Karolina Svensson: Miniaturization of microfluidic control systems for high-pressure chromatography

Abstract

This thesis explores flow control and sensing in microfluidic chips for high-pressure applications. Sub-cm glass chips have been designed and fabricated with the aim of miniaturizing chemical analysis systems. Today, chemical analyses are performed worldwide for medical and environmental purposes. As more tests become available for a wider audience, the demand further increases. The large instruments that are typically used are expensive and have high chemical and power consumption. Miniaturizing components has, on the contrary, the ability to decrease volumes, costs, and environmental impacts. In addition to lower consumption, miniaturization carries several features: quick heat distribution, laminar flow, and higher pressure tolerances, to name a few. In this thesis, microfluidic chips are developed aiming to replace larger-scale instruments. Applications are centered around high-performance chromatography, which is a separation method used to separate and detect compounds in a sample. Different flow phenomena are also investigated, including fluid compressibility and capacitance, which become interesting when working at elevated pressures. Experiments have been made showing how this impacts the regulation of microfluidic flow. Thermal regulation of viscosity has been a centerpiece of this work. Controlling flow rate and pressure in a system by changing the viscosity of a fluid has proven effective for several applications. This was utilized to maintain back pressure at the end of a system as well as to control and stabilize flow at the beginning. It was also used to regulate composition and adjust parallel flows during experiments. Multiple chips were also connected to utilize several features and to get close to fully miniaturized and portable analysis systems. Apart from flow actuation, the microfluidic chips were also equipped with sensors for accurate sensing in close proximity.