Demonstrating at a global scale that water reduces contacts with the surroundings by lubricating the cell wall interior, we again focus on the ions and what drives their differential diffusion. Figure and supporting animations S4 -S6 illustrates as well as quantifies typical cation -cell wall polymer interactions. When the water weight of the plant's secondary cell wall system increases, the contacts between cations and the cell wall polymers are generally reduced. In a solid system, the coordination number of the ions will be approximately constant, and thus the decrease in contacts to biopolymers leads to an increase in contacts to water molecules. For sodium or potassium (Figure and), the changes in contact number are monotonic. Similar trends where contacts are reduced at higher moisture levels are observed for Cu 2+ interaction with cellulose and lignin, but not when interacting with hemicellulose (Figure ). Instead, we find that the reduction in number of contacts between the cation and hemicellulose is not monotonous. Instead, the cation-hemicellulose contacts increase beyond 15% water weight. We attribute this to the strong electrostatic interaction between the cation and carboxylate functional group in hemicellulose in our secondary cell wall model, with representative snapshots shown in Figures . We would anticipate that other divalent cations would have similar strong interactions with hemicellulose carboxylate groups and may need to be avoided when optimizing for diffusion within wood. Overall, for different salts used in this study, we find the cation interaction with hemicellulose is relatively stronger when compared to interactions with lignin or cellulose, due to the carboxylate functional group in hemicellulose.