Abstract
The rheological properties of aqueous suspensions of Na-fluor-tetrasilicic mica [NaMg2.5(Si4O10)F2] are studied with a coaxial cylinder rheometer. When immersed in water, a mica particle swells by absorption of water molecules into the interlayer region and subsequently separates into flakes with an aspect ratio of about 1000.
When the shearing direction turns reversely, stress overshoot is observed on the aqueous suspension. This may be attributed to an anisotropic structure caused by orientation of flakes.
The interlayer Na+ ions in Na-fluor-tetrasilicic mica are ion-exchangeable and ion exchange by various cations brings on the marked change in swelling characteristics. Therefore, the rheological properties of the mica suspensions in inorganic electrolyte solutions vary with the degree of swelling.
Microscopic observation of the mica films prepared by drying suspensions shows that the difference of swelling characteristics has a direct effect on the film structure.
