Releasing and Freezing Phase Separation of Polyvinyl Alcohol/Silica To Control Polymorphs of Silica

Crystalline silica is prepared beyond 1500 degrees C in a traditional process. Here, we prepared both cristobalite-rich and quartz-rich silica by calcinating polyvinyl alcohol (PVA)/silica films at 900 degrees C. Results of characterizations show that polymorphisms of silica were dependent on the phase separation of PVA and silica before calcinations. The phase separation is controlled by a coagulation bath. By soaking PVA/silica hybrid films in a coagulation bath before thermal treatment, phase separation of PVA and silica was frozen and prevented. When PVA/silica hybrid films were not soaked in a coagulation bath before thermal treatment, phase separation of PVA and silica was released. Further research reveals that different phase structures of PVA and silica generate distinct microscopical morphologies and molecular structures of silica, leading to variation of the final polymorphs.