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The active color-changing ability of many living species has inspired scientists to replicate the optical property into soft wet and tissue-like hydrogel materials. However, the color-changing processes of most reported examples are controlled by the traditional stimuli ( e.g. , pH, temperature, and ions), which may suffer from the residual chemical product accumulation, and have difficulty in achieving local control and integration into the commercial robots, especially when applied as biomimetic skins. Herein, inspired by the nervous (bioelectricity) control of skin color change in cephalopods, we present an electrically powered multicolor fluorescent hydrogel system with asymmetric configuration that couples thermoresponsive fluorescent hydrogel with stacked graphene assembly (SGA)-based conductive paper through luminous paint as the middle layer. Owing to the highly controllable electrical stimulus in terms of amplitude and duration, the Joule heat supplied by SGA film can be regulated locally and in real time, leading to precise and local emission color control at low voltage. It also avoids the addition of any chemicals. Furthermore, the electrically powered color-changing hydrogel system can be conveniently integrated into the commercial robots as biomimetic skins that help them achieve desirable camouflage, display, or alarming functions.

Novel thermosensitive nanocomposite (NC) hydrogels consisting of organic/inorganic networks are prepared via in situ free radical polymerization of 2-(2-methoxyethoxy) ethyl methacrylate (MEO2 MA) and oligo(ethylene glycol) methacrylate (OEGMA) in the presence of inorganic cross-linker clay in aqueous solution. The obtained clay/P(MEO2 MA-co-OEGMA) hydrogels exhibit double volume phase transition temperatures, an upper critical solution temperature (UCST), and a lower critical solution temperature (LCST), which can be controlled between 5 and 85 °C by varying the fraction of OEGMA units and the weight percentage of cross-linker clay. These new types of NC hydrogels with excellent reversible thermosensitivity are promising for temperature-sensitive applications such as smart optical switches., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A series of poly(sodium methacrylate) hydrogels, also called superabsorbents, having a theoretical degree of neutralization of 100 mol%, and degree of crosslinking varying from 0.6 to 20 mol%, are synthesized via conventional free radical polymerization. The networks are characterized in detail by inverse size‐exclusion chromatography and 1H‐NMR relaxometry in order to place particular emphasis on the investigation of the pore size distribution (PSD) and the chain mobility, respectively. The two previously mentioned parameters are compared to understand the correlation between the elastic chain mobilities and the average pore size of the hydrogel. From the resulting data, a new empirical equation is proposed, which is valid under the given experimental conditions and permits a rough estimation of the average PSD from the relaxation data. Thus, the equation permits to reduce the number of analytical techniques needed for the characterization of complex systems such as polymer networks. [ABSTRACT FROM AUTHOR]

Many living organisms have amazing control over their color, shape, and morphology for camouflage, communication, and even reproduction in response to interplay between environmental stimuli. Such interesting phenomena inspire scientists to develop smart soft actuators/robotics via integrating color‐changing functionality based on polymer films or elastomers. However, there has been no significant progress in synergistic color‐changing and shape‐morphing capabilities of life‐like material systems such as hydrogels. Herein, we reported a new class of bioinspired synergistic fluorescence‐color‐switchable polymeric hydrogel actuators based on supramolecular dynamic metal–ligand coordination. Artificial hydrogel apricot flowers and chameleons have been fabricated for the first time, in which simultaneous color‐changing and shape‐morphing behaviors are controlled by the subtle interplay between acidity/alkalinity, metal ions, and temperature. This work has made color‐changeable soft machines accessible and is expected to hold wide potential applications in biomimetic soft robotics, biological sensors, and camouflage. [ABSTRACT FROM AUTHOR]

Double thermosensitive clay/P(MEO2MA -co-POEGMA) nanocomposite (NC) hydrogels are prepared by in situ free radical polymerization of 2-(2-methoxyethoxy) ethyl methacrylate (MEO2MA) and oligo(ethylene glycol) methacrylate (OEGMA) in the presence of physical cross-linker clay. The temperature-induced phase transition behavior of NC hydrogels is investigated by turbidity, temperature dependent nuclear magnetic resonance, and variable temperature Fourier transform infrared spectroscopy. 2D infrared analysis is employed to study the sequential order of changes of all groups in NC hydrogels during the heating and cooling process. The obtained novel clay/P(MEO2MA -co-POEGMA) NC hydrogels exhibit an unusual thermally induced multistep aggregation process and successively undergo three consecutive microstructural changes: 'loose clay/polymer microaggregation ↔ homogeneous network structure ↔ dense clay/polymer macroaggregation.' Dynamic light scattering and transmission electron microscopy measurements show similar results of the NC nanogel at the same temperature regions, confirming the three consecutive microstructural changes. This new generation of thermosensitive hydrogel offers promising potential for applications as smart devices, biomedical materials, and drug carriers. [ABSTRACT FROM AUTHOR]

Sulfur and its functional groups are major players in an area of exciting research taking place in modern polymer and materials science, both in academia and industry. In fact, manifold sulfur‐based reactions that are both exceptionally versatile as well as tremendously useful have been implemented, and further utilized for the design and preparation of polymeric materials that lead to a plethora of applications ranging from medicine to optics and nanotechnology to separation science. Hence, within this review, an overview of strategies and developments used over the last 5 years to reinforce the importance of the sulfur functional group in modern polymer and materials science is presented. In particular, many important references in the primary literature of sulfur chemistry are referred to, including thiol–ene, thiol–yne, thiol–Michael addition, disulfide cross‐linking, and thiol–disulfide exchange, among others, by explaining and illustrating the important principles. Last but not least, the grand aim to underpin the importance of sulfur in modern polymer and materials science is achieved by presenting selected examples in diverse fields and postulating the respective potential for real‐world applications. Sulfur‐containing polymers receive great attention because of their unique properties and successful applications. This review summarizes recently reported breakthroughs in the synthesis and applications of various sulfur‐containing polymers, with the goal of stimulating further progress in this field. The outlook of this field is also taken into account. [ABSTRACT FROM AUTHOR]

Novel thermosensitive nanocomposite (NC) hydrogels have been synthesized by copolymerization of 2-(2-methoxyethoxy) ethyl methacrylate (MEO 2 MA), oligo(ethylene glycol) methacrylate (OEGMA), and using inorganic clay as cross-linker via in-situ free radical polymerization. The structure and morphology of clay/P(MEO 2 MA -co- OEGMA) NC hydrogels were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM), and the results indicated that the inorganic clay was uniformly dispersed in the NC hydrogels and obviously affected the network structure. Furthermore, physical properties such as equilibrium swelling/deswelling ratio, water retention, reversible thermosensitivity, and temperature dependence behaviors of NC hydrogels with different chemical compositions (molar ratio of comonomer, clay, and mass fraction of polymer) were investigated carefully. Moreover, the deswelling kinetics at specific temperature was studied, and the deswelling rates were well described with a first-order kinetics equation. The results indicated that the obtained NC hydrogels showed a controllable equilibrium swelling/deswelling behavior and possessed remarkable thermosensitivity. In addition, when the molar ratio of MEO 2 MA and OEGMA was 80 mol%: 20 mol%, the equilibrium swelling ratio of NC hydrogels with 5 wt% clay reached 1640%, which is four times higher than that of N,N ′ - methylenebisacrylamide cross-linked hydrogels (410%). Consequently, this novel clay/P(MEO 2 MA -co- OEGMA) NC hydrogel with interesting thermosensitive properties would be promising for potential applications, such as stimuli-responsive valve, drug delivery system, artificial muscle, and biosensor. [ABSTRACT FROM AUTHOR]