Foley Brandon L, Aubry Sylvie, Murialdo Maxwell, Glascoe Elizabeth A
Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94550, United States.
J Phys Chem B. 2024 Sep 26;128(38):9274-9283. doi: 10.1021/acs.jpcb.4c03888. Epub 2024 Sep 13.
Two key phenomena─immobilization and concentration-dependent mixing free energies─simultaneously alter the sorption thermodynamics and diffusion of vapors in materials. This interrelation is leveraged to fit a unified model simultaneously capturing both sorption dynamics and the equilibrium isotherms. This transport model incorporates quasi-equilibrated immobilization reactions and considers Fick's law rigorously in terms of chemical potential gradients rather than concentration gradients. Five material case studies are discussed with varying characteristics, including fillers that provide sites for surface sorption, pores for capillary condensation, and apparent clustering or pooling at high vapor concentrations. Each case study illustrates that intrinsic diffusivity is constant, while the effective diffusivity changes predictably because of immobilization or changing free energies of mixing.
两个关键现象——固定化和浓度依赖性混合自由能——同时改变了材料中蒸汽的吸附热力学和扩散。利用这种相互关系来拟合一个统一模型，该模型同时捕捉吸附动力学和平衡等温线。这个传输模型纳入了准平衡固定化反应，并严格根据化学势梯度而非浓度梯度来考虑菲克定律。讨论了五个具有不同特性的材料案例研究，包括提供表面吸附位点的填料、用于毛细管冷凝的孔隙，以及在高蒸汽浓度下明显的聚集或汇集。每个案例研究都表明，本征扩散率是恒定的，而有效扩散率由于固定化或混合自由能的变化而可预测地改变。
