Poly(3-hexylthiophene) Grains Synthesized by Solvent-Free Oxidative Coupling Polymerization and Their Use as Light-Responsive Liquid Marble Stabilizer

Solvent-free oxidative coupling polymerization of 3-hexylthiophene using FeCl₃ oxidant was conducted to synthesize poly­(3-hexylthiophene) grains. Optical and scanning electron microscopy studies confirmed production of submillimeter-sized atypical grains with rough surfaces. Solubility test, Fourier transform infrared spectroscopy, and ¹H nuclear magnetic resonance studies indicated the branching and cross-linking of the poly­(3-hexylthiophene). Elemental microanalysis and X-ray photoelectron spectroscopy studies confirmed that the poly­(3-hexylthiophene) grains were doped with chloride ions. The poly­(3-hexylthiophene) grains showed hydrophobic character due to hexyl side chains, and the critical surface tension was determined to be 25.9 mN m^–1. The poly­(3-hexylthiophene) showed a light-to-heat photothermal property, and near-infrared laser irradiation to the poly­(3-hexylthiophene) grains induced a rapid temperature increase up to 664 °C. The poly­(3-hexylthiophene) grains can work as an effective liquid marble stabilizer with a photothermal property, and the liquid marble exhibited locomotion on a water surface due to near-infrared laser-induced Marangoni flow.