Fabrication of covalentlybonded polystyrene/SiOS

Authors: Dezhong Yin Qiuyu Zhang Hepeng Zhang Changjie Yin

Publish Date: 2009/11/25

Volume: 17, Issue: 5, Pages: 689-696

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Abstract

Pickering emulsion polymerization has attracted considerable attention in material fabrication due to its unique surfactantfree character and versatile association of oil water and particles for a large set of materials In this study SiO2 modified with Methacryloxypropyltrimethoxysilane MPTMS was employed to prepare Pickering emulsion and subsequently covalentlybonded polystyrene/SiO2PS/SiO2 composites were synthesized by Oilinwater Pickering emulsion polymerization Optical micrograph contact angle thermogravimetric analysis TGA Fourier transform infrared spectra FTIR scanning electron microscope SEM and dynamic laser scattering DLS were employed to characterize the modified SiO2 Pickering emulsion and prepared composites It was found that prepared composites possess ragged surface morphology and SiO2 concentration has an important effect on the morphology of asprepared composites In addition covalent bond between PS core and SiO2 shell was evidenced by FTIREmulsion polymerization possesses distinguished advantages such as facilitate controlling and high degree of polymerization Surfaceactive agent typically as surfactant with low molar mass is essential in emulsion to stabilize droplet from coalescence However it has been recognized that recycling the surfactant after polymerization is rather tedious and the surfactant has negative effect on the products and potential crisis to the environmentBesides surfactants colloidal particles can also be used to protect droplets from coalescence and stabilize Pickering emulsion as summarized systematically by Robert Aveyard in 2003 1 Subsequently extensive interests and studies have been focused on it due to its surfactantfree character 2 3 4 5 6 Using solid particles conventional emulsifying agents can be reduced and hazardous surfactants may be replaced by less harmful materials In some cases organic emulsifying agents can even be completely avoided This is the dominant reason that Pickering emulsion is of growing interesting in food engineering 7 8 and pharmaceutical fields 9 10Recently arising interesting and efforts have been focused on fabrication of materials by Pickering emulsion It have demonstrated theoretically and experimentally that Pickering emulsion polymerization is a feasible way for the preparation of organic coreinorganic shell hybrid composites In Pickering emulsion solid particles anchor irreversibly on the surface of droplet After polymerization solid particles form a spherical inorganic shell while polymerizable monomer droplet forms an organic core The versatile association of monomer droplet water and solid particles in Pickering emulsion allows a large set of composites to be prepared eg polyanilinePANI/CeO2 11 PANI/SiO2 12 PANI/ Cu2OH2CO3 13 polystyrenePS/ZnO 14 polyvinyl acetate/SiO2 15 However no strong covalent bond exists between the inorganic shell and organic core of the obtained composites because solid particles employed in the literatures are inert in chemical reaction ie have no polymerizable groups on their surfacesHerein nanoSiO2 particles modified by methacryloxypropyltrimethoxysilane MPTMS were employed to prepare Pickering emulsion followed by radical polymerization initiated by Azobisisobutyronitrile AIBN to fabricate PS/SiO2 hybrid composites By variety of MPTMS amount wettability of SiO2 particles was tuned significantly Furthermore SiO2 particles were functionalized with reactive C = C groups which can copolymerize with styrene during polymerization As a result the interaction between SiO2 shell and PS core was enhancedNanoSiO2 particles with an average diameter of 20 nm were provided by GuangzhouYixin New Material Co Guangzhou China MPTMS and AIBN were obtained from Beijing Chemical Reagent CoLTD Beijing China Styrene was supplied by Shanghai Shanpu Chemical Reagent Co Shanghai China 10 NaOH solution was used to eliminate inhibitor in styrene followed by rinse with distilled water to pH 50 Other reagents are analytical grade and used as receivedThe modification of SiO2 was carried out in ethanol/water media based on the hydrolysis/condensation between SiOH of SiO2 surface and hydrolyzed MPTMS In a typical procedure 3 g of SiO2 particles was added to 100 mL of ethanol/ammonia 1 M mixture 3/1V/V and dispersed using a Nankun 250SW ultrasonic processor Kunshan Experimental Instrument China for 15 min A definite amount of MPTMS was added into the suspension under vigorous magnetic agitation and reacted at room temperature under moderate agitation for 8 h or 24 h After reaction the suspension was centrifuged at 6000 rpm and the collected SiO2 particles were washed by dispersion into ethanol and centrifugation for three times Finally the SiO2 particles were ultrasonically dispersed in distilled waterPS/SiO2 composites were synthesized by Pickering emulsion polymerization initiated by AIBN A typical preparation procedure is detailed as follows 10 wt of AIBN was dissolved in styrene to form oil phase and subsequently the oil phase was mixed with the SiO2 suspension described above A stable Pickering emulsion was generated by means of an Ultrasonic processor KunshanChina for 5 min The emulsion obtained was subsequently discharged into a reactor to conduct polymerization under mildly stirring 30 rpm at 55 °C for 4 h and 65 °C for another 4 h The obtained PS/SiO2 composites were filtrated and washed with water and ethanol respectively followed by dried in vacuum at 45 °C

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