Ali Khodayari, David Seveno
Dopamine benchmarks yielded consistent adsorption free energies of -11.56±0.76 and -10.45±1.51 kJ mol-1, establishing the monomer reference scale. PDA adsorption was stronger on the flatter cellulose Iβ (100) surface than on the rougher (110) surface, with a low-rate estimate of -74.93±5.48 kJ mol-1. This difference was associated with a smaller surface-normal PDA-cellulose separation, a larger grouped contact footprint, and lower PDA positional fluctuations on the (100) face. Hydrogen-bond analysis showed more PDA-cellulose and PDA-water hydrogen bonds on (110), indicating that stronger adsorption on (100) is not driven simply by hydrogen-bond number, but by surface-specific contact organization. Temperature-dependent pulling showed less favorable apparent adsorption at elevated temperature, consistent with faster hydrated-interface relaxation during detachment. These results identify surface accommodation, multivalent contacts, adsorbate conformation, and hydration as coupled variables controlling wet adhesion at cellulose-based interfaces.
HYPOTHESIS: Polydopamine (PDA) adhesion to hydrated cellulose is governed by cellulose surface geometry, multivalent contact formation, and interfacial water dynamics. We further hypothesize that rate-dependent nonequilibrium pulling combined with temperature-dependent interfacial relaxation can constrain the low-rate adsorption limit. Simulations: Atomistic molecular dynamics simulations were used to study dopamine monomer and a 10-mer PDA model on cellulose Iβ. Dopamine adsorption was benchmarked by umbrella sampling and alchemical double decoupling, while PDA detachment from cellulose Iβ (100) and (110) was evaluated using multi-rate steered molecular dynamics, Jarzynski-based estimates, and empirical time-temperature superposition.
FINDINGS: Dopamine benchmarks yielded consistent adsorption free energies of -11.56±0.76 and -10.45±1.51 kJ mol-1, establishing the monomer reference scale. PDA adsorption was stronger on the flatter cellulose Iβ (100) surface than on the rougher (110) surface, with a low-rate estimate of -74.93±5.48 kJ mol-1. This difference was associated with a smaller surface-normal PDA-cellulose separation, a larger grouped contact footprint, and lower PDA positional fluctuations on the (100) face. Hydrogen-bond analysis showed more PDA-cellulose and PDA-water hydrogen bonds on (110), indicating that stronger adsorption on (100) is not driven simply by hydrogen-bond number, but by surface-specific contact organization. Temperature-dependent pulling showed less favorable apparent adsorption at elevated temperature, consistent with faster hydrated-interface relaxation during detachment. These results identify surface accommodation, multivalent contacts, adsorbate conformation, and hydration as coupled variables controlling wet adhesion at cellulose-based interfaces.