Free Surface Relaxations of Star-Shaped Polymer Films

Published

November 28, 2017

Author(s)

Alexandros Chremos, Bradley R. Frieberg, Emmanouil Glynos, Kyle Johnson, Hengxi Yang, Suresh Narayanan, Peter F. Green, Georgios Sakellariou

Abstract

X-ray photon correlation spectroscopy (XPCS) studies show that the viscosities of thin film linear chain polymers at temperatures sufficiently high above the bulk glass transition temperature Tg bulk are equal to the bulk zero shear viscosities. The free surface dynamics of thin films of macromolecules of branched topologies have been shown to be slower than the bulk at temperatures above Tg bulk, in some situations. To understand this phenomenon, a study of 8-arm star-shaped polystyrenes (SPS) of varying arm lengths, were investigated using a combination of XPCS, oscillatory shear rheology, dielectric spectroscopy, and molecular dynamics simulations and. The surface dynamics of SPS molecules with short arms are slower than the bulk, whereas for longer entangled arms the surface relaxation dynamics were comparable to the bulk. The mechanism of surface relaxations of the short-arm SPS molecule is also different -cage-like – from the long armed SPS molecule. Molecular dynamics simulations suggest that the slower surface dynamics are associated with spatial ordering of the short-arm molecules at the free surface.

Citation

Physical Review Letters

Volume

119

Pub Type

Journals

Download Paper

https://doi.org/10.1103/PhysRevLett.119.227801

Keywords

star polymers, dynamics, thin films

Citation

Chremos, A. , Frieberg, B. , Glynos, E. , Johnson, K. , Yang, H. , Narayanan, S. , Green, P. and Sakellariou, G. (2017), Free Surface Relaxations of Star-Shaped Polymer Films, Physical Review Letters, [online], https://doi.org/10.1103/PhysRevLett.119.227801 (Accessed April 1, 2025)