(609c) Nano- and Mesoscale Transport and Mechanics in Ionomers
AIChE Annual Meeting
Thursday, November 1, 2018 - 8:40am to 9:00am
In this work, resistor and spring networks coarse-grains the interconnected hydrophilic and hydrophobic domains, respectively, as segments connecting nodes. Conservation of species flux and stress at each node in the hydrophilic and hydrophobic networks dictates electrochemical potential and strain in segments, respectively. A mean-field nanoscale model of the domains parametrizes resistances of the segments as a function of size (thickness and length) and water content. The average and distribution of domain sizes and connectivity are consistent with experiments. Accordingly, there is a distribution of segment resistances and modulus in the networks. Congruent with Onsager-Stefan-Maxwell concentrated solution theory, we treat chemical and electrostatic gradients as driving water and ion transport and their corresponding coupling (electroosmotic effect). We validate the predicted modulus, diffusion and electroosmotic coefficients, and conductivity against experiments.
We find macroscopic transport and mechanics behavior emerges out of the mesoscale. For example, how nanoscale resistance depends on domain size dictates which pathways a species will take across the network. Accordingly, different modes of transport utilize different network pathways and have different effective tortuosities. Moreover, water gradients at the macroscale induce mesoscale electrostatic potential gradients (and visa-versa). These results show how design of emergent behavior improves membrane performance.