Surface Charge Density On The Mg / Aildhs Colloidal Dispersion Liquid Crystal Phase Behavior

Recently, mineral liquid crystals arise more and more interests for their enhanced optical, electrical, magnetic and thermally stable properties. With the studying of mineral liquid crystals and further researching of theories, mineral liquid crystals would be new focus of future investigation.Up to now, there have been hands of mineral liquid crystalline materials, and mostly show isotropic-nematic phase transition, such as V₂O₅, boehmite. Only a few show columnar phase, such as Ni(OH)₂ and gibbsite under special contidions. Lamellar phase has been observed in β-FeOOH and H₃Sb₃P₂O₁₄, but only rarely.Many theroies were found about the forming of liquid-crystal phase, and the most popular model was proposed by Onsager in the 1940s. Onsager model based on the suppose of rigid particles with only rigid repulsion force among particles. However, many kinds of mineral liquid crystals are colloidal suspensions and charged, such as laponite, montmorillonite and LDHs etc. There are van der waals force and electrostatic force existing in suspensions and would effect on the phase transions. So it have further meaning to study the effect of charge on phase transitions in charged particle suspensions.The liquid crystal phase behavior of colloidal dispersions of positively charged plate-like particles, namely MgAl LDH (Mg:Al =1:1), Mg₂Al LDH (Mg:Al = 2:1), and the effect of electrolyte on phase behavior, were investigated. All of the dispersions at low volume fraction show disordered isotropic phase, because the particles can move freely under this situation. Isotropic- birefrigent phase transition occurs with increasing the volume fraction till a threshold value. For MgAl LDH dispersions, an isotropic-lamellar (I-L) phase transition takes place in 1:1 Mg/Al LDH suspensions, in which the particles possess higher surface charge density. While an isotropic-nematic (I-N) phase transition occurs in 2:1 Mg/Al LDH suspensions. Thickness polydispersity plays an important part in the different phase transitions between MgAl LDH and Mg₂Al LDH dispersions, because I-L phase transitions require lower thickness polydispersity. Thickness polydispersities of MgAl LDH and Mg₂Al LDH dispersions...