Manipulation and transport of microparticles and even fluorescent molecules by thermally induced gradient of the order parameter is demonstrated in the nematic liquid crystal. IR light absorption of a focused beam of the laser tweezers is used to heat locally a thin layer of the nematic liquid crystal by several degrees, thus creating a spatial gradient of temperature of the nematic liquid crystal over tens of micrometers. It is observed that a colloidal particle with dipolar symmetry of the director configuration is attracted into the hot spot of the tweezers. The strength of trapping potential increases linearly with particle radius, which indicates that the trapping is due to elastic energy of the distorted nematic liquid crystal around the particle. By using fluorescent molecules instead of colloidal particles, we observed that this thermal trapping of colloidal particles is efficient down to the nanoscale, as fluorescent molecules are also attracted to the hotter regions of the liquid crystal. This effect is absent in the isotropic phase.

Date Published: 16 September 2014
PDF: 9 pages
Proc. SPIE 9164, Optical Trapping and Optical Micromanipulation XI, 91642B (16 September 2014); doi: 10.1117/12.2061308

Published in SPIE Proceedings Vol. 9164:
Optical Trapping and Optical Micromanipulation XI
Kishan Dholakia; Gabriel C. Spalding, Editor(s)