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Tuning Water Density Fluctuations with Surface-Charged Colloidal Nanoparticles Probed by Luminescence
Ramon S Raposo Filho1, Carlos D S Brites1, Luís D Carlos1
1Phantom-g, CICECO - Aveiro Institute of Materials, Department of Physics, University of Aveiro, 3810-193 Aveiro, Portugal.
The Journal of Physical Chemistry Letters
|October 31, 2025
Summary
Surface charge density on nanoparticles controls water structure transitions. Higher surface charge increases the crossover temperature (Tc) in interfacial water, clarifying hydration layer behavior.
Area of Science:
- Physical Chemistry
- Materials Science
- Nanotechnology
Background:
- Water exhibits anomalous properties attributed to structural fluctuations between high-density (HD) and low-density (LD) domains.
- The crossover temperature (Tc) where these fluctuations cease and the fraction of LD domains remain debated, especially at interfaces.
Purpose of the Study:
- To investigate the role of surface charge density of colloidal upconverting nanoparticles (UCNPs) in controlling Tc within the hydration layer.
- To clarify conflicting findings regarding water structure near nanoparticle interfaces.
Main Methods:
- Reanalysis of existing data on UCNPs.
- New experiments using compositionally similar UCNPs with varying surface functionalizations.
Main Results:
- Surface charge density of UCNPs systematically increases Tc in the hydration layer.
- This trend is independent of particle size, surface chemistry, or pH.
- Surface charge is established as a key factor in LD-HD domain transitions in hydration water.
Conclusions:
- Surface charge density is a critical determinant of water structural transitions at interfaces.
- These findings offer a framework for understanding hydration water's role in biological processes like protein stability.
