Synthesis of additive-free cationic polystyrene particles with controllable size for hollow template applications

Studies on the synthesis of organic particles for template applications for facilitating the production of hollow particles have attracted tremendous attention. The unavailability of the commercial templates with a positive zeta charge is the main reason for this demand of study. The purpose of this study was to spotlight the synthesis of pure and cationic polystyrene (PS) particles with controllable size (from 30 to 300 nm) using a single step and relatively simple and cheap process and to demonstrate their application as the template in the production of hollow inorganic particles. Different from other methods, the synthesis method was based on the polymerization of styrene monomer in an aqueous solution system in the absence of any additional components (polymers, surfactants, chemicals, etc.) under 2,2-azobis (isobutyramidine) dihydrochloride (AIBA) as a cationic initiator to facilitate the creation of PS with a positive zeta charge. Precise control of the PS particle size in the nanometer range was achieved by the adjustment of reaction parameters (i.e. temperature, and styrene and AIBA concentrations). The size of the PS particles was proportional to the composition of styrene and the amount of initiator but had an inverse-proportional trend to the temperature. In addition, we also found that the styrene amount had more effect than the initiator (more than 4 times) on controlling PS size. Since an FTIR pattern and a micro-Raman spectrum results detected that the prepared PS particles had pure composition and homopolymer in spite of varying reaction parameters, the change of the particle size was due to changes in nucleus formation and particle growth rates. Flexibility of the process in the nanometer size control also drove to the devise of an equation to predict the particle size, which would be important for further scale-up development. Finally, the loaded positive zeta charge in the PS made it possible to assist the production of hollow inorganic particles (e.g. tungsten oxide, zirconia, and silica), in which this production could not be achieved when using commercial PS particles, verified by the particle formation mechanism hypothesis.