Thermocapillary-driven coherent structures by low-Stokes-number particles and their morphology in high-aspect-ratio liquid bridges

•Coherent structures in the hydrothermal wave with mHTW=1 by low-Stokes-number particles are evinced experimentally.•Correlation between the Poincaré points and the coherent structure is examined by two different types of particles.•Two different types of the coherent structures emerge simultaneously in the liquid bridge. Thermocapillary-driven coherent structures by low-Stokes-number particles are experimentally investigated. Time-dependent convection is induced in a tall or high-aspect-ratio half-zone liquid bridge. We successfully realize coherent structures, which seem rigidly rotating by following the traveling-wave-type convection of mHTW=1 in azimuthal wave number due to so-called hydrothermal-wave instability. The Poincaré sections at different heights of a single particle forming the coherent structure are obtained in the rotating frame of reference by preparing a thin light sheet. Projected distribution of the multiple particles forming the coherent structure are also depicted to examine the correlation with the Poincaré points. The stability of the coherent structures is discussed by tracking the particles exhibiting turnover motion in the liquid bridge.