We report experimental studies on the Saturn ring defect associated with a spherical microparticle across the nematic to smectic-A phase transition. We observe that the director distortion around the microparticle changes rapidly with temperature. The equilibrium interparticle separation and the angle between two quadrupolar particles in the N phase are larger than those of the SmA phase. They are almost independent of the temperature in both phases, except for a discontinuous jump at the transition. We assembled a few particles using a laser tweezer to form a two-dimensional colloidal crystal in the N phase. The lattice structure of the crystal dissolves irreversibly across the N -SmA phase transition. The results on the pretransitional behavior of the defect are supported by the Landau–de Gennes Q -tensor modeling.
COBISS.SI-ID: 2872420
We show that nematic colloids can serve as a highly variable and controllable platform for studying inclusions with changeable topology and their effects on the surrounding ordering fields. We explore morphing of toroidal and knotted colloidal particles into effective spheres, distinctively changing their Euler characteristic and affecting the surrounding nematic field, including topological defect structures. With toroidal particles, the inner nematic defect eventually transitions from a wide loop to a point defect (a small loop). Trefoil particles become linked with two knotted defect loops, mutually forming a three component link, that upon tightening transform into a two-component particle-defect loop link. For more detailed topological analysis, Pontryagin-Thom surfaces are calculated and visualised, indicating an interesting cascade of defect rewirings caused by the shape morphing of the knotted particles.
COBISS.SI-ID: 2837092
In this paper, we show that surfaces of diverse biofibers, including spider silks and cellulosic fibers, can be easily sensed by depositing droplets of a nematic fluid onto the fibers. The droplets reveal the surface properties of the fibers via their optical images, notably showing also the fiber chirality. Further, the droplets are used to study the entanglement of biofibers, as a route toward novel biological and bioinspired materials.
COBISS.SI-ID: 2917220