Influence of Ionomer Loading and Substrate Wettability on the Morphology of Ionomer Thin Films Using Coarse-Grained Solvent Evaporation Simulations

Abstract

Coarse-grained molecular dynamics simulations were performed to understand the evolution of ionomer morphologies in solutions during solvent evaporation. To reproduce experimental fabrication conditions, the simulation conditions, such as evaporation and sedimentation rate, were determined based on a dimensionless parameter, the Péclet number, providing a direct link between simulation results and experimental findings. The effects of ionomer loading and substrate wettability on the morphologies of ionomer thin films after drying were investigated extensively, which exhibit similar trends reported in experiments. At low ionomer loading, a discontinuous patchy film with a minimum thickness of ≈3 nm was formed on the hydrophobic substrate, whereas a high-coverage continuous film of ≈2 nm thickness was found on the hydrophilic substrate. At high ionomer loading, regardless of the substrate wettability, a lamellar-like morphology with multiple water-rich layers was observed, although the stability of the layer structures and the ionomer surface roughness differ between the substrate types because the substrate wettability strongly affects the adsorption behaviors of ionomers and water as the first layer in the interfacial region. Our findings of a decrease in the degree of phase segregation with increasing thickness suggest an eventual collapse of the lamellar structure at a certain thickness within a few tens of nanometers or even thinner.

The role of electrode wettability in electrochemical reduction of carbon dioxide

“…The hydrophobic backbones tend to interact with the non-polar solid phase, so the polar ionic groups tend to point towards the polar liquid phase and promote wettability. 186 On the other hand, the ionic groups can also re-orient towards the polar surfaces of the solid phase instead of the liquid phase, leaving the hydrophobic backbones exposed to the water phase. In this case, the ionomer in the CL promotes hydrophobicity.…”

Dynamics of Water in a Catalyst Layer of a Fuel Cell by Quasielastic Neutron Scattering

“…The direct evidence for the isolated water has been not obtained at the moment but must be due to the effects of the thin film structure of Nafion in the wet CL. As predicted by a computer simulation, the thin film fluctuates in thickness, leading to deformation of the ionomer clusters. This deformation may produce some isolated water regions.…”

“…In addition to the SANS results, it is observed that the Nafion thin film fluctuates in thickness from the computer simulation results. 25 Based on the results, a schematic drawing is shown for the structure of the wet CL in the upper part of Figure 9.…”

The Martini Model in Materials Science

“…Furthermore, Martini has been applied to model ion‐conducting polymeric materials used as ion‐exchange membranes for fuel cell applications. [ 210,220–226 ] Proton‐exchange‐membrane fuel cells use acid polyelectrolytes, such as Nafion, as the membrane material. The membranes are formed by solution‐processing techniques.…”