Dr. Stephan Gekle, Physik Departement, TU Munich, Garching
Dissolving particles in water leads to the formation of a nanometer-sized hydration layer in which the water properties are often very different than in bulk water. Here we use mole- cular dynamics computer simulations to study the behavior of such hydration water when it is subjected to time-dependent electric fields. We find that the absorption characteristics depend strongly on the direction of the applied field: for fields parallel to the surface the absorption peak is shifted slightly towards lower frequencies while for perpendicular fields the peak position is found at much higher frequencies than in bulk water. This anisotropic behavior is generic for hydrophobic and hydrophilic interfaces. Contrary to intuition, the blue-shift of the absorption peak is not connected to an accelerated decay of the molecu- lar correlations in the time domain but instead is caused by a strong reduction in their spa- tial correlations. We finally calculate an effective, isotropic dielectric function (averaged over both directions) which is found to be attenuated and its absorption peak shifted to- wards lower frequencies in agreement with previous experiments.
Nov 28, 2011 | 04:15 PM