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Show moreFreedericksz measurements were performed on mixtures of a nematic mesogen and a V-shaped molecule. The bend elastic constant was found to decrease significantly with increasing concentration of the V-shaped molecule. The results are discussed theoretically, taking into account the detailed structure of the molecules. ©2000 The American Physical Society. Appropriate bibliographic citation and notice of the APS copyright must be included- "Dodge M.R., Rosenblatt C., Petschek R.G., Neubert M.E., Walsh M.E., Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics 62:4 B, 5056-5063 (2000). Copyright 2000 by the American Physical Society."
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Show moreWe investigated 1:1 mixtures of a variety of 4,4′-disubstituted diphenyldiacetylenes (PTTP series) and cyano-containing mesogens for possible complex formation Complexes were formed when alkyl/alkoxy cyanobiphenyls (CB series) were mixed with alkyl/alkoxy PTTP homologues. We found complexes having a melting temperature higher than that for either component, and complexes with lower melting temperatures. A fluoro substituent on the PTTP gave an enhanced nematic phase and a cyclohexane ring in place of a benzene ring yielded an enhanced smectic A phase, but a cyano on the PTTP gave poor liquid crystalline properties. Phase diagrams were constructed for PTTP-24/5-CB and PTTP-24/8O-CB mixtures. Both complexes formed had melting temperatures higher than those for either component. These complexes were recrystallized and shown by X-ray studies to be 1:1 complexes. The PTTP-24/5-CB complex showed only a monotropic nematic phase, but the PTTP-24/8O-CB complex showed induced smectic A and hexatic B phases in addition to an enantiotropic nematic phase. ©1999 Taylor & Francis Ltd.
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Show moreNew diphenyldiacetylenes of the type equation presented with A, B = H and/or F; m = 0, 1; n = 1-4; and X = CnH2n+1, F, CF3 or CN were synthesized and their mesomorphic properties determined by hot stage polarizing microscopy and DSC. When m = 0, all of these compounds showed only a nematic phase except when X = CF3 when both nematic and smectic A phases were seen. Both clearing and melting temperatures were higher than those reported for substitution with the corresponding alkyl chains but the much larger increase in clearing temperatures produced considerably wider nematic phases. Eutectic mixtures of a few of these olefins yielded nematic materials also having much wider temperature ranges and higher clearing temperatures than the eutectic mixtures of the alkyl compounds, while retaining their high birefringence and low viscosities. Such materials are of interest for beam-steering devices. Four of the diacetylenes with m = 1 (A, B = H) were also prepared (X = C6H13, F, n = 2, 3). When X was C6H13 (n = 2), the nematic range was smaller in the 2- than in the 1-olefin but wider than in the alkyl series. When X = F, either no nematic phase or a monotropic one was observed, whereas the 1-olefins gave a much wider nematic phase. Both transition temperatures were lower than those for the corresponding 1-olefin and alkyl analogues. The compound with X = C6H13 and n = 2 had a melting temperature below room temperature.
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Show moreA limited selection of ring modified diphenyldiacetylenes of the type CnH2n+1 C≡C-C≡C Y where A -, Y = C nH2n+1, CF3, F, COMe, NH2, and NMe2, and A = trans and cis with Y = F and trans with Y = C 3H7, were synthesized. Mesomorphic properties were determined by hot stage polarizing microscopy and DSC. These properties were generally poorer than those found in the parent benzene compounds. This was also true of some pyrimidine analogues reported earlier. Birefringence values also decreased as expected.
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Show moreA variety of terminal chain modifications (Y) were made on the diacetylenes (diagram presented) in which X = CnH2n+1, C 12H25O and F, and Y = CH2CH(Me)C 2H5, COCH3, C ≡ CC5H 11, CnF2n+1 _Δ_ CnH 2n+1 and CH = CHCO2C3H7. Mesomorphic properties were determined by hot stage polarizing microscopy and DSC. These were compared with those for the dialkyl analogues (X = CmH 2m+1, Y = CnH2n+1) and a series of 1- and 2-olefins (Y = CH = CHCnH2n+1 and CH2CH = CHCnH2n+1). The 1-olefin series showed wider range nematics than the dialkyl compounds, whereas the above modifications showed either narrow range nematic phases, no mesophase or higher melting temperatures. New transition temperature and enthalpy data are provided for some of the dialkyl and F-alkyl compounds previously reported, for comparisons. Preliminary birefringence data are also included along with the results of some heat and UV stability studies.
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Show moreAn investigation on light scattering above the nematic - smectic-A phase transition in binary mixtures of bent-core mesogens and calamitic was performed. With dopant concentration X, the regular part of the bend elastic constant decreased strongly. It was found that the divergent part of the bend elastic constant decreased rapidly with X, when close to the nematic - smectic-A phase transition temperature. Appropriate bibliographic citation and notice of the APS copyright must be included- "Dodge M.R., Petschek R.G., Rosenblatt C., Neubert M.E., Walsh M.E., Physical Review E - Statistical, Nonlinear, and Soft Matter Physics 68:3 1, 317031-317036, 2003. Copyright 2003 by the American Physical Society."
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