Microfluidic Double Emulsion Synthesis Via Temperature-induced Phase Separation And Its Preliminary Applications

Double emulsions（also known as core-shell droplets）have shown great application potential in the fields of smart materials,cosmetic emulsions,and food storage.The size of the double emulsion prepared by traditional stirring or ultrasonic is different,the number of cores is uncontrollable,and it is difficult to meet the requirement of monodispersity.The microfluidic chip droplet technology uses the chip structure to accurately control the manifold of the multiphase fluid,emulsify in a single step to form homogeneous droplets,and emulsify in a second step to form a double emulsion containing the core.Multi-step emulsification requires the precise manipulation of multiple pressure sources and cannot be scaled up,which limits the production capacity of double emulsions.Single-step emulsification combined with liquid-liquid phase separation process is an effective strategy to increase the production capacity of chip double emulsions.In view of this,this paper developed a method for preparing chip double emulsion based on temperature-induced phase separation.The double emulsion was used as a template to synthesize a core-shell structured material,and the double emulsion was used as a microreactor to enrich the fluorescence signal.The details are as follows:（1）Preparation of microfluidic double emulsion based on temperature-induced phase separation.The homogeneous mixture of water and ionic liquid([P₄₄₄₈]Br)is used as the dispersed phase,and the fluorocarbon oil is used as the continuous phase.The syringe pump drives the two-phase fluid to emulsify in one step to form monodisperse homogeneous droplets.Indium tin oxide（ITO）electrode heating makes the temperature of the system higher than the critical phase transition temperature（LCST）,the homogeneous droplets undergo liquid-liquid separation,and gradually evolve into a double emulsion with a core-shell structure.The double emulsion formed by liquid-liquid separation has a size variation coefficient in the range of 1%to 2%,and has good monodispersity.By adjusting the volume ratio of water and ionic liquid in the homogeneous mixture,the core-shell ratio of the double emulsion can be flexibly adjusted;by adjusting the flow rate,the size of the double emulsion can be precisely controlled;through the reversible temperature change,the droplet configuration can be uniform Reversible change between spherical and core-shell structure.On this basis,the double emulsion prepared by the chip was used as a template,and different hydrogel precursor solutions were used to synthesize hollow hydrogel microcapsules with controllable structure and size and hydrogel particles with different geometric shapes by UV curing.The temperature-induced phase separation microfluidic double emulsion has the characteristics of adjustable size,controllable structure,and reversible morphology.It is compatible with the existing scale-up technology of droplets and is conducive to the large-scale preparation Value of double emulsions.It has advantages in the field of smart materials.（2）Microfluidic double emulsion is used for the study of fluorescence enhancement.Different substance molecules have different partition coefficients in water and ionic liquid.The liquid-liquid separation process can concentrate specific substances in the water component or ionic liquid component of the double emulsion,thereby achieving the enhancement of the fluorescence signal.Experiments have explored the distribution of different types of fluorescent molecules in water and ionic liquids,and found that most fluorescent dyes tend to be ionic liquid components.However,the excitation efficiency of some dyes in ionic liquids is lower than that in water,resulting in insignificant fluorescence enhancement.The screening found that the fluorescence of Cy3 and DBD in the ionic liquid components was significantly enhanced,which laid the foundation for the subsequent development of liquid-liquid separation-induced fluorescent turn-on or turn-off sensor analysis.