Mechanism And Experimental Research On Micro-Nanoparticle Manipulation Using Thermal Buoyancy-Capillary Convection

Microfluidics has emerged as novel technology platforms for biochemical analysis,sensing detection,drug delivery and material synthesis.In microfluidi c systems,flexible manipulation of microparticles including enrichment,trajectory control,directional transportation and release of loaded samples,is often an essential step in these applications.In view of this,researchers have proposed lots of particle manipulation methods relying on fluid properties,channel structures,acoustic/optical/electric/magnectic effects and specialized functional materials.Although these methods have their own unique advantages,they also have some apparent defects including inflexiblity,complexity,strict demanding on soultition and particle properties,which are limitting the further application.And also,the present particle trajectory control techniques mainly focus on single-phase flow system,the particle manipulations in two-phase or multi-phase flow systems are rarely reported.Therefore,it is of great significance to develop a particle manipulation method that can be applied to single-phase/multiphase flow systems with flexible control,simple structure and low requirements on physicochemical properties of samples.Considering these limitations,this thesis studies the following topics:Thermal buoyancy/capillary convections are used as the mechanisms of particle manipulation.According to the theories of heat t ransfer,fluid convection and particle migration,a simulation model coupling electric field,thermal field,and flow field is established.The effects of gravity,thermal buoyancy flow,particle thermophoresis and thermocapillary convection on particle mi gration are analyzed and compared,which can provide the guiding for the chip design.For micro/nanoparticle concentration,microchips based on thermal buoyany convection are designed and fabricated.The effects of voltage,channel height,fluidic viscosity and solution types on particle focusing efficiency in static fluid are first studied by using engineering particles as experimental samples.Then we analyze the particle focusing behavior in continuous flow,the position of focused particles and particle focusing efficiency can be flexibly adjusted by changing the control voltages.Efficient foucsing of micro/nanoparticles in static/continuous oil/water solutions proves the good applicability of this method in various conditions,and this technique can be promising for those applications needing particle focusing.For single particle migration,microfluidic chips based on thermal buoyancy-capillary convection are fabricated.The migration performances of single particle along channel direction are first studied,and the effects of channel configuration and control voltage on the particle migration efficiency are analyzed to demonstrate the feasibility of this method on cargo transportation.Then the two-dimensional manipulation of single particle in singl e-phase flow is studied.The migration direction of particle can be flexibly adjusted within a range of 360° through the cooperative control of single/multiple-electrodes,and the migration trajectory and velocity are both related to the control voltage.Finally,the research objects are extended to gas-liquid and liquid-liquid systems,the two-dimensional trajectory control of single particle at fluidic interfaces can also be achieved via controllable capillary convection.The multi-applicability of this method can provide a new principle for the driving of micro/nanomotors and micro/nanorobots.For double-emulsion droplets,microfluidic device used for droplet migration,core release and released particle focusing is designed and fabricated.Single-core and double-core droplets are prepared by using a glass capillary chip.The transportation behavior of droplets in the microfluidic platform is fisrt studied.When the droplets are transported to the target region,the core release behaviors of droplets as a function of voltage,shell thickness and core number are further analyzed,and functional micro/nanoparticles are encapsulated in the droplets to study the characteristics of particle release and released particle focusing.Finally,the transportation,release and culture of yeast cells through double-emulsion droplets demonstrate the practical applicability of this method in cargo transportation and material preservation.