Glass Transitions in Binary Small-Molecule Organic Mixtures: Models and Planetary Relevance

Abstract The composition dependence of the glass-transition temperature (Tg) in mixtures remains an unresolved problem in glass physics, making empirical parametrizations both valuable and necessary. We evaluate the end point-linear, Fox, Gordon–Taylor, Jenckel–Heusch, and Kwei equations across 19 binary organic systems spanning alcohols, amines, carbonyls, aromatics, hydrocarbons, and halogenated species. Systems were classified from model goodness of fit, parameter uncertainty, and the statistical significance of curvature. Ten systems exhibit convex deviations below end point-linear mixing, one exhibits significant concave behavior above it, and eight are effectively end point-linear within the resolution of the available measurements. Jenckel–Heusch provides the most stable single-parameter description of curved systems, generally yielding the lowest RMSE and AIC while maintaining identifiable parameters. End point-linear fits are preferred without resolved curvature, Gordon–Taylor for supported asymmetry, and Kwei is often poorly constrained despite low residuals. Across the 19 classified systems, the selected models yielded a mean RMSE of 1.00 K and a mean R2 of 0.966. Ultimately, we provide parametrized models for binary organic mixtures and experimentally constrained benchmarks with applicability to modeling amorphous stability in organic-rich and hydrocarbon-bearing planetary and astrophysical ices.