Vibrational energy relaxation and ultrafast thermalization following impulsive excitation of the OH-stretching band of water nanodroplets confined to reverse micelles is studied by infrared pump-probe spectroscopy with sub-100 fs time resolution. The self-consistent analysis of experimental data for micelles diameters ranging from 1 to 10 nm as well as for bulk water reveals distinctly different vibrational lifetimes for the water molecules in the bulk-like core (270 fs) and in the surfactant vicinity (800 fs), which is a direct proof of a strongly disturbed hydrogen-bond network. (c) 2005 Elsevier B.V. All rights reserved.