title: Molecular dynamics study of intermediate phase of long chain alkyl sulfonate/water systems.
abstract: Using atomic level simulation we aimed to investigate various intermediate phases of the long chain alkyl sulfonate/water system. Overall, about 800 ns parallel molecular dynamics simulation study was conducted for a surfactant/water system consisting of 128 sodium pentadecyl sulfonate and 2251 water molecules. The GROMACS software code with united atom force field was applied. Despite some differences, the analysis of main structural parameters is in agreement with X-ray experimental findings. The mechanism of self-assembly of SPDS molecules was also examined. At T = 323 K we obtained both tilted fully interdigitated and liquid crystalline-like disordered hydrocarbon chains; hence, the presence of either gel phase that coexists with a lamellar phase or metastable gel phase with fraction of gauche configuration can be assumed. Further increase of temperature revealed that the system underwent a transition to a lamellar phase, which was clearly identified by the presence of fully disordered hydrocarbon chains. The transition from gel-to-fluid phase was implemented by simulated annealing treatment, and the phase transition point at T = 335 K was identified. The surfactant force field in its presented set is surely enabled to fully demonstrate the mechanism of self-assembly and the behavior of phase transition making it possible to get important information around the phase transition point.
authors.affiliation: The International Scientific-Educational Center of National Academy of Sciences of Armenia, M. Baghramyan ave. 24d, 0019 Yerevan, Armenia. sicnas@sci.am
authors.forename: Armen H
authors.initials: AH
authors.lastname: Poghosyan
authors.forename: Levon H
authors.initials: LH
authors.lastname: Arsenyan
authors.forename: Aram A
authors.initials: AA
authors.lastname: Shahinyan
mesh_terms: D000476:Alkanesulfonates / Q000737:chemistry*; D056004:Molecular Dynamics Simulation; D015394:Molecular Structure; D013501:Surface-Active Agents / Q000737:chemistry; D014867:Water / Q000737:chemistry*
chemical_list: D000476:Alkanesulfonates; D013501:Surface-Active Agents; D014867:Water