Transmission gratings were formed holographically in polymer dispersed liquid crystal (HPDLC) composite materials using commercially available UV-curable acrylate monomers and the nematic liquid crystal TL203. Monomer mixtures with average functionality ranging from 1.3 to 3.5 were used to prepare HPDLC transmission gratings. The phase-separated morphology and surface topology of the transmission gratings as observed through scanning electron microscopy and atomic force microscopy varied profoundly with the different monomer mixtures characterized by their average functionalities. The switching properties of the HPDLC gratings were correlated with the morphological changes.

Thermoplastic elastomer (TPE)-clay nanocomposites based on poly[styrene-(ethylene-co-butylene)-styrene] triblock copolymer (SEBS) were prepared. Natural sodium montmorillonite (MMT) clay was organically modified by octadecyl amine to produce an amine-modified hydrophobic nanoclay (OC). Commercially available Cloisite 20A (CL20) and Cloisite 10A, tallow ammine modified nanoclays, were also used. The intergallery spacing of MMT increased on amine modification as suggested by the shifting of the X-ray diffraction (XRD) peak from 7.6 to 4.5 and 3.8°in the cases of OC and CL20, respectively. The latter demonstrated no XRD peak when it was used at 2 and 4 parts phr in the SEBS system. Transmission electron microscopy studies showed the intercalation-exfoliation morphology in SEBS containing 4 parts of CL20 4 -SEBS, agglomeration in SEBS having 4 parts of MMT, and mixed morphology in SEBS with 4 parts of OC systems. Locations of the clay particles were indicated by the atomic force micrographs.Mechanical and dynamic mechanical thermal analysis studies confirmed the best properties with the CL20 4 -SEBS nanocomposites. Significant improvements in mechanical properties such as tensile strength, modulus, work to break, and elongation at break were achieved with the CL20 4 -SEBS in polymer-layered silicate nanocomposites. Dynamic mechanical studies further showed the affinity of the organoclays toward both segments of the TPE and a compatibilization effect with CL20 at a 4-phr loading. Atomic force microscopy showed distinctly different morphologies in nanocomposites prepared through solution and melt processing. Comparisons of the mechanical, dynamic mechanical, and morphological properties of the nanocomposites prepared by melt and solution intercalation processes were done.

ABSTRACT:The organic-inorganic hybrid composites comprising acrylic rubber and silica were synthesized through sol-gel technique at ambient temperature. The composites were generated through the acid-catalyzed hydrolysis and subsequent condensations of inorganic tetraethoxysilane (TEOS) in the organic acrylic rubber (ACM), solvated in tetrahydrofuran. The morphology of the hybrid materials was investigated by using the transmission electron microscope (TEM) and scanning electron microscope (SEM). Transmission electron micrographs revealed that the silica particles, uniformly distributed over the rubber matrix, are of nanometer scale (20 -90 nm). The scanning electron micrographs demonstrated the existence of silica frameworks dispersed in the rubber matrix of the hybrid composites. The X-ray silicon mapping also supported that observation. There was no evidence of chemical interaction between the rubber phase and the dispersed inorganic phase, as confirmed from the infrared spectroscopic analysis and solubility measurements. Dynamic mechanical analysis indicated mechanical reinforcements within the hybrid composites. The composites containing in situ silica, formed by sol-gel technique, demonstrated superior tensile strengths and tensile modulus values at 300% elongations with increasing proportions of tetraethoxysilane. However, the improvements in physical properties with similar proportions of precipitated silica were not significant. Maximum tensile strength and tensile modulus were obtained when the rubber phase in the hybrid composites was cured with ammonium benzoate and hexamethylenediamine carbamate system, as compared with benzoyl peroxide cured system. Thermal stability of the hybrid composites was not improved appreciably with respect to the virgin rubber specimen. Residue analysis from thermogravimetric study together with infrared spectroscopic analysis indicated the presence of unhydrolyzed tetraethoxysilane in the hybrid composites.