PhD ceremony: G.D. Cringus, 16.15 uur, Academiegebouw, Broerstraat 5, Groningen
Thesis: Femtosecond vibrational dynamics in water nano-droplets
Promotor(s): prof. D.A. Wiersma
Faculty: Mathematical and Natural Sciences
In this thesis we have studied the ultrafast dynamics of liquid water confined on a nanometer scale. Two model systems have been used, namely mixtures of water and acetonitrile and reverse micelles. We have shown that the water clusters consist of two distinct regions, which are characterized by different dynamics, structure of the hydrogen bond network and pathways for vibrational energy relaxation.
The water from the center of the droplet is almost identical to bulk water, especially in the case of H2O in reverse micelles. Still, for the HDO in D2O/acetonitrile samples, the observed variation of the vibrational lifetime of the core water suggests the presence of nanoconfinement effects beyond the interfacial layer. In the outer 1-2 molecular layers of a water cluster, the dynamics and energy transfer processes are mainly determined by the interaction of the interfacial water molecules with the neighboring non-aqueous phase (acetonitrile and respectively micelle membrane). Consequently, the excess vibrational energy is dissipated through a different channel then in bulk water. In addition, the water-water interactions are considerably weaker in the interfacial layer and the intermolecular transfer of vibrational energy is blocked.
This result opens a new perspective on the role of water in biological environments, as it suggests that in the vicinity of a biological interface, for instance near a protein, water cannot transfer the energy as efficiently as in bulk phase.
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