| There are many mixture systems consisting of platelet colloidal suspensions and other particles in natrure and industry. In order to understand the equilibrium properties and phase state of the mixed colloidal systems and to develop soft materials with desired properties and characters, it is necessary to study the phase behavior of mixed systems consisting of platelet colloi d and other particles with different sizes and shapes. In this study, single-layer zirconium phosphate (ZrP) with uniform thickness and controllable diameter was used as template to prepare platelet colloidal system. Silica spheres were added into the colloid to study the phase behavior of ZrP platelets. Due to the significance of platelet particles in the field of research and industry, the synthesis of platelet particles was also studied. The details are listed as follows:1. ZrP crystals and platelet Mn-Kaolinite crystals were synthesized by hydrothermal method, large quantities ZrP was synthesized by refluxing method. By controlling the reaction conditions (temperature, reaction time and mole concentration of phosphoric acid), ZrP crystals with regular shape, intact crystal type and controllable size was synthesized. The diameter range was controlled between 300 and 2000 nanometer. However, the reaction temperature was up to 200℃and the ZrP output of a 1 00mL autoclave is only 4g. So the reflux method of preparing ZrP was improved by using a lager stirred reactor at room temperature or relatively low temperature, and the ZrP possessed good crystal type and uniform particle size (about 250nm). It was worth mentioning that the single output reached 2.24kg. The effect of Si/Al ratio and solid reactant concentration on the synthesis of Mn-Kaolinite was studied. Results showed that the strong alkaline environmental, Si/Al=1 and low solid reactant concentration(mass fraction is0.006) were beneficial to synthesize Mn-Kaolinite. When increasing the solid reactant concentration, the product yield decreased, the lattice defect density increased, and there were acicular Mn-Kaolinite.2. The effect of added spheres on the phase transition of the platelet colloid had been studied when the particle size ratio of sphere/platelet was 0.0901±0.0004. When non-adsorbent particles with different size or shape were added into platelet particle suspension, there was depletion interaction between particles. The addition of spherical particles into platelet colloid affected the isotropic phase-nematic phase transition. Research showed that depletion interaction induced by added spheres accelerated the transition of isotropic phase-nematic phase and decreased the volume fraction of ZrP to form a namatic phase. Meanwhile, the distance between platelets became closer, the arrangement of platelets tended to tighter, and the volume fraction of nematic phase turned out to be decreased. When increasing the volume fraction of sphere up to 0.0014, a tri-phase area emerged in the phase diagram. The appearance of tri-phase area indicated that there was demixing of isotropic phase-nematic phase. However, theoretically there was huge controversy wether there was demixing of isotropic phase-nematic phase or not. This research provided experimental evidence for the existence of demixing of isotropic phase-nematic phase in the sphere/platelet system.3. In this research, cut sphere model and the free energy expression of single platelet colloidal system were applied to construct the free energy density function of sphere/platelet mixed colloid. We have calculated the free volume fraction(α) in colloidal mixture of platelets and spheres which treats spheres as depletants. And when de volume fraction of ZrP reached 0.02, the value of a is close to zero. We have also transform the phase diagram of φP-φswith the diameter of spheres and platelets ratio for 0.0901 ± 0.0004 to φp-φsRby formula of φs=αφsR and with an simple analysis. |
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