Micellar and Lyotropic Liquid Crystalline Phases Containing Nonionic Active Substances

Abstract

Phase diagrams of water, hydrocarbon, and nonionic surfactants (polyoxyethylene alkyl ethers) are presented, and their general features are related to the PIT value or HLB temperature. The pronounced solubilization changes in the isotropic liquid phases which have been observed in the HLB temperature range were limited to the association of the surfactant into micelles. The solubility of water in a liquid surfactant and the regions of liquid crystals obtained from water-surfactant interaction varied only slightly in the HLB temperature range. ^-phe phase equilibria of ionic surfactants combined with water and an A amphiphilic substance such as a long chain alcohol, carboxylic acid, or ester have been investigated in detail for a long time {1,2). The nonionic surfactants have not attracted as much interest despite the fact that they are suitable models for illustrating the association conditions which are responsible for the structure and function of biomembranes; they also present interesting problems in their temperature dependent interaction with water and hydrocarbons. This article discusses some micellar and liquid crystalline phases with nonionic substances, water, and hydrocarbons; and some factors are delineated for their association phenomena. Lipid phase behavior has an extremely important direct influence on certain biological phenomena ( Chapter 10 ) and is treated in Chapter 4. The treatment here is limited 28 Downloaded by STANFORD UNIV GREEN LIBR on September 24, 2012 |

Formation Kinetics of Oil-Rich, Nonionic Microemulsions

“…Although these emulsions might be kinetically stable for weeks or even months, they are inherently unstable from a thermodynamic perspective. Employing a larger amount of surfactantand thereby covering the complete interface between polar and nonpolar substancethermodynamically stable, nanostructured microemulsions may form. − Although their equilibrium properties like phase behavior, − low oil/water interfacial tension, , and multifarious nanostructure − have been studied in great detail for the past quarter of a century, far less is known about their formation kinetics and the formation of the internal interface in particular. In older related studies the pressure- and temperature-induced micelle formation was investigated in (pseudo)­binary water/surfactant mixtures − as well as the transformation of spherical micelles to elongated ones. , For these transitions similar studies have also been conducted using block copolymers. − Beyond that, most of the other related experiments deal with the kinetics of structural transformations, e.g., the well-studied micelle-to-vesicle transition ,− induced mainly by changes in the composition (using the stopped-flow technique) − or the lamellar-to-sponge (L 3 ) transition due to changes in temperature or pressure .…”