Quantum effects in the dynamics of deeply supercooled water.

Despite its simple chemical structure, water remains one of the most puzzling liquids with many anomalies at low temperatures. Combining neutron scattering and dielectric relaxation spectroscopy, we show that quantum fluctuations are not negligible in deeply supercooled water. Our dielectric measurements reveal the anomalously weak temperature dependence of structural relaxation in vapor-deposited water close to the glass transition temperature T(g)∼136K. We demonstrate that this anomalous behavior can be explained well by quantum effects. These results have significant implications for our understanding of water dynamics.

Decoupling of ionic conductivity from structural dynamics in polymerized ionic liquids.

Charge transport and structural dynamics in low molecular weight and polymerized 1-vinyl-3-pentylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquids (ILs) are investigated by a combination of broadband dielectric spectroscopy, dynamic mechanical spectroscopy and differential scanning calorimetry. While the dc conductivity and fluidity exhibit practically identical temperature dependence for the non-polymerized IL, a significant decoupling of ionic conduction from structural dynamics is observed for the polymerized IL. In addition, the dc conductivity of the polymerized IL exceeds that of its molecular counterpart by four orders of magnitude at their respective calorimetric glass transition temperatures. This is attributed to the unusually high mobility of the anions especially at lower temperatures when the structural dynamics is significantly slowed down. A simple physical explanation of the possible origin of the remarkable decoupling of ionic conductivity from structural dynamics is proposed.

An assessment of comparative methods for approaching electrode polarization in dielectric permittivity measurements.

We examine the validity of three common methods for analysis and correction of the electrode polarization (EP) effect in dielectric spectroscopy measurements of conductive liquid samples. The methods considered are (i) algorithmic treatment by modeling the EP behavior at constant phase angle, (ii) varying the size of the electrode gap, and (iii) polypyrrole (PPyPss) layered electrodes. The latter is a relatively recent innovation suggested to be an efficient solution. We demonstrate that PPyPss coated electrodes do not diminish the effect of EP, and even add relaxation processes of its own. Our conclusion is that these polymer coated electrodes are not suitable for the correction of electrode polarization.