Rotational dynamics of anisotropic microscopic particles studied by secondharmonic generation

This letter reports the application of second harmonic generation (SHG) to study the rotational dynamics of anisotropic microparticles. In this study, disk-shaped clay particles of montmorillonites with a diameter of 0.5 mu m and a thickness of 0.01 mu m suspended in liquid media were studied. Fluct uations in the SH signal observed upon irradiating the samples with the fun damental light are attributed to the rotational motion of the particles. Th e relaxation times obtained from the autocorrelation of the fluctuations ar e 0.024 +/- 0.04 s for water, 0.25 +/- 0.01 for glycerol/water (74:26 w/w), and 0.63 +/- 0.01 s for glycerol/water (80:20 w/w). These values are of th e same order of magnitudes for the relaxation times calculated using the St okes-Einstein model for rotation of an oblate particle.