Structure and Dynamics of Star Polymer Films from Coarse-Grained Molecular Simulations

Published

October 5, 2021

Author(s)

Jack F. Douglas, Wengang Zhang, Francis W. Starr, Alexandros Chremos

Abstract

We quantify the structure and dynamics in molecular simulations of star polymer films of varying arm mass Ma and number of star arms f on a supporting solid substrate with an attractive interaction and compare to the corresponding properties of thin films of linear polymers. While the spatial variation of segmental density profile is only weakly dependent on chain topology, the polymer topology changes both the average rate of relaxation and the spatial variation of the average segmental relaxation time τα as function of depth from the film substrate, z. In particular, we observe a general slowing down in the rate of relaxation of the entire film with an increasing f, a general trend attributed to an alteration of the effective cohesive interaction strength when f is increased. The mobility gradients in the film, quantified by the relaxation time obtained from the intermediate scattering function on a layer-by-layer basis, is also significantly altered by f. In particular, the width of the substrate interfacial zone grows with increasing f, saturating in value around f = 12, while the width of the interfacial zone near the 'free' boundary, where the polymer dynamics is greatly accelerated compared to the film interior, is hardly influenced at all by changes in polymer topology. These observations are qualitatively consistent with the interpretation of recent X-ray photon correlation spectroscopy on star polymer melt films.

Citation

Macromolecules

Issue

13

Pub Type

Journals

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Keywords

star polymers, thin films, glass formation, interfacial zone, density gradient, mobility gradient, collective motion, activation energy

Citation

Douglas, J. , Zhang, W. , Starr, F. and Chremos, A. (2021), Structure and Dynamics of Star Polymer Films from Coarse-Grained Molecular Simulations, Macromolecules, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=931924 (Accessed December 14, 2024)