Dresden 2017 – wissenschaftliches Programm
CPP 40.7: Vortrag
Mittwoch, 22. März 2017, 17:15–17:30, ZEU 222
Interface-induced crystallization via prefreezing: A first-order prewetting transition — •Ann-Kristin Flieger, Martha Schulz, and Thomas Thurn-Albrecht — Experimental Polymer Physics, Institute of Physics, Martin Luther University Halle-Wittenberg, 06120 Halle, Germany
Prefreezing is a mechanism of surface-induced crystallization. In prefreezing a crystalline layer is formed at the interface of a solid substrate and the liquid phase already above the melting point. Wetting theory predicts a jump in thickness at the formation and a divergence upon approaching coexistence. However, the thickness of the prefreezing layer has not been experimentally measured so far.
We studied ultrathin films of Polycaprolactone during the crystallization on graphite. With AFM at high temperatures we observe prefreezing instead of heterogeneous nucleation. The corresponding crystalline layer is formed at a temperature above the bulk melting point. Similar observations were already made for polyethylene on graphite (A.-K. Löhmann et al., PNAS 49, 17368-17372 (2014)). In that case however, a direct measurement of the thickness of the prefreezing layer was not possible. Here, we show directly the finite thickness of the prefreezing layer for PCL. It forms with a thickness of a few nanometers which further increases during cooling. This observation demonstrates the transition is of first order, as expected for a prewetting transition.
The results prove that prefreezing can be described by common wetting theory. The studied system PCL-graphite is of importance for applications since graphitic materials are widely used as fillers for PCL.