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Type: Artigo de periódico
Title: Order Profiles Of Host Decyl Sulfate And Decylammonium Chains And Guest Carboxylic Acids And Carboxylates In Allgned Type Ii Dm Lyomesophases
Author: Forrest B.J.
Fujiwara F.Y.
Reeves L.W.
Abstract: Lyotropic liquid crystals type II (DM) have been synthesized from sodium decyl sulfate, decanol, water, and sodium sulfate with low concentrations of lauric, palmitic, and stearic acids and their conjugate anions. A wide variation of specifically deuterated decyl sulfate chains has been incorporated in low concentration as well as perdeuterated decyl sulfate, carboxylic acids, and their anions. Degrees of order profiles have been extracted from the study of deuterium quadrupole splittings in the corresponding NMR spectra of aligned mesophases. The ratios of segmental order along the C-D bonds for host decyl sulfate chains are independent of water content (within the region of the DM phase), a temperature variation of 3 °C, and the presence of small quantities of the guest amphiphiles. The invariance of the kink/jog motions in the decyl sulfate chain as the water content is varied has been interpreted in terms of the invariance in internal packing of host chains inside the disk micelle as these entities are diluted with more interstitial water. The decrease in absolute degrees of order of the decyl sulfate segments as water is added can be explained by increases in the amplitude of micelle motion because the water layer is increased in thickness and perhaps also because the mean disk diameter may decrease with added water. The guest amphiphile chains do not conform in length to the half bilayer thickness of the disk micelle. Several types of behavior have been noted: (a) The guest head group anchoring at the interface determines the form of the order profile of the guest chain to a very large extent within the half bilayer distance; i.e., the form of the order profiles near the anchored end depends on the head group and not on the chain length for long chains, (b) The guests are uniformly of higher order in the first segments at the impurity site than the host segments which form the solvent bilayer. (c) In the case of carboxylic acid guests, the degree of order profile in the region of high probability for single gauche rotations follows very closely that of the solvent SDS/decanol bilayer. (d) The degree of order profiles of carboxylate guests, on the other hand, are quite distinct from the host segments. A higher order of the guest chains persists well beyond the half bilayer distance, (e) A third situation arises for carboxylic acid guests in a decylammonium chloride type II DM mesophase. In this case the fall in order of the guest chains occurs well wiithin the plateau region of the host chains, (f) The excess chain lengths of palmitic, myristic, and stearic acids and anions participate in the disordered region at the center of the disk bilayer structure having low and steadily decreasing order. Nevertheless, the ratio of CD 2 to CD 3 splitting the nonpolar end of the chain falls close to a theoretical ratio of 3 for a rigid chain for the anion guests. © 1980 American Chemical Society.
Rights: fechado
Identifier DOI: 
Date Issue: 1980
Appears in Collections:Unicamp - Artigos e Outros Documentos

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