arXiv subjects

Toru Asahi

Publications and source records attributed to Toru Asahi.

3 recordsLinked to original sources

arXiv2025

Chiral Analogues of Knit Stitches Designed Using Chiral Topology

Fabrics are flexible thin structures made of entangled yarn or fibers, yet the topological bases of their mechanics remain poorly understood. For weft knitted fabrics, we describe how the entanglement of adjacent stitches contributes to the flexibility of the fabric. Interpreting heterogeneous stitch pairs as domain boundaries reveals that the step between pairs of neighboring stitches is responsible for direction-specific flexibility. In typical knitted fabrics, anisotropic flexibility can be attributed to latticed domain boundaries. The intersections between domain boundaries result in point defects that induce frustration that resembles the impossible Penrose stairs. We identify these by a chiral characteristic, defined summing the ascending or descending steps in a cycle surrounding the defect. Remarkably, seed fabric, a knit with high flexibility in both course and wale directions, is characterized as a racemic crystal of these chiral point defects.

cond-mat.soft↗

arXiv2025

Symmetry and Thermodynamic Bounds on Cross-Coupling Transport in Chiral Liquid Crystals

We reformulate the Leslie effects that describe the dynamic cross-couplings in chiral liquid crystals driven by the transport of heat, electric charge, and mass. The Ericksen--Leslie model is extended in the linear response framework by representing nematic order with the Q-tensor. Subsequently, the thermodynamic uncertainty relation is applied to identify the upper bounds of the Leslie cross-coupling coefficients. We reveal that the cross-coupling coefficients are dependent on the scalar order parameter and vanish in the isotropic phase. In addition, the chirality of the phase allows torque induced by a transport current parallel to the director. The mutual signs of the Leslie thermohydrodynamic and thermomechanical coefficients are likely to be opposite in calamitic liquid crystals, as suggested by recent experimental observations. Our model is applicable to the thermal, chemical, and electrical Leslie effects. The present arguments suggest that a common underlying principle may govern both the Leslie effects and the thermal Edelstein effect in chiral solid crystals attributed to chiral phonons.

cond-mat.soft↗

arXiv2024

Reversal in Thermally Driven Rotation of Chiral Liquid Crystal Droplets

Thermomechanical coupling in chiral liquid crystals enables the direct conversion of heat current into mechanical rotation, providing a promising mechanism for the utilisation of low-grade thermal energy and heat-driven soft micro-actuation. However, the physical origin governing the direction and magnitude of this coupling remains elusive. Here, we demonstrate that cholesteric liquid crystal droplets undergo a reversal of their rotational direction with changing droplet size and temperature, even under a fixed temperature gradient and unchanged molecular chirality. This previously unrecognised behaviour cannot be accounted for by the conventional description of the thermal Leslie effect. Systematic investigations of droplet size, temperature and molecular structure, together with phenomenological analysis, reveal that thermomechanical coupling is strongly influenced by molecular orientational order and may even reverse sign with changes in the scalar order parameter. These findings identify molecular ordering as an active design parameter, rather than merely a structural descriptor, for controlling thermomechanical energy conversion. More broadly, our results suggest that thermomechanical coupling should be understood as a property emerging from molecular ordering, providing a new framework for designing heat-to-motion energy conversion in chiral soft matter.

cond-mat.soft↗