Ultra-small-angle X-ray and neutron scattering studies on colloidal crystals

The formation of colloidal crystals by charged colloidal particles in dispersion at a low ionic strength has been interpreted by the DLVO theory that assumes the electrostatic repulsion between particles to be a dominant factor. However, several recent observations can not be interpreted by the DLVO theory, one of which is our finding obtained by the ultra-small-angle X-ray scattering (USAXS) technique, i.e., the effect of added salt concentration on the interparticle distance in colloidal crystals. We obtained interesting and significant information by the ultra-smallangle scattering techniques on the interparticle interaction, which support the existence of a novel factor.