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Capillary Forces (capillary + force)
Terms modified by Capillary Forces Selected AbstractsCapillary forces between two solid spheres linked by a concave liquid bridge: Regions of existence and forces mappingAICHE JOURNAL, Issue 5 2009David Megias-Alguacil Abstract This article focuses on the capillary interactions arising when two spherical particles are connected by a concave liquid bridge. This scenario is found in many situations where particles are partially wetted by a liquid, like liquid films stabilized with nanoparticles. We analyze different parameters governing the liquid bridge: interparticle separation, wetting angle and liquid volume. The results are compiled in a liquid volume-wetting angle diagram in which the regions of existence (stability) or inexistence (instability) of the bridge are outlined and the possible maximum and minimal particle distances for which the liquid bridge may be found. Calculations of the capillary forces discriminate those conditions for which such force is repulsive or attractive. The results are plotted in form of maps that allow an easy understanding of the stability of a liquid bridge and the conditions at which it may be produced for the two particle model. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Influence of moisture content on measurement accuracy of porous media thermal conductivityHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 8 2009Mingzhi Yu Abstract The thermal conductivity measurement accuracy of sand was experimentally studied with a hot disk thermal constant analyzer and water morphologies, distribution, and evolution at the pore scale were observed with a charge coupled device (CCD) combined with a microscope. It was found that thermal conductivities of samples with low moisture content (<25%) could not be accurately measured. For samples with low moisture content, the analysis showed that the water in the region adjacent to the analyzer sensor mainly existed as isolated liquid bridges between/among sand particles and would evaporate and diffuse to relatively far regions because of being heated by the sensor during measurement. Water evaporation and diffusion caused the sample constitution in the region adjacent to the sensor to vary throughout the whole measurement process, and accordingly induced low accuracy of the obtained thermal conductivities. Due to high water connectivity in pores, the rate of water evaporation and diffusion in porous media of high moisture content was relatively slow when compared with that of low moisture content. Meanwhile, water in the relatively far regions flowed back to the region adjacent to the sensor by capillary force. Therefore, samples consisting of the region adjacent to the sensor maintained the constant and thermal conductivities of porous media with relatively high moisture content and could be measured with high accuracy. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20272 [source] The formation of rising liquid thin film on the fluted surface of a horizontal tubeHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 6 2005Li Yan Abstract The purpose of this study is to investigate the mechanism of the formation of the rising liquid thin film and its flow characteristics on the fluted surface of a horizontal tube. By analyzing the wetting behaviors of the fluted tube, which was primarily responsible for the formation of the rising liquid thin film, a numerical model of one-phase fluid was established to analyze the distribution of the velocity and thickness of the rising liquid thin film during its evaporation. The behaviors of the flow characteristics were discussed and the results showed that geometric properties of the fluted surface of a horizontal tube and surface tension of the fluid were essential for the formation of a continuous and uniform liquid thin film. Theoretical analysis suggested that the capillary force created by the fluid surface tension was a key value for the formation of the thin film. The heat and mass transfer characteristics of the formed thin film also had an effect on the formation of the rising film. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(6): 396,406, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20075 [source] Influence of liquid bridges on the mechanical behaviour of polydisperse granular materialsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 3 2006F. Soulié Abstract We investigate a polydisperse granular material in which the particle interactions are governed by a capillary force law. The cohesion force for a grain-pair with unequal diameters is expressed as an explicit function of the inter-particle distance and the volume of the liquid bridge. This analytical relation is validated by experiments on a reference material. Then, it is completed by a rupture criterion and cast in the form of a force law that accounts for solid contact, capillary force and rupture characteristics of a grain-pair. Finally, in order to evaluate the influence of capillary cohesion on the macroscopic behaviour, radial and axial compression tests on cylindrical assemblies of wet particles are simulated using a 3D distinct element method. Copyright © 2005 John Wiley & Sons, Ltd. [source] Stress Development Due to Capillary Condensation in Powder Compacts: A Two-Dimensional Model StudyJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2000Stefan Lampenscherf A model experiment is presented to investigate the relationship between the humidity-dependent liquid distribution and the macroscopic stress in a partially wet powder compact. Therefore, films of monosized spherical particles were cast on silicon substrates. Using environmental SEM the geometry of the liquid necks trapped between particles was imaged as a function of relative humidity. Simultaneously the macroscopic stress in the substrate adhered particle film was measured by capacitive deflection measurement. The experimentally found humidity dependence of the liquid neck size and the macroscopic film stress are compared with model predictions. The circle,circle approximation is used to predict the size of the liquid necks between touching particles as a function of the capillary pressure. Using the modified Kelvin relation between capillary pressure and relative humidity, we consider the effect of an additional solute which may be present in the capillary liquid. The results of the stress measurement are compared with the model predictions for a film of touching particles in hexagonal symmetry. The contribution of the capillary interaction to the adhesion force between neighboring particles is calculated using the integrated Laplace equation. The resulting film stress can be approximated relating this capillary force to an effective cross section per particle. The experimentally found humidity dependence of the liquid neck size is in good agreement with the model predictions for finite solute concentration. The film stress corresponds to the model predictions only for large relative humidities and shows an unexpected increase at small values. As is shown with an atomic force microscope, the real structure of the particle,particle contact area changes during the wet/dry cycle. A solution/reprecipitation process causes surface heterogeneities and solid bridging between the particles. It is claimed that the existence of a finite contact zone between the particles gives rise to the unexpected increase of the stress at small relative humidities. [source] The Genetic Mechanism and Model of Deep-Basin Gas Accumulation and Methods for Predicting the Favorable AreasACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 4 2003WANG Tao Abstract, As a kind of abnormal natural gas formed with special mechanism, the deep-basin gas, accumulated in the lower parts of a basin or syncline and trapped by a tight reservoir, has such characteristics as gas-water inversion, abnormal pressure, continuous distribution and tremendous reserves. Being a geological product of the evolution of petroliferous basins by the end of the middle-late stages, the formation of a deep-basin gas accumulation must meet four conditions, i.e., continuous and sufficient gas supply, tight reservoirs in continuous distribution, good sealing caps and stable structures. The areas, where the expansion force of natural gas is smaller than the sum of the capillary force and the hydrostatic pressure within tight reservoirs, are favorable for forming deep-basin gas pools. The range delineated by the above two forces corresponds to that of the deep-basin gas trap. Within the scope of the deep-basin gas trap, the balance relationship between the amounts of ingoing and overflowing gases determines the gas-bearing area of the deep-basin gas pool. The gas volume in regions with high porosity and high permeability is worth exploring under current technical conditions and it is equivalent to the practical resources (about 10%-20% of the deep-basin gas). Based on studies of deep-basin gas formation conditions, the theory of force balance and the equation of material balance, the favorable areas and gas-containing ranges, as well as possible gas-rich regions are preliminarily predicted in the deep-basin gas pools in the Upper Paleozoic He-8 segment of the Ordos basin. [source] Stable Non-Covalent Large Area Patterning of Inert Teflon-AF Surface: A New Approach to Multiscale Cell Guidance,ADVANCED ENGINEERING MATERIALS, Issue 6 2010Francesco Valle Micro- and nano-patterning of cell adhesion proteins is demonstrated to direct the growth of neural cells, viz. human neuroblastoma SHSY5Y, at precise positions on a strongly antifouling substrate of technolological interest. We adopt a soft-lithographic approach with oxygen plasma modified PDMS stamps to pattern human laminin on Teflon-AF films. These patterns are based on the interplay of capillary forces within the stamp and non-covalent intermolecular and surface interactions. Remarkably, they remain stable for several days upon cell culture conditions. The fabrication of substrates with adjacent antifouling and adhesion-promoting regions allows us to reach absolute spatial control in the positioning of neuroblastoma cells on the Teflon-AF films. This patterning approach of a technologically-relevant substrate can be of interest in tissue engineering and biosensing. [source] Delivery of Two-Part Self-Healing Chemistry via Microvascular NetworksADVANCED FUNCTIONAL MATERIALS, Issue 9 2009Kathleen S. Toohey Abstract Multiple healing cycles of a single crack in a brittle polymer coating are achieved by microvascular delivery of a two-part, epoxy-based self-healing chemistry. Epoxy resin and amine-based curing agents are transported to the crack plane through two sets of independent vascular networks embedded within a ductile polymer substrate beneath the coating. The two reactive components remain isolated and stable in the vascular networks until crack formation occurs in the coating under a mechanical load. Both healing components are wicked by capillary forces into the crack plane, where they react and effectively bond the crack faces closed. Healing efficiencies of over 60% are achieved for up to 16 intermittent healing cycles of a single crack, which represents a significant improvement over systems in which a single monomeric healing agent is delivered. [source] Forces between Surfactant-Coated ZnS Nanoparticles in Dodecane: Effect of Water,ADVANCED FUNCTIONAL MATERIALS, Issue 16 2006Alig, R. Godfrey Abstract The forces between mica surfaces confining solutions of spherical and rod-shaped ZnS nanoparticles (diameter ca. 5,nm) coated with hexadecylamine or octadecylamine surfactant in dodecane have been measured in the absence and after the introduction of trace amounts of water. Initially, or at very low water content, the water molecules cause the nanoparticles to aggregate and adsorb on the hydrophilic mica surfaces, resulting in a long-range exponentially decaying repulsive force between the surfaces. After longer times (>,20,h), water bridges nucleate and grow between the nanoparticles and mica surfaces, and attractive capillary forces then cause a long-range attraction and a strong (short-range) adhesion. It is found, as has previously been observed in nonaqueous bulk colloidal systems, that even trace amounts of water have a profound effect on the interactions and structure of nanoparticle assemblies in thin films, which in turn affect their physical properties. These effects should be considered in the design of thin-film processing methodologies. [source] Inorganic Materials and Ionic Liquids: Large-scale Nanopatterning of Single Proteins used as Carriers of Magnetic Nanoparticles (Adv. Mater.ADVANCED MATERIALS, Issue 5 20105/2010) Ricardo Garcia, Eugenio Coronado, and co-workers demonstrate on p. 588 large-scale patterning of single ferritin molecules by sequential (atomic force microscopy local oxidation) and parallel approaches (lithographically controlled wetting). The nanopattern size matches the size of the protein (,10 nm). Electrostatic interactions, capillary forces, surface functionalization, and nanolithography are used to achieve the desired protein organization. [source] Large-scale Nanopatterning of Single Proteins used as Carriers of Magnetic NanoparticlesADVANCED MATERIALS, Issue 5 2010Ramsés V. Martínez Patterning of single ferritin molecules by sequential (atomic force microscopy local oxidation) and parallel approaches (lithographically controlled wetting). The nanopattern size matches the size of the protein (,10 nm). Electrostatic interactions, capillary forces, surface functionalization, and nanolithography are used to achieve the desired protein organization. [source] Using a pore-scale model to quantify the effect of particle re-arrangement on pore structure and hydraulic propertiesHYDROLOGICAL PROCESSES, Issue 8 2007Oagile Dikinya Abstract A pore-scale model based on measured particle size distributions has been used to quantify the changes in pore space geometry of packed soil columns resulting from a dilution in electrolyte concentration from 500 to 1 mmol l,1 NaCl during leaching. This was applied to examine the effects of particle release and re-deposition on pore structure and hydraulic properties. Two different soils, an agricultural soil and a mining residue, were investigated with respect to the change in hydraulic properties. The mining residue was much more affected by this process with the water saturated hydraulic conductivity decreasing to 0·4% of the initial value and the air-entry value changing from 20 to 50 cm. For agricultural soil, there was little detectable shift in the water retention curve but the saturated hydraulic conductivity decreased to 8·5% of the initial value. This was attributed to localized pore clogging (similar to a surface seal) affecting hydraulic conductivity, but not the microscopically measured pore-size distribution or water retention. We modelled the soil structure at the pore scale to explain the different responses of the two soils to the experimental conditions. The size of the pores was determined as a function of deposited clay particles. The modal pore size of the agricultural soil as indicated by the constant water retention curve was 45 µm and was not affected by the leaching process. In the case of the mining residue, the mode changed from 75 to 45 µm. This reduction of pore size corresponds to an increase of capillary forces that is related to the measured shift of the water retention curve. Copyright © 2007 John Wiley & Sons, Ltd. [source] On the capillary stress tensor in wet granular materialsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 10 2009L. Scholtès Abstract This paper presents a micromechanical study of unsaturated granular media in the pendular regime, based on numerical experiments using the discrete element method, compared with a microstructural elastoplastic model. Water effects are taken into account by adding capillary menisci at contacts and their consequences in terms of force and water volume are studied. Simulations of triaxial compression tests are used to investigate both macro and micro-effects of a partial saturation. The results provided by the two methods appear to be in good agreement, reproducing the major trends of a partially saturated granular assembly, such as the increase in the shear strength and the hardening with suction. Moreover, a capillary stress tensor is exhibited from capillary forces by using homogenization techniques. Both macroscopic and microscopic considerations emphasize an induced anisotropy of the capillary stress tensor in relation with the pore fluid distribution inside the material. Insofar as the tensorial nature of this fluid fabric implies shear effects on the solid phase associated with suction, a comparison has been made with the standard equivalent pore pressure assumption. It is shown that water effects induce microstructural phenomena that cannot be considered at the macro level, particularly when dealing with material history. Thus, the study points out that unsaturated soil stress definitions should include, besides the macroscopic stresses such as the total stress, the microscopic interparticle stresses such as the ones resulting from capillary forces, in order to interpret more precisely the implications of the pore fluid on the mechanical behaviour of granular materials. Copyright © 2009 John Wiley & Sons, Ltd. [source] Capillarity-Driven Assembly of Carbon Nanotubes on Substrates into Dense Vertically Aligned Arrays,ADVANCED MATERIALS, Issue 19 2007S. Kaur Carbon nanotubes are assembled into dense, vertically aligned arrays on substrates by using capillary forces. Modulating the interactions between the nanotubes and the underlying substrate provides control over the assembly of the nanotube array; capillary forces can either cause bending (left) or translation (right) of the nanotube array. The use of this densification strategy enables a four-fold increase in current density through nanotube arrays. [source] Fat Migration in Chocolate: Diffusion or Capillary Flow in a Particulate Solid?,A Hypothesis PaperJOURNAL OF FOOD SCIENCE, Issue 7 2004J. M. Aguilera ABSTRACT: The exact mechanism of fat and oil migration in chocolate and chocolate coatings is still unknown. Nevertheless, the so-called "diffusion equation" derived from Fick's 2nd law has been extensively used to model the phenomenon, giving the impression that molecular diffusion is the single transport mechanism. We propose that chocolate may be microstructurally regarded as a particulate medium formed by an assembly of fat-coated particles (for example, cocoa solids, sugars crystals, and milk powder). Within this matrix the liquid fraction of cocoa fat (which increases with temperature) is likely to move under capillary forces through interparticle passages and connected pores. Based on available evidence (microstructure, kinetic data, temperature dependence of liquid fat fraction, and so on) we demonstrate that capillary forces may have an important role to play in bulk flow of liquid fat and oils. The Lucas-Washburn equation for capillary rise fits available data under most reported experimental conditions. Detailed microstructural analysis in actual products as well as data on key parameters (surface tension, contact angle, viscosity) is necessary to confirm this hypothesis. Bulk flow due to capillary effects, highly disregarded in structured foods, should be considered as a mass transfer mechanism in liquid-filled porous or particulate foods. [source] Capillary forces between two solid spheres linked by a concave liquid bridge: Regions of existence and forces mappingAICHE JOURNAL, Issue 5 2009David Megias-Alguacil Abstract This article focuses on the capillary interactions arising when two spherical particles are connected by a concave liquid bridge. This scenario is found in many situations where particles are partially wetted by a liquid, like liquid films stabilized with nanoparticles. We analyze different parameters governing the liquid bridge: interparticle separation, wetting angle and liquid volume. The results are compiled in a liquid volume-wetting angle diagram in which the regions of existence (stability) or inexistence (instability) of the bridge are outlined and the possible maximum and minimal particle distances for which the liquid bridge may be found. Calculations of the capillary forces discriminate those conditions for which such force is repulsive or attractive. The results are plotted in form of maps that allow an easy understanding of the stability of a liquid bridge and the conditions at which it may be produced for the two particle model. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] The influence of relative humidity on the cohesion properties of micronized drugs used in inhalation therapyJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 3 2004Paul M. Young Abstract The influence of relative humidity (RH) on the cohesion properties of three drugs: salbutamol sulphate (SS), triamcinolone acetonide (TAA), and disodium cromoglycate (DSCG) was investigated using the atomic force microscope (AFM) colloidal probe technique. Micronized drug particles were mounted in heat-sensitive epoxy resin for immobilization. Multiple AFM force,distance curves were conducted between each drug probe and the immobilized drug particulates at 15, 45, and 75% RH using Force,Volume imaging. Clear variations in the cohesion profile with respect to RH were observed for all three micronized drugs. The calculated force and energy of cohesion to separate either micronized SS or DSCG increased as humidity was raised from 15 to 75% RH, suggesting capillary forces become a dominating factor at elevated RH. In comparison, the separation force and energy for micronized TAA particles decreased with increased RH. This behavior may be attributed to long-range attractive electrostatic interactions, which were observed in the approach cycle of the AFM force,distance curves. These observations correlated well with previous aerosolization studies of the three micronized drugs. © 2004 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 93: 753,761, 2004 [source] Numerical simulation of non-viscous liquid pinch off using a coupled level set boundary integral methodPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2007Maria Garzon The pinch off of an inviscid fluid column is described using a potential flow model with capillary forces. The interface velocity is obtained via a Galerkin boundary integral method for the 3D axisymmetric Laplace equation, whereas the interface location and the velocity potential on the free boundary are both approximated using level set techniques on a fixed domain. The algorithm is validated computing the Raleigh-Taylor instability for liquid columns which provides an analytical solution for short times. The simulations show the time evolution of the fluid tube and the algorithm is capable of handling pinch-off and after pinch-off events. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Network models for capillary porous media: application to drying technologyCHEMIE-INGENIEUR-TECHNIK (CIT), Issue 6 2010T. Metzger Jun.-Prof. Abstract Network models offer an efficient pore-scale approach to investigate transport in partially saturated porous materials and are particularly suited to study capillarity. Drying is a prime model application since it involves a range of physical effects: capillary pumping, viscous liquid flow, phase transition, vapor diffusion, heat transfer, but also cracks and shrinkage. This review article gives an introduction to this modern technique addressing required model input, sketching important elements of the computational algorithm and commenting on the nature of simulation results. For the case of drying, it is illustrated how network models can help analyze the influence of pore structure on process kinetics and gain a deeper understanding of the role of individual transport phenomena. Finally, a combination of pore network model and discrete element method is presented, extending the application range to mechanical effects caused by capillary forces. [source] | ||||||||||||||||