Solubilization of ?guest? molecules into polymeric aggregates

Abstract

The solubilization capacity of block copolymer aggregates in aqueous solutions for hydrophobic guest molecules is reviewed in this paper. Experimental results on the solubilization of a number of hydrocarbons and mixtures of hydrocarbons, and hydrophobic molecules with varying degrees of polarity are first summarized. We then describe in detail a predictive molecular thermodynamic theory of solubilization formulated in our earlier studies. Explicit analytical expressions are provided for the standard state free energy change associated with solubilization of hydrocarbons in aggregates having spherical, cylindrical and lamellar shapes. Utilizing these free energy expressions and using only molecular constants, the core size, corona thickness, and aggregation number of the polymeric aggregates and the volume fraction of the hydrocarbon solubilized in the core have been predicted. The characteristics of aggregates formed from diblock and triblock copolymers and their solute uptake capacity are compared and related to the molecular properties of the guest molecules and the block copolymers. Further, theoretical results from a systematic study of solubilization of several hydrocarbons by aggregates formed of the family of Pluronic® triblock copolymers are discussed. Very interestingly, solubilization is shown to induce a transition in aggregate shapes from spheres to cylinders and then to lamellae. The origin of such shape transitions is identified in terms of the different free energy contributions. Finally, a few applications of solubilization in block copolymer aggregates are briefly mentioned. Copyright © 2001 John Wiley & Sons, Ltd.