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11.
Abstract We have introduced an oxygen atom and a carbon-carbon double bond with a trans-configuration (E) into the terminal alkyl chain of a wide variety of liquid crystalline cyclohexane derivatives to produce a variety of new methyl (E)-allyl ethers. The melting points and tendency to form smectic mesophases are often low, while nearly all of the compounds prepared exhibit a nematic phase. Thus, even two-ring derivatives can exhibit nematic phases over a wide temperature range (≤80°C), sometimes starting below room temperature (T m≈10°C). Comparisons with the corresponding derivatives incorporating either just an oxygen atom or just a carbon-carbon double bond in the same position indicate that synergetic effects lead to broader nematic phases than would otherwise have been expected. Thus many of the new methyl (E)-allyl ethers exhibit nematic phases over a wider temperature range than the corresponding materials with an unsubstituted alkyl chain attached to the cyclohexyl ring. The new compounds are easily prepared from known starting materials. Many intermediates are themselves liquid crystalline. This allows investigation of the relationship between liquid crystal transition temperatures and the nature of the terminally substituted alkyl chain (for example, incorporating C[dbnd]C, OH, CO2C2H5 and OCH3 groups). 相似文献
12.
L. M. Renderson F. C. Kracek Ch. L. Parsons R. B. Moore S. C. Lind O. C. Schaefer J. L. Niermann Clarence E. Scholl R. K. Strong H. N. Mc Coy E. Ebler A. J. van Rhyn H. A. Doerner Wm. M. Hoskins und F. E. E. Germann 《Fresenius' Journal of Analytical Chemistry》1928,74(7):255-259
Ohne Zusammenfassung 相似文献
13.
Kadau K Germann TC Lomdahl PS Albers RC Wark JS Higginbotham A Holian BL 《Physical review letters》2007,98(13):135701
The propagation of shock waves through polycrystalline iron is explored by large-scale atomistic simulations. For large enough shock strengths the passage of the wave causes the body-centered-cubic phase to transform into a close-packed phase with most structure being isotropic hexagonal-close-packed (hcp) and, depending on shock strength and grain orientation, some fraction of face-centered-cubic (fcc) structure. The simulated shock Hugoniot is compared to experiments. By calculating the extended x-ray absorption fine structure (EXAFS) directly from the atomic configurations, a comparison to experimental EXAFS measurements of nanosecond-laser shocks shows that the experimental data is consistent with such a phase transformation. However, the atomistically simulated EXAFS spectra also show that an experimental distinction between the hcp or fcc phase is not possible based on the spectra alone. 相似文献
14.
We investigate deformation of pure Cu, pure Nb and 30?nm Cu/30?nm Nb nanolaminates induced by high strain rate shock loading. Abundant dislocation activities are observed in shocked pure Cu and Nb. In addition, a few deformation twins are found in the shocked pure Cu. In contrast, in shocked Cu/Nb nanolaminates, abundant deformation twins are found in the Cu layers, but only dislocations in the Nb layers. High resolution transmission electron microscopy reveals that the deformation twins in the Cu layers preferentially nucleate from the Cu(112)//Nb(112) interface habit planes rather than the predominant Cu(111)//Nb(110) interface planes. Our comparative study on the shock-induced plastic deformation of the pure metals (Cu and Nb) and the Cu/Nb nanolaminates underscores the critical role of heterogeneous phase interfaces in the dynamic deformation of multilayer materials. 相似文献
15.
We have introduced an oxygen atom and a carbon-carbon double bond with a trans-configuration (E) into the terminal alkyl chain of a wide variety of liquid crystalline cyclohexane derivatives to produce a variety of new methyl (E)-allyl ethers. The melting points and tendency to form smectic mesophases are often low, while nearly all of the compounds prepared exhibit a nematic phase. Thus, even two-ring derivatives can exhibit nematic phases over a wide temperature range (≤80°C), sometimes starting below room temperature (Tm≈10°C). Comparisons with the corresponding derivatives incorporating either just an oxygen atom or just a carbon-carbon double bond in the same position indicate that synergetic effects lead to broader nematic phases than would otherwise have been expected. Thus many of the new methyl (E)-allyl ethers exhibit nematic phases over a wider temperature range than the corresponding materials with an unsubstituted alkyl chain attached to the cyclohexyl ring. The new compounds are easily prepared from known starting materials. Many intermediates are themselves liquid crystalline. This allows investigation of the relationship between liquid crystal transition temperatures and the nature of the terminally substituted alkyl chain (for example, incorporating C=C, OH, CO2C2H5 and OCH3 groups). 相似文献
16.
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18.
Du S Germann TC Francisco JS Peterson KA Yu HG Lyons JR 《The Journal of chemical physics》2011,134(15):154508
The recombination of S atoms has been found to be stepwise from the smallest unit, the elemental S atom, to the most abundant molecule S(8). The reaction between S + S(2) → S(3) has not been reported either experimentally or by theory, but may be a key intermediate step in the formation of sulfur aerosols in low-O(2) atmospheres. In this work, the kinetics of this reaction is reported with Ar gas used as the chaperone molecule in the production of S(3) via two complex intermediates: SAr + S(2) and S(2)Ar + S. Quasi-classical and classical trajectory methods are used. The rate constant of the S + S(2) + Ar → S(3) + Ar reaction is determined to be 2.66 × 10(-33) cm(6) mol(-1)?s(-1) at 298.15 K. The temperature dependence of the reaction is found to be 2.67 × 10(-33) exp[143.56(1∕T-1∕298.15)]. The second-order rate constant of S + S(2) → S(3) is 6.47 × 10(-14) cm(3)?molecule(-1)?s(-1) at 298.15 K and the Arrhenius-type rate constant is calculated to be 6.25 × 10(-14) exp[450.15(1∕T-1∕298.15)] cm(3)?molecule(-1)?s(-1). This work provides a rate coefficient for a key intermediate species in studies of sulfur formation in the modern Venus atmosphere and the primitive Earth atmosphere, for which assumed model rate coefficients have spanned nearly 4 orders of magnitude. Although a symmetry-induced mass-independent isotope effect is not expected for a chaperone mechanism, the present work is an important step toward evaluating whether mass-independence is expected for thiozone formation as is observed for ozone formation. 相似文献
19.
Dimonte G Terrones G Cherne FJ Germann TC Dupont V Kadau K Buttler WT Oro DM Morris C Preston DL 《Physical review letters》2011,107(26):264502
We use the Richtmyer-Meshkov instability (RMI) at a metal-gas interface to infer the metal's yield stress (Y) under shock loading and release. We first model how Y stabilizes the RMI using hydrodynamics simulations with a perfectly plastic constitutive relation for copper (Cu). The model is then tested with molecular dynamics (MD) of crystalline Cu by comparing the inferred Y from RMI simulations with direct stress-strain calculations, both with MD at the same conditions. Finally, new RMI experiments with solid Cu validate our simulation-based model and infer Y~0.47 GPa for a 36 GPa shock. 相似文献
20.
We have introduced an oxygen atom and a carbon-carbon double bond with a trans-configuration (E) into the terminal alkyl chain attached to the cyclohexyl ring of a variety of two- and three-ring nematic liquid crystals of positive dielectric anisotropy. The new polar two-ring methyl (E)-allyl ethers often possess low melting points, but are not mesomorphic in general. The related three-ring methyl (E)-allyl ethers exhibit high clearing points and wide nematic ranges. Comparisons with the corresponding derivatives incorporating either just an oxygen atom or just a carbon-carbon double bond in the same position indicate that synergetic effects lead to broader nematic phases than would otherwise have been expected. This is partially due to the low smectic transition temperatures observed for the methyl (E)-allyl ethers. Selected physical properties of three binary mixtures of a weakly polar standard nematic liquid crystal and three difluoro-substituted (polar) liquid crystals (including the new ethers) differing only in the nature of the terminal chain show that, although some of the methyl (E)-allyl ethers exhibit longer switch-off times in TN cells than those of analogous liquid crystals incorporating either a methyl propyl ether or a 1-(E)-propenyl chain instead of the methyl (E)-allyl ether chain, they are still useful components for nematic mixtures, especially where a wide temperature range is required. 相似文献