Cooling rate dependence of the glass transition at free surfaces
S. Streit-Nierobisch, C. Gutt, M. Paulus, and M. Tolan

In-situ x-ray reflectivity measurements are used to determine the cooling rate dependent freezing of capillary waves on the oligomer poly(propylene glycol) (PPG). Only above the glass transition temperature $T_\mathrm{G}$ the surface roughness $\sigma$ can be described by the capillary wave model for simple liquids, whereas the surface fluctuations are frozen in at temperatures below $T_\mathrm{G}$. As the state of a glass forming liquid strongly depends on its thermal history, this effect occurs for fast cooling rates already at a higher temperature than for slow cooling. For the fastest cooling rates a very large shift of $T_\mathrm{G}$ up to $\unit[240]{K}$ compared to the bulk value of $\unit[196]{K}$ was observed.

© 2008 The American Physical Society.