Temperature-induced solubilization of hydrocarbons in aqueous block copolymer solutions

In this study, the use of aqueous solutions of amphiphilic block copolymers as an extractant for hydrocarbons has been examined. The solubilization of naphthalene in poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymer solutions is chosen as a model system. Special attention is paid to the aggregation mechanism and to the transformation of the micelle structure upon a variation in temperature. It is demonstrated that above a certain transition temperature the solubilization of naphthalene will increase exponentially as a result of the micelle growth, which is initiated at this temperature. The solubilization increase will take place over a temperature interval of about 15 degrees C after which the solubilization of naphthalene will stabilize. Values of the distribution ratio of naphthalene over the apolar micelle core and the surrounding aqueous phase in excess of 2000 were measured. Modelling results have shown that the solubilization is predominantly determined by an increase of the micelle radius, while the polarity change of the micelle core is of minor importance. Due to the reversibility of the process, the block copolymer solution seems a promising extractant with favorable regeneration properties.