Micellar weight temperature effect

Table 5.16 The effect of temperature on the micellar weight of methoxydodecaoxyethylene decyl ether. From Kuriyama [162],...

Aqueous solutions of nonionic surfactants become suddenly turbid when the temperature is raised. The temperature at which the sudden onset of turbidity occurs is called the cloud point. The cmc decreases with increasing temperature and the micellar weight increases [103-106]. At the cloud point, the aggregates have become so large that turbidity becomes perceptible even to the naked eye [98,106]. The surfactant solution separates into two coexistent phases a surfactant-rich phase and a phase in which the surfactant is depleted. The cloud point depends on the surfactant concentration, but the concentration effect is usually weak. 

Roe and co-workers (Nojima et al. 1990 Rigby and Roe 1984,1986 Roe 1986) have used SAXS to characterize micelles formed by PS-PB diblocks at low concentrations in blends with low-molecular-weight PB. Micellar dimensions and association numbers were determined for symmetric and asymmetric diblocks (Rigby and Roe 1984,1986). The effective hard sphere radius, the core radius and volume fraction of hard spheres were determined using the Percus-Yevick model (Rigby and Roe 1986). These results were compared (Roe 1986) to the predictions of the theory of Leibler et al (1983). The theory qualitatively reproduced the observed trend for the cmc to increase with temperature for blends containing a particular diblock. The cmc was found to decrease at a fixed temperature... 

The main part is then devoted to the equilibrium exchange kinetics of selected PEP-PEO micellar systems. We report on TR-SANS measurements in pure water that, independently of block copolymer molecular weight, composition, and temperature, revealed frozen micelles. This review further concerns the effect of tuning the kinetics by addition of co-solvents, i.e., reduction of y. The relaxation behavior of some selected systems revealing chain exchange dynamics that can be resolved by TR-SANS wfll be presented, followed by a discussion of the main observation, namely, the unexpected appearance of a pseudo-logarithmic time decay of the relaxation function. 

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