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Spectroscopy Letters
An International Journal for Rapid Communication
Volume 40, 2007 - Issue 1: Spectrometry and Automation
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Original Articles

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

Jie Xu Structure Research Laboratory, University of Science and Technology of China, Hefei, Anhui, People's Republic of China; Department of Polymer Science and Engineering, University of Science and Technology of China, Hefei, Anhui, People's Republic of China; Jiangsu Provincial Key Lab of ASIC Design, Nantong University, Nantong, Jiangsu, People's Republic of ChinaCorrespondence[email protected]
,
Xianfeng Zhang Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui, People's Republic of China
,
Hongwei Chen Department of Polymer Science and Engineering, University of Science and Technology of China, Hefei, Anhui, People's Republic of China
,
Biao Chen Department of Polymer Science and Engineering, University of Science and Technology of China, Hefei, Anhui, People's Republic of China
&
Qijin Zhang Structure Research Laboratory, University of Science and Technology of China, Hefei, Anhui, People's Republic of China; Department of Polymer Science and Engineering, University of Science and Technology of China, Hefei, Anhui, People's Republic of China
Pages 139-147 | Received 24 Apr 2006, Accepted 31 Jul 2006, Published online: 15 Feb 2011
 
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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.

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