Berlin 2024 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 21: Poster II

CPP 21.10: Poster

Tuesday, March 19, 2024, 18:00–20:00, Poster E

Multistep liquid-crystalline ordering of poly(3-hexylthiophene) films induced by the vacuum interface — •Anton Sinner and Oleksandr Dolynchuk — Experimental Polymer Physics, Martin Luther University Halle-Wittenberg, Germany

Crystallization in liquids is often initiated at solid-liquid interfaces, which can result in enhanced nucleation kinetics and crystal orientation. However, the influence of the less specific interface to air or vacuum can be of the same importance for ordering phenomena. Elucidating these processes is especially relevant for films of functional polymers, as the structure orientation induced at interfaces can significantly affect the material properties. Here, the influence of the vacuum interface on the crystallization in films of model semiconducting polymer poly(3-hexylthiophene) (P3HT) is investigated. By using grazing-incidence wide-angle X-ray scattering during crystallization upon cooling from the melt, we show that the ordering of P3HT films starts at the vacuum interface and undergoes multiple sanidic liquid-crystalline state (SLCS) transitions. The same hierarchy of SLCS is observed during melting, largely independent of the film thickness. Furthermore, we show that the vacuum interface induces the SLCS transitions at temperatures higher than that of bulk, which still results in a significant thermal hysteresis between cooling and heating. Our results demonstrate that the SLCS formation in P3HT has both similarities and differences to surface freezing of short alkanes at the vacuum interface, providing new insights into the phenomenon.

Keywords: Crystallization; Liquid crystals; Semiconducting polymers; Surface freezing; Crystal orientation