Mechanical and thermal properties of perfluoroalkyl ethyl methacrylate–methyl methacrylate statistical copolymers synthesized in supercritical carbon dioxide

Pinning Forces on the Omniphobic Dry, Liquid-Infused, and Liquid-Attached Surfaces

Omniphobic coatings effectively repelling water, oils, and other liquids are of great interest and have a broad number of applications including self-cleaning, anti-icing surfaces, biofouling protection, selective filtration, etc. To create such coatings, one should minimize the pinning force that resists droplet motion and causes contact angle hysteresis. The minimization of the free surface energy by means of the chemical modification of the solid surface is not enough to obtain a nonsticky slippery omniphobic surface. One should minimize the contact between the solid and the droplet. Besides coating the surface with flat polymer films, among the major approaches to create omniphobic coatings, one can reveal "lotus effect" textured coatings, slippery liquid-infused porous surfaces (SLIPS), and slippery omniphobic covalently attached liquid (SOCAL) coatings. It is possible to turn one surface type into other by texturizing, impregnating with liquids, or grafting flexible liquid-like polymer chains. There are a number of models describing the pinning force on surfaces, but the transitions between states with different wetting regimes remain poorly understood. At the same time, such studies can significantly broaden existing ideas about the physics of wetting, help to design coatings, and also contribute to the development of generalized models of the pinning force. Here we review the existing pinning force (contact angle hysteresis) models on various omniphobic substrates. Also, we discuss the current studies of the pinning force in the transitions between different wetting regimes.

An experimental and theoretical investigation into the self-assembly of a chemically modified high-χ coil-rod diblock copolymer

A precursor diblock copolymer with a silicon backbone, polystyrene-block-poly(methylvinylsiloxane), was synthesized, and 1H,1H,2H,2H-perfluorodecanethiol was quantitatively introduced into the backbone via a thiol-ene reaction to yield a novel coil-rod diblock copolymer, poly(styrene-block-poly(2-((3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl)thio)ethyl)methylsiloxane). The ultra-hydrophobicity of the introduced perfluoroalkyl side chain enhanced the segregation between counter-blocks and significantly increased the χ value, which is essential for minimizing the size of self-assembled domains for lithographic applications. Thus, self-assembled domains with a minimal spacing of approximately 10 nm were formed. A hexagonally packed array with significant anisotropy was observed in the self-assembled morphology by small-angle X-ray scattering and transmission electron microscopy. Such an array was precisely reproduced by modified self-consistent field theory (SCFT) calculation developed for the coil-rod structure. Furthermore, the phase diagram was estimated, and the morphological dependence on the relative scale of the rod unit was investigated by SCFT prediction.

Preparation of fluoropolymer with gem-bis-fluoroalkylated side-chain and its application on cotton fabric finishing

In this study, three types of fluorinated polyacrylates (PBFB, PBFS, and PMFA) were synthesized by 4-gem-bis(2,2,3,3,4,4,5,5,5-nonafluoropentyl)-1-butene, 4-gem-bis(2,2,3,3,4,4,5,5,5-nonafluoropentyl)-methine-1-styrene, and 3,3,4,4,5,5,6,6,6-nonafluorohexyl acrylate, respectively, as monomers via emulsion polymerization. Particle size, particle size distribution, and zeta potential were tested to assess the emulsion stability. Afterwards, the latexes were coated onto fabrics to obtain gem-bis(fluoroalkyl)-cotton. The surface properties of the treated cotton fabrics were analyzed by X-ray photoelectron spectroscopy and water contact angle. It was found that, when controlling the fluorine content level to be similar, the water contact angles of gem-bis(fluoroalkyl)-cottons were 127° ± 0.5° and 134.9° ± 0.7°, respectively, which were both higher than that of mono-fluoroalkyl-cotton (PMFA-cotton of 125.2° ± 0.2°). This showed that gem-bis-fluoroalkyl groups could provide better hydrophobic performance than the mono-fluoroalkyl group, especially when the rigid benzene was used as a side-chain bridged group.