Eur. Phys. J. E (2013) 36: 66
https://doi.org/10.1140/epje/i2013-13066-3

Regular Article

Confinement effects on glass transition temperature, transition breadth, and linear expansivity: An ultraslow X-ray reflectivity study on supported ultrathin polystyrene films

¹⁹⁸⁷⁹ Shanghai Institute of Applied Physics, Chinese Academy of Sciences, 239 Zhang Heng Road, Pudong New District, Shanghai, 201204, China
²⁹⁸⁷⁹ Department of Physics, Faculty of Science and Technology, Kwansei Gakuin University, Sanda, 669-1337, Japan

^* e-mail: yangchunming@sinap.ac.cn
^** e-mail: z96019@kwansei.ac.jp

Received: 19 October 2012
Revised: 21 May 2013
Accepted: 31 May 2013
Published online: 27 June 2013

Abstract

X-ray reflectivity measurements of the glass transition in thin polystyrene films supported on Si substrates were performed at slow cooling rates ranging from 0.62 to 0.01 ^°C/min. At a cooling rate of 0.14 ^°C/min, a depression in the glass transition temperature was clearly observed with decreasing thickness. However, at a cooling rate of 0.62 ^°C/min, only a slight decrease in for a 12-nm-thick film was observed, while at an ultraslow cooling rate of 0.01 °C/min, a significant reduction in the of ultrathin films (12 and 6 nm) was observed. As the thickness decreased, a broadening in the width of the glass transition, w, was found at higher cooling rates (0.62 °C/min and 0.14 °C/min), while narrowing of w was observed at ultraslow cooling rates of 0.01 °C/min and 0.04 °C/min. A narrow distribution of relaxation time in the ultrathin films indicates that most segments are able to relax under the ultraslow cooling process, thus showing an inherent reduction in the of the confined thin polymer films.