1 research outputs found
Specific Ion Effects in Amphiphile Hydration and Interface Stabilization
Specific ion effects
can influence many processes in aqueous solutions:
protein folding, enzyme activity, self-assembly, and interface stabilization.
Ionic amphiphiles are known to stabilize the oil/water interface,
presumably by dipping their hydrophobic tails into the oil phase while
sticking their hydrophilic head groups in water. However, we find
that anionic and cationic amphiphiles adopt strikingly different structures
at liquid hydrophobic/water interfaces, linked to the different specific
interactions between water and the amphiphile head groups, both at
the interface and in the bulk. Vibrational sum frequency scattering
measurements show that dodecylsulfate (DS<sup>–</sup>) ions
do not detectably perturb the oil phase while dodecyltrimethylammonium
(DTA<sup>+</sup>) ions do. Raman solvation shell spectroscopy and
second harmonic scattering (SHS) show that the respective hydration-shells
and the interfacial water structure are also very different. Our work
suggests that specific interactions with water play a key role in
driving the anionic head group toward the water phase and the cationic
head group toward the oil phase, thus also implying a quite different
surface stabilization mechanism