Switchable and Reversible Superhydrophobic Surfaces: Part Two

Abstract

In this book chapter, most of the methods used in the literature to prepare switchable and reversible superhydrophobic surfaces are described. Inspired by Nature, it is possible to induce the Cassie-Baxter-Wenzel transition using different external stimuli such as light, temperature, pH, ion exchange, voltage, magnetic field, mechanic stress, plasma, ultrasonication, solvent, gas or guest. Such properties are extremely important for various applications but especially for controllable oil/water separation membranes, oil-absorbing materials, and water harvesting systems.Keywords: superhydrophobic, reversible, switchable, bioinspiration, biomimetism Reversible superhydrophobic surfaces: Part twoThis section provides continuation of the description of the stimuli used in the literature to induce reversible changes in surface wettability. Ion exchangeSince 2004, the researchers have shown that the presence of charged species such as quaternary ammonium groups are sensitive to ion exchange and lead to different surface wettabilities. In 2004, Choi et al. prepared self-assembled monolayers (SAM) with imidazolium groups on smooth Au and Si/SiO 2 substrates [1][2][3]. They studied the effect of a series of anions as shown in Figure 1 and In order to elaborate reversible superhydrophobic properties by ion exchange, gold micro and nanostructured substrates were performed by electroless etching process by immersing silicon substrates in aqueous solution of HAuCl 4 and HF (Figure 2). The surface was then modified by SAM using a thiol terminated by a quaternary ammonium. Then, the surface wettability could be reversely changed from superhydrophilic to superhydrophobic after [20]. Here, the presence of TSPM (sol-gel precursor) was used not only to form a polymer network via intramolecular interactions but also to anchor substrates (Figure 3). The membranes could reversely change from superhydrophobic/highly oleophobic to superhydrophilic/superoleophobic after exchanging Cl − ions by heptadecafluorooctanesulfonic acid (C 8 F 17 SO 3 − or HPS − ) ions. Moreover, the membranes were also highly efficient filter medium for removing multiple contaminants such as SO 2 form waster gas streams. A nother strategy was to deposit polyelectrolyte multilayers poly(diallyldimethylammonium chloride (PDDA) and poly(sodium 4-styrenesulfonate) (PSS) on gold micro and nanostructured substrates [21]. The authors studied the influence of the exchanged ions and the highest properties were obtained by exchanging Cl − (θ w < 5°) ions by PFO − (θ w = 164°). The authors also deposited polyelectrolyte multilayers on micro and nanostructured aluminum substrates obtained by etching in HCl and immersion in boiling water [22,23]. Using PFO − ions, the substrates were superhydrophobic and superoleophobic. When the substrates were immersed in seawater, the PFO − ions were exchanged by hydrophilic Cl − or SO 4 2− making the substrates underwater superoleophobic. Magnetic fieldEnvironment protection against oil leakage during oil tankers sinking is ...