(245b) Hemispherical Polystyrene/Clay Nanocomposite Particle Formation in a Miniemulsion Polymerization

Stable water-based polystyrene nano-saponite composite latex was synthesized via mini-emulsion polymerization. The stability of the suspension and the exfoliation degree of clay were strongly affected by the pretreatment of saponite-Ca with cationic surfactant OTAB (octadecyltrimethyl-ammonium bromide) or VBTAC (vinylbenzyl trimethyl-ammonium chloride). This pretreatment process not only exfoliated the clay layers but also converted the nanoclay particles from hydrophilic (water like) to hydrophobic (monomer like). The organophilic clay obtained by above treatment could be well dispersed in the monomer phase by sonification at low saponite concentration (<5%), but formed high viscose solution or gel in organic monomer at higher concentration of saponite. It was found that some hemispheric particles of nanoclay-polymer composite with diameters of 200 to 500 nm were formed during the miniemulsion polymerization. The unique structure of the hemispheric nanocomposite particle has never been reported before. Scanning electron microscope (SEM) and transmission electron microscope (TEM) were used to detect the morphologies of the final latex particles. SEM in combination with a thin window energy dispersive spectrometer (EDS) for microanalysis was used to confirm the composition of final latex composite particles. Based on the analysis of morphology change during the reaction process, the mechanism to form hemispheric polystyrene particles was investigated.