ArticleProceedings of the National Academy of Sciences of the United States of America2020
Amorphous polymer dynamics and free volume element size distributions from ultrafast IR spectroscopy.
Article in Proceedings of the National Academy of Sciences of the United States of America, 2020. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Cited by 4 papers.
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4 citing papers in PubMed.
- Mechanochemistry of Spiropyran under Internal Stresses of a Glassy Polymer.Journal of the American Chemical Society · 2022Article
- The Mechanical, Thermal, and Chemical Properties of PLA-Mg Filaments Produced via a Colloidal Route for Fused-Filament Fabrication.Polymers · 2022Article
- Origin of thiocyanate spectral shifts in water and organic solvents.The Journal of chemical physics · 2022Article
- ROAMing in mutable voids: Polymer free volumes from wobbling vibrational probes.Proceedings of the National Academy of Sciences of the United States of America · 2020Article
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Abstract
A method for measuring the size and size probability distribution of free volume regions in polymeric materials using ultrafast infrared (IR) polarization-selective pump-probe experiments is presented. Measurements of the ultrafast dynamics of a vibrational probe (the CN stretch of phenyl selenocyanate) in poly(methyl methacrylate) show that the probe dynamics are highly confined. The degree of confinement was found to be both time-dependent and dependent on the vibrational frequency of the probe molecule. The experiments demonstrate that different vibrational frequencies correspond to distinct subensembles of probe molecules that have different dynamic properties determined by their local structural environments. By combining the degree of dynamical confinement with the molecular size of the probe molecule, the free volume element size probability distribution was determined and found to be in good agreement with the best established experimental measure of free volume. The relative probability of a free volume element size is determined by the amplitude of the nitrile absorption spectrum at the frequency of the measurement. The inhomogeneous broadening of the spectrum was linked to the vibrational Stark effect, which permits site selectivity. The observed dynamics at each frequency were then associated with a different size free volume element and distinct local electric field. The multiple timescales observed in the pump-probe experiments were connected to local structural fluctuations of the free volume elements.
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