A Microfluidic Platform for the Control and Analysis of Phase Transitions in Concentrating Droplets

• Main Author: Vuong, Sharon M.
• Format: Others
• Published: Research Showcase @ CMU 2014
• Subjects: microfluids; suspension stability; droplets; glycine crystallization
• Online Access: http://repository.cmu.edu/dissertations/383; http://repository.cmu.edu/cgi/viewcontent.cgi?article=1383&context=dissertations

This work describes the development of a microfluidic platform that can be used to study suspension stability and crystallization with in droplets as a function of time and concentration. Techniques for monodisperse droplet formation, droplet trapping and storage, and droplet dehydration are developed and used to design a microfluidic platform that can be adapted for the applications of interest. A geometric model is developed to predict the droplet shape and emulsion structure generated by microfluidic nozzles. However, droplet volume and structure spacing cannot be independently controlled using microfluidic nozzles, and a design consisting of an array of traps is considered to achieve the desired structure for stable, extended droplet observation. The dehydration of aqueous droplets stored in the array is characterized as a function of relative humidity, and is shown to be reasonably estimated as a species diffusing from a sphere into an infinite medium. The microfluidic platform for droplet dehydration is combined with particle tracking to show that the stability of particle suspensions can be probed as a function of salt concentration. The flocculation behavior observed in the trapped droplets agrees well with corresponding macroscale measurements as well as with previously published studies. The platform is also used to generate substantial sample sizes to measure nucleation statistics and crystal growth rates of glycine as a function of initial concentration, environmental conditions, and the presence of additives. These applications show proof of concept that the microfluidic platform is a useful tool for the analysis of the behavior observed during particle aggregation and crystallization.