Aqueous Two-Phase Pickering Emulsion Stabilized By Particles Based On Conjugated Linoleic Acid

Aqueous two-phase systems are widely used in various field,such as natural product separation and extraction,and bioreactors due to their excellent biocompatibility and environmental friendliness.However,stabilizing aqueous two-phase emulsions has been challenging due to the low interfacial tension and large interfacial thickness of the water-water interface,which prevents small molecules like surfactants from stabilizing the emulsion.Currently,common emulsifiers used for stabilizing aqueous two-phase emulsions include polyelectrolytes,block copolymers,and colloidal particles.While the first two methods involve complex preparation processes or organic solvents,stabilizing emulsions using colloidal particles is simpler and more environmentally friendly.Colloidal particles can be spherical or non-spherical,with non-spherical particles,such as flakes,rods,and fibers,exhibiting better stability due to their larger aspect ratios and higher adsorption energy at the interface.Previous studies have demonstrated that non-spherical particles can stabilize aqueous two-phase Pickering emulsions.Conjugated linoleic acid（CLA）is a naturally occurring unsaturated fatty acid with self-assembly and self-crosslinking properties.Recent research has shown that phospholipid bilayers can adsorb at the water-water interface and stabilize polymer-polymer aqueous two-phase systems.In our previous work,we successfully prepared CLA vesicles with a similar bilayer structure to liposomes,which were used to stabilize polymer-salt emulsions.However,it remains to be determined whether these vesicles can stabilize polymer-polymer aqueous two-phase emulsions.Additionally,by modulating the system environment,we induced the self-assembly of sodium conjugated linoleate（SCL）into micelles with various morphologies and used SCL to modify nanoparticles such as SiO₂,Fe₃O₄,and Ca CO₃.The stability of these different micelles and modified particles in aqueous two-phase emulsions and the underlying stabilization mechanism need to be investigated.To address the aforementioned questions,this study focuses on three types of structurally ordered self-assembled particles using CLA as the assembly monomer:self-crosslinked ufasomes of CLA（SCU）,self-crosslinked SCL micelles with different morphologies（SSCLM）,and SCL-modified TiO₂ nanosheets（SCL@TiO₂ NSs）.These particles have similar surface functional groups but different morphologies,providing insights into the relationship between emulsifier morphology,particle size,and emulsion stability.The main contents and results of this study are as follows:（1）Stabilization of PEG 20000-DEX 500000 aqueous two-phase Pickering emulsions by self-crosslinked ufasomes of CLA.SCU with a stable structure was successfully prepared through self-assembly and self-crosslinking using CLA as the assembly monomer.SCU was used to stabilize PEG 20000-DEX 500000 aqueous two-phase Pickering emulsions.The pHsensitivity of SCU enabled the emulsion to be broken or formed by adjusting the system p H.The emulsion type could be altered by adjusting the mass ratio of the two phases.Due to the superior distribution of DEX-rich phase relative to proteins,localized mineralization reactions could be conducted within the droplets of DEX/PEG emulsions stabilized by SCU.（2）Stabilization of PEG 20000-Na₂SO₄ aqueous two-phase Pickering emulsions by self-crosslinked SCL micelles with different morphologies.SCL micelles with various morphologies,including spherical,disc-like,and thread-like,were obtained through concentration-driven self-assembly of SCL monomers.By using these micelles as emulsifiers,PEG 20000-Na₂SO₄ aqueous two-phase Pickering emulsions were stabilized.The results showed that only disclike and threadlike SSCLM could stabilize Na₂SO₄/PEG 20000 emulsions,while spherical SSCLM failed to do so.The emulsion type remained unchanged regardless of the mass ratio of the two phases.The emulsification-demulsification process was achieved by adjusting the system p H,demonstrating that disclike and threadlike SSCLM acted as p H-responsive emulsifiers in aqueous two-phase Pickering emulsions.（3）Stabilization of PEG 20000-DEX 500000 aqueous two-phase Pickering emulsions by SCL-modified TiO₂ nanosheets Ultra-thin TiO₂ nanosheets were synthesized through a hydrothermal method,and SCL@TiO₂ NSs were obtained by adsorbing SCL onto the surface of TiO₂ NSs,followed by thermal polymerization to stabilize the SCL.SCL@TiO₂ NSs were used to stabilize PEG 20000-DEX 500000 aqueous two-phase Pickering emulsions.The results demonstrated that emulsion stability could be achieved using 0.5 wt%SCL@TiO₂ NSs.However,the large density difference between TiO₂ NSs and the aqueous phase resulted in suboptimal emulsion stability.The emulsion type could be changed by adjusting the mass ratio of the two phases.Moreover,the carboxylic acid groups on SCL@TiO₂ NSs conferred p H-responsive properties to the emulsion.