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Interest in the design and development of artificial molecular muscles has inspired scientists to pursue new stimuli-responsive systems capable of exhibiting a physical and mechanical change in a material in response to one or more external environmental cues. Over the past few decades, many different types of stimuli have been investigated as a means to actuate materials. In particular, materials that respond to reduction and oxidation of their constituent molecular components have shown great promise on account of their ability to be activated either chemically or electrochemically. Here, we introduce a novel redox-responsive mechanism of actuation in hydrogels by describing a systematic investigation into the radical-based self-assembly of a series of unimolecular viologen-based oligomeric links, present at only 5 mol % of the polymer linkers in a three-dimensional network. The actuation process results in an overall reversible contraction of a family of hydrogels, down to 35% of their original volume in the first 25 min and ultimately to 9% after a few hours, even while remaining submerged in water. The mechanism of contraction starts with a decrease in electrostatic repulsion upon chemical reduction, leading to a loss of counterions and intramolecular self-assembly of the main-chain viologen subunits. The overall mode of actuation takes place relatively quickly in comparison to hydrogels of similar size, and the rate of contraction is accelerated as higher molecular weight oligoviologen links are implemented. The contraction process ultimately leads to a 2-fold increase in elasticity of the material, and upon exposure to oxygen and water, the hydrogels quickly oxidize and regain their original size and mechanical properties, thus resulting in a reversible actuation process that is capable of lifting objects which are 5–6 times heavier than the contracted hydrogel itself.

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MXenes exhibit great promise for energy storage. Fluorine-based reagents have always been the mainstream of MXenes preparation. However, the high toxicity of fluorine-containing reagents is the bottleneck restricting the development and application of MXene. Furthermore, layered MXenes are easily stacked, reflecting unsatisfactory performance of lithium ion batteries. Considering the shortcomings of the fluorine-containing reagent etching MAX, it has aroused great research interest in exploring the morphology and fluorine-free synthetic method. Here, Ti 3 C 2 with a unique hierarchical porous structure (P-Ti 3 C 2 ) was first prepared by a fluorine-free chemical-combined ball-milling method. The as-produced P-Ti 3 C 2 shows a significantly increased specific surface area, which is 8 times higher than that of HF-Ti 3 C 2 obtained from traditional HF treatment. Benefitting from the porous structures as well as fluorine-free terminal groups, P-Ti 3 C 2 exhibits excellent electrochemical performances, for example, high reversible capacity of 310 mAh g −1 at a current density of 100 mA g −1 , better than that of HF-Ti 3 C 2 . Especially, after cycling 3000 cycles at a high current density of 1 A g −1 , a reversible capacity of 97 mA h g −1 could be steadily maintained. Therefore, this simple strategy could be extended as a universal approach for preparing various fluorine-free and porous MXenes with potential performance.

A series of copoly(aryl ether sulfone)s containing double-decker-shaped silsesquioxane (DDSQ) in the main chain was prepared. Toward this end, a novel diphenol polyhedral oligomeric silsesquioxane macromer was synthesized by hydrosilylation between 3,13-dihydro octaphenyl double-decker silsesquioxane (denoted dihydro DDSQ) and eugenol. The poly(aryl ether sulfone)s were synthesized from diphenol DDSQ, bisphenol A (BPA), and 4-fluorophenyl sulfone using a onestep high-temperature solution method. By adjusting the ratio of diphenol DDSQ to BPA, copolymers with variable DDSQ content in the main chains were obtained. With increased DDSQ content in the main chain, the glass transition temperature decreased based on differential scanning calorimetry, and anti-degradation was enhanced based on thermogravimetric analysis. Moreover, the dielectric constant j of pure polymer (3.19 at 1 MHz) initially increased to 4.04 (DDSQ molar ratio 5 10%), and then decreased to 2.68 at 1 MHz (DDSQ molar ratio 5 100%). Crystallization behavior, solubility, and surface hydrophobicity were also investigated. V C 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 780-788