A comparative study on bulk and nanoconfined water by time-resolved optical Kerr effect spectroscopy
Faraday Discussions
|March 20, 2014
Summary
Investigating hydrated porous silica reveals that water in pores behaves like bulk water above 10% hydration. Below this, hydrogen bond connectivity changes significantly, impacting water
Area of Science:
- Physical Chemistry
- Materials Science
- Spectroscopy
Background:
- Porous silica's low-frequency vibrational spectra offer insights into water's hydrogen bonding.
- Understanding water behavior in confined environments is crucial for materials science and physical chemistry.
Purpose of the Study:
- To analyze the vibrational spectra of water in Vycor porous silica at varying hydration levels.
- To differentiate spectral contributions from hydration layers and bulk-like water.
- To investigate the impact of pore confinement on water's structural and dynamical properties.
Main Methods:
- Fourier transform analysis of time-resolved heterodyne detected optical Kerr effect (HD-OKE) measurements.
- Systematic investigation of porous silica samples (approx. 4 nm pore size) at different hydration levels.
- Comparison of spectra with bulk water to isolate contributions from confined water layers.
Main Results:
- Water entering pores above 10% hydration exhibits bulk-like behavior.
- At lower hydration levels, hydrogen bond connectivity differs significantly from bulk water, evidenced by disappearing spectral bands.
- Structural relaxation times for inner water resemble bulk liquid, while the first two hydration layers show ~4x longer relaxation times.
Conclusions:
- Pore confinement alters water's hydrogen bond network, especially at low hydration levels.
- The observed changes in water structure and dynamics are critical for understanding supercooled water behavior in confined systems.
- Findings inform strategies for utilizing pore confinement to access lower temperatures for supercooled water.
