73 on the flat PVDF surface. In the above specification, an assumption that the lubricating liquid fully governed the structural surface features [15]. With this supposition given the porous architecture of the PVDF film holds

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the liquefied wax through capillary action and able to hold the wax even on solid state, this satisfy the criteria for its corresponding working condition [44]. Also, values for DE1 and DE2 were calculated with the corresponding measured contact angels [32]. The calculated values for DE1 and DE2 listed on Table S1 is greater than zero which constitutes that the liquid droplet suspend on top of the wax lubricant and did not have contact onto the film’s surface. Droplet mobility and temperature stimuli response performance of the fabricated WIS film The temperature response of the waxed infused porous PVDF surface rooted on the rheological properties of the infused lubricant, wax was chosen as a lubricant due to its phase reversibility property from solid to liquid when exposed in different temperature. Fundamentally, this mechanism is collectively regulating how the responsive surface system adjust from the driving force and convert it into a responsiveness and mobility [24,45]. Moreover, this structural design channels how the testing liquid travel in various scales and setting the surface is exposed, tailoring it for broader scope of dynamic functionality. The wax applied in this publication have a melting point of 55  C (Tm) which is solid state at atmospheric temperature and does not involve high energy consumption for phase transition in which correlated with heating. Illustrated on Scheme 1, the temperature response surface was produced by submerging the porous PVDF film to the wax melted at 80  C. Projected at Fig. 3a and b, the WIS film transitioned from opaque to a translucent film with a milky white color and upon exposure to Tm the film changes to optically transparent film and supported by transmittance spectra, the optical changes were observed to be reversible upon heating and cooling. To validate the stimuli responsiveness of the waxed WIS film, contact and sliding angles were scrutinized by applying of various testing liquids with ranges of surface tension and viscosity, their contact and sliding angle were investigated. Consideration on variance in the applied testing liquids relying on different parameters such as density, polarity, surface tension and viscosity were looked up. Test liquids composing of water, glycerol, ionic liquid and ethylene glycol were chosen to represent different liquid characteristics coming from broad parametric range to diversify and intercalate its potential application. Demonstrated on Table S2, 10 ml of test liquids were tested on the WIS at Tm, the contact angle decreases as the surface tension decrease as projected in Fig. 3f [46]. Interrelation of the sliding angle and testing liquids volume were studied, as projected in Fig. 3c it was observed that upon increase on the test liquid amount the sliding angle decreases [47]. The increase in the amount of testing liquid corresponds to the elevation on the droplet size that led to the circumstantial effect of the gravitational pull [48]. We first measure the droplet dynamics from 4 ml to 12 ml (incremented by 2 ml) droplets on the WIS at Tm to apprehend the droplet volume effects on the movement of the droplet. The larger droplets acquired droplet sliding at lower tilting angle, regardless of enforcing them to enough tilt as observed. It was also showed the feasibility of the mobility of the small volume droplet that can be viable for microfluidics utilization. Hence, it can be concluded that one of the significant assets that determine the mobility of a drop is its geometrical constraints [25]. Furthermore, experiment on the relationship of sliding angle and temperature was thoroughly inspected projected at Fig. 3d. The mobility behaviour of the droplets can be credited to the intrinsic property of the incorporating lubricant [17,47,49]. It was discerned that sliding angle decreases as the temperature increases due to phase and property transition of the infused lubricant, the drop slowly overcoming the pinning effect of the solidified wax as it transitions to its liquid state by increasing the

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Fig. 3. (a, b) Optical property transition at 25  C and 55  C temperature exposure with its relative transmittance spectra. (e) Images of microreactor application under acidic and basic conditions from 25  C to 55  C temperature using 5 ml test liquid with 25 sliding angle, Bromophenol blue protonation by hydrochloric acid solution and Thymol blue deprotonation by sodium hydroxide solution. Sliding angle response of testing liquids (a) at different volume drop amount (b) and temperature variation from 25  C to 55  C and its corresponding (f) Contact angle measurement.

temperature at its Tm. As the temperature increase the wax liquifies that lets the testing liquid slid off easily. The results displayed variation on sliding angles of different testing liquids on the same surface. Apparent mobility of glycerol droplet showcases a smaller sliding angle at Tm compared to water, ethylene glycol and ionic liquid droplets. This determine that the rolling motion presented onto the surface by the drops is not only dependent on contact angle and surface tension as observe in the difference of the sliding angle of glycerol and water that both demonstrate higher contact angle. Conferring to previous publications [50,51], the movement behaviour of the test liquid droplets can be correlated with the droplet viscosity, with an incremental growth in the viscosity value evidently reduce the occurrence of droplet slipping and intensify the influence of droplet rolling. Since glycerol tend to have a higher viscosity compared to the other test liquids, it can be perceived that glycerol droplet tend to roll rather than slip [51]. Discrepancy towards the sliding angle of the test liquids on the WIS were dependent on physical characteristics of the liquids parametric contribute on the different movement of the liquids on the designed surface [25,52–54]. These findings are viable for mobility trajectories on various utilization. It should also be noted that exposure of the film beyond lubricant melting temperature is not that great and but can still be utilize. The sliding switching reversibility of the film was also discerned above and below Tm, shown in Fig. S6a–d is the series of experiments performed at temperature range of 25 and 55  C. Reversible motion control of droplets on the film was comprehended by consecutively changing the temperature. The sliding angle of the testing liquid droplets traveling over the liquified lubricant interface is cited, the four types of testing liquid droplets slide at 55  C with different sliding angles, and all of them were pinned on the surface of the films at 25  C. The droplets seem to

follow the sliding response above Tm and upon heat removal the surface regain its original surface property and immediately return to its original state. In fact, this whole reversible “pinning” process film behaviour in turns out to be yet additional twist on the film’s capability to perform perfectly toward repetitive variation in operating temperature. It is observed in most cases of responsive surfaces where pinning is influenced by adjustment in the surface individuality, the droplet reversibility transitions from a state of solidified wax interface to a wet wax state. Obviously, the designed PVDF surface efficiently confine lubricant after five reversible cycles. To further demonstrate temperature driven motion of liquid droplet on WIS surfaces, a microreactor testing were done. As shown in Fig. 3e, aqueous solution of bromophenol blue and thymol blue was used to interact with droplets of aqueous solution of HCl and NaOH. Sample droplets (5 mL) placed simultaneously in the WIS surface at 25  C. At 55  C the droplet is starting to slide on downward direction and coalesced on the opposing droplet. The droplet undergone a chemical reaction and changed its color, the aqueous HCl become yellowish color after contact with bromophenol blue, provided with corresponding reaction mechanism. Likewise, the aqueous NaOH became blue after the contact with thymol blue. Thus, these temperature stimulus surfaces may be used to develop a new temperature controlled microreactor system. This temperature stimulated sliding mechanism is suitable to design interfacial reactions using related liquids. Anticorrosion performance of WIS film Anti-corrosion property of WIS film on Cu foil was evaluated through EIS technique. Assessment of the corrosion resistance of the prepared samples using EIS were all performed under 3.5%

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Fig. 4. Nyquist plots of bare, PVDF covered and WIS film coated Cu foil (a) immersed in 3.5% NaCl. Electrochemical impedance spectroscopy (EIS) measurement of bare, PVDF covered and WIS film coated Cu foil (b) phase of Bode plot and impedance and (e) immersed for varied time in 3.5% NaCl (0, 1 and 2 weeks). Potentiodynamic polarization plots of bare, PVDF covered and WIS film coated Cu foil (c) immersed in 3.5% NaCl and (f) immersed for varied time in 3.5% NaCl (0, 1 and 2 weeks). (d) Barrier resistance obtained from the calculated results.

NaCl solution. Comparison of corrosion protection behaviour of the WIS film and bare and PVDF coated film is demonstrated. The Nyquist plot were projected in Fig. 4a, it can be observed that the capacitive loops diameter of the WIS film covered Cu foil is larger compare to the PVDF film and bare Cu foil, suggesting the increase in charge transfer resistance that is associated to its anticorrosion effectiveness of the WIS film [55]. It can also be observe that the capacitive loops does not follow a semicircle configuration this can be accounted due to dispersing effect [56]. The wax loaded onto the WIS acts as an inhibitor that restricts the contact of the corrosive media onto the metal interface, the reduction of the electric resistance due to the presence of the wax onto the polymeric structure decrease the corrosion rate by inhibiting the diffusion rate of the corrosive media onto the metal surface [57]. Bodemodule and Bode-phase was shown in Fig. 4b. As perceived, Cu foil covered with WIS film, PVDF film and the bare Cu demonstrated a larger Z value in a low frequency which is linked to the wettability and barrier layer for better corrosion performance. In the case of WIS film the lubricated porous structure serves as a barrier layer inhibiting the penetration of the corrosive media onto underlayer substrate and promote corrosion shield. It was shown that WIS illustrated a wide and high phase angle which suggest that the aqueous corrosive media cannot penetrate the interface between the substrate and the WIS film easily. Based on previous works [55,58,59], electrochemical charges tend to transfer in through solution-film and film substrate interfaces. Hence, equivalent circuit shown in Fig. S7a–c was used to fit the EIS readings of the WIS film. Where Rs corresponds to the NaCl solution resistance, the resistance was represented as RWIS for WIS film and RPVDF for the pristine PVDF film, Rct means for the charge transfer resistance of the films and substrate interface, while Cdl stands for the double electrode layer capacitance. CPEf was used to substitute coating capacitance due to the dispersal of relaxation cycles ensuing from the various heterogeneities at the interacting surface [60,61]. The CPE can be expressed based on the equation below [33,62]. ZCPE = [Q0(jv)n]
1

(4)

where Q0 is respectively the proportionality factor which independent on the frequency, j is an imaginary value while v is the angular frequency (v = 2pf), n is a parameter that can be
1 for inductor and 1 for capacitor. While on the other hand, bare and

PVDF coated Cu follows an equivalent circuit shown in Fig. S7b and c. The resistance barrier layer approximately the Rct value was yielded from the fitting analysis. The Rbarrier of the bare Cu is 3.19  104 V cm2 while 4.28  104 V cm2 for PVDF coated Cu film and 7.88  104 V cm2 for the WIS film which is higher by 2–2.5 folds. The presented results above fits well with the Bode-module and Bode-phase plots. Evaluation of surface corrosion resistance was also evaluated electrochemical setup. Potensiodynamic polarization (Tafel plots) measurements were elucidated to estimate quantitatively the anticorrosion properties of the samples. The corrosion potential (Ecorr) and current density (icorr) were extracted from the plots through extrapolation method using below [31,60,63]. icorr ¼

ba bc

2:3Rp ðba þ bc Þ

ð5Þ

The icorr of the samples were calculated and presented on Fig. 4d. The bare and PVDF film coated Cu substrate configured a higher icorr compared to WIS that can be accounted for faster corrosion rate [64]. As demonstrated from the plots in Fig. 4c, anodic tafel slope (ba ) is higher than the cathodic tafel slope (bc ) which indicates that Ecorr slowly change with the incremental increase in the applied potential, this signifies that the coated and the bare surface are protected from hydrogen evolution reaction [35,62]. Compared with bare and PVDF film coated Cu substrate, WIS demonstrate lower Ecorr results which can be stipulated the suppression of corrosion reaction and decrease corrosion rate. This can be attributed to water repellence of wax impregnated into porous PVDF film. The result is also founded to be coincided with the EIS data that indicates the WIS anti-corrosion effectiveness [33]. To demonstrate the prolong performance of WIS film the coated samples were immersed into 3.5% NaCl solution for 1 and 2 weeks. Bode-module and Bode-phase plots were depicted in Fig. 4e, it can be observed that there is no drastic change in the Z values with respect to the time of immersion with NaCl solution. Meanwhile, a minor change in the intermediate frequency of the Bode-phase plots were detected as the immersion time increase. However, the yielded WIS film performance is still higher than the bare and PVDF film coated Cu that divulge the long-term corrosion protection of WIS film. The Tafel plots were also analysed

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G Model JIEC 4821 No. of Pages 9

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quantitatively to adequately illustrate the long-term corrosion resistance of WIS film. As demonstrated in Fig. 4f upon exposure of the samples under 3.5% NaCl solution for 1 to 2 weeks Ecorr tend to move towards the negative region, Ecorr of WIS are observed to slightly change owing to the water attack on the surface layer. This minimal change in Ecorr specifies that there is almost no change in the samples surface during the duration of the corrosion test. While the Icorr minimally shifts to a negative value as shown in Fig. 4d. Even though there’s changes in Icorr after the prolong immersion in NaCl solution the WIS film performance is still better than the Bare and PVDF coated Cu that suggest its long-term anticorrosion effectiveness [32,33]. Stability performance of WIS film With growing design sophistication of interfacial materials to adapt and respond to stimuli is always part of the ongoing functionalization and self-sustenance improvement [36,65]. To figure this adaptability ability of this material, we look once more to the scaffold design [66]. The film demonstrated an outstanding stability under several conditions. As represented, the hydrophobicity of the film surface is maintained, and its contact angle is sustained around 120 upon immersion in liquids with different kind of pH. It was exemplified that the film be used on harsh conditions, for example the film able to sustain its surface properties. In contrast, the WIS film proved its robust water shielding properties despite the prolong exposure into challenging environment, as shown through contact angles measurement as projected in Fig. S8a–c. Though slight variation will be observe on the contact angle of WIS upon prolong exposure onto the basic and acidic media that can be accounted for scaling moiety phenomena on the WIS surface [36,57]. In accordance to this WIS film also demonstrated self-healing ability, the robust wax infused scaffold was examined by abrading the surface with sandpaper. After such treatment, wax infused film loses its ability to shield liquid, as demonstrated by the changes in contact angle from 107 for the abraded surface to 120 to the healed surface, it can be observed that the film regains its surface property upon heating and cooling by regenerating the wax on the parts physically eroded with abrasion as shown in Fig. S9. As the wax infused porous structures become damaged, the damaged interface self-heals by inertly wicking adjacent lubricants to fill the localize surface defects [33,67]. Although the wax may originally cover the porous surface, the abrasion lessens the wax level to that of the exposed distended microstructures. The trapping of the lubricant films by the interconnected cavities also reduces further lubricant displacement thermal exposure, which can easily remove and expose the underlying nonlubricated areas. The ability of the porous film to confine a lubricant onto its surface was accounted with considerations on chemical compatibility between the scaffold and the lubricating liquid. The concept can be attributed in the versatility of the interfacial material by integrating and expanding its dynamic design to yield a new breed of LIS. Conclusion In summary inspired by “bottom-up approach” and by taking advantage of the properties of the compounding materials, we successfully generated a multi-functional film that has a temperature responsive surface and anti corrosion capability through introduction of responsive lubricant onto a porous structure. And exploring the contribution of interfacial compatibility with the lubricant absorption stability. Due to the rheological properties of the lubricant, sliding and pinning of different liquid is achieved by altering the temperature. The stimulated temperature response lead to alterations in the mobility of the droplets over the surface.

The smart control of this waxed infused film can be utilized on micro-reactors, biochips and biomedical system. With variation in the functionality that make the most of its dynamic structural capabilities yet simultaneously making it robust enough to be applies on other field sections such as anti-corrosion. Based on resistance and hydrophobic interaction, WIS multifunctional film offers an effective defense on aggressive environments, the film establishes a potential to manage effectively a long-term protection towards harsh environments. Declaration of interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgment This work was supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) and the Ministry of Trade, Industry & Energy (MOTIE) of the Republic of Korea (No. 20194010201750). Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.jiec.2019.10.015. References [1] E. Ueda, P.A. Levkin, Adv. Mater. 25 (9) (2013) 1234. [2] Y. Tian, B. Su, L. Jiang, Adv. Mater. 26 (40) (2014) 6872. [3] G.S. Watson, D.W. Green, L. Schwarzkopf, X. Li, B.W. Cribb, S. Myhra, J.A. Watson, Acta Biomater. 21 (2015) 109. [4] M. Gleiche, L.F. Chi, H. Fuchs, Lett. Nature 13 (403) (2000) 173–175. [5] P. Laboratories, Adv. Mater. 404 (03) (2000) 1999. [6] D. Xia, L.M. Johnson, G.P. López, Adv. Mater. 24 (10) (2012) 1287. [7] M.J. Hancock, K. Sekeroglu, M.C. Demirel, Adv. Funct. Mater. 22 (11) (2012) 2223. [8] A.M.A. Mohamed, A.M. Abdullah, N.A. Younan, Arab. J. Chem. 8 (6) (2015) 749. [9] T.-B. Nguyen, S. Park, Y. Jung, H. Lim, J. Ind. Eng. Chem. 69 (2019) 99. [10] B. Bhushan, Y.C. Jung, Prog. Mater. Sci. 56 (1) (2011) 100. [11] N. Vogel, R.A. Belisle, B. Hatton, T.-S. Wong, J. Aizenberg, Nat. Commun. 4 (1) (2013) 2176. [12] P. Zhang, F.Y. Lv, Energy 82 (2015) 1068. [13] H. Chen, P. Zhang, L. Zhang, H. Liu, Y. Jiang, D. Zhang, Z. Han, L. Jiang, Nature 532 (7597) (2016) 85. [14] H.F. Bohn, W. Federle, Proc. Natl. Acad. Sci. 101 (39) (2004) 14138. [15] T.-S. Wong, S.H. Kang, S.K.Y. Tang, E.J. Smythe, B.D. Hatton, A. Grinthal, J. Aizenberg, Nature 477 (7365) (2011) 443. [16] S. Sett, X. Yan, G. Barac, L.W. Bolton, N. Miljkovic, ACS Appl. Mater. Interfaces 9 (41) (2017) 36400. [17] A. Grinthal, J. Aizenberg, Chem. Mater. 26 (1) (2014) 698. [18] Y. Mao, P. Zhao, G. McConohy, H. Yang, Y. Tong, X. Wang, Adv. Energy Mater. 4 (7) (2014)1301624. [19] Z. Liu, H. Wang, E. Wang, X. Zhang, R. Yuan, Y. Zhu, Polymer 82 (2016) 105. [20] M.S. Sorayani Bafqi, R. Bagherzadeh, M. Latifi, J. Polym. Res. 22 (7) (2015) 130. [21] M. Nasir, H. Matsumoto, T. Danno, M. Minagawa, T. Irisawa, M. Shioya, A. Tanioka, J. Polym. Sci. B Polym. Phys. 44 (5) (2006) 779. [22] E. Fontananova, M.A. Bahattab, S.A. Aljlil, M. Alowairdy, G. Rinaldi, D. Vuono, J. B. Nagy, E. Drioli, G. Di Profio, RSC Adv. 5 (69) (2015) 56219. [23] B. Yao, C. Li, F. Yang, J. Sjöblom, Y. Zhang, J. Norrman, K. Paso, Z. Xiao, Fuel 166 (2016) 96. [24] X. Yao, J. Ju, S. Yang, J. Wang, L. Jiang, Adv. Mater. 26 (12) (2014) 1895. [25] B.L. Wang, L. Heng, L. Jiang, ACS Appl. Mater. Interfaces 10 (8) (2018) 7442. [26] P. Che, L. Heng, L. Jiang, Adv. Funct. Mater. 27 (22) (2017)1606199. [27] T. Guo, P. Che, L. Heng, L. Fan, L. Jiang, Adv. Mater. 28 (32) (2016) 6770. [28] X. Yao, Y. Hu, A. Grinthal, T.-S. Wong, L. Mahadevan, J. Aizenberg, Nat. Mater. 12 (6) (2013) 529. [29] G.H. Zhu, C. Zhang, C. Wang, N.S. Zacharia, Adv. Mater. Interfaces 3 (20) (2016) 1600515. [30] J. Li, L. Li, X. Du, W. Feng, A. Welle, O. Trapp, M. Grunze, M. Hirtz, P.A. Levkin, Nano Lett. 15 (1) (2015) 675. [31] Q. Li, Z. Guo, J. Colloid Interface Sci. 536 (2019) 507. [32] P. Wang, D. Zhang, Z. Lu, S. Sun, ACS Appl. Mater. Interfaces 8 (2) (2016) 1120. [33] T. Xiang, M. Zhang, H.R. Sadig, Z. Li, M. Zhang, C. Dong, L. Yang, W. Chan, C. Li, Chem. Eng. J. 345 (2018) 147.

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