PHOTOPHORESIS OF LARGE ABSORBING PARTICLES IN A TRANSPARENT LIQUID

A theory of solid absorbing particle photophoresis for the case rho = 2 pi a/lambda much greater than 1, where a is the particle radius and lambda is the wavelength of light, was designed. Using the geometrical optics approximation, the light intensity distribution inside the par ticle, which depends on rho and the optical parameters of a particle, was obtained. On this basis, the characteristic temperature distributi ons, which are caused by the light absorption inside the particle, wer e calculated. Photophoretic mobility (PPM) of a particle surrounded by an electrolyte solution was calculated based on the solution of the N avier-Stokes equation for a thin subsurface layer of a liquid with the Boltzmann ion concentration distribution in the field of the particle surface potential. Numerical calculations were made; a general analys is of the optical and thermal fields was carried out; and an analysis of the particle PPM, depending on rho and indices of refraction n(r) a nd absorption kappa of the particle material, was conducted. It was sh own that, at kappa rho much less than 1, the PPM of such particles has a negative value, and, at kappa rho > 1, it has a positive value.