Small angle neutron scattering from dilute aqueous dispersions of clay

Abstract

The small angle neutron scattering from dilute montmorillonite sols containing either Li⁺, K⁺ or Cs⁺ has been measured and marked differences in the state of aggregation of the clay platelets observed. By means of contrast variation experiments the structures of the basic units in the sols have been determined. In Li sols the platelets are fully dispersed, in K sols the average unit consists of a pair of platelets with two molecular layers of water between them, and in Cs sols it consists of three platelets again interleaved with double molecular layers of water. The water between the platelets only undergoes very slow isotopic exchange with the solvent although the self-diffusion coefficient of water within the interplatelet region is known to be fast.