UNDERSTANDING THE HYDROPHOBIC EFFECT

The hydrophobic effect is the common expression for processes where no npolar groups in molecules are spontaneously removed from water. Therm odynamic analysis of hydrocarbon solubility in water, micellization an d adsorption of surfactants show that the hydrophobic effect can be un derstood in terms of two contributions. The first contribution is attr ibuted to the structuring, or rearrangement, of water molecules in the vicinity of a hydrophobe. This contribution is favorable, and hence i ncreases the solubility of hydrocarbons in water, increases the cmc, a nd decreases the adsorption of surfactants. The second contribution is attributed to the formation of a cavity in the water in order to acco modate the hydrophobe. This contribution dominates over the first one and is unfavorable, i.e. it decreases the solubility of hydrocarbons i n water, decreases the cmc, and increases the adsorption of surfactant s. Thus, the cause of the hydrophobic effect is to be found in the lar ge energy required to form a cavity in the water. On the other hand th e temperature dependence of the hydrophobic effect is entirely determi ned by the water structuring, or rearrangement, in the vicinity of a h ydrophobe.