Direct Observation of the Relationship between Thixotropic Behavior and Shear-Induced Orientation of Clay Particles in Synesthetic Hectorite Suspensions.

A thixotropic characteristics of aqueous gels containing smectite clay minerals were used in various industrial applications such as paint additives, which have been affected by the clay types and clay particle sizes. A model called a house-of-card arrangement of clay particles and anisotropic arrangement in aqueous gels has been proposed. We prepared different sizes of synthetic hectorite and studied them by scanning electron-assisted dielectric microscopy (SE-ADM) and simultaneous small-angle neutron scattering and rheological measurements (Rheo-SANS). The Rheo-SANS results indicated that the clay particles with the cross-sectional radius of 30 nm were clearly oriented in the direction of shear-flow (1 × 103 s-1) direction, but the anisotropic change was not observed for an aqueous gel with clays whose average radius was 19.5 nm. The present study suggested the thixotropic characteristics of aqueous gels depend on the hectorite particle size and aggregation structure under shear conditions.