Pitch rotation of hexagonal microparticle using single beam thermo-optical tweezers

Single beam thermo-optical tweezers has been used for rotating particles continuously by 360o in pitch sense. The particle is rotated by placing it in a sample chamber with a thin layer of gold coated coverslip in an optical tweezers setup. The combined effects of convection current generated from heating of water and the optical trap rotate the particle in pitch sense near the hot spot present at the gold layer. This method works effectively until a water vapor bubble is formed due to continuous heating of the gold layer. We have tried to delay the onset of bubble formation by using viscoelastic medium instead of water. Viscoelastic medium is prepared by mixing polyacrylamide in water. Pitch rotation of hexagonal shaped particle has been observed for media having different concentrations of polyacrylamide. The frequency of rotation is measured at various concentrations. A suitable mathematical function is determined empirically which can describe the change in frequency while varying the concentration.