Molecular dynamics (MD) simulations are used to predict the partitioning of per- and polyfluoroalkyl substances (PFASs) to smectite clay, a high surface area adsorbent ubiquitous in temperate soils. Simulated systems model a stack of flexible smectite lamellae in contact with a bulk aqueous reservoir containing PFAS molecules. Perfluorobutanesulfonic acid (PFBS), perfluorohexanesulfonic acid (PFHxS), and perfluorooctanesulfonic acid (PFOS) are simulated at various aqueous chemistry conditions to examine the effect of PFAS size, salinity, and coordinating cation type (K⁺, Na⁺, and Ca²⁺) on adsorption. The metadynamics technique is employed to facilitate the exploration of the simulation cell and to reconstruct the underlying free energy landscape. Adsorption is favorable on the hydrophobic domains of the external basal surfaces with the fluorinated chain adopting a flat orientation on the surface. Analysis of the adsorption energetics reveals large favorable entropic contributions to adsorption. The enthalpy of adsorption is unfavorable, though much less so in the presence of Ca²⁺ due to stabilizing ‘lateral cation bridging’ interactions between divalent cations and PFAS sulfonate head groups. Overall, this research advances the mechanistic understanding of PFAS-smectite interactions and provides new insights that could help inform fate and transport models and the development of adsorbents and remediation techniques.

分子动力学（MD）模拟用于预测全氟烷基物质和多氟烷基物质（PFAS）与蒙脱石粘土的分配，蒙脱石粘土是在温带土壤中普遍存在的高表面积吸附剂。模拟系统模拟了与包含PFAS分子的大量水库接触的柔性蒙皂石薄片的堆叠。在各种水性化学条件下模拟全氟丁烷磺酸（PFBS），全氟己烷磺酸（PFHxS）和全氟辛烷磺酸（PFOS），以检查PFAS尺寸，盐度和配位阳离子类型（K ⁺，Na ⁺和Ca ^{2+）的影响}）吸附。运用元动力学技术来促进对模拟单元的探索并重建潜在的自由能态势。在基底表面的疏水区域上的吸附是有利的，而氟化链在表面上采取平坦的取向。吸附能的分析表明，熵对吸附有很大的贡献。吸附的焓是不利的，尽管在存在Ca ²⁺的情况下要少得多由于稳定了二价阳离子和PFAS磺酸根首基之间的“侧向阳离子桥接”相互作用。总的来说，这项研究提高了人们对PFAS-蒙脱石相互作用的机理的理解，并提供了新的见解，可以帮助人们了解命运和运输模型以及吸附剂和修复技术的发展。