Microfluidic Preparation Of Functional Janus Particles And Their Applications

In recent years,Janus particles gained considerable attention in the research field of functional materials.Due to the integration of multiple physical and chemical features,Janus particles offer unique advantages over monophasic particles in the applications of catalysis,sensing,biomedicine,e-paper,etc.It is worth mentioning that,the structures and functions of Janus particles can be facilely regulated to meet the requirements of diverse applications.Conventional production methods of Janus particles are mainly limited by poor control of particle size and structure,while microfluidic droplets can provide an ideal platform for producing Janus particles of high quality.Taking the microdroplets as producing templates,Janus particles can be manufactured with precisely controlled size and structure.This work is focused on microfluidic production methods of functional Janus particles and their applications.Three microfluidic preparation methods respectively based on centrifugal force,phase separation and electric field were established,and various polymer based Janus particles were produced with highly controllable size and morphology.Additionally,the as-prepared particles showed great potentials in the applications of biomolecule detections as well as drug loading and controlled release.In the first chapter,the new connotation and classification of Janus particles in the state-of-the-art research background were described,and the preparation strategies of Janus particle were reviewed from the viewpoint of microfluidics.Taking a few typical examples of applications in analytical chemistry,biomedicine,display and interface stabilizing using Janus particles,the nonnegligible value of Janus particles in the interdisciplinary research field was revealed.At last,the purpose and design of works in the present thesis were proposed.In the second chapter,a preparation method of Janus particle based on a centrifugal microfluidic system was developed,and Janus particles produced from alginate hydrogel were obtained taking the rotating centrifugal chip as the production platform.Multitarget and visualized sensing of glucose and cholesterol within one particle sensor was realized by physically encapsulating concanavalin A-fluorescein tagged dextran and y-Fe2O3 nanoparticles respectively into the hemespheres of Janus particles.It was indicated that the sensitivity and selectivity of visualized determination were effectively enhanced by taking the particles as sensors.Furthermore,visualized sensing of glucose and cholesterol in human serum samples was realized using the particles.In the third chapter,based on the phenomenon of phase separation in microdroplets,polymer-lipid Janus particles were prepared using a flow-focusing microfluidic chip.The microdroplets were formed using a mixture of poly(lactic-co-glycolic acid)(PLGA)and hydrogenated cocoglyceride lipid.Phase separation occurred in the microdroplets due to the evaporation of solvent,and Janus structures formed owing to the domination of interfacial tension,giving rise to the production of Janus droplets.Phase transition of the lipid hemisphere from solid to liquid occurred as it was stimulated by physiological temperature,which is applicable for burst release of loaded drug.When paclitaxel was loaded in Janus particles during preparation,the drug molecules distributed in both phases,leading to staged release of paclitaxel.As hydrochloride doxorubicin was co-loaded with paclitaxel in Janus particles,doxorubicin molecules distributed in the polymer phase selectively,thus the drugs would be released in sequence.In the fourth chapter,in an attempt to overcome the limitation that the size of particles produced from microdroplets is too large,an electrospray microfluidic chip integrated with microelectrodes was designed for droplet formation and simultaneous reduction of the droplet size by an electric field.The microfluidic electrospray system is versatile for a host of fluids including water,ink and both aqueous and organic solutions of polymers.And the diameter of ink Janus droplets could be decreased from 135 ?m down to 3 ?m with the voltage of 1600 V.Under an electric field of 1600 V,Janus droplets were formed taking PLGA solutions(in dimethyl sulfoxide)as dispersed phases,and Janus particles of 145 nm in diameter were prepared by using the nanoprecipitation method.The as-prepared particles might have potential applications in molecule sensing,cell and tissue imaging,drug loading and delivery,etc.In the fifth chapter,the microfluidic preparation methods of Janus particles and their applications were summarized.