Theoretical And Experimental Studies Of Multi-scales Particle Manipulation Based On Light-fluid Interaction

In the liquid environment,the manipulation of micro-nano particles based on the interaction of light and liquid is a key technology in the fields of biomedical screening,material performance evaluation,micro-assembly,chemical synthesis and analysis,etc,which is developing in achieving precise capture and long-distance directional transmission of multi-scales particles.At present,there are still bottlenecks in this technology: such as cross-scale capture;long-distance transmission and stable capture on the same platform;interference of side effects in nanoparticle manipulation.The reason for the bottleneck lies in two key scientific issues:(1)the force balance mechanism and scale effect of micro-nano particles in microfluidics;(2)the multi-physics coupling and interaction of high-precision capture and transmission of micro-nano particles on the same platform.disturb.Therefore,exploring the kinetic mechanism and equilibrium conditions of particles of different scales from the two levels of transport and capture will help to comprehensively improve the performance of micro-nano particle manipulation technology and related application development.Combining theoretical analysis,experiments and numerical simulations,this thesis studies the manipulation of 100-micron,sub-micron and nano-particles by means of multi-physics,focusing on the dynamic equilibrium and regulation involved in the transport and capture process.The four main studies are as follows:(1)Study on the force mechanism of multi-physics coupled particles in the liquid environment: First,an analysis model of the particle force in the microfluidic environment under the action of incident light was established,and the optical theory and heat transfer principles involved were analyzed.The control characteristics of each physical field on particle transport and trapping,and a reasonable multi-physics coupling manipulation scheme was designed for three-scale(hundred-micron,sub-micron,and nanometer)particles,and the equilibrium conditions between trapping and transport were analyzed.The influence of the control parameters has laid a research foundation for the experimental preparation of the full studies.(2)Study on 100-micron-scale particle manipulation technology based on the combination of particle inertial force and thermal convection effect: In view of the current research gaps in the transmission and capture of particles at this scale by optical manipulation technology,this study proposes a long-distance transmission based on optical fiber thermal convection,combined with the gravity and volume properties of the particles to achieve accurately captures.Two kinds of microparticle transport devices,fiber embedded and fiber separated,are designed.The fiber embedded device completes the circular transport and stable capture of 100 μm silica particles of 4000 μm;the fiber separation system uses the combination of optical switches,light splitters and fiber array to realize continuous transmission of 5-120 μm particles up to 7.5 mm.By analyzing the influence of control parameters such as optical power,fluid field distribution,fiber position,and liquid level height on the control performance,the feasibility and equilibrium mechanism of using thermal convection transport combined with particle inertial force capture are verified.And in the optical fiber separation system,the comparative experiments of silica,polystyrene and zirconia have proved that stable capture does not depend on the dielectric properties of particles,and the sorting based on particle density is realized.(3)Study on micron-scale particle manipulation technology based on the combination of photothermophoresis and thermal convection: In view of the problem that the current micro-particle manipulation technology has a small action area and is difficult to transmit over long distances,this study proposes a manipulation scheme based on thermal convection and thermophoretic.The particles are captured and transported respectively by the thermophoresis and thermal convection effects generated by the fiber detachable structure combined with the gold film.Long-distance transport and high-throughput self-assembly of2 μm and 0.5 μm particles were achieved,with a maximum transport distance of 51 μm and30 μm,respectively.By exploring the transmission rate and thermophoretic capture efficiency of particles under different power and gold film thickness,the equilibrium principle of particle transmission and capture is explained.Finally,the conjecture that thermophoresis is the main trapping force is further verified by comparative experiments with different salt concentrations in the solution.(4)Study on nanoscale particle capture and interference suppression technology based on interface photothermal effect: In view of the problem that the plasma surface thermal effect interferes with the stable capture of nanoparticles,this study proposes to use the low absorption characteristics of silicon material itself to suppress the local temperature rise.The trapping stiffness of nanoparticles is guaranteed by the special silicon-based optical tweezers structure,the reason for the local electric field enhancement is elucidated,and the designed structures are verified to reduce the dissipation loss by 3 orders of magnitude compared with the plasmonic surface,local temperature rise and thermal convective effects interfere negligibly with capture stability.The optical force and trapping potential energy exerted on polystyrene particles are calculated,and the trapping properties of the designed structures for 20 nm particles are analyzed,which proves the feasibility of nanoparticle manipulation based on fiber-optic microfluidics.Based on the above studies,the innovations of this study are as follows: a new manipulation mechanism of 100-micron particles is discovered,which can increase the transmission distance of micro-sized particles to the millimeter level and achieve stable capture;innovatively use silicon-based optical tweezers to eliminate the interference of medium thermal effect in nanoparticle capture;the transmission and capture of various particles are realized by replacing the lens coupling device with the optical fiber system,which simplifies the equipment and reduces the cost while improving its application range.The research results of this study will provide key technologies for the application of micronano particle manipulation.