SELF-ASSEMBLY IN AQUEOUS BLOCK COPOLYMER SOLUTIONS

The aggregation of EO99-PO65-EO99 (EO and PO being ethylene oxide and propylene oxide, respectively) in water has been studied. By gel permeation chromatography (GPC) and self-diffusion studies, it was found that micelles are formed in dilute solutions, but only at higher temperatures. The micelles formed have a hydrodynamic radius of approximately 10 run over a wide temperature range. The residence time of the polymer molecules in the micelles is extremely long ( approximately hours). At higher polymer concentrations, a clear isotropic gel is formed at intermediate temperatures. The extension of the gel region depends strongly on the presence of cosolutes, such as inorganic salts and hydrocarbons; detailed phase diagrams are presented and discussed. Furthermore, the self-diffusion of the polymer and of solubilized oil was studied. The diffusion of the polymer molecules is slow (D(p) almost-equal-to 10(-11)-10(-12) M2/s), decreasing with increasing polymer concentration (roughly as D(p) almost-equal-to c-1) up to 20 wt %. In the gel region, the echo-amplitude decay curves reveal a distribution of diffusion coefficients, precluding detailed analyses. The self-diffusion of the oil is comparable to that of the polymer (D(oil) almost-equal-to D(p)), and several orders of magnitude slower than the diffusion of water (D(w) almost-equal-to 10(-9) m2/s).