Mechanism And Experimental Research On Morphology Control And Electrotriggered Release Of Droplets Confined In Microfiber

Microfluidics has emerged as novel technology platforms for the synthesis of micro and nano materials with exquisite structures and diverse components.In particular,the fabrication of droplet-filled microfiber based on droplet microfluidics combining droplet generation and fiber spinning steps has experienced growing interest in the fields of life science and materials science.Due to their unique morphology,hierarchical structure an d good biocompatibility,multicompartmental microfibers are widely used in diverse fields such as environmental protection,biomedicine and multifunctional composite materials.On the one hand,with the favorable mechanical strength and good visibility of hydrogel matrix,the manipulation of microfiber enables to flexibly adjust the shapes of embedded droplets,which provides a new thought for the fabrication of nonspherical microparticles.However,most of studies work only for photocurable polymers.On the other hand,the droplet microcompartments in fiber allow separate encapsulation of multiple contents without cross-contamination.Thus multicompartmental microfibers provide favorable microenvironments for co-encapsulation of functional actives such as c ells,proteins and drugs.But the selective controlled release of distinct encapsulants from multicompartmental fiber upon one triggering event has rarely been reported.Considering these limitations,this thesis studies the following topics:Based on the basic theory of microdroplet generation in the microchannel,a relationship between the droplet diameter and the flow rate ratio of dispersed to continuous phase fluids is deduced under dripping mode for co-flowing emulsification.The simulation model of droplet generation based on phase field method is established,and the effects of interfacial tension and flow velocities of dispersed and continuous phases on the size and production frequency of droplet are analyzed,which provides support for shape adju stment of droplet-filled microfibers.Further more,a simulation model of droplet deformation under confined space is built to analyze the stress status and deformation behavior of droplets constrained in microfiber.Finally,the dielectric response and mechanical behavior of double-emulsion droplets within microfiber in alternating current(AC)electric field are analyzed by simulations based on the Maxwell-Wagner interfacial polarization theory.It lays the theoretical foundation for experimental investigation of droplet release.Considering the fabrication of non-spherical microparticles with controllable shapes made from a wide range of materials,a capillary microfluidic system to continuously create shape-anisotropic microparticles using both photocurable and thermocurable materials is presented.Taking the oil-droplet-filled microfibers as research objects,the shape and size changes of oil-droplets against different fluid flow conditions are analyzed in detail.Furthermore,anisotropic microparticles with spherical,pear-like,maraca-like and rod-like shapes are produced from templates of deformed oil-droplets within microfiber via thermo/photo-polymerization.We finally compare the performance of porous spherical and rod-like microparticles with equal volume in photocatalytic degradation of organic contaminants.The results demonstrate that increasing specific surface area of microparticles can enhance the removal efficiency of organic pollutants.A critical requirement for hydrogel microfibers intended for various practical applications is the precise control of their length.We present a novel microfluidic strategy to cut the hydrogel microfiber into discrete microfiber segments of prescribed length by an AC electric field.Multicompartmental microfibers with structure of periodic fiber-joints and double-emulsion-droplet-knots are produced via a capillary microfluidic system.In addition,the sizes of microfibers and droplets and the length of fiber-joints can be flexibly controlled during generation p rocess.Subsequently,an imposed AC electric field induces a rapid rupture of the embedded double-emulsion droplets,enabling to cut the microfibers into acquire the pure or magnetic fiber segments with prescribed lengths.Finally,the precise manipulation of magnetic fiber segments including controlled motion of a predefined trajectory and 3D assembly are achieved under magnetic field,which demonstrates the feasibility of using these fiber segments as micromotors and building blocks.For the time-dependent breakup behavior of double-emulsion droplets constrained in microfiber,we experimentally study the influence of various physical properties of droplets and the parameters of electric field on the trigger time for droplets from exposure to AC electric fi eld to shell film rupture.After that,a cascaded microfluidic device consisting of two independent droplet-generators and one fiber spinning unit is used to prepare the multicompartmental microfibers containing two kinds of double-emulsion droplets.During this process,the encapsulation mode and packing density as well as shell thickness of two distinct droplets can be flexibly controlled.Considering the time-dependent breakup feature of double-emulsion droplets in microfiber,the concept of selective release behavior for compound-droplet-pairs-filled-microfibers is finally demonstrated based on the discrepancy in core conductivities or shell thicknesses of two distinct droplets.And the typical working conditions for practical applications are determined based on simulation and experimental results.