Dynamics of water nanodroplets and aqueous protons in non-ionic reverse micelles

RODRIGUEZ, J.; LARIA, D.; GUARDIA, E.; MARTI, J.

PHYSICAL CHEMISTRY CHEMICAL PHYSICS

Royal Society of Chemistry

Lugar: Londres; Año: 2009 vol. 11 p. 1484 - 1490

1463-9076

We present a study of the microscopic dynamics of water trapped in reverse non-ionic micelles bymeans of a series of molecular dyanmics simultions. The analysis of the effects of micellarconfinement on spectroscopical properties of an excess proton has also been considered. Ourmicelles were microemulsions made with the neutral surfactant diethylene glycol monodecyl ether[CH3(CH2)11(OC2H4)2OH]. Simulation experiments including the proton species were performedusing a multistate empirical valence bond Hamiltonian model. Diffusion of water in the micelle ismarkedly slower than that in the bulk liquid, in the same fashin as happens with reorentationaldynamics. Spectral densities of hydrogens revealed a blue-shift of the OH-stretching vibrationtogether with a split of the main band into two components. Absorption lineshapes of thesolvated proton in the vicinity of the internal surfact of the micelle indicate the coexistence of Eigen-like and Zundel-like structures and a tendency to red-shifting (compared to the aqueousunconstrained excess proton case) of the two relevant spectral bands (around 2000 and 2500wavenumbers) mainly due to the slower dynamics of proton vibrations in water near interfaces.