Physics PhD graduate student Yannic Gagnon and Professor Connie Roth have demonstrated that the local glass transition temperature Tg, the temperature at which the material locally transitions from an equilibrium liquid to a non-equilibrium solid glass, is strongly impacted by the modulus of a neighboring polymer domain. Polymer materials are often made of blends of glassy and rubbery polymers to improve the toughness of the material. The mechanism behind how rubber toughening occurs at the molecular level near glassy-rubbery polymer interfaces is still unknown.
A localized fluorescence method was used to measure the local Tg(z) as a function of distance z from a glassy-rubbery polymer interface between glassy polystyrene (PS) and rubbery polydimethylsiloxane (PDMS). By systematically varying the cross-link density of the PDMS rubber, the PDMS Young’s modulus was varied from 0.9 to 2.6 MPa. Surprisingly, this change in PDMS modulus was shown to shift the local Tg(z) by 40 Kelvin within PS at a distance of z = 50 nm away from the interface. These results defy current theoretical efforts in the field to understand how local properties are changed near polymer interfaces. The Roth lab is using targeted studies like these to map how local glass transition dynamics are coupled across polymer-polymer interfaces.
Yannic J. Gagnon and Connie B. Roth, ACS Macro Letters 2020, 9, 1625-1631. “Local Glass Transition Temperature Tg(z) Within Polystyrene Is Strongly Impacted by the Modulus of the Neighboring PDMS Domain” DOI: 10.1021/acsmacrolett.0c00659 https://pubs.acs.org/doi/10.1021/acsmacrolett.0c00659