Study On CO₂/N₂Triggered Switchable Pickering Emulsifiers

Pickering emulsifiers are widely used in the food industry, pharmaceutical industry, during oil recovery and paper processing. They possess a number of advantages over conventional surfactants such as better stability and lower toxicity. However, in many practical applications, the emulsion needs to be stable for only part of the process, thus control over when the system is a Pickering emulsion is a desirable property. A major advantage would be the ability to control phase separation of the final system for easy product recovery. Development of environmentally friendly CO2/N2triggered switchable emulsifiers fully reflects this contemporary demand, having very important theoretical and practical significance.This work focused on the development of a CO2/N2switchable surfactant for use in Pickering emulsions. We innovatively designed a zwitterionic polymer nanoparticle with a small fraction of cross-linking structures, which can rapidly respond to a CO2/N2trigger generating a reversible structural transition. The Pickering emulsions stabilized by these nanoparticles show consistent CO2/N2triggered switchable performance over multiple cycles.The main work is divided into three major sections:(1) Section one focuses on the synthesis and characterization of the Pickering emulsifier. The emulsifier (PDEAEMA-co-PSMA nanoparticle) was prepared by soap-free emulsion copolymerizations of2-(diethylamino)ethyl-methacrylate(DEAEMA) and sodium methyl acrylate(SMA) with a bisacrylamide(BisAM) cross linker under alkaline conditions at70℃. The influence of co-monomer ratio and cross linker content on the polymerization was investigated. The results showed that nanoparticles of the desired size (-200nm) with a narrow size distribution were prepared. Cross linker concentration was found to have a large effect on the polymer. Low cross linker concentration produced branched co-polymers, while high cross linker concentration produced microgels.(2) Investigating the as prepared Pickering emulsifier nanoparticles, their CO2/N2response was studied, and their isoelectric points (IEP) were obtained by acid titration. It shows that polymer’s response to N2was mainly affected by their IEP. In addition the cross-linking concentration was found to affect the pH responsive behavior.(3) The prepared Pickering nanoparticles were used to prepare a dodecane-water emulsion to test their emulsifying properties and switchablity performance. All the nanoparticles displayed excellent emulsification properties. Moreover, particles with low cross linking density showed great CO2/N2switchablity. Complete demulsification was rapidly achieved after bubbling CO2through the emulsion at room temperature. Subsequent bubbling of N2for a short time under the same conditions could recover the nanoparticle surface activity. This CO2/N2response was cycled5times with little change in emulsifier performance.