Preparation And Characterization Of Self-assembled Raspberry-like Colloidal Particles From Pickering-like Emulsion Polymerization

In this paper,two kinds of complex colloidal polymeric particles(CCPs)were generally synthesized following the traditional free radical polymerization mechanism.In both systems,poly(vinylidene fluoride)(PVDF)latex particles were used as seeds,styrene(St)or 4-vinylpyridine(4VP)were used as monomers,respectively,and then two kinds of strawberry-shaped composite particles with controllable protrusion orientations were prepared through Pickering-like emulsion polymerization.In this work,the effects of monomer/seed feed ratio,polymerization temperature,and polymerization time on the morphology of the composite particles were studied.The formation mechanism of raspberry-like composite particles was proposed according to the results of various test and analysis.At the same time,the PVDF/PS composite particle coatings were prepared by deposition method,and water contact angle of nanocoatings were tested to study the influence of the morphology of different composite particles on the hydrophobicity of the nanocoatings.Chemical composition,particle size and particle size distribution,microstructure,confined crystallization of PVDF,surface element types and their relative content in the composite particles were analyzed and characterized by fourier transform infrared spectrometer(FTIR),dynamic light scattering(DLS)particle size analyzer,scanning electron microscope(SEM),differential scanning calorimetry(DSC),energy dispersive X-ray spectrum(EDS),X-ray photoelectron spectroscopy(XPS).The hydrophobicity of nanocoatings constructed with different morphologies of the composite particles were investigated by contact angle(CA)tester.The research results for the two systems showed that the polymerization time,polymerization temperature,and monomer/seed feed ratio were the key factors for the formation of raspberry-like composite particles with controllable protrusion orientation.At the initial stage of the reaction,surface nucleation occurred,which was attributed to minimum surface energy and incompatibility of a pair of polymer.Then,two kinds of snowman-like particles,PVDF/PS and PVDF/P4 VP,were produced,finally the complex colloidal particle clusters were formed with the outward hydrophilic end and the inward hydrophobic end.The different hydrophobicity of PVDF,PS,and P4 VP could drive the self-assembly of Janus particles,and induced Pickering-like emulsion polymerization in the systems.Finally,the controllable raspberry-like composite particle with a relative uniform size could be obtained.In detail,the PVDF bulbs in the PVDF/PS composite particles presented outwards,the PVDF in the PVDF/P4 VP composite particles acted as part of the inner core and presented inwards.The Janus particle can act as both a solid particle stabilizer and a precursor for self-assembly of the colloidal particles.Heteromorphous raspberry-like PVDF/PS@PS composite particles with hierarchical protrusions could be obtained after 4 h of reaction in the former system.The static water contact angle of latex nanocoating prepared with the heteromorphous raspberry-like PVDF/PS CCPs reached 153.9°,exhibiting a superhydrophobicity.As a result,a facile and alternative way is provided for fabrication of controllable protrusion orientation of hierarchical colloidal particles and even superhydrophobic smart coatings.The raspberry-like particles obtained from the latter system also could be functionalized in the later stage due to the existence of special functional groups.In summary,two kinds of controllable protrusion orientation of raspberry-like composite particles were successfully prepared via simple Pickering-like emulsion polymerization in this paper.The heteromorphous raspberry-like PVDF/PS@PS composite particles have potential applications in the field of coatings,and raspberry-like PVDF/P4VP@PS composite particles can be further modified and assembled.