Effect of Aerosol Size on Glass Transition Temperature.

The amorphous phase state of suspended nanoparticles affects their atmospheric lifetimes and environmental impact. Influence of relative humidity and chemical composition on the glass-to-liquid transition is well-known. However, the influence of the particle size on the phase transition remains uncertain. Here we show experimental data that probe the amorphous phase transition of suspended sucrose particles as a function of particle size. The depression in glass-transition temperature follows the Gibbs-Thomson or Keesom-Laplace predicted proportionality of Δ T g ∝ D -1 for particles 100-700 nm in diameter, but the proportionality changes to Δ T g ∝ D -1/2 for smaller sizes. Literature data for glass-transition temperature depression in thin films and nanoconfined compounds show similar and strong deviations from the expected D -1 behavior. While the observed proportionalities remain incompletely understood, the results here provide evidence that the deviation from Δ T g ∝ D -1 is not attributable to substrate effects.