Investigating Effect of Thermal Gradient on Diffusion of Microbial Respiration Byproducts through PTFE for Soil Profiling

The agricultural industry utilizes crop rotation to take advantage of plant species differing in nutrient requirements to lessen the adverse impacts of successive crop planting on soil quality. As the need for more sustainable and efficient agriculture develops, a deeper understanding of the influence of soil characteristics on crop production and quality is necessary. Few tools are currently available for farmers to profile their soil, particularly on a molecular level where microbial decomposition synthesizes the nutrients that crops require. The research group focuses on the investigation of gaseous diffusion through hydrophobic membranes protecting sensor components for use in an encompassing project designing a subsurface soil sensor profiling soil characteristics via the detection of gaseous byproducts of organic decomposition by microbes. Prior to data collection, the project required the development and construction of a membrane testing structure and standardized protocol to evaluate diffusive properties of hydrophobic membranes. The acrylic testing structure encloses a thin membrane between its two halves where gas flows on each side, contacting the membrane surface through fritted glass connected to gas flow. PTFE (polytetrafluoroethylene) is selected as a selectively permeable membrane to evaluate the effects on diffusion rate with an induced temperature gradient inside the membrane testing device to determine efficacy of a heated chamber in the soil sensor. Carbon dioxide, a primary byproduct of microbial respiration, is selected as the gas investigated while nitrogen is used as a carrier gas on the opposite side of the membrane and testing device. Computational methods (COMSOL, Python) are used to verify the increased diffusion detected and calculate mass balances.