Preparation Of Janus Particles Modified By Sodium Alginate And Its Application In Pickering Emulsion

In recent years,the research on Pickering emulsion has become a hot topic for researchers.However,for the traditional emulsion,the demulsifications always occur in the process of application due to the unstable property.How to improve the stability of emulsion is an imperious demand to be solved.Janus particles have both surfactant properties and solid particle feature due to their unique structure of hydrophilic on one side and hydrophobic on the other.Therefore,as a solid particle emulsifier,Janus particles have great advantages in improving the stability of Pickering emulsions.Sodium alginate is a natural polymer with the advantages of renewable,abundant resources and environmental protection.Its molecular chain contains abundant carboxyl and hydroxyl functional groups,which can be modified to the surface of Janus particles.In addition,sodium alginate can quickly form a stable gel in Ca²⁺aqueous solution with a mild process,which can effectively avoid the inactivation of proteins,cells and enzymes and other active substances.These properties give sodium alginate to be ideal biological materials.Therefore,the combination of sodium alginate and Janus material to prepare a new solid particle emulsifier can improve the stability of emulsion.In this paper,amphiphilic SA-silica@PDVB/PS Janus composite particles modified by sodium alginate were successfully prepared by paraffin protection modification method.The Pickering emulsion prepared by using SA-silica@PDVB/PS Janus particles as particle emulsifier formed a calcium alginate gel shell at the interface of water/n-heptane under the existence of Ca²⁺to construct a high stability Pickering emulsion.Afterwards,the catalytic activity and reuse performance of alginate microgel reactor composed of calcium alginate microgel shell encapsulated lipase in organic/aqueous two-phase were investigated.The specific research contents of this paper are as follows:(1)Preparation and emulsifying properties of SA-silica@PDVB/PS Janus composite particles.Firstly,snowman-like silica@PDVB/PS Janus particles were prepared by seed emulsion polymerization and these particles were also modified with amino groups.At the same time,sodium alginate was oxidized with sodium periodate to prepare aldolized sodium alginate.Next,aldolized sodium alginate was selectively modified to the silica region of amino-modified silica@PDVB/PS Janus particles by paraffin protection method to obtain SA-silica@PDVB/PS Janus composite particles successfully.Whereafter,SEM,TEM,EDS-point,FT-IR,TGA,XPS,DLS and Zeta potential analysis were used to characterize the morphology,surface element composition,component content,functional groups,particle size and surface potential of SA-silica@PDVB/PS Janus particles,which proved the sodium alginate has been successfully directionally modified to the silica end of NH₂-silica@PDVB/PS Janus particles.Finally,the Pickering emulsion of water/n-heptane system was prepared by using SA-silica@PDVB/PS Janus composite particles as granular emulsifier.The morphology of the emulsion was observed by optical microscope,and it was found that the prepared emulsion had a good morphology and stability for more than 1 month,which indicated that the Janus particles modified by sodium alginate had good emulsifying properties.(2)Construction of calcium alginate gel microcapsules and application of enzyme immobilization.Firstly,the above synthesized SA-silica@PDVB/PS Janus composite particles were used as granular emulsifiers to prepare water/n-heptane Pickering emulsion.Then,calcium alginate gel microcapsules were constructed by crosslinking sodium alginate and added calcium ion(Ca²⁺)aqueous solution.The morphology of calcium alginate gel microcapsules was observed by optical microscope.Then,the effects of emulsifier dosage,p H value and temperature on the stability of calcium alginate gel microcapsules were investigated and the stability of Pickering emulsion was analyzed.Next,lipase was encapsulated in the aqueous phase of calcium alginate gel microcapsules by self-assembly of emulsifier particles at the oil-water interface.Specifically,lipase was used as the model enzyme,the esterification of hexanol and hexanoic acid was used as the model reaction,and lipase was immobilized by calcium alginate gel microcapsules to conduct catalytic reaction.Finally,the activity and reusability of calcium alginate microcapsules immobilized enzyme in water/n-heptane phase were investigated.The experimental results showed that the immobilized lipase activity of the calcium alginate microcapsules was three times higher than that of the free enzyme,and 81%of the immobilized lipase activity was retained after five cycles of reaction,which indicated that the immobilized lipase method had good activity and reusability.