Effect Of Surface Forces Research Articles

Effects of surface forces and phonon dissipation in a three-terminal nanorelay

We have performed a theoretical analysis of the operational characteristics of a carbon–nanotube-based three-terminal nanorelay. We show that short range and van der Waals forces have a significant impact on the characteristics of the relay and introduce design constraints. We also investigate the effects of dissipation due to phonon excitation in the drain contact, which changes the switching time scales of the system, decreasing the longest time scale by 2 orders of magnitude. We show that the nanorelay can be used as a memory element and investigate the dynamics and properties of such a device.

The Effect of Surface Forces on the Thermal Slip of a Simple Gas

The flow of a simple gas along a plane surface under the action of tangential temperature gradient is considered. The velocity of thermal slip is calculated by the variational method with account of the effect of surface forces. It is shown that, in some situations, surface forces can substantially affect the value of the thermal slip coefficient.

Effect of Surface Forces on the Gas Flow in Nanosized Capillaries

The flow of temperature-inhomogeneous gas in ultrathin capillary is considered with allowance for the action of surface forces. It is shown that the presence of surface forces considerably increases the effect of thermal transpiration compared to the classical value determined in a free molecular regime of gas flow. The coefficient responsible for the mechanocaloric effect for the case of the gas flow under the pressure gradient was also determined using Onsager relations for the kinetic coefficients calculated with account of the effect of surface forces.

Nano-lubricant film formation due to combined elastohydrodynamic and surface force action under isothermal conditions

This paper presents the results of numerical prediction of the lubricant film thickness and pressure distribution in concentrated counterformal point contact under isothermal conditions. The operating conditions, which include load and speed of entraining motion, promote the formation of ultra-thin films; these are formed under the combined action of elastohydrodynamic lubrication (EHL), the surface contact force of solvation and molecular interactions due to the presence of Van der Waals forces. A numerical solution has been carried out, using the low-relaxation Newton-Raphson iteration technique, applied to the convergence of the hydrodynamic pressure. The paper shows that the effect of surface forces become significant as the elastic film (i.e. the gap) is reduced to a few nanometres. The numerical predictions have been shown to conform well to the numerical work and experimental findings of other research workers.

Effect of surface forces and surfactant adsorption on the thinning and critical thickness of foam films

The new experimental results on thinning and rupture of microscopic foam films, obtained by the dynamic method of Scheludko and Exerowa, are analyzed with respect to the observed discrepancies with the theoretical predictions. The possible reasons for the deviations from the frequently used Reynolds’ equation, describing the thinning rate of planar circular horizontal liquid films with non-deformable and tangentially immobile surfaces, are discussed. The applicability of the theoretical description of the thinning process (accelerated drainage), advanced in a previous study, is tested here experimentally. The effect of surface tension and surface mobility on the thinning rate and critical thickness of rupture is established. The relative effects of different factors are estimated through specially designed experiments. They comprehend: bulk and surface diffusion of the surfactant; evaporation of liquid from the film; variation of the film radius during the process of drainage; inhomogeneity of the film thickness, etc. It is concluded that the influence of the surface forces and the surfactant concentration is significant for the thinning and rupture, and respectively for the life-time of the microscopic films, while the influence of evaporation is negligible under the conditions of the experiment.

Opening‐mode fracture in siliceous mudstone at high homologous temperature—effect of surface forces

In analogy to high‐temperature sintering of ceramics and metal powder compacts, the formation of opening‐mode fractures in siliceous mudstone during natural in‐situ combustion of hydrocarbons is attributed to contractile surface forces between mineral grains and an interstitial melt phase. A comparison between bulk density increase during sintering and created fracture space indicates that fracturing resulted from contraction of the rock matrix due to porosity reduction, grain‐scale mass transfer, and high‐temperature mineral formation. It is suggested that contractile surface forces between mineral grains and between mineral grains and pore fluid contribute to subcritical fracture formation under a wide range of subsurface conditions.

SURFACE PHENOMENA IN THE HYDRODYNAMICS OF AN INCOMPRESSIBLE FLUID

By taking as an example the outflow of an incompressible fluid through a hole with small geometric parameters under the conditions of supersmall pressures, we attempted to evaluate the effect of surface phenomena on its flow by the similarity method. The Navier–Stokes differential equation was supplemented by parameters allowing for the effect of surface forces. The modified Navier–Stokes equation was subjected to similarity conversion. This yielded a dimensionless group that includes the whole range of variable parameters affecting the fluid flow, namely, the generalized criterion Pv. The graphic dependence of the coefficient of the fluid flow rate on the generalized criterion Pv is presented on the basis of experimental data.

Effect of surface forces on oscillatory behavior of lungs.

The effect of alveolar surface tension on lung dynamic behavior was investigated by measuring total lung and tissue impedances in excised rabbit lungs at breathing frequencies of 0.2-0.8 Hz and tidal volumes of 10, 20, and 30 ml before and after lavage with 3-dimethyl siloxane, which provided a constant surface tension of 16 dyn/cm. The lungs were oscillated around the mean deflation pressures of 5 (control) and 8 cmH2O (lavaged), i.e., lung volume of 60% of total lung capacity. The total lung impedance was calculated from measurements of pressure and airflow at the trachea, and tissue impedance was measured by the alveolar capsule technique. The airway contribution was obtained as the difference between total lung and tissue impedances. In the lavaged lungs, dynamic elastance (Edyn) decreased and tissue resistance (Rti) increased relative to the control values over the entire frequency range. Airway resistance increased at the higher flow rates only. The decrease in Edyn could be attributed to the absence of surface film elastance in the lavaged lungs. The increase in airway resistance could be attributed to accentuated flow dependence due to changes in airway geometry and residual lavage liquid. However, the most intriguing result was the increase in Rti in the lavaged lungs. It could be attributed to altered mechanics at the alveolar duct level after lavage. It is concluded that dissipative properties of lung tissue are major determinants of Rti, whereas elastic properties of both tissue and surface film are important determinants of Edyn.

Intergranular solid‐fluid phase transformations under stress: The effect of surface forces

Existing work on mineral solubility in fluid‐infiltrated and stressed rock has remained limited in that it has neglected surface forces. These forces are appreciable only when the fluid exists as a thin film, as in the grain‐to‐grain contact zone and in microcracks. Indeed, when the film thickness is of the order of 10−9 m or so, the strength of the forces can be comparable to overburden stress at several kilometers depth. In this contribution we develop the thermodynamics of the phase reaction between nonhydrostatically stressed grains and an intervening water layer by using the concept of the disjoining pressure to account for surface forces acting in the grain‐to‐grain contact zone. Using a thermodynamic extremum principle, we find an extended version of Gibbs's classical condition for the equilibrium of a stressed solid in contact with its solution phase. We then employ nonequilibrium thermodynamics to formulate kinetic equations describing phase boundary migration and intergranular mass transfer. It is demonstrated that surface forces weaken the efficacy with which diffusion removes dissolved material from the grain‐to‐grain contact zone and enhance the tendency of intergranular pressure solution to flatten initially rough surfaces.

Physico-chemical synthesis of diamond in metastable range

The present paper discusses the synthesis of diamond in its metastable region from carbonaceous gases, in particular methane. The diamond synthesis on seed crystals is made possible owing to the orientation effect of surface forces on the formation of a new phase. Discussed is also the joint crystallization of diamond and graphite. The basic experiments were made on highly dispersed diamond powders. The growth of diamond in kinetic and diffusion regions has been studied. Presented are results of studying the fractionation of stable carbon isotopes when growing a diamond.

Effect of surface forces on the properties of boundary and thin layers of liquids and disperse systems

Effect of surface forces on the properties of boundary and thin layers of liquids and disperse systems

Attenuation mechanisms in sands: Laboratory versus theoretical (Biot) data

The velocity and attenuation of compressional([Formula: see text], [Formula: see text] respectively) and shear waves ([Formula: see text], [Formula: see text], respectively), determined with the Pulse Transmission technique at a frequency of about 100 kHz, are compared with the grain size, shape, porosity, density, and static frame compressibility of dry and water‐saturated sands. Except for [Formula: see text], all the quantities [Formula: see text], [Formula: see text] and [Formula: see text] are dependent on grain size and are higher in coarser grains than in finer grains. [Formula: see text] decreases significantly with increasing differential pressure in coarse‐grained sediments, but the same sediments show an anomalous increase with differential pressure in [Formula: see text] at low pressures. We have also modeled the [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] of these samples to understand the mechanisms governing the observed changes. The Contact Radius model with surface force effects predicts both [Formula: see text] and [Formula: see text] to be dependent on grain size. Frictional losses in unconsolidated coarse‐grained sands must also be considered at small strains [Formula: see text]. Velocity and losses measured in saturated sands are higher than those predicted by the Biot model, which does not account for any grain size dependence of the seismic qualities.

Effect of Surface Forces on Subcritical Crack Growth in Glass

Data on the growth of cracks tested in aqueous solutions were interpreted in terms of surface force theory. For applied stress intensity factors greater than 0.25 MPa · m½, the position and the slope of the curves and their dependence on pH and ion concentration can be explained in terms of surface force theory, provided these forces are of a magnitude and range that are representative of those involved in the cohensive bonding of solids. Weaker forces, such as structural, double‐layer, or dispersion forces, have little effect on crack growth in silica glass for KI > 0.25 MPa · m½.

Some relations between thermodynamic and kinetic parameters in heterogeneous catalysis

The results of our preceding work on irreversible (rational) thermodynamics of reacting mixture of fluids and a solid substance are applied to the problem of heterogeneous catalysis. The negative effect of diffusion and the positive effect of surface forces are justified, and the Bronsted-Polanyi equation for the activation energy of surface reaction is obtained.

Effect of externally applied skin surface forces on tissue vasculature.

The effect of surface forces on the morphologic pattern of skin capillaries was examined on the anterior surface of the forearm of healthy volunteers. A rig was designed to permit the application of uniaxial forces between two pads attached to the skin surface. A grid was printed onto the skin surface, and mechanical data are presented in terms of force intensity versus strain. During force application the skin capillaries were monitored using vital capillary microscopy. Mean values of force intensity and strain of 1.33N/mm and 10%, respectively, were sufficient to produce virtual obliteration of the blood flow to the capillaries. A simplified finite element model of the tissue was also employed to illustrate the effect of surface forces at different depths within the tissue. This study emphasizes the potentially damaging effects of surface forces on the integrity of the skin vasculature. If these forces are maintained or repeated, cell necrosis and eventual tissue damage would result.

Study of the mechanism of film condensation of vapor under the influence of surface forces

Measurements are made of local heat-transfer coefficients in the condensation of vapor with allowance for the effect of surface forces on hydrodynamics.

Effect of surface forces on fluid flow in thin pores

The structure of fluids near solid surfaces differs from that in the bulk [i]. In the case of isotropic simple fluids with a spherically symmetric intermolecular interaction potential, these variations extend to several molecular layers. For anisotropic fluid crystals the surface effect is manifested at distances of the order of several micrometers. Polar associated fluids, including water, occupy an intermediate position. Boundary layers of water with varying structure reach nearly hydrophilic, well-wettable surfaces of dozens, sometimes hundreds of angstrom. A worsening of the wetting leads to a decrease in the width of boundary layers. In the case of hydrophobic surfaces, breakdown of the sticking condtion becomes possible, and we have slipping of water over the solid surface.

Adhesion between metal surfaces: The effect of surface roughness

Adhesion between metal surfaces and the effect of nanometre scale surface roughness were studied in ultrahigh vacuum. A significant adhesion force is detected after the applied load has exceeded a critical value. This value is identified with the load required to produce plastic deformation, using an expression for the effect of surface forces during plastic loading. A criterion for determining the mode of separation (brittle or ductile) is obtained by considering the influence of the microasperities. For ioncleaned Ti-Ti contacts, values of adhesion energy and microhardness are found to be 0.041 J m −2 and 0.91 GPa respectively.

Modelling reinforced earth : Bolton, M D; Choudhúry, S P; Pang, P L R Ground Engng, V11, N6, Sept 1978, P19–24

Centrifugal modelling offers an opportunity to witness collapses of soil, structured or composite models in circumstances which are not unlike those of full-scale constructions. It is hoped that the new form can be safely analyzed in terms of existing mechanical principles. If so, then these principles will allow the refinement of the new technique, allow its extension more quickly into improved areas, and allow a more rigorous analysis of safety that can be gained by having not yet made an error in practice. The models used were proportioned and oriented so as to reduce those errors in stress which are due to the non-uniformity of the acceleration field to below 10% in the critical region. The capacities of the models were specifically chosen so that a number of tension failures and slippage failures could be observed to disrupt the reinforcement and cause collapse. The dry sand used in all the models was a well-graded coarse to fine glacial sand. The conclusions include among others, that centrifugal models confirm the usefulness of the anchor concept of reinforced earth. An actual earth pressure coefficient measured on loose soil would have safely underpredicted the failure of anchors in tension by a factor of 2.2 to 3.3 and in slippage by a factor of 1.6 to 2.2. Since the friction capacity of an anchor may be made larger without using a greater weight of reinforcement, simply by spreading the same material wider and thinner, it may be economical to employ factors of safety against slippage which are very much larger than two. Future work should be devoted to a further understanding of the stresses in reinforced earth walls, the effects of surface forces and poor foundations, and the feasibility of clay fills.

The deposition of colloidal particles onto the surface of a rotating disk

The deposition rate of colloidal particles onto a rotating disk was calculated as a function of time by using the convective-diffusion equation subject to the boundary condition of a first order surface reaction which incorporates the effect of surface forces and a charge balance which allows for changes in the charge of the disk due to deposition. Calculations show that such a model accounts for the experimentally observed fact that the deposition rate decreases with time.