Elucidation of the physical factors that control activated transport of penetrants in chemically complex glass-forming liquids

Journal Article · Tue Oct 04 00:00:00 EDT 2022 · Proceedings of the National Academy of Sciences of the United States of America

DOI:https://doi.org/10.1073/pnas.2210094119· OSTI ID:1891040

Mei, Baicheng ^[1]; Sheridan, Grant S. ^[1]; Evans, Christopher M. ^[2]; Schweizer, Kenneth S. ^[3]

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1. Department of Materials Science, University of Illinois at Urbana-Champaign, Urbana, IL 61801, Material Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL 61801
2. Department of Materials Science, University of Illinois at Urbana-Champaign, Urbana, IL 61801, Material Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL 61801, Department of Chemical &, Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801
3. Department of Materials Science, University of Illinois at Urbana-Champaign, Urbana, IL 61801, Material Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL 61801, Department of Chemical &, Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801

Understanding the activated transport of penetrant or tracer atoms and molecules in condensed phases is a challenging problem in chemistry, materials science, physics, and biophysics. Many angstrom- and nanometer-scale features enter due to the highly variable shape, size, interaction, and conformational flexibility of the penetrant and matrix species, leading to a dramatic diversity of penetrant dynamics. Based on a minimalist model of a spherical penetrant in equilibrated dense matrices of hard spheres, a recent microscopic theory that relates hopping transport to local structure has predicted a novel correlation between penetrant diffusivity and the matrix thermodynamic dimensionless compressibility, S ₀ ( T ) (which also quantifies the amplitude of long wavelength density fluctuations), as a consequence of a fundamental statistical mechanical relationship between structure and thermodynamics. Moreover, the penetrant activation barrier is predicted to have a factorized/multiplicative form, scaling as the product of an inverse power law of S ₀ ( T ) and a linear/logarithmic function of the penetrant-to-matrix size ratio. This implies an enormous reduction in chemical complexity that is verified based solely on experimental data for diverse classes of chemically complex penetrants dissolved in molecular and polymeric liquids over a wide range of temperatures down to the kinetic glass transition. The predicted corollary that the penetrant diffusion constant decreases exponentially with inverse temperature raised to an exponent determined solely by how S ₀ ( T ) decreases with cooling is also verified experimentally. Our findings are relevant to fundamental questions in glassy dynamics, self-averaging of angstrom-scale chemical features, and applications such as membrane separations, barrier coatings, drug delivery, and self-healing.

• Sponsoring Organization: USDOE
• Grant/Contract Number: SC0020858
• OSTI ID: 1891040
• Alternate ID(s): OSTI ID: 2421654
• Journal Information: Proceedings of the National Academy of Sciences of the United States of America, Journal Name: Proceedings of the National Academy of Sciences of the United States of America Journal Issue: 41 Vol. 119; ISSN 0027-8424
• Publisher: Proceedings of the National Academy of Sciences
• Country of Publication: United States
• Language: English