Temperature and Pressure Effects on Micelles

Micelle formation takes place by the aggregation of monomeric surfactant molecules dispersed in a solvent. Aggregation is opposed by both an 

An explanation for this increase involves the peculiar properties of water as a solvent. Water molecules in the liquid state have a structure of hydrogen bonds similar to that of ice, and the cavities in the structure are large enough to accommodate a hydrocarbon chain. The water molecules display equilibria for the formation and destruction of hydrogen bonds with a lifetime of 10 s, and movement of free water molecules takes place by stepwise jumps through the cavities. Thus, occupation of a cavity by hydro-phobic solute hinders the movement of free water molecules, which therefore remain stationary for longer periods. In other words, the water molecules surrounding a hydrophobic solute become more ordered than bulk water molecules and have lower entropy. 

By analogy to the above discussion, the driving force for micellization results from the transfer of nonpolar surfactant chains from an ordered 

Detailed examination of m and n values over a wide temperature range have made it clear that both variables change with temperature. These changes should be taken into account when considering changes in thermodynamic variables of micelle formation. The micelle aggregation number of ionic surfactants decreases almost linearly with increasing tem- 

Since the change in CMC with pressure was measured by Tuddenham and Alexander/many reports have appeared on the effect of pressure on micelle formation for and nonionic surfactants. 

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