Wetting and spreading of nanofluids on solid surfaces driven by the structural disjoining pressure: statics analysis and experiments.
Summary of "Wetting and spreading of nanofluids on solid surfaces driven by the structural disjoining pressure: statics analysis and experiments."
The wetting and spreading of nanofluids composed of liquid suspensions of nanoparticles have significant technological applications. Recent studies have revealed that, compared to the spreading of base liquids without nanoparticles, the spreading of wetting nanofluids on solid surfaces is enhanced by the structural disjoining pressure. Here, we present our experimental observations and the results of the statics analysis based on the augmented Laplace equation (which takes into account the contribution of the structural disjoining pressure) on the effects of the nanoparticle concentration, nanoparticle size, contact angle, and drop size (i.e., the capillary and hydrostatic pressure); we examined the effects on the displacement of the drop-meniscus profile and spontaneous spreading of a nanofluid as a film on a solid surface. Our analyses indicate that a suitable combination of the nanoparticle concentration, nanoparticle size, contact angle, and capillary pressure can result not only in the displacement of the three-phase contact line but also in the spontaneous spreading of the nanofluid as a film on a solid surface. We show here, for the first time, that the complete wetting and spontaneous spreading of the nanofluid as a film driven by the structural disjoining pressure gradient (arising due to the nanoparticle ordering in the confined wedge film) is possible by decreasing the nanoparticle size and the interfacial tension, even at a nonzero equilibrium contact angle. Experiments were conducted on the spreading of a nanofluid composed of 5, 10, 12.5, and 20 vol % silica suspensions of 20 nm (geometric diameter) particles. A drop of canola oil was placed underneath the glass surface surrounded by the nanofluid, and the spreading of the nanofluid was monitored using an advanced optical technique. The effect of an electrolyte, such as sodium chloride, on the nanofluid spreading phenomena was also explored. On the basis of the experimental results, we can conclude that a nanofluid with an effective particle size (including the electrical double layer) of about 40 nm, a low equilibrium contact angle (<3°), and a high effective volume concentration (>30 vol %) is desirable for the dynamic spreading of a nanofluid system with an interfacial tension of 0.5 mN/m. Our experimental observations also validate the major predications of our theoretical analysis.
Affiliation
Department of Chemical and Biological Engineering, Illinois Institute of Technology , Chicago, Illinois 60616, United States.
Journal Details
This article was published in the following journal.
Name: Langmuir : the ACS journal of surfaces and colloids
ISSN: 1520-5827
Pages: 3324-35
Links
- PubMed Source: http://www.ncbi.nlm.nih.gov/pubmed/21395240
- DOI: http://dx.doi.org/10.1021/la104204b
Medical and Biotech [MESH] Definitions
Wetting Agents
A surfactant that renders a surface wettable by water or enhances the spreading of water over the surface; used in foods and cosmetics; important in contrast media; also with contact lenses, dentures, and some prostheses. Synonyms: humectants; hydrating agents.
Corpse Dismemberment
Disjoining the limbs or other parts of a corpse, often in association with criminal acts.
Immunologic Surveillance
The theory that T-cells monitor cell surfaces and detect structural changes in the plasma membrane and/or surface antigens of virally or neoplastically transformed cells.
Gene Products, Tat
Trans-acting transcription factors produced by retroviruses such as HIV. They are nuclear proteins whose expression is required for viral replication. The tat protein stimulates LONG TERMINAL REPEAT-driven RNA synthesis for both viral regulatory and viral structural proteins. tat stands for trans-activation of transcription.
Freeze Etching
A replica technique in which cells are frozen to a very low temperature and cracked with a knife blade to expose the interior surfaces of the cells or cell membranes. The cracked cell surfaces are then freeze-dried to expose their constituents. The surfaces are now ready for shadowing to be viewed using an electron microscope. This method differs from freeze-fracturing in that no cryoprotectant is used and, thus, allows for the sublimation of water during the freeze-drying process to etch the surfaces.
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