Micellar properties, effect temperature

Micellar properties are affected by changes in the environment, eg, temperature, solvents, electrolytes, and solubilized components. These changes include compHcated phase changes, viscosity effects, gel formation, and Hquefication of Hquid crystals. Of the simpler changes, high concentrations of water-soluble alcohols in aqueous solution often dissolve micelles and in nonaqueous solvents addition of water frequendy causes a sharp increase in micellar size. 

In investigating temperature effects on drug solubilization in micellarsystems, changes in the micellar properties as well as those in the aqueous solubility of the solute signiLcantly affect the solubilization... 

In this present study we report the effect of graded doses of y-irradiation on the properties of the micelles of Pluronic FI27 and on the temperature induced micellar changes which lead to the eventual gelation of these solutions. In view of the batch variability of the micellar properties of poloxamers (3) comparisons have been made with solutions of the same batch which have not been subjected to irradiation. 

Effect of Temperature on Micellar Properties. Figure 5 compares the influence of temperature on the diffusion properties of the micelles in solutions previously irradiated with a dose of 4.56 Mrad with those not subjected to radiation treatment. Hydrated radii calculated from the limiting diffusion coefficients for micelles not treated with radiation remain independent of temperature over the range 25° to 40° (Table III). 

Table III. Effect of Temperature on the Micellar Properties of Irradiated and Non-irradiated solutions...

Temperature has a comparatively small effect on the micellar properties of ionic surfactants. The temperature dependence of the cmc of sodium lauryl (dodecyl) sulfate shown in Fig. 6.29 is typical of the effect observed. 

In this study we examined the influence of concentration conditions, acidity of solutions, and electrolytes inclusions on the liophilic properties of the surfactant-rich phases of polyethoxylated alkylphenols OP-7 and OP-10 at the cloud point temperature. The liophilic properties of micellar phases formed under different conditions were determined by the estimation of effective hydration values and solvatation free energy of methylene and carboxyl groups at cloud-point extraction of aliphatic acids. It was demonstrated that micellar phases formed from the low concentrated aqueous solutions of the surfactant have more hydrophobic properties than the phases resulting from highly concentrated solutions. The influence of media acidity on the liophilic properties of the surfactant phases was also exposed. 

The development of monoalkyl phosphate as a low skin irritating anionic surfactant is accented in a review with 30 references on monoalkyl phosphate salts, including surface-active properties, cutaneous effects, and applications to paste and liquid-type skin cleansers, and also phosphorylation reactions from the viewpoint of industrial production [26]. Amine salts of acrylate ester polymers, which are physiologically acceptable and useful as surfactants, are prepared by transesterification of alkyl acrylate polymers with 4-morpholinethanol or the alkanolamines and fatty alcohols or alkoxylated alkylphenols, and neutralizing with carboxylic or phosphoric acid. The polymer salt was used as an emulsifying agent for oils and waxes [70]. Preparation of pharmaceutical liposomes with surfactants derived from phosphoric acid is described in [279]. Lipid bilayer vesicles comprise an anionic or zwitterionic surfactant which when dispersed in H20 at a temperature above the phase transition temperature is in a micellar phase and a second lipid which is a single-chain fatty acid, fatty acid ester, or fatty alcohol which is in an emulsion phase, and cholesterol or a derivative. 

Recently membrane lipids from Brassica napus root cells were examined with respect to effects from dehydration-acclimatised plants [59]. It was found that the lipids formed a cubic phase with excess water vmder physiological conditions. On heating, this phase transformed directly into a reversed micellar phase. The transition was also foxmd to coincide with the temperature limit of survival of the plant. Also after repeated water-deficient stress, a cubic phase is formed in excess water, although there are differences in the phase properties compared to lipids from membranes of plants grown normally. 

Besides influencing the critical micellar temperature, the number and position of hydroxy groups also influence the critical micellar concentration. The critical micellar concentration of dihydroxy bile acids is significantly below that of trihydroxy acids (1,63), but no values have been reported for monohydroxy acids. Conjugation with glycine or taurine does not appear to have any particular effect on those properties of bile acids which are related to the steroid nucleus, provided that experiments are carried out at pH sufficiently alkaline that all bile acid molecules present are ionized (64). 

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