Capillary rise of liquids in rectangular tubings

The capillary rise of liquids was investigated in square capillary tubings of different dimensions (e. g. 300 m · 300 m to 1000 m · 1000 m) in the temperature range 25° to 35°C.The data were fitted to an equation:=1/2 · ·g · (S · (C ·H/2 +C ·S)) where is the surface tension of the liquid,S is the side length of the square tubing,H is the capillary rise,C (= 1.089) is a capillary constant.     

Spreading of non-Newtonian liquids over solid substrates

The spreading of drops of a non-Newtonian liquid (Ostwald-de Waele liquid) over horizontal solid substrates is theoretically investigated in the case of complete wetting and small dynamic contact angles. Both gravitational and capillary regimes of spreading are considered. The evolution equation deduced for the shape of the spreading drops has self-similar solutions, which allows obtaining spreading laws for both gravitational and capillary regimes of spreading. In the gravitational regime case of spreading the profile of the spreading drop is provided.     

Capillary rise of superspreaders

Trisiloxane surfactants, known as 'superspreaders', are commonly employed in numerous applications where enhanced wetting is of the utmost importance. The underlying mechanisms of superspreader wetting have been a focus of scientific interest for ca. 2 decades, and a number of mechanisms have been proposed to explain the unique trisiloxane dynamics. We have studied trisiloxane behaviour in thin capillaries to get further insight into their interfacial activity. Additionally, our knowledge of the capillary rise of superspreaders is surprisingly limited, and the effect of this extraordinary group of surfactants on capillary phenomena has been largely overlooked. Diffusion was confirmed to be the limiting factor of trisiloxane behaviour. A tentative theoretical explanation for the phenomenon studied and an appropriate mathematical model are presented. It is concluded that the enhancement of wetting due to surfactant addition is also a function of geometry: the effect is clear for a sessile drop, but more complex and less beneficial in a capillary.     

Capillary rise of a meniscus with phase change

The Lucas-Washburn equation, describing the motion of a liquid body in a capillary tube, is extended to account for the effect of phase change - evaporation or condensation. The system is found to always possess a stable equilibrium state when the temperature jump across the interface is confined to a certain range. We show that phase change affects the equilibrium height of the meniscus, the transition threshold from monotonic to oscillatory dynamics, and the frequency of oscillations, when present. At higher mass transfer rates and/or large capillary radii, vapor recoil is found to be the dominant factor. Evaporation lowers the equilibrium height, increases the oscillation frequency and lowers the transition threshold to oscillations. For condensation, two regimes are identified: at high mass transfer rates similar trends to those of evaporation are observed, whereas the opposite is found for low mass transfer rates, resulting in an increased equilibrium height, lower oscillation frequencies and a shift of the transition threshold toward monotonic dynamics.     

Molecular-dynamic simulation of nanosized droplet spreading over a continual solid surface

Molecular dynamics methods are employed for a comparative study of the spread of nanosized simple fluid droplets and nanodroplets composed of model chains that reflect molecules of normal alkanes over a solid substrate. The effects of the droplet size, the energy of the molecule-substrate interactions, temperature, and degree of chain rigidity on the spreading kinetics are investigated. The substrate is described in terms of the continual Lennard-Jones model.     

Capillary rise kinetics of some building materials

The presence of water in masonry is one of the main factors in deterioration. Capillary rise is the most usual mechanism of water penetration into building materials. In this study the kinetics of the capillary rise phenomenon was studied for various building materials: four stones, two bricks, and six plasters. A first-order kinetic model was proposed, in which the equilibrium moisture height derived from Darcy law. The capillary height time constant found to be strongly affected by the material characteristics. Moreover, the capillary height time constant can be predicted if the average pore radius of the materials is known.     

Capillary rise in Hele-Shaw models of disordered media

We study the capillary rise of a viscous liquid in large Hele-Shaw models of disordered media, both analytically and experimentally. Compared to the Fries-Dreyer and Lucas-Washburn solutions for capillary rise with and without gravity, our experimental data reveal a systematic deviation at short and intermediate times. The original pressure balance equation leading to Washburn's results is reformulated in order to include an additional resisting term, proportional to the mean velocity of the front h˙, which appears naturally as a result of the geometry of the cell. Analytical solutions h(t) are found for displacements with and without gravity. These new solutions reproduce the experimental results very accurately in Hele-Shaw cells of constant gap thickness, where the capillary pressure can be approximated by a constant. In cells of fluctuating gap thickness, where the capillary pressure fluctuates in space, a small additional pressure contribution is required. This correction that depends on h˙ is also studied.     

Comparison of contact angle hysteresis of different probe liquids on the same solid surface

Advancing and receding contact angles of water, formamide and diiodomethane were measured on 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) layers deposited on three different solid supports—glass, mica and poly(methyl methacrylate). Up to five statistical monolayers were deposited on the surfaces by spreading DPPC solution. It was found that even on five statistical DPPC monolayers, the hysteresis of a given liquid depends on the kind of solid support. Also on the same solid support the contact angle hysteresis is different for each probe liquid used. The AFM images show that the heights of roughness of the DPPC films cannot be the primary cause of the observed hysteresis because the heights are too small to cause the observed hystereses. It is believed that the hysteresis is due to the liquid film present right behind the three-phase solid surface/liquid drop/gas (vapour) contact line and the presence of Derjaguin pressure. The value of contact angle hysteresis depends on both the solid surface and liquid properties as well as on intermolecular interactions between them.     

Capillary electrophoresis monitoring of halide impurities in ionic liquids

Quantification of impurities in ionic liquids is a crucial task in assessing the reliability of physical constants and solvent properties: taking into account the particularities of the ionic matrix, a simple routine method using capillary electrophoresis (CE) is developed to determine the halide content at the ppm level in water-immiscible ionic liquids.     

Scalable synthesis of ionic liquids: comparison of performances of microstructured and stirred batch reactors

A range of alkylpyridinium bromide ionic liquids have been synthesized in a stirred reactor at multigram scale and characterized by physical methods (viscosity, conductivity, melting point, electrochemical window, and water content). One ionic liquid, octylpyridinium bromide, was chosen to be synthesized in both macro and reduced scale reactors, in order to compare its performance and to afford evidence of the advantages of a cross channel micro reactor (channel width = 1 mm) compared to a stirred reactor.     

Dynamic wetting of a fluoropolymer surface by ionic liquids

The spontaneous spreading of ionic liquids on a fluoropolymer surface (Teflon AF1600) in air is investigated by high-speed video microscopy. Six ionic liquids (EMIM BF(4), BMIM BF(4), OMIM BF(4), EMIM NTf(2), BMIM NTf(2) and HMIM NTf(2)) are used as probe liquids. The dependence of the dynamic contact angle on contact line velocity is interpreted with a hydrodynamic model and a molecular-kinetic model. The usefulness of the hydrodynamic model is rather limited. There is a good correspondence between the molecular dimensions of the liquids and the physical parameters of the molecular-kinetic model. The viscous and molecular-kinetic contributions to energy dissipation are calculated, revealing that energy is dissipated in the bulk as well as at the contact line during dynamic wetting. There are wide ramifications of these results in areas ranging from lubrication and biology to minerals processing and petroleum recovery.     

Capillary electrophoretic separation of cationic constituents of imidazolium ionic liquids

A capillary electrophoretic method for resolving selected imidazolium ionic liquid cations is reported. The method, in which citric buffer is used as the running electrolyte, is simple and reproducible. The separation of a standard mixture is in linear accordance with the relative molecular mass (M(r)) of solutes regardless of the type of substitution (alkyl or aryl). The theoretical prediction of compounds as yet not analyzed is therefore possible; however, cations with identical molecular masses are inseparable with this method. Nevertheless, the method's quantitative analytical performance was excellent. The paper also discusses the applicability of a method for tracking the photodegradation kinetics of an exemplary ionic liquid.     

Thermophoretic motion of a solid spherical particle near a solid planar surface

The thermophoretic motion of a solid spherical aerosol particle directed normally to an infinite planar solid surface is analyzed. The solution is performed in a bispherical coordinate system with allowance for linear corrections in the Knudsen number. The finite thermal conductivity of a solid body is taken into account in the analysis.     

Biosorption: a new rise for elemental solid phase extraction methods

Biosorption is a term that usually describes the removal of heavy metals from an aqueous solution through their passive binding to a biomass. Bacteria, yeast, algae and fungi are microorganisms that have been immobilized and employed as sorbents in biosorption processes. The binding characteristics of microorganisms are attributed to functional groups on the surface providing some features to the biosorption process like selectivity, specificity and easy release. These characteristics turn the biosorption into an ideal process to be introduced in solid phase extraction systems for analytical approaches. This review encompasses the research carried out since 2000, focused on the employment of biosorption processes as an analytical tool to improve instrumental analysis. Since aminoacids and peptides as synthetic analogues of natural metallothioneins, proteins present in the cell wall of microorganisms, have been also immobilized on solid supports (controlled pore glass, carbon nanotubes, silica gel polyurethane foam, etc.) and introduced into solid phase extraction systems; a survey attending this issue will be developed as well in this review.     

Dynamic surface tension and surface rheology of biological liquids

The paper presents results of dynamic and equilibrium surface tension measurements (using a maximum bubble pressure instrument) of serum and urine samples that were obtained from 80 healthy human of various sexes and ages. These data were compared with surface tension measurements of biological liquids obtained from patients suffering from malignant neoplasm of corpus uteri (n=5) and cervix uteri (n=31). In addition, surface dilatational rheology was determined on 32 samples using a drop shape method. The dilatational rheology data were compared with the dynamic surface tension data. Although some trends were found, no significant correlations exist between surface tension and rheology data and any of the disease states or stages. It is difficult to explain these findings in the framework of known mechanisms. However, our studies demonstrate that dynamic interface tensiometry of human biological liquids provide new insight into the biophysical behavior of these liquids, most likely reflecting compositional changes of them during ageing, the course of cancer and as a consequence of therapeutical interventions.     

The surface tension of polymer liquids

A brief review of the surface tension of polymer liquids is presented. A strong emphasis is placed on recent measurements of surface tensions of homologous liquid series up to high-molecular-weight polymers, and the thermodynamic liquid properties of these same homologous series obtained from sources such as pressure-volume-temperature (PVT) data. The accuracy and limitations of the thermodynamic information which are used as input to many of the theories applied to the surface properties of polymer molecules are discussed. By scaling the surface tension data using a true measure of the cohesive energy density of the liquid state, we can clearly observe the entropic contribution to the surface tension caused by the conformational restriction of a large molecule at the liquid-vapor interface. The scaling implies the existence of a corresponding states principle for both polymer liquids and for low-molecular-weight liquids. The ramifications of the existence of a corresponding states principle for the surface tension of polymer melts are discussed. One consequence of the corresponding states principle is that it allows us to use surface tension measurements to compute the cohesive energy density of polymer melts using PVT data.     

Condensation of a non-wetting fluid on a solid surface

Theoretical studies of a drop moving under condensation from the surrounding vapor, have been provided. Two cases are considered. In the first, the rate of condensation is large that the drop "moves" because condensation has changed its dimensions. The model provided here shows that the rate of spreading is a constant, proportional to the heat flux and inversely proportional to the macroscopic contact angle. This compares well with available experimental data. The other model where the rate of condensation is small, is taken from existing results and comes close to explaining one set of experimental data. It is based on the use of viscous forces as the primary rate mechanism. Its shortcomings have been discussed.     

Dynamic control of surface energy and topography of microstructured conducting polymer films

Microstructured polymer surfaces, including conducting and insulating polymers, have been prepared to achieve electrochemical control of the surface energy and topography. The reported surface switches include pillar- and mesh-like surface patterns of polypyrrole (PPy), poly(3,4-ethylene-dioxythiophene) (PEDOT), and photoresists. The structures have been evaluated by contact angle measurements and optical and scanning electron microscopy to determine the surfaces characteristics. These microstructured polymer surface switches can be electrochemically modified from dewetting to wetting conditions, with a maximum associated change of the water contact angle from 129 degrees to 44 degrees . This contact angle switching was observed for samples in which dynamic control of the surface topography and surface tension was coupled. Control of topography was achieved with a dynamic height-switching range of more than 3 mum. In addition, dynamic control of anisotropic wetting is reported. Our experiments were carried out under conditions that are suitable for a biointerface, implying potential application in biotechnology and cell science. In particular, switching of the energy, chemistry, and topography of the surface, along with their associated orientation, are interesting features for dynamic (electronic) control of the seeding and proliferation for living cells. The technology reported promises for electronically controlled cell-growth within Petri dishes, well plates, and other cell-hosting tools.