Topological Defects in Tactoid Nematic Phase

The purpose research of the work is to illustrate the role of point surface topological defects in nematics in phase transitions using the example of inorganic sols of vanadium pentoxide in water V2O5/H2O.Methods. Basing on the measurements on polarization light microscopy and theoretically, in frames of the Landau-de Gennes model and the Kibble-Zurek model for defects, the influence of point topological defects at the surface of nematic colloid of lyotropic liquid crystals, in particular, in inorganic sols of the V2O5/H2O system, on their critical thermodynamic, electric, optical, elastic and mechanical properties is estimated. For the system V2O5/H2O, we study the developed models of nematic colloid phases with non-trivial topology composed of spindle-shaped particles, in which their topological defects are classified; geometrical parameters of nematic particles in dynamics and evolution depending on physicochemical conditions, phase stability criteria, conditions for coalescence of particles, including, under external magnetic field, and also, experimental observations confirmed the proposed theories and models, are considered.Results. With a glance of coalescence regime, the critical size of a colloid particle of the system V2O5/H2O, ~ 10 nm in the long axis direction, in which the value of magnetic energy equals to the sum of elastic and surface energy of acolloid particle, is estimated.Conclusion. We confirmed, that the prerequisite of sol particle coalescence in the system V2O5/H2O in the magnetic field is annihilation of the point topological defects at their poles, the geometrical criterion of tactoid coalescence in magnetic field is established basing on the different theories of their surface defects.