Nanosheet-assembled tungsten oxide microspheres have been synthesized using rapid sonochemistry followed by thermal treatment. Transient observation of controllable synthesis reveals that the morphological evolution of the product is highly dependent on the ultrasonication time. An assembly mechanism based on oriented attachment and reconstruction is proposed for the sonochemical formation of the nanosheet-assembled microspheres. The obtained samples possess intrinsic nonstoichiometry and a hierarchically porous nano/microstructure, which is beneficial for their utilization in sensing materials and for fast diffusion of gas molecules. The maximum response of the tungsten oxide hierarchical microspheres is 3 times higher than that of commercial nanoparticles for NO 2 gas. The gas adsorption-desorption kinetics during the sensing process were mathematically simulated by a derivative method. The first-principles calculation reveals that the NO 2 molecule is most likely adsorbed at the terminal O 1c site of tungsten oxide, leading to the introduction of new surface states, which are responsible for the intrinsic NO 2 -sensing properties.

No abstract

No abstract

No abstract

A series of mesogen-jacketed liquid crystalline polymers, poly{2,5-bis[(4-butoxyphenyl)oxycarbonyl]-styrenes} (PBPCS), with a wide range of molecular weights (M n ) 1.24 × 10 4 -35.6 × 10 4 ) and narrow molecular weight distributions (M w /M n e 1.18) have been synthesized by atom transfer radical polymerization. The resulting polymers have been investigated by a combination of techniques including differential scanning calorimetry, polarized optical microscopy, and X-ray scattering. The samples with M n e 2.42 × 10 4 are isotropic. The samples with M n g 3.36 × 10 4 display a thermodynamically stable isotropic phase at lower temperature and a liquid crystalline (LC) phase at higher temperature. The phase behavior shows a phenomenon quite similar to the reentrant isotropic phase. These transitions are correlated with the rheological properties measured as a function of temperature. The rheological behavior of the polymer in the isotropic phase and in the LC phase has been studied as well. On the basis of these experimental observations, a generalized phase diagram is constructed for the polymers showing the influence of the molecular weight on the phase transition temperature. It is illustrated that LC phase is formed through a global change of the whole molecule from the coiled to extended chain conformation accompanied by an increase of the entropy. Higher entropy originating from the free mobilities of bulky side chains in LC phase has been proposed to be an important factor to stabilize the LC phase.