Elastic Mechanical Response of Thin Supported Star-Shaped Polymer Films

Peter C Chung; Emmanouil Glynos; Georgios Sakellariou; Peter F Green

doi:10.1021/acsmacrolett.5b00944

Elastic Mechanical Response of Thin Supported Star-Shaped Polymer Films

ACS Macro Lett. 2016 Apr 19;5(4):439-443. doi: 10.1021/acsmacrolett.5b00944. Epub 2016 Mar 15.

Authors

Peter C Chung¹, Emmanouil Glynos¹, Georgios Sakellariou², Peter F Green¹

Affiliations

¹ Department of Materials Science and Engineering, Biointerfaces Institute, University of Michigan, Ann Arbor, Michigan 48109, United States.
² Department of Chemistry, University of Athens, Panepistimiopolis, Zografou, 15771, Athens Greece.

PMID: 35607244
DOI: 10.1021/acsmacrolett.5b00944

Abstract

We show evidence of thickness-dependent elastic mechanical moduli that are associated largely with the effects of architecture (topology) and the overall shape of the macromolecule. Atomic force microscopy (AFM) based nanoindentation experiments were performed on linear chain polystyrene (LPS) and star-shaped polystyrene (SPS) macromolecules of varying functionalities (number of arms, f) and molecular weights per arm M_w^arm. The out-of-plane elastic moduli E(h) increased with decreasing film thickness, h, for h less than a threshold film thickness, h_th. For SPS with f ≤ 64 and M_w^arm > 9 kg/mol, the dependencies of E(h) on h were virtually identical for the linear chains. Notably, however, for SPS with f = 64 and M_w^arm = 9 kg/mol (SPS-9k-64), the h_th was over 50% larger than that of the other polymers. These observations are rationalized in terms of the structure of the polymer for high f and sufficiently small M_w^arm and not in terms of the influence of interfacial interactions.