Surfactant lyotropic liquid-crystalline

Like other surfactants, alkanesulfonates generate lyotropic liquid-crystalline phases. But the phase equilibria can only be inadequately described because of the enormous experimental difficulties in, for instance, establishing an appropriate equilibrium. Nevertheless, for simple ternary systems the modeling of surfactant-containing liquid-liquid equilibria has been successfully demonstrated [60],... 

Lyotropic liquid crystalline nanoparticles have also been described. Concentrated solutions of gold nanorods in water in the presence of a surfactant (cetyltrimethyl-ammonium bromide) display a nematic mesophase stable up to 200 °C [74[. The N mesophase was identified by optical microscopy by their typical nematic droplets texture. 

G.S. Attard, P.N. Bartlett, N.R.B. Coleman, J.M. Elliott, and J.R. Owen, Lyotropic liquid crystalline properties of nonionic surfactant/H20/hexachloroplatinic acid ternary mixtures used for the production of nanostructured platinum. Langmuir 14, 7340-7342 (1998). 

Another feature of surfactant-water systems is that they can also aggregate into lyotropic liquid crystalline phases when Intermicellar interactions are significant. Typically, non-Newtonian behavior is usually found for these liquid crystalline phases. For the 3LDA0/ISDS mixed system, all evidence suggests that they do form liquid crystalline phase. 

Kinetic studies have been important in many areas of chemistry, but, to date, classic kinetic approaches have not played a major role in the area of colloidal science related to self-organisation of surfactants. Although micellar kinetics were investigated in some detail in the 1970s, related work involving other self-assembly systems, e.g., vesicles, lyotropic liquid-crystalline phases, have been limited. 

The results showing augmentation of the surfactant alcohol ratio for maximum aqueous solubility with added electrolytes are not amenable to a similarly simple explanation, and the influence of the presence of electrolytes must be discussed against the relative stability of the inverse micelles and of the lyotropic liquid crystalline phase with which the inverse micellar solution is in equilibrium (7). 

Similar to germanium sulfides or selenides, [SiqSeio] adamantine clusters also exist and have been found to form mesostractured semiconductors with Pt + when templated by the lyotropic liquid-crystalline phase of alkylpyridiniinn surfactant [Ci6H33NC5H5]Br. This mesophase designated as CiePyPtSnSe has a band gap of 1.5 eV. 

S.A. El-Safty and T. Hanaoka, Monolithic Nanostructured Silicate Family Templated by Lyotropic Liquid-crystalline Nonionic Surfactant Mesophases. Chem. Mater., 2003, 15, 2892-2902. 

Attard, G.S. Leclerc, S.A.A. Maniguet, S. Russell, A.E. Nandhakumar, I. Bartlett, P.N. Mesoporous Pt/Ru alloy from the hexagonal lyotropic liquid crystalline phase of a nonionic surfactant. Chem. Mater. 2001,13 (5), 1444—1446. 

More lipophilic surfactants form larger, nonspherical micelles, vesicles, or lyotropic liquid crystalline phases at rather low concentrations in water. For example, at temperatures above those where the chains form crystalline structures, phospholipids and other surfactants with two relatively long hydrocarbon chains typically form the lamellar liquid crystalline phase consisting of many parallel surfactant bilayers separated by water layers. The hydrocarbon interiors of the bilayers are rather fluid as in micelles. Of course, in this case a true phase separation occurs beginning at a definite surfactant concentration. 

As their name implies, liquid crystals are materials whose structures and properties are intermediate between those of isotropic liquids and crystalline solids (2). They can be of two primary types. Thermotropic liquid crystalline phases are formed at temperatures intermediate between those at which the crystalline and isotropic liquid phases of a mesogenic compound exist. Substances which exhibit thermotropic phases are generally rod- or disc-like in shape, and contain flexible substituents attached to a relatively rigid molecular core. Lyotropic liquid crystalline phases are formed by amphiphilic molecules (e.g. surfactants) in the presence of small amounts of water or other polar solvent. In general, the constituent molecules in a liquid crystal possess orientational order reminiscent of that found in the crystalline phase, yet retain some degree of the fluidity associated with the isotropic liquid phase. 

At higher concentrations block copolymers form lyotropic liquid-crystalline phases. Their range of stability can depend strongly on temperature. In aqueous solutions polyethylene oxide (PEO) is usually the soluble block. An increase of temperature reduces the solubility of the PEO block which can result in phase transitions into different phases. Most of the present knowledge on lyotropic phase behavior of block copolymers was obtained from studies of Pluronics,i.e., poly(ethyleneoxide-h-propyleneoxide-h-ethyleneoxide) (PEO-PPO-PEO) [31]. Phase diagrams of block copolymers with shorter chains resemble those of low-molecular surfactants. 

Using a y-irradiation technique, hexagonal PANI nanoparticles have been prepared in the hexagonal lyotropic liquid crystalline phases of a non-ionic and biodegradable surfactant alkyl polyglucoside (GP215 CS UP) in water and/or medium and long chain alkanes, used as a template [421]. 

Boyd BJ, Whittaker DV, Khoo S-M, Davey G. Lyotropic liquid crystalline phases formed from glycer-ate surfactants as sustained release drug delivery systems. International Journal of Pharmaceutics. 2006 309(l-2) 218-226. 

For these transient networks formed by the interaction of an ABA triblock copolymer and a microemulsion it has been shown that their principal viscoelastic properties are not affected significantly by the chemical nature of the microemulsion, i.e., they are similar for systems with both nonionic and ionic surfactants. Also it should be noted that the phase behavior of the corresponding microemulsion is qualitatively preserved, i.e., the reversible aggregation of the nanodroplets and the phase transitions to lyotropic liquid crystalline phases remain essentially unchanged (although the concentrations at which they occur might... 

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