A novel azobenzene-siloxane hybrid material displaying photoinduced macroscopic motions has been prepared by one-step organosilane self-assembly. Two types of alkoxysilane precursors with either pendant or bridging azobenzene groups were synthesized via thiol-ene click reactions. Hybrid films with well-ordered lamellar structures were obtained by hydrolysis and polycondensation of these precursors. The film with solely pendant azobenzene groups showed reversible and rapid d-spacing variation upon UV-vis irradiation, which was induced by the trans-cis isomerization of azobenzene moieties. The flexible, free-standing film obtained by co-condensation of two types of precursors showed reversible bending-unbending motions upon UV-vis irradiation. The partial cross-linking between the siloxane layers by bridging azobenzene groups was crucial for photoinduced distortion of the film. This film possesses high elastic modulus, good thermal stability, and shows large amplitude of photoinduced bending-unbending over a wide temperature range. This is the first report on photoinduced macroscopic motions of azobenzene-containing siloxane-based materials. These materials possess great potential for applications in smart devices and energy conversion systems.

ABSTRACT:The present study is aimed at investigating the molecular structure, crystallinity, and morphology of polyethylene (PE) and polypropylene (PP) blends by using Raman mapping, scanning electron microscopy (SEM), wide-angle X-ray diffraction (WAXD), and differential scanning calorimetry (DSC). In this study, three kinds of PEs, high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), and metallocene polyethylene (MEPE) were used. MEPE is one of the LLDPEs but its density is very low and its melt flow index (MFI) is very high. Blends of each PE and PP with a PP content ranging from 20 to 80 wt % with an increment of 20 wt % were prepared. Raman mapping images and SEM images show that the 80/20 blends of HDPE/PP and LLDPE/PP have similar dispersibility behavior and that only the 80/20 blend of MEPE/PP shows a different behavior in this respect. For the 20/80 blends, the differences are not so large. For the Raman mapping, the intensity ratio of the two bands at 1128 and 974 cm À1 was used. The former is due to a symmetric C-C stretching mode of all-trans -(CH 2 ) n -groups of PE while the latter is assigned to a CH 3 rocking mode of PP. MEPE/PP blends yield quite different X-ray diffraction patterns compared to HDPE/PP and LLDPE/PP blends; the MEPE/PP blends show that with increasing MEPE content the crystalline size of PP become smaller. DSC curves of MEPE/PP show that the peak area changes linearly with the blending ratio and that the crystallization temperature does not change for any blend. These results mean that the density and MFI of PE influences the blend properties.

Generalized two-dimensional (2D) FT-Raman correlation spectroscopy has been applied to the study of the composition-induced structural changes in eleven different ethylene/vinyl acetate (EVA) copolymers with vinyl acetate (VA) content varying from 6 to 42 wt %. The eleven copolymer samples have been divided into four sets according to their composition range, and 2D correlation analysis has been applied to detect the characteristic bands for each set. Throughout the composition range of EVA copolymers, the increase of VA content always causes the crystalline lamellae to shrink, the amorphous interlamellar layers to expand, the all-trans −(CH2)− n conformers to decrease, and the gauche conformers to increase in population. In particular, for the EVA with 7 wt % VA, small addition of VA comonomers acts as spacers between adjacent methylene segments and converts the orthorhombic unit cell to the anisotropic unit cell, manifested by the correlation splittings at (1438 cm-1, 1415 cm-1) and (1446 cm-1, 1434 cm-1), respectively. For the EVA with 26 wt % VA, small addition of VA comonomers mainly shortens the length of continual methylene segments and shifts the orthorhombic band from 1415 to 1419 cm-1. The 2D correlation analysis has identified the cause-effect relationship for structural events occurring both at the supermolecular phase scale and at the segmental submolecular level.

Generalized two-dimensional (2D) correlation spectroscopy has been applied to the study of the composition-dependent near-infrared (NIR) spectral changes in 11 different ethylene/vinyl acetate (EVA) copolymers with vinyl acetate (VA) content from 6 to 42 wt %. The 2D synchronous correlation analysis of the 11 NIR spectra has separated the bands due to ethylene units from those due to the VA units. The obtained results are consistent with those reached by the calculation of the second derivative and by chemometrics analysis reported in our previous paper. However, the 2D correlation analysis has given clearer evidence for the band separation. Two-dimensional asynchronous correlation analysis has revealed out-of-phase variations between some bands due to ethylene and some bands due to VA and has determined the order of intensity change between them. On the basis of the order of intensity change, the bands of ethylene in the orthorhombic crystalline phase have been discriminated from those in the amorphous and disordered phases. This paper discusses the potentials of three powerful techniques, 2D correlation analysis, the calculation of the second derivatives, and that of regression coefficients in chemometrics, in unraveling rather complicated NIR spectra.

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Organically modified niobate nanosheets are promising building blocks for the design of advanced hybrid materials. Nanosheets with controlled thickness and surface composition are important for precise structural design of the nanosheet-based materials. In this work, single-layered and double-layered niobate nanosheets functionalized by phenylphosphonate moieties were selectively prepared by interlayer grafting of A-type and B-type intercalation derivatives of potassium hexaniobate (K4Nb6O17·3H2O) with phenylphosphonic acid (PPA), followed by exfoliation by ultrasonication in acetonitrile. The interlayer grafting of PPA was monitored using X-ray diffraction (XRD), Fourier transform infrared (FTIR), and solid-state NMR spectroscopy, and the thicknesses of the exfoliated nanosheets were measured by atomic force microscopy (AFM). Transparent hybrid films were obtained by incorporating the single- and double-layered nanosheets into an epoxy matrix.