Measuring The Nucleation Kinetics Of Calcium Carbonate Using A Self-Digitization Microfluidic Chip

As an important biological mineral and natural ore,revelation of nucleation mechanism of calcium carbonates is of great significance for both industrial production and scientific research.The nucleation rate is one of the most important parameters determining the crystal quality and production efficiency of calcium carbonate.Nucleation is a stochastic process and the nucleation rate can only be estimated statistically by creating simple random sample.There is still a research gap in the field of providing reliable experimental data for the nucleation rate of calcium carbonate,since calcium carbonate is a typical non-temperature-sensitive crystal,it has special requirements for measurement devices.Supersaturated droplets should be formed in a chemical reaction,and the moisture of droplet should remain unchanged during a long-time nucleation process.For statistical estimation,the reactor should be independent and identical.The disturbance from environment cannot influence the microreactor.To meet these requirements,conventional microfluidic droplet method needs complicated structure,cumbersome operation and expensive equipments for controlling and driving fluid.In this paper,we propose a digital microfluidics chip with high-density microwell array integrated with a void cavity.The chip can meet the requirements for measuring the nucleation rate of calcium carbonate with a more convenient and economical way.The main content of this paper mainly includes:In order to meet the special requirements for nucleation rate measurement of calcium carbonate,a digital microfluidic chip with a high-density microwell array was designed and fabricated.The microwell array and the oil phase partition on this chip can split the sample into a large number of uniform and stable droplets,which is called self-digitization,and meet the requirements for statistical measurement of nucleation.A large-volume void cavity is added under the patterned PDMS structure in the typical glass-PDMS-glass(GPG)chip,which can accelerate the loading process and avoid the nucleation of the mixed solution before forming droplets.The void cavity can ensure that the water of a large number of droplets remains unchanged during a few days.To verify the feasibility of the digital microfluidic chip,which has a high-density microwell array and a void cavity,in exploring the nucleation mechanism and measuring the nucleation rate,two important calcium carbonate crystals—high magnesium calcite and aragonite were studied on chip.We measured nucleation rate with different solution concentrations.A control experiment in bulk solution was performed under each condition.The morphology and polymorphs of crystals were characterized.We studied the effect of supersaturation and confined space on the nucleation of high-magnesium calcite and aragonite.The experimental results show that high supersaturation can significantly increase the nucleation rate and crystallized rate.In addition,the small volume can truly extend the mean nucleation time.This chip can be utilized to measure the nucleation rate of other non-temperature-sensitive crystal.