arXiv subjects

Oleksandr Dolynchuk

Publications and source records attributed to Oleksandr Dolynchuk.

2 recordsLinked to original sources

arXiv2026

Substrate-induced crystallisation in polymers: Exceptional impact of prefreezing versus heterogeneous nucleation on kinetics and morphology

Crystallisation of liquids often occurs at solid surfaces, via heterogeneous nucleation or prefreezing. Understanding this process is crucial for controlling crystal morphology in thin films and developing efficient nucleating agents - especially for polymers, typically processed in a molten state. However, the efficiency of nucleation and prefreezing with respect to crystallisation kinetics and semicrystalline polymer morphology has not been well studied and remains unclear. Here, we address this challenge by conducting a systematic study of substrate-induced crystallisation in dewetted droplets of the model polymer poly($\varepsilon$-caprolactone) (PCL) on various crystalline and amorphous substrates. Using polarized light optical microscopy, droplet crystallisation temperature was monitored and varied across the substrates, revealing three scenarios: close-to-homogeneous nucleation on glass and silicon; heterogeneous nucleation on ordered and disordered carbon-rich substrates; and prefreezing on graphene. The temperature-dependent nucleation rate was analysed and found to obey classical nucleation theory for all systems except PCL on graphene, where it diverges as all the droplets crystallise simultaneously. The highest in- and out-of-plane PCL crystal orientation is found on graphene, where the epitaxially grown lamellae extend vertically over several hundred nanometres. These results demonstrate that prefreezing has a superior influence on crystallisation kinetics and crystal morphology, making prefreezing substrates perfect nucleating agents.

cond-mat.soft↗

arXiv2026

Surface-induced ordering and continuous breaking of translational symmetry in conjugated polymers

Surface-induced liquid crystalline phase transitions evoke fundamental interest and can provide deeper insight into the nature of low-dimensional phases. Board-like conjugated polymers are of particular interest because they exhibit novel sanidic liquid crystalline mesophases that have not been widely studied. Furthermore, films of these polymers often exhibit preferential molecular orientation near the free surface, suggesting that the surface influences the ordering process. However, the underlying mechanism of this surface-induced ordering remains unclear. Here, we use surface-sensitive grazing-incidence X-ray scattering to monitor the formation and disappearance of positional order in situ in thin films of two board-like conjugated polymers representative of two classes: polythiophenes and polydiketopyrrolopyrroles. The results show that the free surface induces the formation of a highly oriented, sanidic disordered mesophase at the surface of both conjugated polymers, thus marking the emergence of positional order. This ordering process continues upon cooling and involves multiple transitions into more ordered liquid crystalline mesophases, both at the surface and in the bulk. The positional smectic-like order parameter exhibits continuous temperature dependence near the transition, signifying that the breaking of translational symmetry by the surface occurs continuously. Theoretical analysis allows us to accurately describe the temperature-dependent order parameter when critical behavior is considered.

cond-mat.soft↗