Aqueous ionic and complementary zwitterionic soluble surfactants: molecular dynamics simulations and sum frequency generation spectroscopy of the surfaces.
An aqueous ionic surfactant, 1-dodecyl-4-(dimethylamino)pyridinium (DMP) bromide, and the corresponding zwitterion 2-[4-(dimethylamino)pyridinio]dodecanoate (DPN) were explored by means of molecular dynamics (MD) simulations and, for the ionic system, by infrared-visible sum frequency generation (IR-vis SFG). The molecular structure of the interfacial layer was investigated for the ionic and zwitterionic systems as a function of surfactant concentration, both in water and in salt (KF or KBr) solutions, by MD simulations in a slab geometry. The buildup of the surface monolayer and a sublayer was monitored, and density and orientational profiles of the surfactants were evaluated. The difference between the ionic and zwitterionic systems and the effect of the added salt were analyzed at the molecular level. The results of MD simulations were compared to those of nonlinear optical spectroscopy measurements. IR-vis SFG was employed to study the DMP ionic surfactant in water and upon addition of simple salts. The influence of added salts on the different molecular moieties at the interface was quantified in detail experimentally.
Petrov
Michal
M
Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Molecular Systems, Flemingovo nam. 2, 16610 Prague 6, Czech Republic.
Minofar
Babak
B
Vrbka
Lubos
L
Jungwirth
Pavel
P
Koelsch
Patrick
P
Motschmann
Hubert
H
D007477:Ions; D012995:Solubility; D013057:Spectrum Analysis / Q000379:methods*; D013501:Surface-Active Agents / Q000737:chemistry*; D014867:Water
D007477:Ions; D013501:Surface-Active Agents; D014867:Water