Study On Synthesis And Morphology Evolution Mechanism Of Styrene Copolymer/Silica Janus Particles

In this study,poly（styrene-co-glycidyl methacrylate）/silica[P（St-co-GMA）]/SiO₂snowman-like Janus hybrid nanoparticles with distinct phase compartmentalization were prepared by combination of one-stage soap-free emulsion polymerization（SEP）with sol-gel technology.It is well known that the nucleating silica on the surface of polymeric seed by a sol-gel method always gains a conventional core-shell particle while a snowman-like Janus particle is difficult to achieve directly.Herein,a fascinating transition to snowman-like Janus morphology can be accomplished by simply adding a low-boiling oil-soluble vinylidene chloride（VDC）under an ice bath.In order to clarify the formation mechanism of snowman-like Janus hybrid nanoparticles,the effects of addition amount of VDC,MTES,NH₃·H₂O,ice bath time,temperature of hydrolysis and polycondensation and type of oil-soluble solvents on the morphological evolution of the hybrid nanoparticles were systematically investigated.The study results show that the VDC monomer plays an important role in the formation of snowman-like Janus particles.The VDC on the seed surface not only plays a lubrication role,but also acts as a gas“motor”to drive the precursor polycondensate migrating when the system temperature rises,thus reducing the surface energy.The strategy utilizes a silica precursor,methyltriethoxysilane（MTES）,as a sole stabilizer at the oil/water interface due to its amphiphilicity induced by partial hydrolysis.In this experimental investigation,the morphological evolution of hybrid nanoparticles can be achieved by changing the addition amounts of VDC,MTES,and NH₃·H₂O,time of ice bath,and temperature of hydrolysis polycondensation.Snowman-like Janus nanoparticles can only be obtained by adding appropriate amount of VDC.When VDC is not added,strawberry-like hybrid nanoparticles are formed;when the amount of VDC is added too much,the collapsed capsule shape of SiO₂ nanoparticles are gained,indicating that the high softness of silica shell was formed,because the increase of VDC amount made the silica shell thinner.When the amount of MTES is too low,the fusion cannot perform between the tiny polycondensate bulges,then snowman-like hybrid nanoparticles cannot be obtained.When the addition mass of MTES exceeded a certain value,the excess MTES will homogeneously nucleate in water.In addition,the ammonia solution affects the hydrolysis and polycondensation rates of the precursor MTES.Therefore,when the ammonia amount is increased greatly,the degree of condensation became so large that the migration became difficult,snowman-like P（St-co-GMA）/SiO₂ hybrid particles cannot be formed.The synthesized snowman-like P（St-co-GMA）/SiO₂ hybrid particles had pronounced amphiphilicity and anisotropy,which can serve as an ideal candidate for emulsion stabilization and blend interface compatibilization.Therefore,the obtained snowman-like P（St-co-GMA）/SiO₂ hybrid nanoparticles could be used to stabilize oil-in-water Pickering emulsion.When a mass fraction of 0.8 wt%hybrid nanoparticles is used,the Pickering emulsion can be stabilized beyond 30 days.This process offers a new avenue for the preparation of snowman-like polymer/SiO₂ hybrid particles,which is facile,low cost,easy scale-up,enabling the asymmetric particles to apply in practice.