Dresden 2020 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 21: Crystallization, Nucleation and Self-Assembly

CPP 21.5: Vortrag

Montag, 16. März 2020, 16:00–16:15, ZEU 255

Independent Variation of Transition Temperature and Order Parameter at Prefreezing Transition — •Muhammad Tariq, Oleksandr Dolynchuk, Ann-Kristin Flieger, and Thomas Thurn-Albrecht — Institute of Physics, Martin Luther University Halle-Wittenberg, Germany

A solid substrate can induce crystallization of a liquid by either heterogeneous nucleation or prefreezing. Prefreezing refers to the formation of a crystalline layer of thickness lmin at the melt-solid interface at a temperature Tmax above the melting point Tm, and is an equilibrium phenomenon. Recently developed phenomenological theory of first-order prefreezing predicts that the transition temperature Tmax depends mainly on the difference of interfacial free energies γsm−(γsccm), whereas the order parameter lmin depends on the ratio γsccmsm. To test these predictions, we performed series of in situ AFM experiments on different polymer-substrate systems. Experiments on polyethylene PE films on a molybdenum disulfide MoS2 substrate evidence a significantly higher Tmax than on highly oriented pyrolytic graphite HOPG. In case of poly(є-caprolactone) PCL, where direct experimental measurements of the prefrozen layer thickness are possible, Tmax of the prefrozen PCL on MoS2 remains nearly same as on HOPG, whereas lmin decreases to a smaller value and, thereby, indicates that Tmax and lmin are independent. As such, these experimental findings are consistent with the above-mentioned predictions of the phenomenological theory.

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