Liquid-crystalline phases, nonionic

In recent studies, Friberg and co-workers (J, 2) showed that the 21 carbon dicarboxylic acid 5(6)-carboxyl-4-hexyl-2-cyclohexene-1-yl octanoic acid (C21-DA, see Figure 1) exhibited hydrotropic or solubilizing properties in the multicomponent system(s) sodium octanoate (decanoate)/n-octanol/C2i-DA aqueous disodium salt solutions. Hydrotropic action was observed in dilute solutions even at concentrations below the critical micelle concentration (CMC) of the alkanoate. Such action was also observed in concentrates containing pure nonionic and anionic surfactants and C21-DA salt. The function of the hydrotrope was to retard formation of a more ordered structure or mesophase (liquid crystalline phase). 

Bai [2] performed similar drop dissolution experiments with sodium oleate (NaOl) and Ci2(EO)4. For drops initially containing 7 and lOwt. % NaOl (particle size < 38 jim) the behavior was similar to that described above for drops having 8 wt. % SDS. However for drops with 15 and 17 wt. % NaOl dissolution was faster—comparable to that of the pure nonionics—and neither a surfactant-rich liquid immiscible with water nor emulsification was seen. Instead a concentrated liquid crystalline phase transformed directly into a micellar solution, as seen for the pure nonionics and nonionic mixtures well below their cloud points. 

As indicated above, miscibiUty gaps are small and intermediate lamellar liquid crystalline phases dissolve rapidly into the aqueous phase if the surfactant or surfactant mixture is rather hydrophihc with a high spontaneous curvature (low (v/la)), for instance at temperatures below Tq for pure nonionic surfactants. In this case dissolution, which converts lamellae of zero curvature to aggregates with significant curvature as surfactant concentration decreases, occurs spontaneously because it reduces system free energy. 

Micellar and Lyotropic Liquid Crystalline Phases Containing Nonionic Active Substances... 

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... 

The presence of a liquid crystalline phase at high surfactant concentrations has been shown by Shinoda (31), but the method of presentation renders the evaluation of the temperature dependence of necessary emulsifier concentrations to obtain the liquid crystalline phase difficult. Although several phase diagrams of the system (water, emulsifier, and nonionic surfactant) have been published (4, 45, 46, 47, 48), no results have been given on the relation between the surfactant phase and the lamellar liquid crystalline phase in these systems. 

The behavior of a series of polyoxyethylene alkyl ether nonionic surfactants is also illustrative. According to Figure 11 the dioxyethylene (A) compound does not form liquid crystals when combined with water. Its solutions with decane dissolve water only in proportion to the amount of emulsifier. The tetraoxyethylene dodecyl ether (B) forms a lamellar liquid crystalline phase and is not soluble in water but is completely miscible with the hydrocarbon. The octaoxyethylene compound (C) is soluble in both water and in hydrocarbon and gives rise to three different liquid crystals a middle phase, an isotropic liquid crystal, and a lamellar phase containing less water. If the hydrocarbon p-xylene is replaced by hexadecane (D), a surfactant phase (L) and a lamellar phase containing higher amounts of hydrocarbon are formed in combination with the tetraoxyethylene compound (B-D). 

Regions containing a liquid crystalline phase in systems comprised of water, a hydrocarbon, and a nonionic emulsifier (polyoxyethylene... 

The phase diagrams of two-component surfactant-water systems are typically quite different for nonionic and ionic compounds. As exemplified in Fig. 2.22 there are at low temperatures different liquid crystalline phases while at intermediate temperatures there may be a total mutual solubility of surfactant and water98. At higher temperatures, there is, as already noted, a separation into two phases with a very large two-phase region. One of the phases contains very little surfactant, while the other contains appreciable amounts of both components. The cloud-point curve can be described as a liquid-liquid solubility curve with a lower consolute tempera-... 

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. 

With nonionic surfactants of the efhoxylate type, an increase in the temperature of a solution at a given concentration causes dehydration of the PEO chains and, at a critical temperature, the solution will become cloudy. This is illustrated in Figure 3.6, which shows the phase diagram of Cyj E. Below the CP curve it is possible to identify the different liquid crystalline phases hexagonal-cubic-lamellar, which are shown schematically in Figure 3.7. 

Liquid-crystalline phase or microemulsion formation between surfactant, water, and oily soil accompanies oily soil removal from hydrophobic fabrics such as polyester (Raney, 1987 Yatagai, 1990). It has been suggested (Miller, 1993) that maximum soil removal occurs not by solubilization into ordinary micelles, but into the liquid-crystal phases or microemulsions that develop above the cloud point of the POE nonionic. 

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... 

If a suitable microemulsion is formulated, there is no guarantee that it will not leak. In general, only twin-tailed surfactants displayed acceptable results, and often these systems were near phase transitions to liquid crystalline phases. However, experience has shown that if a microemulsion can be formed using a twin-tailed nonionic surfactant, chances are good that it will not leak provided no cosurfactant or cosolvent is used. 

Part Two, Surfactants, contains chapters on the four major classes of surfactants, i.e. anionics, nonionics, cationics and zwitterionics, as well as chapters on polymeric surfactants, hydrotropes and novel surfactants. The physico-chemical properties of surfactants and properties of liquid crystalline phases are the topics of two comprehensive chapters. The industrially important areas of surfactant-polymer systems and environmental aspects of surfactants are treated in some detail. Finally, one chapter is devoted to computer simulations of surfactant systems. 

A number of other NMR-probed w/o microemulsions have appeared in recent literature. The diffusion coefficients in water/SDS/pentanol and ammonium hydro-xide/SDS/pentanol microemulsions investigated by Olsson et al. [35] estabhshed that replacement of water by ammonium hydroxide destabilizes the liquid crystalline phase and reduces the size of the colloidal association structure in the isotropic liquid region, Olsson and Schurtenberger [36] worked on nonionic microemulsions prepared from D2O, pentaethylene glycol dodecyl ether and decarie. Discrete oil-swollen micelles have been evidenced by NMR self-diffusion measurements the preparations are in conformity with the hard-sphere model. The NMR self-diffusion measurements on a water/octyl glucoside/pentanol/decane microemulsion system advocated a progressive decrease in the mean curvature of the surfactant film with water addition at a constant level of the oil [37]. It was concluded that the... 

Nonionic surfactants with pronounced hydrophilic character behave like ionic surfactants they show a normal micellar formation in the aqueous phase with a hydrocarbon non-micellar phase in equilibrium. Higher surfactant concentrations give rise to liquid crystalline phases with a structure dependent on the length of the hydrophilic part of the surfactant. 

Microelectrodes with high real surface areas and well-defined periodic nanostmctures have recently attracted much interest because of their potential applications in electrocatalysis and electroanalysis [94-96]. These electrode systems can be prepared, using templating techniques, from lyotropic liquid crystalline phases of nonionic surfactants [94,95]. In particular, the normal topology hexagonal (Hj) liquid crystalline phase has been used as a template for the synthesis of mesoporous metal thin films via the electrochemical reduction of metal salts dissolved in the aqueous domain of the liquid crystalline phases [119, 120]. 

An interesting type of diblock copolymer is the group of PEO-poly(dimethyl-siloxane) polymers [129]. Recently, the phase behavior of these polymers was investigated as a function of added nonionic surfactant (C12E5). Mixing of these two compounds in water induces the formation of several liquid crystalline phases [130]. 

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