Colloidal Suspensions Confined to a Film: Local Structure and Film Stability

Wasan,; Nikolov,; Trokhymchuk,; Henderson,

doi:10.5488/cmp.4.2.361

Cited by 6 publications

(9 citation statements)

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“…The film structural disjoining pressure (i.e., the osmotic component in the excess pressure) in the wedge film exerted by the particles normal to the confining surfaces is high near the vertex. It has an oscillatory decay with the increasing film thickness, and both the period of oscillation and decay factor are equal to the average diameter (including the double layer) surrounding the nanoparticle − (Figure ).…”

Section: Introductionmentioning

confidence: 99%

Wetting and Spreading of Nanofluids on Solid Surfaces Driven by the Structural Disjoining Pressure: Statics Analysis and Experiments

et al. 2011

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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.

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Section: Introductionmentioning

confidence: 99%

Wetting and Spreading of Nanofluids on Solid Surfaces Driven by the Structural Disjoining Pressure: Statics Analysis and Experiments

et al. 2011

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“…Uniformly sized spherical nanoparticles, or surfactant micelles, globular proteins, and macromolecules are known to form ordered microstructures (layering) between the two solid surfaces or in thin liquid films between bubbles or drops, such as those associated with foam and emulsion systems. − These ordered microstructures exert the structural disjoining pressure (i.e., the excess pressure in a film relative to that in the bulk solution) in a thin liquid film, separating its two surfaces confining the nanofluid, thereby imparting stability to these systems. − The structural disjoining pressure has an oscillatory exponential decay with the increasing film thickness (gap), with both the period of oscillation and decay factor equal to the average effective diameter of the nanoparticles. − , The structural disjoining pressure dominates on scales larger than the effective diameter of a nanoparticle, below which other disjoining pressure components (such as van der Waals, electrostatic and solvation forces) are prevalent. , …”

Section: Introductionmentioning

confidence: 99%

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14] These ordered microstructures exert the structural disjoining pressure (i.e., the excess pressure in a film relative to that in the bulk solution) in a thin liquid film, separating its two surfaces confining the nano-fluid, thereby imparting stability to these systems. [15][16][17][18][19][20][21][22] The structural disjoining pressure has an oscillatory exponential decay with the increasing film thickness (gap), with both the period of oscillation and decay factor equal to the average effective diameter of the nanoparticles. [15][16][17]19 The structural disjoining pressure dominates on scales larger than the effective diameter of a nanoparticle, below which other disjoining pressure components (such as van der Waals, electrostatic and solvation forces) are prevalent.…”

Section: Introductionmentioning

confidence: 99%

“…[15][16][17][18][19][20][21][22] The structural disjoining pressure has an oscillatory exponential decay with the increasing film thickness (gap), with both the period of oscillation and decay factor equal to the average effective diameter of the nanoparticles. [15][16][17]19 The structural disjoining pressure dominates on scales larger than the effective diameter of a nanoparticle, below which other disjoining pressure components (such as van der Waals, electrostatic and solvation forces) are prevalent. 23,24 Recent experiments have revealed that ordered structures also form near the three-phase contact line (wetting wedge) of a drop or bubble on a solid surface, which promotes the spreading of liquids containing nanoparticles (nanofluids).…”

Section: Introductionmentioning

confidence: 99%

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Nanoparticle Self-Structuring in a Nanofluid Film Spreading on a Solid Surface

2010

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Liquids containing nanoparticles (nanofluids) exhibit different spreading or thinning behaviors on solids than liquids without nanoparticles. Previous experiments and theoretical investigations have demonstrated that the spreading of nanofluids on solid surfaces is enhanced compared to the spreading of base fluids without nanoparticles. However, the mechanisms for the observed enhancement in the spreading of nanofluids on solid substrates are not well understood. The complex nature of the interactions between the particles in the nanofluid and with the solid substrate alters the spreading dynamics [Wasan, D. T.; Nikolov, A. D. Nature 2003, 423, 156]. Here, we report, for the first time, the results of an experimental observation of nanoparticles self-structuring in a nanofluid film formed between an oil drop and a solid surface. Using a silica-nanoparticle aqueous suspension (with a nominal diameter of 19 nm and 10 vol %) and reflected light interferometry, we show the nanoparticle layering (i.e., stratification) phenomenon during film thinning on a smooth hydrophilic glass surface. Our experiments revealed that the film thickness stability on a solid substrate depends on the film size (i.e., the drop size). A film formed from a small drop (with a high capillary pressure) is thicker and contains more particle layers than a film formed from a large drop (with a lower capillary pressure). The data for the film-meniscus contact angle verses film thickness (corresponding to the different number of particle layers) were obtained and used to calculate the film structural energy isotherm. These results may provide a better understanding of the complex phenomena involved in the enhanced spreading of nanofluids on solid surfaces.

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“…From the definitions of excess surface moles in the film and membrane models (compare Eqs. (31) and (56)), we find that…”

Section: Membrane-model Thermodynamicsmentioning

confidence: 55%

Film and membrane-model thermodynamics of free thin liquid films

Radke

2015

Journal of Colloid and Interface Science

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In spite of over 7 decades of effort, the thermodynamics of thin free liquid films (as in emulsions and foams) lacks clarity. Following a brief review of the meaning and measurement of thin-film forces (i.e., conjoining/disjoining pressures), we offer a consistent analysis of thin-film thermodynamics. By carefully defining film reversible work, two distinct thermodynamic formalisms emerge: a film model with two zero-volume membranes each of film tension γ(f) and a membrane model with a single zero-volume membrane of membrane tension 2γ(m). In both models, detailed thermodynamic analysis gives rise to thin-film Gibbs adsorption equations that allow calculation of film and membrane tensions from measurements of disjoining-pressure isotherms. A modified Young-Laplace equation arises in the film model to calculate film-thickness profiles from the film center to the surrounding bulk meniscus. No corresponding relation exists in the membrane model. Illustrative calculations of disjoining-pressure isotherms for water are presented using square-gradient theory. We report considerable deviations from Hamaker theory for films less than about 3 nm in thickness. Such thin films are considerably more attractive than in classical Hamaker theory. Available molecular simulations reinforce this finding.

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Colloidal Suspensions Confined to a Film: Local Structure and Film Stability

Cited by 6 publications

References 9 publications

Wetting and Spreading of Nanofluids on Solid Surfaces Driven by the Structural Disjoining Pressure: Statics Analysis and Experiments

Wetting and Spreading of Nanofluids on Solid Surfaces Driven by the Structural Disjoining Pressure: Statics Analysis and Experiments

Nanoparticle Self-Structuring in a Nanofluid Film Spreading on a Solid Surface

Film and membrane-model thermodynamics of free thin liquid films

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