Smectite Structure
Laponite is the commercial name of a synthetic hetorite with the general fomula {Si8[Mg6-xLix]O20[(OH)4-yFy]}x-Mxx+. It has the general layered structure of smectite. Some Mg atom are replaced by Li, leaving the layers negatively charged. The exchangable cations between layers diffuse away upon immersed in water, and the layers exfoliate into monodispersed nano platelet with diameter of 30nm and thickness of 1nm.
Phase Diagram
Above a certain concentration, the viscosity of Laponite suspension increases and gradually forms a thixotropic gel. Therefore Laponite is widely used in food and paint industry as a rheological modifier. The nature of the gelation process is controversial. Currently an understanding represented by the phase diagram is mostly accepted.
Theoretically, Laponite in the glass state can be largely described by glass theories, esp. the mode coupling theory (MCT). MCT was originally a model of supercooled liquid above and close to glass transition temperature. For colloidal glass, the effect of increasing volume fraction ϕ is analogous to decreasing temperature for molecular glass, and assuming the stress correlation function has the same form as the density correlation function, rheology behavior of colloidal glass near the glass transition limit ϕgcan be derived. Although Laponite undergoes aging at a volume fraction much lower than that predicted by the theory, but its effective volume fraction is much larger taking the Debye–Hückel diameter.
A useful resource of the detail of MCT can be found in J. Stat. Mech. P05013 (2005) DOI: 10.1088/1742-5468/2005/05/P05013.