Heat-Induced Self-Assembling of Thermosensitive Block Copolymer. Rheology and Dynamic Light Scattering Study

The dynamic aspects of the thermoreversible morphological transition of poly(2-ethoxyethyl vinyl ether)- b -poly(2-hydroxyethyl vinyl ether) (PEOVE- b -PHOVE) in aqueous solutions have been investigated by dynamic light scattering (DLS) and rheological measurements. A sample-position-dependent DLS study, employed here, allowed us to resolve two transitions, i.e., (1) molecular dispersion-to-micelle transition and (2) micelle-to-macrolattice transition, which were not clearly resolved by small-angle neutron scattering studies in the previous work. These transitions are characterized by (1) an abrupt increase in the scattered intensity and (2) an appearance of speckle patterns. The temperature where the abrupt increase in intensity was observed was a few degrees lower than that the speckle pattern appeared. Rheological behaviors also supported the two transitions as (1) Newtonian-to-non-Newtonian transition and (2) non-Newtonian-to-plastic flow transition. It is concluded that a pseudo-sol-to-gel transition without chain anchoring is enough for an ergodic-to-nonergodic transition.