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Lee R. White - One of the best experts on this subject based on the ideXlab platform.
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terraced spreading of nanofilms under a nonmonotonic Disjoining Pressure
Physics of Fluids, 2011Co-Authors: Kerry A Landman, Lee R. WhiteAbstract:A thin (∼nanometer) film of a viscous, essentially nonvolatile liquid spreads over a substrate controlled by the Disjoining Pressure Π(h) exerted by the two interfaces on one another. Such films are commonly used as hard disk lubricants in the magnetic recording industry. Macroscopic nonuniformities in the film caused by a perturbation of the uniformly spread state flow away and the film is “healed” in a time frame governed by the appropriate hydrodynamic equations. Lubrication theory may be used to derive a diffusion equation for the local film height h(x,t) as a function of position and time which shows that an effective height-dependent diffusion coefficient D(h)=−[h3/3μBξ(h)][dΠ(h)/dh] controls the spreading dynamics, where μB is the bulk liquid viscosity and ξ(h) is a function accounting for any variation of local viscosity near the substrate due to molecularity of the liquid. Such an approach is possible due to the very small ratio of the film height to the in-plane length scale of the disturbance. ...
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van der waals interaction energy and Disjoining Pressure at small separation
Journal of Colloid and Interface Science, 2010Co-Authors: Lee R. WhiteAbstract:Abstract The divergence of the van der Waals interaction energy E 132 ( L ) between plane half-spaces 1 and 2 separated by medium 3 as the separation distance L tends to zero is naively thought of as due to the overlap of the atomic polarization centers. It follows that it may therefore be prevented by properly allowing for the finite size of the atomic species which would prevent the overlap. The distance cutoff model is a simple example of such a modification. The present paper demonstrates that this is not ultimately the origin of the divergence and, that although finite atomic dimensions would alleviate the embarrassment, non-overlap does not properly address the thermodynamic restriction that pertains to the interaction energy. By allowing in an albeit approximate way for the wavelength dependence of the material dielectric response functions e ( i ξ , k ) which arise naturally in the modern Lifshitz theory for this interaction, a form for the van der Waals energy and the corresponding Disjoining Pressure may be derived which obey the thermodynamic constraint and remove the divergence as L → 0 . The energy and Disjoining Pressure in this new model are compared with the classic non-retarded results and the length cutoff model.
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Quasi-equilibrium AFM measurement of Disjoining Pressure in lubricant nanofilms II: Effect of substrate materials.
Langmuir : the ACS journal of surfaces and colloids, 2009Co-Authors: Adam P. Bowles, Yiao Tee Hsia, Paul M. Jones, Lee R. White, James W. SchneiderAbstract:Atomic force microscopy (AFM) was used to measure the Disjoining Pressures of perfluoropolyether lubricant films (0.8-4.3 nm of Fomblin Z03) on both silicon wafers and hard drive disks coated with a diamondlike carbon overcoat. Differences in the Disjoining Pressure between the two systems were expected to be due to variations in the strength of van der Waals interactions. Lifshitz theory calculations suggest that this substrate switch will lead to relatively small changes in Disjoining Pressure as compared to the more pronounced effects reported due to changes in lubricant chemistry. We demonstrate the sensitivity of our AFM method by distinguishing between these similar systems.
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quasi equilibrium afm measurement of Disjoining Pressure in lubricant nano films i fomblin z03 on silica
Langmuir, 2006Co-Authors: Adam P. Bowles, Yiao Tee Hsia, Paul M. Jones, James W. Schneider, Lee R. WhiteAbstract:We have identified conditions in which the atomic force microscope can be used to stretch a meniscus of a perfluoropolyether (PFPE) lubricant pinned between an AFM tip and a nanometer-thick PFPE film to obtain the Disjoining Pressure of the film. Under quasi-equilibrium conditions, the chemical potential of the film can be equated to that of the stretched meniscus. A theory is presented that provides a complete description of the capillary force of a stretched meniscus. Fits of the theory to quasi-equilibrium force-extension curves yield the effective meniscus curvature and, by extension, the Disjoining Pressure of the underlying film. AFM force curves collected at varying film thicknesses compare very well with predictions from Lifshitz theory of dispersive interactions in thin films, with no adjustable parameters. This complete description of meniscus deformation during atomic force microscopy force-extension experiments makes possible the measurement of unknown Disjoining Pressures as required for screening of lubricant-overcoat combinations required for next-generation data storage systems.
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Measurement of Disjoining Pressure of Z-type perfluoropolyether lubricants on Si and SiNx surfaces
Tribology International, 2005Co-Authors: Paul M. Jones, Lee R. White, Min Luo, James W. Schneider, Christopher L. Platt, Yiao Tee HsiaAbstract:Abstract An AFM based measurement of the Disjoining Pressure ( Π ) is described. For the measurement of nano-thin fluids on hard substrates it was shown that specific experimental requirements are placed on the cantilever stiffness and probe radius. The Disjoining Pressure of Fomblin Z03 was then measured on a Si surface and found to be consistent with literature values. The Disjoining Pressures ( Π ) of 25 A Zdol on SiN x films deposited under a flowing-gas of N 2 was measured and a sharp decrease in Π was observed with increasing N 2 concentration (in the gas) that was assigned to the decrease in the polarizability and/or the density of polarizable species in the surface.
Ying Sun - One of the best experts on this subject based on the ideXlab platform.
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Model of Meniscus Shape and Disjoining Pressure of Thin Liquid Films on Nanostructured Surfaces with Electrostatic Interactions
Journal of Physical Chemistry C, 2015Co-Authors: Christopher R. Weinberger, Ying SunAbstract:The effect of electrostatic interactions on the stability of thin liquid films on nanostructured surfaces is important in lubrication, wetting, and phase change but is poorly understood. In this study, a general, closed-form model is developed to account for both the effects of electrostatic and van der Waals interactions on meniscus shape and Disjoining Pressure for thin liquid films on nanostructured surfaces based on the minimization of free energy, the Derjaguin approximation, and the Disjoining Pressure theory for flat surfaces. The model is verified using the molecular dynamics (MD) simulations for a water–alumina system with both triangular and square nanostructures of varying depth and film thickness. Good agreement is obtained between MD results and model predictions, demonstrating the robustness of the analytical model. The results show that the electrostatic interactions enhance the Disjoining Pressure, thereby making the meniscus more conformal to the nanostructured surfaces. In addition, the ...
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Effect of nanostructures on the meniscus shape and Disjoining Pressure of ultrathin liquid film.
Nano letters, 2014Co-Authors: Christopher R. Weinberger, Ying SunAbstract:The stability of thin liquid films on nanostructured surfaces is important but poorly understood. Here, we develop a general model of the meniscus shape and Disjoining Pressure for thin liquid films on nanostructured surfaces based on the minimization of the free energy and the Derjaguin approximation. This model is then compared with molecular dynamics simulations for a water–gold system with triangular and square nanostructures of varying depth and film thickness, demonstrating the robustness of the analytical model.
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Effect of Nanostructures on the Meniscus Shape and Disjoining Pressure of Ultrathin Liquid Film
2014Co-Authors: Christopher R. Weinberger, Ying SunAbstract:The stability of thin liquid films on nanostructured surfaces is important but poorly understood. Here, we develop a general model of the meniscus shape and Disjoining Pressure for thin liquid films on nanostructured surfaces based on the minimization of the free energy and the Derjaguin approximation. This model is then compared with molecular dynamics simulations for a water–gold system with triangular and square nanostructures of varying depth and film thickness, demonstrating the robustness of the analytical model
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Molecular dynamics simulations of Disjoining Pressure effect in ultra-thin water film on a metal surface
Applied Physics Letters, 2013Co-Authors: Ying SunAbstract:Molecular dynamics (MD) simulations are used to examine the Disjoining Pressure effect of a water thin film adsorbed on a metal surface. The model was validated against experiments and verified against previous MD simulations. The variation of vapor Pressure with film thickness was examined for a water thin film adsorbed on a gold surface. The results agree well with the classic Disjoining Pressure theory without surface charges and show that liquid layering does not affect Disjoining Pressure. However, surface charges of the gold substrate enhance the Disjoining Pressure of the water thin film, consistent with experimental evidences for polar liquids.
Marie-caroline Jullien - One of the best experts on this subject based on the ideXlab platform.
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Laplace Pressure based Disjoining Pressure isotherm in non symmetric conditions
Applied Physics Letters, 2017Co-Authors: Axel Huerre, Marie-pierre Valignat, A. C. Maggs, Olivier Theodoly, Marie-caroline JullienAbstract:Understanding the stability and dynamics of two phase systems, such as foams and emulsions, in porous media is still a challenge for physicists and calls for a better understanding of the intermolecular interactions between interfaces. In a classical approach, these interactions are investigated in the framework of Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory by building Disjoining Pressure isotherms. This paper reports on a technique allowing the measurement of Disjoining Pressure isotherms in a thin liquid film squeezed by either a gas or a liquid phase on a solid substrate. We couple a Reflection Interference Contrast Microscopy set-up to a microfluidic channel that sets the Disjoining Pressure through the Laplace Pressure. This simple technique is found to be both accurate and precise. The Laplace Pressure mechanism provides extremely stable conditions and offers opportunity for parallelizing experiments by producing several drops in channels of different heights. We illustrate its potential ...
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Laplace Pressure based Disjoining Pressure isotherm in non symmetric conditions
Applied Physics Letters, 2017Co-Authors: Axel Huerre, Marie-pierre Valignat, Olivier Theodoly, A Maggs, Marie-caroline JullienAbstract:Understanding the stability and dynamics of two phase systems, such as foams and emulsions, in porous media is still a challenge for physicists and calls for a better understanding of the intermolecular interactions between interfaces. In a classical approach, these interactions are investigated in the framework of Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory by building Disjoining Pressure isotherms. This paper reports on a technique allowing the measurement of Disjoining Pressure isotherms in a thin liquid film squeezed by either a gas or a liquid phase on a solid substrate. We couple a Reflection Interference Contrast Microscopy set-up to a microfluidic channel that sets the Disjoining Pressure through the Laplace Pressure. This simple technique is found to be both accurate and precise. The Laplace Pressure mechanism provides extremely stable conditions and offers opportunity for parallelizing experiments by producing several drops in channels of different heights. We illustrate its potential by comparing experimental isotherms for oil—[(water and sodium dodecyl sulfate (SDS)]—glass systems with different models focusing on the electrostatic contribution of the Disjoining Pressure. The extracted values of the interface potentials are in agreement with the constant surface potential model and with a full computation. The derived SDS surface concentration agrees with values reported in the literature. We believe that this technique is suitable for investigating other working fluids and intermolecular interactions at smaller scales.
Clayton J. Radke - One of the best experts on this subject based on the ideXlab platform.
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Molecular Simulation of Disjoining-Pressure Isotherms for Free Aqueous Thin Films
The Journal of Physical Chemistry B, 2003Co-Authors: Divesh Bhatt, And John Newman, Clayton J. RadkeAbstract:We present canonical-ensemble molecular-dynamics (MD) simulations of Disjoining-Pressure isotherms for symmetric, free aqueous thin films. For such symmetric films, the Disjoining Pressure is purely attractive. Lifshitz's theory, based on continuum dispersion forces, predicts that the Disjoining Pressure varies as an inverse cube of film thickness, with a constant of proportionality that can be calculated within the framework of this theory. Our MD results indicate that Lifshitz theory, which assumes a slab geometry for the water density profile and neglects the fluid structure, underpredicts the Disjoining Pressure by about 50 times for films ranging from about 1 to 2 nm at 479 K. To investigate more closely actual experimental conditions, we also perform simulations of water films surrounded by inert gas molecules. The additional gas component adds an extra thermodynamic degree of freedom to the system, allowing for the chemical potential of the water in the external liquid reservoir to be maintained co...
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Molecular simulation of Disjoining-Pressure isotherms for free liquid , Lennard-Jones thin films
The Journal of Physical Chemistry B, 2002Co-Authors: Divesh Bhatt, John Newman, Clayton J. RadkeAbstract:We present canonical-ensemble molecular-dynamics simulations of Disjoining-Pressure isotherms in Lennard-Jones free liquid films. Thermodynamics demands that the Disjoining Pressure is determined uniquely as a function of the chemical potential purely from the phase diagram of the fluid. Our results from molecular dynamics validate this argument. The inverse-sixth-power distance term in the Lennard-Jones intermolecular potential represents van der Waals dispersion forces. Hence, we compare our results with classical Hamaker theory that is based on dispersion forces but assumes a slab geometry for the density profile and completely neglects fluid structure and entropy. We find that the Hamaker constant obtained from our simulations is about an order of magnitude larger than that from classical theory. To investigate the origin of this discrepancy, we calculate the Disjoining-Pressure isotherm using a density-functional theory relaxing the inherent assumptions in the Hamaker theory and imparting to the fluid an approximate structure. For Disjoining Pressure as a function of chemical potential, the results of density-functional theory and molecular dynamics are very close. Even for Disjoining-Pressure isotherms, and the subsequently calculated Hamaker constant, results of the density-functional theory are closer to the molecular-dynamics simulations by about a factor of 4 compared to Hamaker theory. [References: 44]
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The influence of Disjoining Pressure on foam stability and flow in porous media
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1994Co-Authors: A.s. Aronson, V. Bergeron, M.e. Fagan, Clayton J. RadkeAbstract:Foam flowing in porous media can exhibit large flow resistances that make it an attractive fluid for improving underground oil recovery. To be an effective displacement fluid, however, the lamellae, which discretize the gas into foam bubbles, must remain stable. This work studies how the stability of single foam films, as gauged by the magnitude of their Disjoining Pressures, influences the flow resistance of foam in porous media. Steady state Pressure gradients of flowing foam in 2.3 μm2 permeability glass beadpacks and Disjoining Pressure isotherms of single foam films are measured for 10−3 M and 0.017 M sodium dodecyl sulfate (SDS) solutions with and without NaCl. The constant-rate flow experiments show that the addition of salt to 10−3 M SDS increases the Pressure gradient in the beadpacks from 0.1 to 4 MPa m−1 at 0.50 M NaCl. Surfactant solutions of 0.017 M SDS content exhibit Pressure gradients of 22 MPa m−1, quite independent of salt concentration. Likewise addition of salt to the 10−3 M SDS solutions dramatically influences the Disjoining Pressure isotherms by raising the rupture Pressure from 0.5 to above 15 kPa at 0.50 M NaCl. The 0.017 M SDS solutions display rupture Pressures above 30 kPa, independent of salt concentration. We conclude that high repulsive Disjoining Pressures in single foam films lead to strong foam in porous media with large flow resistance. Further, we find that the limiting capillary Pressure for rapid foam coalescence in porous media is close to the rupture Pressure of foam lamellae as obtained from measured Disjoining Pressure isotherms.
D T Wasan - One of the best experts on this subject based on the ideXlab platform.
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structural Disjoining Pressure induced solid particle removal from solid substrates using nanofluids
Joint International Conference on Information Sciences, 2017Co-Authors: Sangwook Lim, D T WasanAbstract:Abstract Nanofluids comprising nanoparticle suspensions in liquids have significant industrial applications. Prior work performed in our laboratory on the spreading of a nanofluid on a solid substrate has revealed that the structural Disjoining Pressure gradient caused by the layering of the nanoparticles normal to the confining plane of the film with the wedge profile is a new mechanism for oily soil detachment from the solid substrate. In the present work, we explore the application of this new mechanism for the solid particle detachment using latex particles on glass and a copper-coated wafer substrate using nanofluids. In the experiment, we employed the nanofluids to observe the detachment of the latex particles adhered to the glass substrate. We found that the structural Disjoining Pressure exerted by the nanoparticles can detach the solid particles on the glass substrate. A video depicting this mechanism is provided. Our results showed that the detachment of the particulate solid particles on the solid substrate was clearly enhanced by the nanofluids, compared to using only pure liquids (such as water). The detachment efficiency was increased with the increase in the nanoparticle volume fraction. Our nanofluids also showed a greater detachment efficiency for the particulate soil removal from the copper-coated wafer substrates compared to that of pure liquids. We found that the detachment efficiency is well correlated with the calculated structural Disjoining energy. Our findings in this paper provide new insights for the novel application of the structural Disjoining energy mechanism for cleaning hard surfaces.
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the dynamic spreading of nanofluids on solid surfaces role of the nanofilm structural Disjoining Pressure
Journal of Colloid and Interface Science, 2016Co-Authors: Sangwook Lim, Hua Zhang, Alex Nikolov, D T WasanAbstract:Nanofluids comprising nanoparticle suspensions in liquids have significant industrial applications. Prior work performed in our laboratory on the spreading of an aqueous film containing nanoparticles displacing an oil droplet has clearly revealed that the structural Disjoining Pressure arises due to the layering of the nanoparticles normal to the confining plane of the film with the wedge profile. The Pressure drives the nanofluid in the wedge film and the nanofluid spreads. We observed two distinct contact lines: the inner contact line, where the structural Disjoining Pressure dominates the Laplace capillary Pressure, and the outer contact line, given by the Laplace equation prediction extrapolated to the solid substrate where the structural Disjoining Pressure contribution is negligible. We report here our results of the effects of several parameters, such as the nanoparticle concentration, liquid salinity, temperature, and the substrate contact angle, on the motion of the two contact lines and their effects on the detachment of the oil droplet. We also studied the equilibrated and non-equilibrated oil/nanofluid phases, the time of adhesion of the oil droplet on the solid substrate and the drying time of the substrate. We employed the frictional model to predict the outer contact line velocity and our previous theoretical model (based on the structural Disjoining Pressure) to predict the inner contact line velocity. The theoretical predictions agreed quite well with the experimentally measured values of the velocities. Our experimental results showed that the motion of the inner contact line was accelerated by the increase in the nanoparticle concentration, temperature, and hydrophilicity of the substrate for the pre-equilibrated oil/nanofluid phases, which resulted in the faster detachment of the oil droplet. The speed of the two contact lines decreased upon the increase in the drying time of the substrate and the oil adhesion time on the substrate. The present results provide new insights into the complex spreading behavior of nanofluids on solid substrates.
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the wetting and spreading of nanofluids on solids role of the structural Disjoining Pressure
Current Opinion in Colloid and Interface Science, 2011Co-Authors: D T Wasan, Alex Nikolov, Kirti KondipartyAbstract:Abstract The wetting and spreading behavior of pure liquids over solid surfaces changes if liquids contain nanosized spherical particles or surfactant micelles, globular proteins and macromolecules. Recent studies on the spreading of nanofluids have demonstrated the inadequacy of well-known concepts of the spreading and adhesion of pure liquids on solid surfaces in understanding nanofluid spreading behavior. This paper reviews the progress made in the wetting and spreading of nanofluids over solid surfaces with an emphasis on the complex interactions between the particles in the nanofluid and with the solid substrate, as well as the spreading of thin nanofluid films containing nanoparticles on hydrophilic surfaces driven by the structural Disjoining Pressure gradient. The spreading droplet advances as a series of distinct nanoparticle layers.
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wetting and spreading of nanofluids on solid surfaces driven by the structural Disjoining Pressure statics analysis and experiments
Langmuir, 2011Co-Authors: Kirti Kondiparty, Alex Nikolov, D T WasanAbstract: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 ( 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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spreading of nanofluids driven by the structural Disjoining Pressure gradient
Journal of Colloid and Interface Science, 2004Co-Authors: Anoop Chengara, A D Nikolov, D T Wasan, Andrij Trokhymchuk, Douglas HendersonAbstract:Abstract This paper discusses the role of the structural Disjoining Pressure exerted by nanoparticles on the spreading of a liquid film containing these particles. The origin of the structural Disjoining Pressure in a confined geometry is due to the layering of the particles normal to the confining plane and has already been traced to the net increase in the entropy of the system in previous studies. In a recent paper, Wasan and Nikolov (Nature, 423 (2003) 156) pointed out that the structural component of the Disjoining Pressure is strong enough to move a liquid wedge; this casts a new light on many applications—most notably, detergency. While the concept of spreading driven by the Disjoining Pressure is not new, the importance of the structural Disjoining Pressure arises from its long-range nature (as compared to the van der Waals' force), making it an important component of the overall force balance near the contact line. In this paper, we report on a parametric study of the spreading phenomena by examining the effects of nanoparticle size, concentration and polydispersity on the displacement of an oil–aqueous interface with the aqueous bulk containing nanoparticles. The solution of the extended Laplace–Young equations for the profile of the meniscus yields the position of the nominal contact line under the action of the structural Disjoining Pressure. Simulations show that the displacement of the contact line is greater with a high nanoparticle volume fraction, small particles for the same volume fraction, monodispersed (in size) particles rather than polydispersed particles and when the resisting capillary Pressure is small, i.e., when the interfacial tension is low and/or the radius of the dispersed phase drop/bubble is large.