Different metrics for connecting mobility and glassiness in thin films

Data continue to accrue indicating that experimental techniques may differ in their sensitivity to mobility and glassiness. In this work the Limited Mobility (LM) kinetic model is used to show that two metrics for tracking sample mobility yield quantitatively different results for the glass transiti...

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Bibliographic Details
Published in:Soft matter 2019-02, Vol.15 (7), p.1651-1657
Main Authors: DeFelice, Jeffrey, Lipson, Jane E. G
Format: Article
Language:English
Subjects:
Dependence
Film thickness
Free surfaces
Glass transition temperature
Mapping
Mobility
Optimization
Temperature scales
Thin films
Tracking
Transition temperatures
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Summary:Data continue to accrue indicating that experimental techniques may differ in their sensitivity to mobility and glassiness. In this work the Limited Mobility (LM) kinetic model is used to show that two metrics for tracking sample mobility yield quantitatively different results for the glass transition and mobile layer thickness in systems where free surfaces are present. Both LM metrics track the fraction of material that embodies mobile free volume; in one it is relative to that portion of the sample containing any kind (mobile and dormant) of free volume, and in the other it is relative to the overall sample. Without any kind of optimization, use of the latter metric leads to semi-quantitative agreement with experimental film results, both for the mobile layer thickness and the dependence of sample glass transition temperature on film thickness. Connecting the LM predictions with experiment also produces a semi-quantitative mapping between LM model length and temperature scales, and those of real systems. Alternative perspectives of mobility method 1 (blue) vs. method 2 (red) compared to experimental data (symbols).
ISSN:1744-683X
1744-6848
DOI:10.1039/c8sm02355g