Tuning Interfacial Concentration Enhancement through Dispersion Interactions to Facilitate Heterogeneous Nucleation

Abstract

Classical molecular dynamics simulations were used to investigate how dispersion (van der Waals) interactions between non-polar, hydrophobic surfaces and aqueous glycine solutions affect the solution composition, molecular orientation, and dynamics at the interface. Simulations revealed that dispersion interactions lead to a major increase in the concentration of glycine at the interface in comparison with the bulk solution, resulting from a competition between solute and solvent molecules to be or not to be near the interface. This can then lead to kinetic and/or structural effects facilitating heterogeneous nucleation of glycine at non-polar surfaces, in agreement with recent observations for tridecane, graphene, and polytetrafluoroethylene. A novel parameterization process was developed to map a model surface with tunable dispersion interactions to heptane, tridecane, and graphite materials. The model surface was capable of reproducing the solution structure observed in fully atomistic simulations with excellent agreement and also provided good agreement for dynamic properties, at a significantly reduced computational cost. This approach can be used as an effective tool for screening materials for heterogeneous nucleation enhancement or suppression, based on non-specific dispersion interactions based on bulk material molecular properties, rather than interfacial functional groups, templating or confinement effects.

Secondary Nucleation of α-Glycine Induced by Fluid Shear Investigated Using a Couette Flow Cell

“…These values can also be compared with those previously reported for laminar Couette flow with similar shear rates and surface-to-volume ratios, which were about 20–100 times higher but at a significantly higher supersaturation ( S = 1.4). These results are consistent with previous observations that overall primary nucleation rates (per vessel) JV at given supersaturation and temperature can be expected to depend not only on solution volume V but also on the solution agitation and resulting fluid shear, ,− as well as solution interfacial area and materials of construction involved. ,, …”

“…These results are consistent with previous observations that overall primary nucleation rates (per vessel) JV at given supersaturation and temperature can be expected to depend not only on solution volume V but also on the solution agitation and resulting fluid shear, 13,25−27 as well as solution interfacial area and materials of construction involved. 24,28,29 We can also see that the characteristic times of primary nucleation kinetics under conditions investigated here, which can be expressed as 1/JV, are 87 and 25 min for S = 1.14 and 1.18, respectively, and as will be seen below, the primary nucleation kinetics is therefore much slower than the secondary nucleation kinetics under these conditions.…”