Abstract
The ultra-small-angle X-ray scattering (USAXS) is a very powerful technique for a structural study in the order of several thousand Å to micrometers. In this study, the colloidal crystal structure in aqueous dispersion of latex particle has been studied by USAXS using the advantage that USAXS can be applied to turbid systems. The nearest neighbor interparticle distance in colloidal crystal first increased with increasing ionic strength, and passing through a maximum then decreased. This observation was never reported both by other experimental technique such as microscope and theoretical considerations. It was found that the maximum position was well scaled by product of inverse Debye screening length and particle radius for various kinds of latex particles and that this maximum is the solid-liquid transition point of colloidal crystal. This observation may mean that some additional factor for interparticle interaction should be taken into account.
