| Microfluidic chip has the advantages of small volume,high specific surface area and energy and mass transfer.Therefore,it has the advantages of small sample consumption,rapid response,high sensitivity,high integration and portability.Thus microfluidic chips have great application prospects in the fields of biochemical detection,material synthesis,energy-efficient applications and so on.In the process of biochemical analysis and detection,the concentration of sample solution is an important procedure,and it is also the best method to improve the detection sensitivity.Photothermal evaporation concentration technology heats the sample solution by irradiating light on the fluid or photothermal material to produce photothermal effect.It can realize non-contact sample concentration and has the characteristics of local accurate adjustment and rapid response.There are some problems of microfluidic photothermal evaporation and concentration technology:（1）For the closed photothermal evaporation microfluidic chip,the steam generated by evaporation is difficult to discharge,resulting in the increase of steam partial pressure,which will inhibit the evaporation process and reduce the evaporation efficiency;（2）The instability of gas-liquid interface will appear after the bubbles generated in the channel,which will seriously affect the evaporation stability;（3）Lack of efficient evaporator structure design.Porous photothermal materials have the characteristics of photothermal conversion,and can separate the gas-liquid phase.Rich pores can facilitate the discharge of steam,which can not only improve the efficiency of photothermal evaporation,but also ensure the stability of evaporation.However,the existing porous photothermal materials are not easy to combine with microfluidic chips,and the preparation method is complex,which is not convenient to adjust and customize flexibly according to the demand.Based on the above problems,this thesis focused on porous photothermal materials and their application in microfluidic chip concentration.Firstly,PDMS porous photothermal evaporation materials with good biocompatibility and easy processing were prepared.The effects of light intensity,porous layer thickness and pore structure on photothermal evaporation performance and the evaporation characteristics of salt solution were studied,and the methods of efficient utilization of energy and prevention of salt precipitation were put forward.Then,the microchannels of pore network were processed by photolithography.Through visual experiments,the effects of light intensity,porosity and salt solution concentration on the characteristics of photothermal evaporation in the pore scale of porous materials were studied,and the characteristics of interfacial evaporation and mass transport in the channels of photothermal pore network were revealed.Finally,according to the mass transfer characteristics in porous photothermal media,the prepared PDMS porous materials were integrated into the photothermal evaporation and concentration device,and the evaporation and concentration microfluidic chip with porous photothermal evaporation layer was designed.The effects of operating conditions such as light intensity and flow rate on the concentration effect of photothermal evaporation and concentration were studied.The concentration effects of Cu SO4 solution and lysozyme solution were tested,and the regulation methods of concentration effect were put forward.The main outcomes of this thesis are summarized as follows:（1）Based on PDMS and carbon nanoparticles,porous photothermal materials were prepared by salt template method.The preparation method is simple,and the pores and thickness can be adjusted as needed.The prepared PDMS porous material had good process performance and excellent photothermal evaporation characteristics.Under the condition of one solar irradiation,the evaporation rate could reach 1.36 kg/（m2·h）,and the light-vapor conversion efficiency was 77.89%.The increase of porous layer thickness would reduce heat loss and increase evaporation rate.When used for photothermal evaporation of salt solution,the evaporation rate decreased with the increase of salt solution concentration,and the increase of pore size could alleviate the salt precipitation of porous materials.（2）The phase change and component transport in photothermal porous media were studied by simulating two-dimensional slices of porous layer with microchannel network structure.In the process of interface evaporation,the gas-liquid interface at the opening in the pore area remained stable under the action of capillary force.Evaporation occurred at the gas-liquid interface,and the steam transmission resistance was much less than the internal evaporation,which was conducive to evaporation,and the evaporation effect was significantly improved.Under the same light intensity,when the porosity increased,the steam transmission resistance decreased,which was conducive to the evaporation,and the evaporation rate was higher.For evaporation of salt solution,when the pores were large,the diffusion mass transfer resistance from the interface to the main body of liquid phase was low,which could reduce the precipitation of solute crystallization,and was conducive to the operation of porous photothermal media under high solution concentration conditions.（3）An evaporation concentration microfluidic chip with porous evaporation layer was designed and fabricated.The effects of different working modes,light intensity,solution flow rate and sample types on its evaporation concentration characteristics were explored.The microfluidic chip with hydrophilic porous layer had higher evaporation concentration efficiency.The concentration effect could be adjusted online by adjusting the light intensity and solution flow rate.By exploring the concentration performance of different kinds of sample solution,it showed that the designed microfluidic concentration chip had good adaptability to different working fluids. |
