X-ray diffraction and rheology study of highly ordered clay platelet alignment in aqueous solutions of sodium tripolyphosphate

Highly ordered parallel alignment of a synthetic clay, referred to herein as an expandable mica (ME) but similar in behavior and physical characteristics to montmorillonite, in sodium tripolyphosphate (STP) solutions has been observed by an X-ray diffraction method. The weight ratio of the clay was 7%, and the ME/STP by weight ratio was varied from 0.1 to0.4. The X-ray diffraction patterns of the suspensions at high STP concentrations were very sharp, and the basal reflections of the clay gave up to fifth order reflections in some samples. The basal spacing of the clay in the suspensions decreased from 8.70 to 4.82 nm with increasing STP concentrations. The rheological properties of the same suspensions showed non-Newtonian behavior at zero STP addition. The steady shear viscosity of the suspensions decreased dramatically with increasing STP addition at a given shear rate. The total potential energy for particle-particle interaction calculated using classical DLVO theory indicates that the clay particles fall into a secondary minimum and that phosphate anions play an important role in controlling the alignment of the platelets.