Design Of High Throughput Microfluidic Chip With Concentration Gradient And Study On Crystal Morphology Control

The chemical and physical properties of crystals such as optical,thermal,magnetism performance and electric conductivity would be greatly affected by their morphology.Precise controlling of crystal morphology is an important research field.Different types or concentrations of additives,even their ratios have huge influence on the morphology of crystals.Precise controlling of crystal morphology always requires many experimental dates and rich experience and it takes both time and efforts.Thus,it is extremely important and necessary to develop a method which could screen the crystallization conditions rapidly.Since the 1990 s,microfluidic chips with different functions have been widely applied in many aspects,such as biology,chemistry,medical and so on.There is a variety of microfluidic chips,but the implementation of different functions always based on the design of different microchannel networks.In order to achieve precise control of microfluidics,one of the most commonly used design methods is to use the inherent characteristics of fluids at the microscale to construct microfluidic chips with specific functions.Based on the inherent characteristics of laminar flow of fluids and the mass transfer process through diffusion at the micro-scale,this thesis focuses on the analysis of the mass transfer in the microfluidic chip and the resulting concentration distribution,and then designs two high throughput microfluidic chips with concentration gradient.The microfluidic chip can create a concentration gradient of reactant and a microenvironment to achieve rapid screening of optimal conditions for reactions.The effect of additives on the morphology of calcium carbonate was studied by conducting calcium carbonate crystallization experiments in the microfluidic chip.Calcium carbonate is selected as the target crystal because it is an important inorganic crystal material.Many additives(such as inorganic ions,amino acids,polymers,surfactants,etc.)can greatly affect the crystal morphology of calcium carbonate.The final morphology,and the influence of multiple additives on the morphology is more complicated.At present,the depth of mechanism of this influence law is insufficient.The study of the influence of additives on the morphology of calcium carbonate crystals is of great significance in industry and scientific research.The main research contents of this thesis include:1.Based on the laminar flow and diffusion induced mass transfer of the fluid at the micro-scale,the flow and mass transfer process of the fluid are analyzed,and two high throughput concentration gradient microfluidic chips are designed and prepared,and then the COMSOL Mutiphysics software is used to simulate the concentration distribution and flow velocity and it is verified by R6G fluorescence experiment.The results show that both the prepared microfluidic chips can generate the required concentration gradient and microenvironment.2.The influence of Mg²⁺in the calcium carbonate crystallization was studied with one-layer high-throughput concentration gradient microfluidic chip with coprecipitation method.The sizes and morphologies were characterized by SEM,and polymorphism was confirmed by Raman spectroscopy.In addition,the mole ratios of magnesium in the precipitated crystals were examined.The results indicated that the one-layer microfluidic chip could rapidly screen the ion compositions for calcium carbonate morphology.In addition,the CO₃^2-:Ca²⁺ratio induces a calcite morphology transition from regular rhombohedral to irregular rhombohedral and nanoparticle aggregations within a narrow range of Mg²⁺:Ca²⁺ratios,which enriches the controlling of morphology theory of calcium carbonate.3.The influence of multiple additives on calcium carbonate crystallization was studied with three-layer high-throughput concentration gradient microfluidic chip.The sizes and morphologies were characterized by SEM.The results indicated that the three-layer microfluidic chip could rapidly studying different concentrations or types of additives in morphology of calcium carbonate.With the increase of Mg²⁺and L-glutamic acid concentration,the lifetime of amorphous calcium carbonate(ACC)is increased.In the situation of single additive exist,whatever Mg²⁺or L-glutamic acid,the continuous transition of crystal morphologies is occured with the change of additive concentration.Under the combined action of the two additives,the additives have a greater impact on the crystal morphology.