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|Type:||Artigo de periódico|
|Title:||Mesophase Behavior And Structure Of Type I Lyotropic Liquid Crystals|
|Abstract:||Mesophases prepared from binary mixtures (detergent/water) and ternary mixtures (detergent/water/electrolyte) have been investigated as a function of water content and temperature by studying deuterium magnetic resonance of the heavy water and in some cases deuterated hydrocarbon segments. The binary mixtures cover the region of H α hexagonal mesophase formation, and at higher water contents these mixtures pass directly to isotropic phases, with which they may coexist in equilibrium. With the addition of small amounts of electrolyte, the intermediate nematic type I Δx > 0 mesophase is formed in all three cases investigated. In the region of coexistence with H α mesophases, both uniaxial liquid crystals have been shown to be type I; the hexagonal phase aligns over a period of about 1 week with the director along the direction of the magnetic field. The variation of temperature causes large variations of order in the intermediate nematic mesophase, which has been named "CM" type I for cylindrical micellar nematic mesophase. At high temperatures coexistence regions of H α and CM mesophases are found. A sequence of structures is proposed, where a concentrated isotropic micellar phase of rodlike micelles passes, as water content is decreased, into a region of type I properties for the CM mesophase in which there is long-range orientational order but no positional order of the micelles. In cases where the CM mesophase coexists with the H α phase, a nucleation of two degrees of positional degrees of order is postulated. The sequence of mesophases derived from La structures of lamellar form is somewhat analogous. In the concentrated micellar solutions the micelles can be disklike but isotropically tumbling entities which gain orientational order at lower water contents. These "DM" disk micelle nematic mesophases are type II in magnetic anisotropy and nucleate out regions of the L α mesophase which has one degree of positional order. Low-angle X-ray diffraction indicates a lack of positional long-range order in both type II and type I, DM and CM nematic mesophases, respectively. In a system which undergoes a transition from a type I CM nematic to a type II DM nematic mesophase, the covariation of the quadrupole splitting of deuterium in water and the hydrocarbon chain segments -CD 2- near the interface shows that the relative motions at these different locations are unchanged by the curvature of the interface. The degree of order profile of the perdeuterated laurate chain in L α, DM, H α, and CM mesophases has been compared. Although the condition of constant surface area of the detergent at the interface cannot be preserved, there are notable similarities and differences in the ratios of some segment CD 2 splittings which have been associated with the interface curvature and host/guest interactions. © 1980 American Chemical Society.|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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