The Effect of Temperature on Solubilization

In our discussion of the effect of temperature on solubilization capacity (Chapter 4, Section 1B7), we mentioned that when the temperature of an aqueous micellar solution Wo of a POE nonionic surfactant is increased, its solubilization of nonpolar material O increases due to the increased dehydration of the POE chains, which increases the lipophilic character of the surfactant. If this occurs for POE nonionics of the proper structure in the presence of excess nonpolar material, the volume of the aqueous phase Wo increases and that of the nonpolar phase oil decreases as the temperature increases (Figure 5-5a,b). This is accompanied by a decrease in the tension yow at the O/W interface. With further increase in temperature, the POE chains become more and more dehydrated, the surfactant becomes more lipophilic, and more and more nonpolar material oil is solubilized into the increasingly asymmetric micelles. When the vicinity of the cloud point of the nonionic is reached the surfactant micelles, together with solubilized material, will start to separate from Wo as a separate phase D. If excess oil is still present, the system now contains three phases (Shinoda, 1968) excess oil a phase D, the... 

---