Alkanol-induced micelles of a very hydrophilic eo-po-eo block copolymer: Characterization by spectral and scattering methods

The aqueous solution behavior of a PEO-PPO-PEO block copolymer (EO ₁₀₃PO₃₉EO₁₀₃), was investigated in the presence of aliphatic alkanols (C₂, C₄, C₆ and C ₈). The non-associated polymer chains remain extremely hydrated in water, but aggregation in the form of spherical micelles was evidenced, triggered by the interaction of polymer chains with hydrophobic alkanol. We assume that the hydrophobic interaction between the PPO block of the copolymer and alkanol promotes micellization, which increases further with the introduction of higher chain length species. The critical micellization temperature (CMT), as measured by UV-visible spectroscopy, indicates an interaction of polymer chains with the alkanol bearing a higher chain length, which triggers aggregation. The micelles were characterized by small angle neutron scattering to elucidate the size and related micellar parameters. The gradual increase in the alkanol content increases the aggregation number, though the micelles were spherical in shape. We conclude that ethanol, due to its preferential solubility in the aqueous phase, does not affect the aggregation. The alkanols with chain lengths of C₄-C₈ chain, interact with the PPO block through hydrophobic interaction and shifts the CMTs to lower values. The combined effect of inorganic salt (NaCl) and alkanols show enhanced micellar properties.