Thesis Format
Monograph
Degree
Master of Science
Program
Chemical and Biochemical Engineering
Supervisor
Boutilier, Michael
Abstract
Separation membranes are widely used in a variety of industrial and environmental applications, including water purification and desalination. However, these membranes can see their performance limited because of the inherent trade-off between permeance (rate of flow of a fluid through a membrane) and selectivity (ability of the membrane to separate different components of a fluid mixture) where high permeance typically means low selectivity and vice versa. Nanoporous atomically thin membranes (NATM), such as graphene membranes, have the potential to overcome the permeance-selectivity trade-off due to their atomic thickness and the capacity to be fabricated with pores of very small size and uniform geometry. While permeance is a key membrane performance metric, liquid flow rate measurements through single graphene nanopores have never been reported due to lack of a suitable measurement technique. In this study, we develop a method to measure flow rates through micro and nanopores in membranes by analyzing velocity fields obtained through micro particle image velocimetry (micro-PIV). We validate our method and determine the Reynolds number limit for which it is valid by conducting experiments with micropores of defined sizes (50, 6, 5, 3 μm) in transmission electron microscope (TEM) grids and comparing the results with values obtained by calibrated flow sensors. The technique is then applied to measure flow rates through pores of 500 and 200 nm in graphene, obtaining flow rates as low as 2 nl/min, which is lower than the minimum detectable flow rate of 10 nl/min for commercial sensors. We also report permeation coefficients ranging from 7.0x10-19 to 1.5x10-18 m3/s-Pa for the 500 nm pore and 8.5x10-20 to 2.0x10-19 m3/s-Pa for the 200 nm pore. Furthermore, we demonstrate that our method is valid regardless of the geometry of the pore, showing its importance for applications involving irregularly shaped pores. This research makes a significant contribution to the NATM field by enabling non-invasive flow quantification through graphene nanopores, which could not be measured by conventional sensors.
Summary for Lay Audience
Separation membranes are thin barriers that allow certain substances to pass through while blocking others. They are widely used in various applications, such as water purification, gas separation, and drug delivery. However, conventional membranes often face a trade-off between permeance (related to the ability of a substance to flow through) and selectivity (the ability to separate different components). Atomically thin materials like graphene have the potential to overcome this limitation due to their thinness and the possibility of perforating the material with holes similar in size to small molecules. To further develop and optimize graphene membranes, it is essential to study the flow rates through specific areas of these membranes at the nano-scale. However, measuring such low flow rates remains a challenge, as they are expected to be below the detection limit of commercial sensors. This study aims to develop an optical method to measure very low flow rates through nanopores in graphene, which cannot be detected by currently available commercial sensors. The method builds upon previous work and involves seeding particles in a reservoir downstream of the pore and using a technique called micro-particle image velocimetry (micro-PIV) to map the movement of these particles. By comparing the observed velocity fields with analytical solutions, the flow rate can be determined. The experiments are divided into two parts. First, the method is validated using larger pores on the micro-scale, and the results are compared with values obtained from calibrated sensors. Second, the validated method is applied to measure flow rates through sub-micron pores, including those in graphene.
Recommended Citation
Gomez Suarez, Samuel Francisco De Jesus, "Liquid Flow Rates Measurements Through Graphene Nanopores by Micro-PIV" (2024). Electronic Thesis and Dissertation Repository. 10190.
https://ir.lib.uwo.ca/etd/10190