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 C˭O group and the free amino group on the o‐Ps formation.
Acknowledgment
This work was supported by the National Natural Science Foundation of China (50025309 and 90201096). Special thanks are given to Prof. Y. Ozaki and his co‐workers for providing the optimized structures of dimer models of PNIPAM for use in this research. The original o‐Ps lifetime data for PNIPAM aqueous solution and distilled water at other temperatures (25.0–50.0°C) are available from the author.