Aqueous Two-phase Pickering Emulsions Stabilized By Conjugated Linoleic Acid Self-Assemblies

Aqueous two-phase emulsions are colloidal dispersions of an aqueous solution into another aqueous phase.They have the advantages of non-toxicity,good biocompatibility,and environmental friendliness,so they can be widely used in the design of new encapsulation and delivery systems for unstable components,artificial simulation of cells,biomineralization,production of functional materials and other fields.The main problem encountered in the actual application of the aqueous two-phase emulsions is the lack of stability.Due to the extremely low interfacial tension and large interface scale of the aqueous two-phase system,amphiphilic molecules such as surfactants cannot be adsorbed at the water-water interface,which makes it very difficult to find a suitable emulsifier for aqueous two-phase emulsions.Block polymers and colloidal particles are two commonly used kinds of emulsifiers to stabilized aqueous two-phase emulsions,but most of them lack biocompatibility,environmental friendliness or are difficult and complicated to prepare.Early in our lab,natural unsaturated fatty acid conjugated linoleic acid（CLA）,which has physiological activity,self-assembly activity,and self-crosslinking activity,was used as a molecular building block to self-assemble in an aqueous solution,and then utilize the polymerizability of CLA.The self-assembly is chemically bound through the self-crosslinking method to obtain a stable assembly structure that maintains its original morphology,and the stability of various self-assembly to O/W Pickering emulsion is studied.However,whether the CLA self-assembly,which has a simple,green preparation process and excellent performance,can be used as an emulsifier for the aqueous two-phase emulsions needs to be further explored.If the CLA self-assembly can be used to stabilize the emulsion,the types of particle emulsifiers in the aqueous two-phase emulsions will be enriched.At the same time,the carboxylic acid group of the fatty acid can undergo protonation and deprotonation processes with the change of pH,bringing pH stimulus responsiveness to the emulsion,and can be effectively extended to encapsulate hydrophilic active ingredients for drug delivery,as well as a completely bionic microreactor to reproduce biological reactions and other practical applications.The main research contents and results of this article are as followings:（1）Using CLA as a molecular building block,CLA ufasomes（CLA-FAV）are formed in response to self-assembly under the condition of pH 8.6.Stable self-crosslinking CLA vesicles（SCLA-FAV）were constructed by UV polymerization,and its stabilizing effect on aqueous two-phase Pickering emulsions was explored.The results show that SCLA-FAV is an effective Na₂SO₄/PEG aqueous two-phase emulsion stabilizer,which can stabilize the Na₂SO₄-in-PEG aqueous two-phase Pickering emulsions with 60%internal phase.The emulsification-demulsification of the emulsion was achieved by adjusting the pH of the system,which proved that SCLA-FAV is an aqueous two-phase emulsion Pickering stabilizer with pH stimulus responsiveness.（2）Sodium conjugated linoleate（SCL）is used to self-assemble on the surface of CaCO₃ nanoparticles to form admicelles,and thermal polymerization is used to trigger the self- crosslinking reaction of SCL admicelles to stabilize the self-assembled structure.Using SCLA@CaCO₃ as the emulsifier expands the range of the Na₂SO₄/PEG aqueous two-phase system that can be stabilized by the CLA self-assembly as an emulsifier,reduces the dosage of emulsifier,and obtains a pH stimulus-responsive aqueous two-phase Pickering emulsion.（3）Using carbon nanotubes（CNT）,an anisotropic nanoparticle as a template,SCL on the surface of CNT forms a monolayer and uses thermal crosslinking to stabilize its structure.Further explore the stabilizing effect of SCLM@CNT on Na₂SO₄/PEG aqueous two-phase Pickering emulsions.And because of the larger particle size and tubular morphology of SCLM@CNT,we explore its stabilizing effect on PEG/Dex aqueous two-phase system.The results show that SCLM@CNT has a good stabilizing effect on these two types of aqueous two-phase emulsions,and the obtained emulsions both have pH stimulus responsiveness.