Structural characterization of poly(N-isopropylacrylamide) gels and some of their copolymers with acrylamide through positron annihilation lifetime spectroscopy

In this work, poly(N-isopropylacrylamide) (NIPAAm), poly(acrylamide) (AAm) and poly(N-isopropylacrylamide)-co-acrylamide (NIPAAm/AAm) gels were characterized through positron annihilation lifetime spectroscopy (PALS). PALS was used to determine the average free volume radii of NIPAAm and NIPAAm/AAm gels, through the measurement of the ortho-positronium (o-Ps) Lifetime. NIPAAm gel 10 x 1 showed a radius of approximately 2.9 Angstrom. The copolymers with acrylamide, NIPAAm/AAm 10 x 1, with the acrylamide composition varying from 2 to 100 wt%, showed a decreased radius down to 2.1 Angstrom in AAm 10 x I gel. The free volume estimated for the gels decreases with increasing acrylamide concentration. The results are discussed in terms of the changes in the gels' structure due to different polymer-polymer interactions. (C) 1998 Published by Elsevier Science Ltd. AU rights reserved.