Conductive hydrogels are a class of stretchable conductive materials that are important for various applications. However, water-based conductive hydrogels inevitably lose elasticity and conductivity at subzero temperatures, which severely limits their applications at low temperatures. Herein we report anti-freezing conductive organohydrogels by using an H O/ethylene glycol binary solvent as dispersion medium. Owing to the freezing tolerance of the binary solvent, our organohydrogels exhibit stable flexibility and strain-sensitivity in the temperature range from -55.0 to 44.6 °C. Meanwhile, the solvent molecules could form hydrogen bonds with polyvinyl alcohol (PVA) chains and induce the crystallization of PVA, greatly improving the mechanical strength of the organohydrogels. Furthermore, the non-covalent crosslinks endow the conductive organohydrogels with intriguing remoldability and self-healing capability, which are important for practical applications.

Various natural materials have hierarchical microscale and nanoscale structures that allow for directional water transport. Here we report an ultrafast water transport process in the surface of a Sarracenia trichome, whose transport velocity is about three orders of magnitude faster than those measured in cactus spine and spider silk. The high velocity of water transport is attributed to the unique hierarchical microchannel organization of the trichome. Two types of ribs with different height regularly distribute around the trichome cone, where two neighbouring high ribs form a large channel that contains 1-5 low ribs that define smaller base channels. This results in two successive but distinct modes of water transport. Initially, a rapid thin film of water is formed inside the base channels (Mode I), which is followed by ultrafast water sliding on top of that thin film (Mode II). This two-step ultrafast water transport mechanism is modelled and experimentally tested in bio-inspired microchannels, which demonstrates the potential of this hierarchal design for microfluidic applications.

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When a liquid film of colloidal solution consisting of particles of different sizes is dried on a substrate, the colloids often stratify, where smaller colloids are laid upon larger colloids. This phenomenon is counter intuitive because larger colloids which have smaller diffusion constant are expected to remain near the surface during the drying process, leaving the layer of larger colloids on top of smaller colloids. Here we show that the phenomenon is caused by the interaction between the colloids, and can be explained by the diffusion model which accounts for the interaction between the colloids. By studying the evolution equation both numerically and analytically, we derive the condition at which the stratified structures are obtained.Drying of a colloidal film is important in many places such as in printing [1], spreading and coating [2] and material science [3,4]. An important problem is how the structure of dried film is controlled by drying conditions. It is known that the spatial distribution of colloidal particles in the drying process is determined by two competing processes. One is the Brownian motion [5][6][7] which is characterized by the diffusion constant D, and the other is evaporation [4], characterized by the speed v ev at which the surface recedes. The competition between them can be quantified by the film formation Peclet number Pe = v ev h 0 /D [8], where h 0 is the initial thickness of the film. If Pe < 1, the concentration gradient created by evaporation is quickly flattened by diffusion, and the colloid concentration remains uniform. On the other hand, if Pe > 1, the concentration gradient increases, and the colloids accumulate near the top of the film.If there are two types of colloids of different size [9-12], the above consideration predicts that the larger colloids will accumulate near the free surface (large-on-top), because larger colloids have a smaller diffusion constant, therefore a larger Peclet number. Recently, however, the opposite phenomenon has been reported by Fortini and coworkers [13]. By simulation and experiments, they have shown that smaller colloids appear on top of larger colloids (small-on-top). They argued that this is due to the osmotic pressure of smaller colloids, but no quantitative theory has been given.In this Letter, we show that the phenomenon can be explained by the standard diffusion model [14] if the interaction between colloids are taken into account. We will use a simple hard sphere model, and show that the small-on-top structure is created by the cross-interaction between colloids of different sizes. The effect of crossinteraction on colloidal motion is not symmetric: it is much stronger on larger colloids than smaller colloids and * jjzhou@buaa.edu.cn † yjiang@buaa.edu.cn ‡ masao.doi@buaa.edu.cn pushes the larger colloids towards the bottom of the film. We will give a criterion when the small-on-top structure is created, and the corresponding experimental conditions, such as the drying rate, initial colloidal concentrations, and size ratio. Evolut...