Matt W. England

Self-lubricating organogels (SLUGs) with exceptional syneresis-induced anti-sticking properties against viscous emulsions and ices

“Self-lubricating organogels (SLUGs)” are successfully prepared via a simple crosslinking reaction of polydimethylsiloxanes in the presence of several organic liquids. Due to the syneresis of organogels, a liquid layer is continuously formed on the topmost SLUG surfaces under appropriate conditions. The resulting surfaces show multi-liquid repellency, regenerative superhydrophobicity, and thermo-sensitive anti-icing properties.

Oil/water separation techniques: a review of recent progresses and future directions

Oil/water separation is a field of high significance as it has direct practical implications for resolving the problem of industrial oily wastewater and other oil/water pollution. Therefore, the development of functional materials for efficient treatment of oil-polluted water is imperative. In this feature article, we have reviewed the recent progress of oil/water separation technologies based on filtration and absorption methods using various materials that possess surface superwetting properties. In each section, we present in detail representative work and describe the concepts, employed materials, fabrication methods, and the effects of their wetting/dewetting behaviors on oil/water separation. Finally, the challenges and future research directions of this promising research field are briefly discussed.

Continuous, High-Speed, and Efficient Oil/Water Separation using Meshes with Antagonistic Wetting Properties

We report a novel oil/water separation device, allowing continuous, high-speed, and highly efficient purification of large volumes of oily water. This device uses a pair of hydrophilic/hydrophobic polymer-brush-functionalized stainless steel meshes, which have antagonistic wetting properties, i.e., superoleophobic and superhydrophobic properties, when submerged in the opposite liquid phase. This device can purify large volumes of n-hexadecane/water mixture (∼1000 L) in a continuous process rather than in batches, to high purities (∼99.9% mol/mol) at high flow rates (∼5 mL s(-1) cm(-2)), unlike the oil/water separation meshes reported so far.

Anti-Fogging/Self-Healing Properties of Clay-Containing Transparent Nanocomposite Thin Films

Highly transparent antifogging films were successfully prepared on various substrates, including glass slides, silicon, copper and PMMA, by spin-coating a mixture of polyvinylpyrrolidone and aminopropyl-functionalized, nanoscale clay platelets. The resulting films were superhydrophilic and showed more than 90% transmission of visible light, as well as excellent antifogging and self-healing properties.

Polymer Brush Surfaces Showing Superhydrophobicity and Air-Bubble Repellency in a Variety of Organic Liquids

Silicon (Si) substrates were modified with polyalkyl methacrylate brushes having different alkyl chain lengths (C(n), where n = 1, 4, 8, and 18) using ARGET-ATRP at ambient temperature without purging the reaction solution of oxygen. The dynamic hydrophobicity of these polymer brush-covered Si surfaces when submerged in a variety of organic solvents (1-butanol, dichloromethane, toluene, n-hexane) depended markedly on the alkyl chain length and to a lesser extent polymer solubility. Long-chain poly(stearyl methacrylate) brushes (C(n) = 18) submerged in toluene showed excellent water-repellant properties, having large advancing/receding contact angles (CAs) of 169°/168° with negligible CA hysteresis (1°). Whereas polymer brushes with short alkyl-chain (C(n) ≤ 4) had significantly worse water drop mobility because of small CAs (as low as 125°/55°) and large CA hysteresis (up to 70°). However, such poor dynamic dewetting behavior of these surfaces was found to significantly improve when water drops impacted onto the surfaces at moderate velocities. Under these conditions, all brush surfaces were able to expel water drops from their surface. In addition, our brush surfaces were also highly repellant toward air bubbles under all conditions, irrespective of C(n) or polymer solubility. These excellent surface properties were found to be vastly superior to the performance of conventional perfluoroalkylsilane-derived surfaces.

Surface roughness rather than surface chemistry essentially affects insect adhesion

Summary The attachment ability of ladybird beetles Coccinella septempunctata was systematically investigated on eight types of surface, each with different chemical and topographical properties. The results of traction force tests clearly demonstrated that chemical surface properties, such as static/dynamic de-wettability of water and oil caused by specific chemical compositions, had no significant effect on the attachment of the beetles. Surface roughness was found to be the dominant factor, strongly affecting the attachment ability of the beetles.

Self-Healing Superhydrophobic Materials Showing Quick Damage Recovery and Long-Term Durability

Superhydrophobic coatings/materials are important for a wide variety of applications, but the majority of these man-made coatings/materials still suffer from poor durability because of their lack of self-healing ability. Here, we report novel superhydrophobic materials which can quickly self-heal from various severe types of damage. In this study, we used poly(dimethylsiloxane) (PDMS) infused with two liquids: trichloropropylsilane, which reacts with ambient moisture to self-assemble into grass-like microfibers (named silicone micro/nanograss) on the surfaces and low-viscosity silicone oil (SO), which remains within the PDMS matrices and acts as a self-healing agent. Because of the silicone micro/nanograss structures on the PDMS surfaces and the effective preserve/protection system of a large quantity of SO within the PDMS matrices, our superhydrophobic materials showed quick superhydrophobic recovery under ambient conditions (within 1-2 h) even after exposure to plasma (24 h), boiling water, chemicals, and outside environments. Such an ability is superior to the best self-healing superhydrophobic coatings/materials reported so far.

Transparent Gel Composite Films with Multiple Functionalities: Long-lasting Anti-fogging, Underwater Superoleophobicity and Anti-bacterial Activity

Transparent gel-based composite films with multiple functionalities, showing long-lasting anti-fogging properties, underwater superoleophobicity, and anti-bacterial activity were successfully prepared from polyvinylpyrrolidone (PVP) and aminopropyl-functionalized clay (AMP-clay). Due to the addition of glutaraldehyde (GA, cross-linker) into the PVP matrices, and AMP-functionalities to the substrate surfaces, both the adhesion properties in water and durability of the anti-fogging properties were significantly improved. In addition, this durability was also found to be markedly improved by increasing the film thickness via deposition of several PVP/AMP/GA layers, while still retaining excellent transparency.

Polyurethane-Based Ionogels Exhibiting Durable Thermoresponsive Optical Behavior Under High-Temperature Conditions

Polyurethane (PU)-based transparent and flexible ionogels, showing unusual thermo-responsive optical properties, were successfully prepared by mixing PU-precursor and a hydrophobic ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMIM-TFSI). Although the initial ionogels were transparent at room temperature, significant increases in opacity were observed with increasing temperature up to 120°C, because of macroscopic phase separation of the PU-matrix and hydrophobic EMIM-TFSI. In addition, the optical transition temperature could be arbitrarily controlled simply by varying the mixing ratio of EMIM-TFSI within the PU-matrix. As confirmed by UV-Vis spectra acquired at different temperatures, this thermo-responsive optical behavior was found to be reversible, repeatable and durable even after 30 cycles of a thermal-stress testing between 30 and 100°C.

Roughness Versus Chemistry: Effect of Different Surface Properties on Insect Adhesion

In order to study the effect of different surface properties on the attachment ability of seven-spotted ladybird beetles Coccinella septempunctata, traction forces of both male and female beetles were systematically measured on eight types of surface, each with different chemical and topographical properties. Three of these surfaces were smooth with different surface wettabilities, including two types of hydrophobic monolayers, with alkyl- and perfluoroalkyl-terminated functional groups. The third smooth surface was a hydrophobic/oleophilic alkylsilane-derived hybrid film, showing low contact angle hysteresis for water and n-hexadecane. In addition, we also tested three rough surfaces with different roughness values and different wettabilities. Smooth, hydrophilic silicon wafers (Si) and glass surfaces were used as two reference surfaces. The results of traction force tests clearly demonstrated that chemical surface properties, such as static/dynamic dewettability of water and oil caused by specific chemical compositions, had a certain effect on the beetle attachment: hydrophobic and oleophobic substrates tend to reduce the attachment forces. Surface roughness was found to be the dominant factor, strongly affecting the attachment ability of the beetles up to complete diminishing of attachment.