Thermoresponsive behavior of micellar aggregates from end-functionalized PnBA-b-PNIPAM-COOH block copolymers and their complexes with lysozyme

Abstract

The temperature response of micellar aggregates of poly(n-butyl acrylate)-b-poly(N-isopropylacrylamide)-carboxylic acid (PnBA-b-PNIPAM-COOH) end-functionalized diblock copolymers in aqueous solutions is investigated by small angle neutron scattering and light scattering techniques. The particular micellar aggregates present –COOH groups at their surface due to the molecular architecture of the block copolymer chains. Above the critical solution temperature micellar aggregation depends on the initial solution concentration, while at the highest polymer content intermicellar correlations are observed as a hard-sphere interaction intensity peak. Addition of lysozyme induces this morphological transition even at low concentrations. The scattering profiles are consistent with lysozyme accumulating in the vicinity of the micellar cores, a finding that is supported by measurements in lysozyme contrast matched solvent. Upon temperature increase negatively charged units are exposed to the surface of the aggregates during thermal transition which is a stabilizing force against the phase separating coil-to-globule transition of poly(N-isopropylacrylamide) (PNIPAM).