title: Simulation of dynamic behavior of surfactants on a hydrophobic surface using periodic-shell boundary molecular dynamics.
abstract: The adsorption and aggregation behaviors of sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) on a hydrophobic graphite surface were examined using a novel molecular dynamics (MD) simulation with the periodic-shell boundary condition (PSBC). Differences in the adsorption behavior of SDS and CTAB molecules were clearly shown on the hydrophobic surface. Unexpectedly, the SDS molecules approached the graphite surface with their hydrophilic head groups. This unexpected approach mode was thought to be due to the aqueous layer on the graphite surface. The hydrophobic moiety of SDS molecules repeatedly adsorbed and desorbed on the graphite surface. In addition, SDS molecules kept moving on the graphite surface; thus, they did not form a stable adsorption layer. In contrast to SDS, the hydrophobic moiety of CTAB molecules approached the graphite surface at the primary step of adsorption. The hydrophobic moieties of CTAB molecules came close to each other, whereas the hydrophilic groups separated from one another. This result suggests that the CTAB molecules form molecular assemblies with a curved structure. The simulation results were consistent with the experimental observations. A clear difference between the adsorption behavior of SDS and CTAB molecules was revealed by MD simulations with PSBC.
authors.affiliation: Department of Pure and Applied Chemistry, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Chiba, Japan. j7208709@ed.noda.tus.ac.jp
authors.forename: Daiki
authors.initials: D
authors.lastname: Minami
authors.forename: Satoshi
authors.initials: S
authors.lastname: Horikoshi
authors.forename: Kenichi
authors.initials: K
authors.lastname: Sakai
authors.forename: Hideki
authors.initials: H
authors.lastname: Sakai
authors.forename: Masahiko
authors.initials: M
authors.lastname: Abe
mesh_terms: D000327:Adsorption; D000077286:Cetrimonium; D002593:Cetrimonium Compounds / Q000737:chemistry*; D006108:Graphite / Q000737:chemistry; D057927:Hydrophobic and Hydrophilic Interactions; D056004:Molecular Dynamics Simulation; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry*; D013499:Surface Properties; D013501:Surface-Active Agents / Q000737:chemistry*
chemical_list: D002593:Cetrimonium Compounds; D013501:Surface-Active Agents; D012967:Sodium Dodecyl Sulfate; D006108:Graphite; D000077286:Cetrimonium