Eur. Phys. J. E (2012) 35: 129
https://doi.org/10.1140/epje/i2012-12129-3

Regular Article

Competition between substrate-mediated π-π stacking and surface-mediated T_g depression in ultrathin conjugated polymer films

¹ Department of Physics and Astronomy, University of Sheffield, S3 7RH, Sheffield, UK
² Department of Chemical and Biological Engineering, University of Sheffield, S1 3JD, Sheffield, UK
³ Diamond Light Source Ltd, Diamond House, Harwell Science and Innovation Campus, OX11 0DE, Oxfordshire, UK
⁴ Department of Chemistry, University of Sheffield, S3 7HF, Sheffield, UK

^* e-mail: t.wang@hotmail.com

Received: 4 July 2012
Revised: 5 October 2012
Accepted: 22 November 2012
Published online: 14 December 2012

Abstract

We report surface and interface effects in dynamics and chain conformation in the thin film of conjugated polymer PCDTBT. To probe dynamic anomalies, we measure the glass transition temperature (T_g) of PCDTBT films as a function of thickness, and find that there is a significant depression in T_g for films less than 100nm thick; a result qualitatively similar to that observed in many other polymer film systems. However, for films less than 40nm, the T_g converges to a constant value of 20K below its bulk value. Grazing incidence X-ray diffraction shows depth-dependent molecular organization that is associated with the unusual thickness-dependent dynamics.