Preparation And Mechanism Of Silica Sol/Polyacrylate Composite Latex Using Bare Silica Sol

Silica sol/Polyacrylate composite latex was prepared through simple drop wise polymerization process under the condition of electrostatic repulsion between negative surface charge of silica and negatively charged polymer particle (derived from the anionic initiator KPS) without any surface modification. The influence of acrylate monomer ratio (MMA:BA) on structure of composite emulsion particles and stability of composite latex has been studied. The results indicated that the encapsulation of silica sol by polyacrylate increased with the monomer ratio (MMA:BA) decreased. The composite particle with core-shell structure can be synthesized when monomer ratio (MMA:BA) is 1:2, which silica particles served as shell and polyacrylate served as core. With the increase of amount of SiO2, polymerization rate and composite particle size had decrease trend. Also, the stability of composite emulsion was significantly improved due to the addition of silica sol.Based on experiment, it was found that the experimental law of drop wise processes was different from that of Pickering polymerization processes. Through the research on particle size distribution of polymerization process, a composite mechanism was proposed, that precursor particles of polyacrylate, which are formed in the early stage of soap-free emulsion polymerization, are very unstable, so they tend to be absorbed on colloidal silica particles to lower interfacial energy, thus forming composite particles.The structure of composite film was characterized by Scanning electron microscope (SEM). The images indicated that porous structure existed. Based on the discussion on the influence of composite particle size on porous structure, the mechanism of hollow formation was proposed. Water absorption of coating film of emulsion polymerization with emulsifier and emulsifier-free emulsion polymerization was studied and the result shows that water resistant property of coating film had obviously progress when there wasn't any low-molecular-weight emulsifier involved. With the increase of silica amount, the hardness of coating film enhanced, but shock resistant and flexibility maintain a high-level, which is likely duo to the well-dispersed of silica particles in polymer matrix.