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Probing the Structure and Dynamics of Interfacial Water with Scanning Tunneling Microscopy and Spectroscopy
Published on: May 27, 2018
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Supercooling and freezing processes in nanoconfined water by time-resolved optical Kerr effect spectroscopy
A Taschin1, P Bartolini, A Marcelli
1European Laboratory for Non-Linear Spectroscopy (LENS), Università di Firenze, Via N. Carrara 1, I-50019 Sesto Fiorentino, Firenze, Italy.
Summary
Water confined in nanopores shows altered dynamics and structural relaxation. Hydration levels significantly impact temperature dependence, with some water remaining supercooled even when ice forms.
Area of Science:
- Physical Chemistry
- Materials Science
- Nanotechnology
Background:
- Understanding the behavior of water under confinement is crucial for various scientific and technological applications.
- Nanoconfined water exhibits unique properties distinct from bulk water due to surface interactions and geometric constraints.
Purpose of the Study:
- To investigate the vibrational dynamics and structural relaxation of water confined in 4 nm pores of Vycor silica.
- To explore the effects of varying hydration levels and temperatures on water's behavior within these nanopores.
Main Methods:
- Utilizing heterodyne-detected optical Kerr effect (HD-OKE) spectroscopy to probe water dynamics.
- Analyzing the time-dependent HD-OKE signal decay for structural relaxation times.
- Performing Fourier transforms of the HD-OKE signal to obtain low-frequency vibrational spectra.
Main Results:
- At low hydration, water remains mobile and exhibits dynamics similar to bulk water, without freezing.
- Fully hydrated samples show ice formation around 248 K, with a portion of water remaining in a supercooled state.
- Structural relaxation times are strongly influenced by hydration levels, while low-frequency vibrational spectra (ν < 500 cm(-1)) are less affected by confinement.
Conclusions:
- Hydration level is a critical factor governing the dynamics and relaxation of nanoconfined water.
- Confinement can lead to complex phase behavior, including partial freezing and the persistence of supercooled water.
- Low-frequency vibrational modes appear robust against confinement effects in this system.
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