Characterisation of thermally controlled chain association in aqueous solutions of poly(N-isopropyl acrylamide)-g-poly(ethylene oxide): Dynamic light scattering

Laser light scattering was used to characterise intrachain and interchain associations in aqueous solutions of poly(N-isopropyl acrylamide) chain grafted with poly(ethylene oxide) (PNIPA-g-PEO) at different copolymer concentrations and temperatures. The dynamic light scattering (DLS) experiments revealed the existence of two diffusive relaxation processes, one is ascribed to the diffusion of individual polymer coils, or small clusters of molecules, and the other is attributed to interchain aggregation where nanoparticles are formed with a hydrophobic PNIPA core and a hydrophilic PEO shell. It is only for the most diluted solution (0.02 wt.%), that a single relaxation mode is observed. In the other cases a bimodal distribution of relaxation times is found. At higher concentrations, the interchain structures exhibit a pronounced contraction with increasing temperature. The time evolution of the structures upon a temperature quench (from 55 to 25 °C) was investigated and the results suggest that the reorganisation of the structures is quite fast.