Fabrication of multifunctional wax infused porous PVDF film with switchable temperature response surface and anti corrosion property
Graphical abstract
Introduction
Scientific and technological advancement towards the development of interfacial surfaces offers great opportunities in various fields [1], [2], [3]. And due to its domination on various applications, such as self-cleaning coatings [4], [5], [6], [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 ‘nature-inspired 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 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], [14], [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 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, γ, and δ), 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 stimulus-responsive materials fabricated to respond onto mechanical, electrical, chemical, strain, light, temperature and other types of stimuli [24], [26], [27], [28], [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], [35], [36].
Section snippets
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
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 Fourier-transform infrared (FTIR) spectrum (Thermo Scientific, Nicolet iS5), with a scanning window value of 32 in the
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, γ, and δ), relying on the preparation conditions. Normally the β-phase crystallite is attained
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
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).
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