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Abstract All cloud and climate models assume ice crystals grow as if they were formed from pure water, even though cloud and haze droplets are solutions. The freezing process of a solution droplet is different than that of a pure water droplet, as shown in prior work. This difference can potentially affect the particle’s subsequent growth as an ice crystal. We present measurements of ice crystal growth from frozen sodium chloride (NaCl) solution droplets in the button electrode levitation diffusion chamber at temperatures between −61° and −40°C. Measured scattering patterns show that concentrated solution droplets remain unfrozen with classical scattering fringes until the droplets freeze. Upon freezing, the scattering patterns become complex within 0.1 s, which is in contrast with frozen pure water particles that retain liquid-like scattering patterns for about a minute. We show that after freezing, solution particles initially grow as spherical-like crystals and then transition to faster growth indicative of a morphological transformation. The measurements indicate that ice formed from solution droplets grows differently and has higher growth rates than ice formed from pure water droplets. We use these results to develop a power-law-based parameterization that captures the supersaturation and mass dependencies.
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Structural Formation and Pore Control of Freeze-Cast Directional Graphene Aerogel (DGA)
Directional graphene aerogels (DGAs) are proposed as electrode materials to alleviate ionic and mass transport issues in organic redox flow batteries (ORFBs). DGAs with high pore directionality would provide low resistance channels for effective ionic charge and liquid electrolyte transport in these devices. DGAs’ porous and directional characteristics can be controlled by the growth of ice crystals during freeze casting, which is influenced by the self-diffusivity of water, phase change driving forces, water−ice graphene interactions, and convection in the water−graphene media. It is found that mass transport-related properties of DGAs, including pore size and directionality, show a significant dependence on freezing temperature, graphene oxide (GO) loadings, and synthesis vessel diameter-to-height ratio (D/H). For the freezing temperature change from −20 to −115 °C, the average pore size progressively decreased from 120 to 20 μm, and the pore directionality transitioned from lamellar to ill-defined structures. When GO loadings were increased from 2 to 10 mg/mL at a fixed freezing temperature, pore size reduction was observed with less defined directionality. Furthermore, the pore directionality diminished with an increased width-to-height aspect ratio of DGA samples due to the buoyancy-driven convective circulation, which interfered with the directional ice/pore growth. Understanding the comprehensive effects of these mechanisms enables the controlled growth of ice crystals, leading to graphene aerogels with highly directional microstructures.
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- Award ID(s):
- 1933800
- PAR ID:
- 10492643
- Publisher / Repository:
- ACS Publications
- Date Published:
- Journal Name:
- ACS Applied Materials & Interfaces
- Volume:
- 16
- Issue:
- 1
- ISSN:
- 1944-8244
- Page Range / eLocation ID:
- 425-434
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1021/acsami.3c10998
