Inspired by the water self-circulation mechanism that contributes to the motion of Mimosa leafs, a hydrogel actuator with a reverse thermal responsive bilayer structure was prepared, which can generate motions in water, oil and even in open-air environment.

Static light scattering measurements performed on poly(N-isopropylacrylamide) hydrogels having a polymer volume fraction around 0.05−0.09 reveal that spatial inhomogeneities grow stronger with rising preparation temperature of the gels, increasing cross-linker concentration, and decreasing monomer concentration. Quantitative analysis of the angular dependence of the excess scattering intensity via the Debye−Bueche method results in correlation lengths of several 10 nm. Relative mean-square concentration fluctuations on this length scale are around 15−35% depending on preparation conditions. The cross-linking efficiency as determined by shear modulus measurements declines when the degree of inhomogeneity is enhanced. Comparison of the experimental results with Panyukov−Rabin (PR) theory indicates that the general trends are well predicted and that thermal concentration fluctuations can be calculated almost quantitatively. However, the theory significantly underestimates the static spatial concentration fluctuations. This discrepancy may be a consequence of preparing the gels by cross-linking polymerization, which leads to much stronger heterogeneity than presumed in PR theory.

An electrically tunable negative permeability metamaterial consisting of a periodic array of split ring resonators infiltrated with nematic liquid crystals is demonstrated. It shows that the transmitted resonance dip of the metamaterial can be continuously and reversibly adjusted by an applied electric field, and the maximum shift is about 210MHz with respect to the resonance frequency around 11.08GHz. Numerical simulation shows that the permeability is negative near the resonance frequency, and the frequency range with negative permeability can be dynamically adjusted and widened by about 200MHz by the electric field. It provides a convenient means to design adaptive metamaterials.

Static light scattering measurements reveal two levels of organization, i.e., two static correlation lengths, in poly(N-isopropylacrylamide)/clay nanocomposite hydrogels prepared by polymerizing the monomer in an aqueous suspension of uniformly dispersed exfoliated clay particles. One characteristic correlation length is in the range of 200-250 nm irrespective of the preparation conditions. It is assumed to arise from a kinetically controlled rearrangement of the clay particles during the formation of the gels. The other correlation length of several tens of nanometers is in the same order of magnitude as that observed in chemically cross-linked gels and shows a similar dependence on the preparation conditions. The shear modulus of the gels rises with increasing the clay concentration and the monomer concentration. The results infer that clay particles act as multifunctional cross-links with an average effective functionality around 50. Measurements of the equilibrium swelling ratio are in agreement with this view.

The micelles of a poly(ε-caprolactone)-b-poly(ethylene oxide) block copolymer (PCL 59 -b-PEO 113 ) in different mixed solvents were held at 53 °C for 5 min, and seed solutions with different micellar morphologies and amounts of micellar semicrystalline seeds were prepared. The crystallinity of these seed micelles was identified by high-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED). It is found that mostly amorphous spherical micelles are formed by heating micellar solutions in H 2 O/THF (5/1 v/v) and H 2 O/dioxane (5/1 v/v) mixed solvents, a mixture of amorphous spherical micelles and short semicrystalline cylindrical micelles is yielded in H 2 O/DMF (5/1 v/v), whereas mostly short semicrystalline cylindrical micelles are obtained in H 2 O/DMSO (5/1 v/v) mixed solvent. The seed solutions were placed at 4 °C for micellar growth. Transmission electron microscope (TEM) shows that micellar growth driven by epitaxial crystallization of core-forming PCL chains takes place and the length of grown cylindrical micelles increases with time. Two growth modes are observed. One is the growth of unimers (or amorphous spherical micelles) on the active ends of semicrystalline cylindrical micelles in micellar solution in H 2 O/DMF (5/1 v/v) at the initial growth period. The other is the growth by end-to-end coupling of cylindrical micelles in H 2 O/DMSO (5/1 v/v). The kinetics of micellar growth is strongly dependent on the growth mechanism. The growth of the cylindrical micelles in the H 2 O/DMF (5/1 v/v) solution is much faster than that in the H 2 O/DMSO (5/1 v/v) solution. On long time scale, micellar growth by end-to-end coupling of semicrystalline cylindrical micelles occurs with slow rate in both H 2 O/DMF (5/1 v/v) and H 2 O/DMSO (5/1 v/v) solutions, and the growth rate in H 2 O/DMF (5/1 v/v) solution is even slower than that in H 2 O/DMSO (5/1 v/v).