skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Reversible Surface Energy Storage in Molecular-Scale Porous Materials
Forcible wetting of hydrophobic pores represents a viable method for energy storage in the form of interfacial energy. The energy used to fill the pores can be recovered as pressure–volume work upon decompression. For efficient recovery, the expulsion pressure should not be significantly lower than the pressure required for infiltration. Hysteresis of the wetting/drying cycle associated with the kinetic barrier to liquid expulsion results in energy dissipation and reduced storage efficiency. In the present work, we use open ensemble (Grand Canonical) Monte Carlo simulations to study the improvement of energy recovery with decreasing diameters of planar pores. Near-complete reversibility is achieved at pore widths barely accommodating a monolayer of the liquid, thus minimizing the area of the liquid/gas interface during the cavitation process. At the same time, these conditions lead to a steep increase in the infiltration pressure required to overcome steric wall/water repulsion in a tight confinement and a considerable reduction in the translational entropy of confined molecules. In principle, similar effects can be expected when increasing the size of the liquid particles without altering the absorbent porosity. While the latter approach is easier to follow in laboratory work, we discuss the advantages of reducing the pore diameter, which reduces the cycling hysteresis while simultaneously improving the stored-energy density in the material.  more » « less
Award ID(s):
1800120
PAR ID:
10488799
Author(s) / Creator(s):
Publisher / Repository:
mdpi
Date Published:
Journal Name:
Molecules
Volume:
29
Issue:
3
ISSN:
1420-3049
Page Range / eLocation ID:
664
Subject(s) / Keyword(s):
molecular porosity interfacial energy wetting/dewetting hysteresis open ensemble molecular simulations
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; (, The Journal of Physical Chemistry C)
    Permeation of water in a poorly wettable material results in a conversion of pressure/volume work into surface free energy representing a novel form of energy storage. The addition of salt increases the amount of stored energy and can reduce the hysteresis of the infiltration−expulsion cycle. Our molecular simulations provide a theoretical perspective into the mechanisms involved in the process and underlying structures and interactions in compressed nanoconfined solutions. We consider aqueous NaCl in nanosized confinements at pressures of up to 3 kbar. Open ensemble Monte Carlo simulations utilizing fractional exchanges of molecules for efficient addition−removal of ions have been utilized in conjunction with pressure-dependent chemical potentials to model bulk phases under pressure. Confinements open to these pressurized bulk, aqueous electrolyte phases show reversibility at narrow pore sizes and irreversibility in wider ones, consistent with experiment. The addition of salt increases in the solid−liquid interfacial tension in narrower pores and associated infiltration and expulsion pressures. These changes are consistent with strong desalination effects at the lower pore size observed irrespective of external pressure and initial concentration. 
    more » « less
  2. ; ; ; ; (, Nanoscale)
    Understanding the invasion of a liquid into porous structures is the foundation of the characterization of the porosity-related properties of materials and is also of fundamental importance in the design of porous solid–liquid enabled energy protection systems, yet whether solid pores deform has been unclear so far. Here, we present a competition mechanism between liquid infiltration and cell wall buckling deformation by investigating a liquid nanofoam (LN) system subjected to quasi-static compression. The critical buckling stress of the cell wall and the infiltration pressure of liquid invasion into nanopores are studied and correlated through numerical simulation and experimental validation to reveal the quantitative relationship between nanopore deformation and liquid invasion. The analysis shows that liquid infiltration occurs, independent of the axial buckling stress of the cell wall; in contrast, the nanopore collapses radially when the radial collapse pressure is lower than the pressure of liquid infiltration, preventing the liquid invasion. Comprehensive molecular dynamics (MD) simulations are performed and demonstrate the deformation behavior of nanopores and cell wall–liquid interactions in a broad range. Pressure-induced compression experiments on a silica-based LN system are carried out and validate these theoretical and MD results. 
    more » « less
  3. ; ; (, Colloids and Surfaces A: Physicochemical and Engineering Aspects)
    Effective separation of two immiscible liquids with filters requires a difference in the pressures to permeate between the two liquids, and setting the applied pressure between these two pressures. To help design such filters, we present an equation that enables the calculation of the pressure for a liquid phase to permeate through a smooth pore in the shape of a truncated cone as a function of (a) the contact angle of the liquid on the filters and (b) the angle of the pore wall. The equation was derived by considering the interfacial energy required to push a liquid meniscus from the top of the pore to the bottom, and then to exceed the maximum curvature required at the exit. This equation was tested experimentally by adding a hydrostatic head with water on the 3Dprinted filters of acrylate polymer while systematically varying the pore radii and contact angle with water. Experimental results showed an increased pressure to permeate with higher contact angles while the equation predicted the opposite. We hypothesized that the reason for the disagreement was the assumption of a smooth pore. For a liquid on a rough pore wall, the curvature of the meniscus is not solely determined from the microscopic contact angle and the pore wall angle, but the liquid would adopt a lower curvature meniscus. Therefore, the developed equation was modified after reflecting the lower curvature, which showed much better agreement with the experimental results. The remaining discrepancy from the theory was attributed to the pressure fluctuation from the fluid flow occurring while adding water. 
    more » « less
  4. ; ; ; ; ; ; ; ; ; ; et al (, Science Advances)
    Polycrystalline ion conductors are widely used as solid electrolytes in energy storage technologies. However, they often exhibit poor ion transport across grain boundaries and pores. This work demonstrates that strategically tuning the mesoscale microstructures, including pore size, pore distribution, and chemical compositions of grain boundaries, can improve ion transport. Using LiTa2PO8as a case study, we have shown that the combination of LiF as a sintering agent with Hf4+implantation improves grain-grain contact, resulting in smaller, evenly distributed pores, reduced chemical contrast, and minimized nonconductive impurities. A suite of techniques has been used to decouple the effects of LiF and Hf4+. Specifically, LiF modifies particle shape and breaks large pores into smaller ones, while Hf4+addresses the chemical mismatches between grains and grain boundaries. Consequently, this approach achieves nearly two orders of magnitude improvement in ion conduction. Tuning mesoscale structures offers a cost-effective method for enhancing ion transport in polycrystalline systems and has notable implications for synthesizing high-performance ionic materials. 
    more » « less
  5. ; ; ; ; ; ; ; (, Physics of Fluids)
    We derived equations and closed-form solutions of transit time for a viscous droplet squeezing through a small circular pore with a finite length at microscale under constant pressures. Our analyses were motivated by the vital processes of biological cells squeezing through small pores in blood vessels and sinusoids and droplets squeezing through pores in microfluidics. First, we derived ordinary differential equations (ODEs) of a droplet squeezing through a circular pore by combining Sampson flow, Poiseuille flow, and Young–Laplace equations and took into account the lubrication layer between the droplet and the pore wall. Second, for droplets wetting the wall with small surface tension, we derived the closed-form solutions of transit time. For droplets with finite surface tension, we solved the original ODEs numerically to predict the transit time. After validations against experiments and finite element simulations, we studied the effects of pressure, viscosity, pore/droplet dimensions, and surface tension on the transit time. We found that the transit time is inversely linearly proportional to pressure when the surface tension is low compared to the critical surface tension for preventing the droplet to pass and becomes nonlinear when it approaches the critical tension. Remarkably, we showed that when a fixed percentage of surface tension to critical tension is applied, the transit time is always inversely linearly proportional to pressure, and the dependence of transit time on surface tension is nonmonotonic. Our results provided a quick way of quantitative calculations of transit time for designing droplet microfluidics and understanding cells passing through constrictions. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email