Separation of Micro-Brownian Motion and Side-Group Rotational Motion for Poly(N-isopropylacrylamide) in 1,4-Dioxane Studied by Dielectric Relaxation Spectroscopy

Dielectric relaxation of poly-(N-isopropylacrylamide)(PNiPAM) was investigated in 1,4-dioxane as a low-polarity solventat a concentration between 0 and 20 wt %, temperature between 40 and-35 degrees C, and a frequency range between 40 Hz and 1.8 GHz.Results suggest that relaxation due to the molecular motion of PNiPAMhas two components: relaxation of side-group rotational motion at similar to 100 MHz and micro-Brownian motion of PNiPAM chain at similar to 1MHz at room temperature. These processes are described by the sumof two Cole-Cole equations. Furthermore, the relaxation timesof these processes showed distinct temperature dependences, as confirmedby activation energies obtained from the Arrhenius plot. In addition,asymmetric relaxation was observed in the MHz region of PNiPAM invarious solvents comprising two individual relaxations. This couldexplain some fundamental aspects of PNiPAM solution properties andprovide a deeper understanding of the molecular dynamics of PNiPAM.