APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014;
Denver, Colorado
Session Q3: Focus Session: Solvation, Dynamics, and Reactivity in Complex Environments II
2:30 PM–5:30 PM,
Wednesday, March 5, 2014
Room: 107
Sponsoring
Unit:
DCP
Chair: Francesco Paesani, University of California, San Diego
Abstract ID: BAPS.2014.MAR.Q3.1
Abstract: Q3.00001 : Water in Room Temperature Ionic Liquids
2:30 PM–3:06 PM
Preview Abstract
Abstract
Author:
Michael Fayer
(Stanford University)
Room temperature ionic liquids (or RTILs, salts with a melting point below
25 $^{\circ}$C) have become a subject of intense study over the last
several decades. Currently, RTIL application research includes synthesis,
batteries, solar cells, crystallization, drug delivery, and optics. RTILs
are often composed of an inorganic anion paired with an asymmetric organic
cation which contains one or more pendant alkyl chains. The asymmetry of the
cation frustrates crystallization, causing the salt's melting point to drop
significantly. In general, RTILs are very hygroscopic, and therefore, it is
of interest to examine the influence of water on RTIL structure and
dynamics. In addition, in contrast to normal aqueous salt solutions, which
crystallize at low water concentration, in an RTIL it is possible to examine
isolated water molecules interacting with ions but not with other water
molecules. Here, optical heterodyne-detected optical Kerr effect (OHD-OKE)
measurements of orientational relaxation on a series of
1-alkyl-3-methylimidazolium tetrafluoroborate RTILs as a function of chain
length and water concentration are presented. The addition of water to the
longer alkyl chain RTILs causes the emergence of a long time bi-exponential
orientational anisotropy decay. Such decays have not been seen previously in
OHD-OKE experiments on any type of liquid and are analyzed here using a
wobbling-in-a-cone model. The orientational relaxation is not hydrodynamic,
with the slowest relaxation component becoming \textit{slower} as the viscosity \textit{decreases} for the
longest chain, highest water content samples. The dynamics of isolated
D$_{2}$O molecules in 1-butyl-3-methylimidazolium
hexafluorophosphate (BmImPF$_{6}$) were examined using two
dimensional infrared (2D IR) vibrational echo spectroscopy. Spectral
diffusion and incoherent and coherent transfer of excitation between the
symmetric and antisymmetric modes are examined. The coherent transfer
experiments are used to address the nature of inhomogeneous broadening by
observing $\sim$ 100 fs time scale oscillations in the shape of the
2D IR spectra.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2014.MAR.Q3.1