# 2019 CAP Congress / Congrès de l'ACP 2019

2-7 June 2019
Simon Fraser University
America/Vancouver timezone
Welcome to the 2019 CAP Congress Program website! / Bienvenue au siteweb du programme du Congrès de l'ACP 2019 !

## $\beta$-NMR Studies of the Temperature and Depth Dependence of Dynamics in Polystyrene Thin Films

Jun 3, 2019, 1:15 PM
30m
ASB 10900 (Simon Fraser University)

### ASB 10900

#### Simon Fraser University

Invited Speaker / Conférencier(ère) invité(e) Condensed Matter and Materials Physics / Physique de la matière condensée et matériaux (DCMMP-DPMCM)

### Speaker

Dr Iain McKenzie (TRIUMF)

### Description

The decrease of the glass transition in polystyrene thin films with decreasing film thickness has given rise to the suggestion that there is a region near the free surface where there are faster dynamics than in the bulk. This surface mobility has been directly measured, but there are few studies of how the enhanced dynamics varies with distance from the free surface. We have used $\beta$-detected nuclear magnetic resonance ($\beta$-NMR) of implanted $^8$Li$^+$ to directly probe the temperature and depth dependence of the $\gamma$-relaxation mode, which is due to phenyl rings undergoing restricted rotation, in thin films of atactic deuterated polystyrene (PS-d8). I will show that the activation energy for the $\gamma$-relaxation is lower near the free surface and returns to bulk values at depths of $\sim$10 nm and discuss how the depth dependence of $\gamma$-relaxation is affected by sample processing (such as annealing, floating on water and the inclusion of a surfactant), and by the presence of a buried interface. I will introduce a novel hole-burning (selective saturation) $\beta$-NMR technique that has been used to measure the depth dependence of the fluctuation rate of a much slower relaxation process.

### Primary author

Dr Iain McKenzie (TRIUMF)

### Co-authors

Dr Yu Chai (University of Waterloo) Dr David Cortie (University of British Columbia) Prof. James Forrest (University of waterloo) Mr Derek Fujimoto (University of British Columbia) Ms Victoria Karner (University of British Columbia) Prof. Robert Kiefl (University of British Columbia) Dr Phillip Levy (TRIUMF) Prof. Andrew MacFarlane (University of British Columbia) Mr Ryan McFadden (University of British Columbia) Dr Gerald Morris (TRIUMF) Dr Matthew Pearson (TRIUMF) Dr Adam Raegen (University of Waterloo) Mr Shipei Zhu (University of Waterloo)

### Presentation materials

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