Impact of Additives on the Microstructural Properties of DIDMAMS Bilayers: Studied by Molecular Dynamics Simulations.

To further understand the mechanism of the impact of perfume raw materials (PRMs) such as allyl heptoate (AHT) and cashmeran (CMR) on distearoyl isopropyl dimethylammonium methyl sulfate (DIDMAMS) bilayers, 90 ns molecular dynamics simulations were conducted to investigate the structure of bilayers consisting of DIDMAMS and PRMs at 350 K on the molecular scale. Structural properties such as density profiles, order parameters, radial distribution functions (RDFs), and bilayer thickness were analyzed. The bilayers appear to be the structure of the ripple phase whether PRMs are added or not. The RDF and density profiles show that CMR molecules tend to locate in the region close to head groups and AHT molecules prefer to uniformly distribute among hydrocarbon chains. The special distribution of CMR molecules results in hydrocarbon chains twining around CMR molecules. The existence of CMR molecules between bilayers and the consequent highest bilayer thickness may be the main cause of higher viscosity. We expect that this work can help to screen stable vesicular formula and understand the relationship between microstructures of the vesicles and macroscopic fluidic properties.