Enthalpic Interactions and Solution Behaviors of Solvent-Free Polymer Brushes

We performed molecular dynamics simulations to characterize the role of enthalpic interaction in impacting the static and dynamic properties of solvent-free polymer brushes. The intrinsic enthalpic interaction in the simulation was introduced using different attraction strengths between distinct species. Two model systems were considered: one consisting of binary brushes of two different polymer types and the other containing a mixture of homopolymer brushes and free molecules. In the first system, we observed that, when two originally incompatible polymers were grafted to opposing surfaces, the miscibility between them was significantly enhanced. A less favorable intrinsic enthalpic interaction in the brushes resulted in a more stretched chain configuration, a lower degree of inter-brush penetration, and faster segmental relaxation. In the second system, we characterized the solvent capacity of the homopolymer brushes from variations in the energy components of the system as a function of the number of free molecules. We determined that molecular absorption was driven by the release of the entropic frustration for the grafted chains in conjunction with the chemical affinity between the solutes and polymers. The solute distribution function within the inter-wall space showed that solute-polymer mixing in the middle of the gap occurred preferentially when the enthalpic interaction was more favorable. When this was not the case, absorption was predominantly localized near the grafting surface. From the mean square displacement of the solute, we found that the brush profiles restrained the molecular diffusion perpendicular to the grafting wall; the weaker the attraction from the brush, the higher the solute mobility.

Automated summary

We conducted molecular dynamics simulations to investigate the impact of enthalpic interaction on the static and dynamic properties of solvent-free polymer brushes. The results showed that a less favorable enthalpic interaction led to a more stretched chain configuration, lower inter-brush penetration, and faster relaxation. Additionally, the molecular absorption was found to be driven by the release of entropic frustration and the chemical affinity. The distribution function of solute within the inter-wall space indicated that solute-polymer mixing occurred preferentially in the middle of the gap when the enthalpic interaction was more favorable. The brush profiles restrained the molecular diffusion perpendicular to the grafting wall, with higher solute mobility observed when the attraction from the brush was weaker.