Raspberry-shaped particles of a polymethylmethacrylate (PMMA) core chemically binding silica nanoparticles (NPs) could be synthesized with heterocoagulation in combination with two-step addition of a polymerizable silane coupling agent of 3-methacryloxypropylmethoxysilane (MPTMS) before and after the heterocoagulation, respectively. Submicron-sized PMMA particles were prepared in soap-free emulsion polymerization in the presence of MPTMS that was introduced into the PMMA particles as a scaffold for the chemical bonding. The PMMA particles were mixed with silica NPs under an acidic condition of pH = 2 to cause electrostatic heterocoagulation of the PMMA cores and the silica NPs. Then, MPTMS was added to the acidic suspension, and the suspension pH of heterocoagulated particles was raised to 8 to generate strong chemical bonding between the PMMA and silica NPs in stable particle dispersion. The strong interaction between the PMMA cores and silica NPs was demonstrated in sonication experiments where desorption of silica NPs from the PMMA cores was drastically suppressed by the two-step MPTMS addition.
- Silane coupling agent