Mechanism And Experimental Study On Particle Separation Based On Induced-charge Electro-osmotic Vortex Effect

In the field of microfluidics,particle separation plays an indispensable part in addressing important issues in our life,involving isolation of promising microalga strains to deal with energy crisis,separation of crumpled graphene oxide(CGO)balls to develop high-efficiency electronic device,and separation of cells to diagnose early-stage diseases.In practice,states of particle samples are complex and diverse.For instance,target microalgal cells live together with other microalgae and they are easy to be adhered and accumulated;fabricated CGO balls have various sizes and other parameters are uncertain.Therefore,it is necessary to develop flexible and reliable method to deal with above critical issues.Many mechanisms have been applied in the development of separation techniques,including acoustic radiation force,magnetic force,optical force,dielectrophoretic force,centrifugal force and vortices.Among these separation technologies,vortex-based separation method is the most promising approach to address the issues for its advantages,including contact-free manner,and particle dispersion.However,when dealing with above issues,existing vortex-based separation technologies based on the passive vortices present obvious limitations,including monotonous control manner and weak applicability.Therefore,flexibly controllable vortices are needed to develop effective particle separation method to deal with above pressing issues.Strength of induced-charge electro-osmotic(ICEO)vortices can be precisely adjusted by regulating the voltage amplitude,frequency,and buffer conductivity.Besides,the profiles of ICEO vortices can be tuned by changing distribution of electric field and geometry of bipolar electrode,enabling it present good potential in particle separation.From these aspects,we conducted a series of investigations as follows:From induced double layer charging dynamics and Maxwell interface polarization,we analyzed polarization features and the forces exerted on different particles in ICEO vortices.Physical model was established to investigate particle movement and separation by coupling electric,flow and gravity fields.Particle trajectories in ICEO vortices and parametric effects,involving voltage parameters and particle properties,were investigated numerically.Moreover,we also investigate numerically the separation processes,and further revealed principles of ICEO-vortex-based particle separation,providing theoretic foundation for subsequent experiments of particle separation.We design and fabricate microfluidic device to form symmetrical and asymmetrical ICEO vortices and establish the platform for particle separation using ICEO vortices.We investigate the regulation of particle different electrokinetic equilibrium state(EES)via symmetrical ICEO vortices.According to validation of separation capability of symmetrical ICEO vortices in particle separation,we study performance of this technology in size-and density-based separation,and flow-rate effect on separation.Next,we investigate the regulation of particle EES via asymmetrical ICEO vortices.4-μm Polymethyl methacrylate(PMMA)and silica particles are separated to explore the performance of asymmetrical ICEO vortices in density-based separation.Different-size yeast cells are separated to study the performance of this method in size-based particle separation.Finally,we exploited influence of buffer conductivity on the separation.By evolving symmetrical ICEO vortices,we propose a novel approach based on widening symmetrical ICEO vortices for separation of positive dielectrophoretic(DEP)particles.We instantaneously separated and mixed 4-μm silica and different-sized PS particles to test the flexibility of this separation technology.Moreover,we investigate the movement processes of droplet system to study the adaptability of ICEO vortices in manipulation of large-scale particles.Furthermore,based on regulation of EES of nanoparticles via ICEO vortices,we separate 500-nm PS and 600-nm copper nanoparticles to validate the effectiveness of this approach.According to regulation of EES of C.vulgaris,we isolate C.vulgaris from heterogeneous microalgae.Moreover,this separation technology is engineered in cell-based separation of Oocystis sp.to obtain sing-cell one.With regulating the work parameters,we can isolate desired-cell-number Oocystis sp.,providing a reliable method to obtain high-quality neutral lipid.By evolving asymmetrical ICEO vortices,we design tilted-angle ridge floating electrode sequence(TARFES)to actuate cyclical asymmetrical ICEO vortices for simultaneous separation of multiple particles.Based on flow-field distribution,we investigate particle separation processes under two models.After validating separation of the particles with different EES,we investigate the influences of voltage intensity,frequency,flow rate and concentration ratio on the separation.Based on validation of separation of the particles with the same EES,we study parametric effects on particle separation and achieve simultaneous separation of particles of three types.Based on characterizing CGO balls,we accomplish size fractionation of CGO balls and investigate the voltage effect on the separation.Furthermore,we separate nanoscale CGO balls from the original samples by regulating the work parameters.This work presents a continuous and contact-free approach for size fractionation of CGO balls,reducing the cost of uniform-sized CGO ball fabrication.In addition,this technology can be extended to separation of other applied materials.