Large Pores Dominate Flow Through Nanomembranes (FOW)

Because of the non-linear dependence of volumetric flow rate on pore size …

where t is the membrane thickness and r is the pore radius, large pores contribute disproportionately to the total flow through a membrane than small pores. The magnitude of this phenomenon can be appreciated by using the Dagan equation to calculate the flow per pore in an image (method and figure adapted from Gaborski et al., ACS Nano 2010; 4:6973-6981). The total flow is the integral under this curve multiplied by the ratio of the total membrane area to the imaged area. The pores in red in the pore size histogram account for all the flow to the right of the vertical line in the flow curve. Fewer than 20% of the pores account for more than half of the area under the curve.

One of the consequences of this phenomena is that when filtering a mixed population of nanoparticles some of which are larger than all of the pores, the largest pores in the membrane pores will clog first. This effectively leaves behind a smaller pore membrane. Karl Smith (PhD ’17) was the first to think about this as potentially useful as a means to make smaller pore membranes out of larger ones (Smith, et al, (2017), Sep Purif Technol; 189:40-47) – just mix in some particles to ‘knock out’ the pores you don’t want to contribute to your processes.


Professor McGrath holds a BS degree in Mechanical Engineering from Arizona State and a MS degree in Mechanical Engineering from MIT. He earned a PhD in Biological Engineering from Harvard/MIT's Division of Health Sciences and Technology. He then trained as a Distinguished Post-doctoral Fellow in the Department of Biomedical Engineering at the Johns Hopkins University. Professor McGrath has been on the Biomedical Engineering faculty at the University of Rochester since 2001 where he also serves as the director of the graduate program BME and associate director of the URNano microfab and metrology core. McGrath's research was focused on the phenomena of cell migration until 2007 when he founded the interdisciplinary Nanomembrane Research Group to development and apply silicon membrane technologies. Professor McGrath is also a co-founder and past president of SiMPore Inc., a company founded to commercially manufacture silicon membranes and related technologies.

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