Molecular-Structure-Induced Under-Liquid Dual Superlyophobic Surfaces

Abstract

Surfaces with under-water superoleophobicity or under-oil superhydrophobicity have attractive features due to their widespread applications. However, it is difficult to achieve under-liquid dual superlyophobic surfaces, that is, under-oil superhydrophobicity and under-water superoleophobicity coexistence, due to the thermodynamic contradiction. Herein, we report an approach to obtain the under-liquid dual superlyophobic surface through conformational transitions of surface self-assembled molecules. Preferential exposure of either hydrophobic or hydrophilic moieties of the hydroxythiol (HS(CH 2 ) n OH, where n is the number of methylene groups) self-assembled monolayers to the surrounding solvent (water or oil) can be used to manipulate macroscopic wettability. In water, the surfaces modified with different hydroxythiols exhibit under-water superoleophobicity because of the exposure of hydroxyl groups. In contrast, surface wettability to water is affected by molecular orientation in oil, and the surface transits from under-oil superhydrophilicity to superhydrophobicity when n ≥ 4. This surface design can amplify the molecular-level conformational transition to the change of macroscopic surface wettability. Furthermore, on-demand oil/water separation relying on the under-liquid dual superlyophobicity is successfully demonstrated. This work may be useful in developing the materials with opposite superwettability.

Multifunctional Switchable Nanocoated Membranes for Efficient Integrated Purification of Oil/Water Emulsions

“…23−26 In addition, the existing of both hydrophilic and oleophobic groups is beneficial to the construction of under-liquid dual lyophobic surface. 27 Thus, ZIF-8 was selected to explore oil/ water separation after careful comparison mainly because that ZIF-8 possesses good water stability and both hydrophilic and oleophobic groups. 26 Herein, we report a successful in situ growth of high-quality ZIF-8 nanorods on PPVDF surfaces without a specific requirement toward the substrate material and its application in rapid filtration for highly emulsified oily wastewater.…”

“…Semiconductor particles modified membranes are potential composite materials with antifouling ability and exhibit good mechanical strength and complete/nondestructive reclamation performance. , However, their decontamination efficiency and retention rate of soluble organics are far from satisfactory, especially after being exposed to highly complex emulsified emulsions. Alternatively, metal–organic frameworks (MOFs)-based membranes have exhibited capacity to solve the above problems. − In addition, the existing of both hydrophilic and oleophobic groups is beneficial to the construction of under-liquid dual lyophobic surface . Thus, ZIF-8 was selected to explore oil/water separation after careful comparison mainly because that ZIF-8 possesses good water stability and both hydrophilic and oleophobic groups …”

Formulating Multiphase Medium Anti-wetting States in an Air–Water–Oil System: Engineering Defects for Interface Chemical Evolutions

“…Inspired by the microstructures and anti-wetting behaviors of fish scales, Namib desert beetle, and lotus leaf, the mechanism of the anti-wetting evolution was illustrated. The membrane with micro–nanoscales architecture can capture air, water, and oil on the interface to prevent the spontaneous transition of liquid from Cassie to Wenzel state. , The membrane maintains its superoleophilicity in air during the whole period (Figure S17). Therefore, the micro-/nanostructures are always wrapped by an oil layer to maintain the constant under oil superhydrophobicity.…”

A Universal Strategy for the Preparation of Dual Superlyophobic Surfaces in Oil–Water Systems

“…Inspired by nature’s fish scale and clam shell, − the interface material with underwater superoleophobicity (UWSOB) and underoil superhydrophobicity (UOSHB) has captured tremendous attention owning to its potential applications in self-cleaning, antifogging, nonloss liquid transfer, drag reduction, microfluidics, oil–water separation, and so forth. − Studying the interaction of the material surface in water or oil becomes thus of significance for understanding complex multiphase fluids, which in turn enhances our ability to control and utilize surface wetting performance . In a given oil–water–solid system, the oil contact angle (OCA) under water (θ o/w * ) and the water contact angle (WCA) under oil (θ w/o * ) can exhibit a complementary relationship according to Young’s equation . , In other words, an underwater oleophobic surface (90 o < θ o/w * < 150 o ) is usually hydrophilic under oil (θ w/o * < 90 o ) with a lower intrinsic WCA, whereas an underoil hydrophobic surface (90 o < θ w/o * < 150 o ) is oleophilic under water (90 o < θ o/w * ) with a higher intrinsic WCA . From the perspective of thermodynamics, these two extreme states are not favorable phenomena for a constant surface. ,, Therefore, it is generally accepted that the two wetting states are contradictory and cannot occur on the same solid surface.…”