Modeling the crystal morphology of alkali-metal alkyl surfactants: Sodium and rubidium dodecyl sulfates

Refined interatomic potential parameters are determined for sodium dodecyl sulfate (SDS) and rubidium dodecyl sulfate (RDS) and used to calculate the lattice energies of these systems. Comparisons of these values with the experimental "sublimation enthalpies" show good agreement between the calculated and experimental (-173.13, 145.50 kcal/mol; -176.40, 155.76 kcal/mol) values, respectively. These parameters are utilized to predict the morphology of sodium and rubidium dodecyl sulfates using the attachment energy method, with the simulations revealing a platelike morphology for both materials, in good agreement with the experimental morphologies. Analysis of the intermolecular bonding within the crystal structures of both SDS and RDS reveal weak van der Waals interactions between the hydrocarbon tails, resulting in a predicted slow growth perpendicular to the principal faces of these crystals.