Rheology And Gelation Of α-Zirconium Phosphate Monolayer Suspensions

a-zirconium phosphate (a-ZrP) is a kind of lamellar compound with a quasi orthohexagonal shape. a-ZrP crystals can be exfoliated by tetra-n-butyl-ammonium hydroxide (TBAOH) solution into monolayers, resulting in a two-dimensional platelets of larger specific surface area and aspect ratio. Anisometric discotic suspensions, in contrast to colloidal suspensions of spherical and rod-shaped particles, can be used for liquid crystals, polymer nanocomposites, bionic materials, Pickering emulsions, drilling fluids, etc. a-ZrP monolayer suspension, involved in a variety of subjects, is typical discotic suspension and of applicable and academic values. In this dissertation, we studied rheolgical properties and gelation of colloidal suspensions of highly anisometric ZrP nanoplates, with the main results as follows:1. The pristine a-ZrP crystals were synthesized by a hydrothermal method from zirconyl chloride octahydrate and phosphoric acid, and then exfoliated into monolayers by tetra-n-butyl-ammonium hydroxide solution. The particle size and its distribution of a-ZrP crystals were tailored by the control of phosphoric acid concentration, reaction time and temperature. The size fractionation of the isotropic-nematic transition facilitated the increase of suspension concentration and the decrease of particle size polydispersity.2. Both the scanning electron microscope and the transmission electron microscope showed the a-ZrP crystals had well-defined morphology, a quasi orthohexagonal shape and a small polydispersity in particle size which mainly has a diameter of about 1500 nm. The a-ZrP crystals had good crystallinty with the evidence that transparent diffraction peaks in the X-ray diffraction pattern conformed to standard peaks in position, intensity and full width at half maximum. ZrP monolayer suspensions were characterized via the dynamic light scattering with particle diameter of about 1400 nm.3. In contrast to other suspensions, a super-strong shear-thinning behavior in a-ZrP monolayer suspensions of concentrations higher than that of isotropic-nematic transition was observed, which resulted from the slicing of hydroclusters by platelet rotation. The introducing of tetra-n-butyl-ammonium chloride increased the shear viscosity of a-ZrP monolayer suspensions, shortened the Newtonian plateau during the high-shear region and facilitated shear thickening. Within a certain range of strain or angular frequency, both storage modulus and loss modulus increased with the suspension concentration. In the amplitude scanning, storage modulus was larger than loss modulus in the linear viscoelastic region. In the angular frequency scanning, storage modulus and loss modulus varied mildly with low angular frequency, yet increased with medium-high angular frequency.4. The reduced pH value or introduced sodium chloride solution induced the gelation of a-ZrP monolayer suspensions. The gel height rised with the increasing concentration of suspensions. The formation of gels required enough Na+ or H+ to exchange.