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Phase Transition in Monolayer Water Confined in Janus Nanopore
Hemant Kumar1, Chandan Dasgupta2,3, Prabal K Maiti2
1Department of Material Sciences and Engineering , University of Pennsylvania , Philadelphia , Pennsylvania 19104 , United States.
Langmuir : the ACS Journal of Surfaces and Colloids
|September 15, 2018
Summary
Researchers studied water in nanopores, finding an ordered structure at higher temperatures in asymmetric pores. This reveals a phase transition for confined water above room temperature.
Area of Science:
- Thermodynamics
- Materials Science
- Physical Chemistry
Background:
- Water exhibits unique properties when confined in nanoscale environments.
- Understanding phase transitions of confined water is crucial for nanofluidic applications.
Purpose of the Study:
- Investigate the thermodynamics and phase transitions of a water monolayer in a quasi-two-dimensional nanopore.
- Compare confinement effects in asymmetric (hydrophilic/hydrophobic) versus symmetric (hydrophobic) nanopores.
Main Methods:
- All-atom molecular dynamics simulations were employed to compute thermodynamic quantities.
- Analysis of potential energy (U) and entropy (S) identified phase transitions.
- Structural analysis characterized the water molecule ordering.
Main Results:
- An asymmetric nanopore (hexagonal boron nitride/graphene) induced an ordered water structure at higher temperatures than a symmetric hydrophobic nanopore (graphene/graphene).
- A first-order phase transition was observed in the temperature range of 320-330 K, indicated by discontinuous changes in thermodynamic quantities.
- Water molecules transitioned from a disordered to an ordered state, with a 4-fold symmetric phase observed at lower temperatures.
Conclusions:
- The asymmetric nanopore design facilitates a monolayer water melting transition above room temperature.
- This study provides a microscopic understanding of confined water behavior, relevant for nanofluidic systems.
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