Paper Citing NAMD - Abstract
Khurana, Ekta; Nielsen, Steven O.; Klein, Michael L.
Gemini surfactants at the air/water interface: A fully atomistic molecular dynamics study
JOURNAL OF PHYSICAL CHEMISTRY B, 110:22136-22142, NOV 9 2006
Gemini surfactants typically consist of two single-chain surfactants chemically linked by a spacer molecule. We report herein the results of fully atomistic molecular dynamics (MD) simulations of a series of Gemini surfactants: CsH2s-alpha,omega-bis(C12H25N+(CH3)(2)Cl-), at the air/water interface with s=3, 4, 6, 12, 14, and 16, at values of the initial surface area per surfactant A(S)=70 angstrom(2), 77 angstrom(2), 95 angstrom(2), 151 angstrom(2), 133 angstrom(2), and 103 angstrom(2), respectively. The AS values employed were obtained from surface tension and neutron reflection experiments at the respective cmc of each surfactant. The Gemini surfactant corresponding to s=3 was also simulated at A(S)=105 angstrom(2), which is the experimentally derived value of surface area per surfactant at 1/10th of cmc. Only the surfactants with s=12 and 14 and the surfactant with s=3 at A(S)=105 angstrom(2) gave a stable monolayer at the air/water interface. In other cases, we observe movement of some surfactant molecules from the air/water interface into the aqueous phase, resulting in a stable primary monolayer of surfactants at the air/water interface and a small concentration of surfactant molecules below it. The latter form aggregates, with their hydrophobic chains in the core. The density profiles along the normal to the interface are compared with the ones obtained from neutron reflection experiments. The MD simulations confirm the bending of the spacer toward the hydrophobic chains as the spacer length is increased and the spacer becomes more hydrophobic. The simulations have helped to shed light on the low-resolution picture which emerges from experimental analyses.
