Preparation and properties of paraffin Pickering emulsion and its microcapsule phase change nonwoven materials
Objective Pickering emulsion uses solid-particles as emulsifier instead of small-molecule surfactants,in which solid particles are embedded on the surface of emulsion droplets,and thus its interfacial adsorption energy is far greater than the thermodynamic energy of the solid particle Brown motion.Consequently,it is difficult for the solid particles to escape from the oil-water interface,providing the emulsion with excellent storage stability.Pickering solid emulsifier in the paraffin emulsion does not cut down the paraffin crystalline temperature,and eliminates the subcool phenomenon,and improves its phase-change energy storage performance.Unfortunately,very few Pickering emulsifiers have existed,such as nano-silica,graphene oxide,nano-cellulose crystals,more often being applied with organic polymer co-emulsifier.Methods Soap-free emulsion polymerization was carried out with styrene(St)and methacryloxyethyl-trimethylammonium chloride(DMC)as monomers,divinyl benzene(DVB)as crosslinker,ethanol as auxiliary solvent.Cationic copolymer particles characterized with monodispersity,clean surface,and designed size were obtained.The paraffin Pickering emulsions and paraffin droplets on viscose fabric phase change materials(Vis-PCM)were prepared by using the resultant copolymer nanoparticles(P(St-co-DMC)).The microstructure and properties,monomer conversion,nanoparticle size,Zeta potential and contact angles of P(St-co-DMC)particles as well as Vis-PCM were investigated by Fourier transform infrared spectrometry,scanning electron microscopy,thermogravimetry,differential scanning calorimetry,and contact angle goniometry.Results The influences of DMC and initiator dosages,and ethanol contents on the monomer conversion and the nanoparticle size,as well as of DMC dosages on the contact angle and Zeta potential of the nanoparticles were studied.The results showed that cationic P(St-co-DMC)copolymer nanoparticles were successfully prepared,and the two major monomers were merged into the copolymer chain.The resulted polymers were shown to withstand the thermal shock during emulsification process,as well as phase change energy storage and heat release recycling processes.The monomer conversion presented bell-shape behavior,whereas the particle size and its dispersion index showed reversed bell tendency with the increases of DMC,initiator and ethanol.However,the Zeta potential of the copolymer particles initially soared up and then tended to be constant,whereas the hydrophilicity was improved with the increase of DMC dosage.When the amounts of DMC,KPS and ethanol were fixed at 25%,2.5%and 15%,respectively,the monomer conversion reached 83%,the size,the Zeta potential,and the surface contact angle of the resultant copolymer particles were 114 nm,47.2 mV,and 58°,respectively.The over three-month shelf life,oil-in-water paraffin Pickering emulsion at the oil-to-water volume ratio of 3∶1 and at the droplet size of(4.4±0.5)μm was eventually obtained.The phase change latent heat of Vis-PCM,which was obtained by impregnating spunlaced viscose nonwoven fabric into the Pickering emulsion,reached up to 139.3 J/g,and the paraffin leakage rate of Vis-PCM was only 0.6%after 20 thermal cycls.Conclusion Copolymer particles with controllable surface features such as water contact angle,particle size and electricity,instead of the small molecule surfactant,can be adsorbed firmly at the oil-water interface to obtain a long shelf life Pickering emulsion.P(St-co-DMC)emulsifier copes with the paraffin subcool phenomenon due to small molecule surfactant plasticizer based on heterogeneous nucleation mechanism.Also it is emulsion droplets rather than de-emulsified paraffin bulk that adhere to the nonwoven surface,which ensures the paraffin-microencapsulated fabric acting as reusable phase change energy storage materials.All the results confirm that P(St-co-DMC)possesses excellent emulsifying ability,and Vis-PCM has good heat storage and heat release properties.
methacryloyloxyethyl trimethylammonium chloridesoap-free emulsion polymerizationparaffinPickering emulsionviscose nonwovenphase change material
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