Study On The Preparation And Emulsification Properties Of PH-responsive Janus Particles

Janus particles have two different components and structures with different chemical properties and wettability on both sides,and are widely used in stabilizing emulsions.As an emulsifier,Janus particles not only have higher surface activity and stronger interfacial adsorption capacity than homogeneous solid particles,but also can reduce surface tension more effectively to obtaining a more stable emulsion.In this paper,we prepared a Janus particle with p H responsiveness and realized the structures and morphology regulation of Janus particles by changing the feed ratio and environmental p H value.Janus particles can stabilize different types of emulsions and induce emulsion phase inversion with the change of environmental conditions.The specific research contents are as follows:（1）The p H-sensitive Janus particles with one side enriched in hydrophobic unit styrene（St）and the other side enriched in hydrophilic unit acrylic acid（AA）were obtained through the combination of seed emulsion polymerization and polymerization-induced phase separation.Typically,polystyrene（LPS）was used as the seed particle,and 2,2’-azobis（2,4-dimethylvaleronitrile）（ABVN）initiated the polymerization of tert-butyl acrylate（t BA）in the presence of a cross-linking agent.After acid hydrolysis,the morphology and size of the particles can be changed by changing the feeding rate,feed ratio and p H value of the solution.（2）The types of emulsions stabilized by Janus particles were discussed through toluene-water as a mixed system.The results showed that（St 1/AA 3）,（St 1/AA 2）and（St 1/AA 1）Janus particles could form stable W/O emulsion at p H 2.0,and stable O/W emulsion at p H 12.0,while（St 3/AA 1）Janus particles can only stabilize W/O emulsion.The amount of Janus particles selected as the solid surfactant was 0.50 wt%in the experiment.The ratio of oil to water affected the stability of the emulsion but not the type of the emulsion.When p H was 2.0,the stable W/O emulsion was formed by selecting the oil phase with low interfacial tension between oil and water,while the emulsion was unstable and the emulsion droplet was larger when the oil phase with larger interfacial tension was selected.The increase of p H value made the inversion of W/O emulsion to O/W emulsion,which had good reversibility and cycleability.In addition,the surface of Janus particles can be loaded with Fe₃O₄nanoparticles so that it had good magnetic response,which could quickly separate tiny oil droplets from water with different p H values.