Unique Free‐Volume Change During the Phase Separation of Poly(N‐isopropylacrylamide) Aqueous Solution Studied by Positron Annihilation Lifetime Spectroscopy

Abstract

The change in free-volume during phase separation of poly(N-isopropylacrylamide) (PNIPAM) aqueous solution was studied in situ by positron annihilation lifetime spectroscopy. The average size of a free-volume nanohole exhibited a co-nonsolvent change, affirming the trans-to-gauche conformational change of PNIPAM chains during phase separation. The results obtained for the ortho-positron (o-Ps) intensity accounted for the competitive effects of the variations in composition of the free C5 5O group and the free amino group on the o-Ps formation.