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SUMMARY:From Darcy to the Nanoscale: How Emerging Contaminants Challenge E
 xisting Modeling Approaches in Contaminant Hydrology - Dr Kaveh Sookhak La
 ri\, CSIRO
DTSTART:20241113T143000Z
DTEND:20241113T153000Z
UID:TALK220423@talks.cam.ac.uk
CONTACT:Lisa Masters
DESCRIPTION:Traditionally\, contaminant hydrology in the subsurface has re
 lied on Darcy-scale models derived from upscaling the Navier-Stokes equati
 ons. These approaches have been effective for various complex scenarios\, 
 including multiphase and multi-component systems such as oil-contaminated 
 sites undergoing microbial degradation. These models approximate fluid flo
 w and contaminant transport based on bulk properties and averaged behavior
 s at the continuum scale. However\, emerging contaminants like perfluoroal
 kyl substances (PFAS) present unique challenges that extend beyond the cap
 abilities of these conventional approaches.\nPFAS are a large group of per
 sistent and potentially carcinogenic chemicals characterized by their rema
 rkable stability. They are prevalent in numerous contaminated sites\, ofte
 n at concentrations exceeding safe thresholds. Unlike typical passive solu
 tes\, PFAS can actively modify interfacial properties through solutocapill
 ary effects\, where concentration gradients change surface tension. Additi
 onally\, PFAS molecules can form micelles with diverse shapes\, sizes\, an
 d aggregation numbers\, depending on environmental conditions such as the 
 types of counterions present. These nanoscale behaviors significantly affe
 ct transport properties\, complicating the prediction of PFAS fate and mob
 ility using traditional continuum models.\nAddressing these limitations ne
 cessitates a computational roadmap to upscale complex transport phenomena 
 from the nanoscale to the Darcy scale. Molecular dynamics (MD) simulations
  have emerged as a valuable tool for characterizing PFAS interactions at t
 he molecular level. However\, most studies have focused on PFAS adsorption
  characteristics on solids as part of remediation strategies\, leaving the
  behavior of PFAS at fluid interfaces underexplored. This is a critical ga
 p that challenges the ability of Darcy-scale models to accurately represen
 t PFAS transport and retardation.\nEven at the classical MD level\, PFAS b
 ehavior in multiphase systems—such as micelle formation\, adsorption at 
 interfaces\, and aggregation characteristics—varies significantly with e
 nvironmental factors like counterion type. This variability raises questio
 ns about the reliability of fixed force fields traditionally used in MD si
 mulations. It is necessary to validate the appropriateness of the force fi
 elds under given conditions\, which can be achieved by comparing MD result
 s with experimental data or through ab initio MD simulations.\nAs a first 
 step in this direction\, we explore various options to study our system us
 ing ab initio MD. Given the computational demands of these methods\, a hyb
 rid QM/MM approach may be applied\, where the quantum mechanical region ca
 ptures chemically significant interactions while the molecular mechanics r
 egion accounts for the larger environment. The feasibility of Density Func
 tional Theory (DFT) and wavefunction-based approaches will be assessed. Th
 ese results can then be used to validate classical MD simulations and ensu
 re the accuracy of the applied force fields under specific conditions. Thi
 s multi-scale framework aims to bridge the gap between nanoscale molecular
  insights and macroscale modeling in contaminant hydrology\, providing a m
 ore robust approach to addressing PFAS-related challenges.
LOCATION:Unilever Lecture Theatre\, Yusuf Hamied Department of Chemistry
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