A Novel Inverse Method For Determining The Refractive Indices Of Medium And Dispersed Particles Simultaneously By Turbidity Measurement

The refractive indices of particles and dispersion medium are important parameters in many colloidal experiments using optical techniques, such as turbidity and light scattering measurements. These data are in general wavelength-dependent and may not be available at some wavelengths fitting to the experimental requirement. in this Study we present a novel approach to inversely determine the refractive indices of particles and dispersion medium by examining the consistency of measured extinction cross sections of particles with their theoretical values using a series of trial values of the refractive indices. The colloidal suspension of polystyrene particles dispersed in water was used as an example to demonstrate how this approach works and the data obtained via such a method are compared with those reported in literature, showing a good agreement between both. Furthermore, the factors that affect the accuracy of measurements are discussed. We also present some data of the refractive indices of polystyrene over a range of wavelengths smaller than 400 nm that have been not reported in the available literature. (C) 2008 Elsevier Inc. All rights reserved.

Interfacial behavior of DEHEHP and the kinetics of cerium(IV) extraction in nitrate media

The effects of diluents, temperature, acidity, and ionic strength of the aqueous phase on the interfacial properties of DEHEHP have been extensively investigated using the Du Nouy ring method. In addition, the effect of cerium(IV) concentration loaded in the organic phase on the interfacial tension has also been studied. With the increase of DEHEHP concentration, the value of interfacial tension (gamma) decreases in the studied system, which shows that DEHEHP has interfacial activity as a kind of surfactant. The surface excess at the saturated interface (Gamma(max)) and the minimum bulk concentration of the extractant necessary to saturate the interface (C-min) under the different conditions are calculated according to two adsorption equations such as the Gibbs and Szyszkowski functions to be presented in comprehensive tables and figures. The relationship between the interfacial activity of DEHEHP and cerium(IV) extraction kinetics by DEHEHP has been discussed by considering different factors such as the effects of diluents and temperature. However, the interfacial activity parameter of extractant only is a qualitative parameter, but cannot provide strong enough evidence to quantitatively explain the relationship between extraction kinetics and interfacial properties of an extractant.

The Head-On Colliding Process Of Binary Liquid Droplets At Low Velocity: High-Speed Photography Experiments And Modeling

The experimental and theoretical studies are reported in this paper for the head-on collisions of a liquid droplet with another of the same fluid resting on a solid substrate. The droplet on the hydrophobic polydimethylsiloxane (PDMS) substrate remains in a shape of an approximately spherical segment and is isometric to an incoming droplet. The colliding process of the binary droplets was recorded with high-speed photography. Head-on collisions saw four different types of response in our experiments: complete rebound, coalescence, partial rebound With conglutination, and coalescence accompanied by conglutination. For a complete rebound, both droplets exhibited remarkable elasticity and the contact time of the two colliding droplets was found to be in the range of 10-20 ms. With both droplets approximately considered as elastic bodies, Hertz contact theory was introduced to estimate the contact time for the complete rebound case. The estimated result Was found to be on the same order of magnitude as the experimental data, which indicates that the present model is reasonable. (C) 2008 Elsevier Inc. All rights reserved.

Adsorption of human serum albumin onto gold: a combined electrochemical and ellipsometric study

Human serum albumin adsorption onto gold surfaces was investigated by electrochemical and ellipsometric methods. Albumin adsorption onto gold was confirmed by the change of the open circuit potential of gold and by the ellipsometric parameter variation during albumin immobilization. In both experiments the parameters reached stable values within 10-15 min. The albumin adsorption layer thickness measured with the ellipsometer was about 1.5 nm. The adsorption of albumin Under applied potential was also investigated and it was found that both positive and negative applied potential promote albumin adsorption. Changes in the optical parameters of bare gold and albumin adsorbed onto gold surface under applied potential were investigated with in Situ ellipsometry. The similarity and reversibility of the optical changes showed that adsorbed albumin was stable on the gold surface Under the applied potential range (-200-600 mV). The cyclic voltammograms of K3Fe(CN)(6) on the modified gold surface showed that albumin Could partly block the oxidation and reduction reaction. (C) 2004 Elsevier Inc. All rights reserved.

Thermophoretic deposition of particles onto cold surfaces of bodies in two-dimensional and axisymmetric flows

The problem of thermophoretic deposition of small particles onto cold surfaces is studied in two-dimensional and axisymmetric flow fields. The particle concentration equation is solved numerically together with the momentum and energy equations in the laminar boundary layer with variable density effect included. It is shown explicitly to what extent the particle concentration and deposition rate at the wall are influenced by the density variation effect for external flow past bodies. The general numerical procedure is given for two-dimensional and axisymmetric cases and is illustrated with examples of thermophoretic deposition of particles in flows past a cold cylinder and a sphere.

Deformation Of Pdms Membrane And Microcantilever By A Water Droplet: Comparison Between Mooney-Rivlin And Linear Elastic Constitutive Models

In this paper, we studied the role of vertical component Of Surface tension of a water droplet on the deformation of membranes and microcantilevers (MCLs) widely used in lab-on-a-chip and micro-and nano-electromechanical system (MEMS/NEMS). Firstly, a membrane made of a rubber-like material, poly(dimethylsiloxane) (PDMS), was considered. The deformation was investigated using the Mooney-Rivlin (MR) model and the linear elastic constitutive relation, respectively. By comparison between the numerical solutions with two different models, we found that the simple linear elastic model is accurate enough to describe such kind of problem, which would be quite convenient for engineering applications. Furthermore, based on small-deflection beam theory, the effect of a liquid droplet on the deflection of a MCL was also studied. The free-end deflection of the MCL was investigated by considering different cases like a cylindrical droplet, a spherical droplet centered on the MCL and a spherical droplet arbitrarily positioned on the MCL. Numerical simulations demonstrated that the deflection might not be neglected, and showed good agreement with our theoretical analyses. (C) 2008 Elsevier Inc. All rights reserved.

Dissolution of kaolinite induced by citric, oxalic, and malic acids

Kaolinite is a dominant clay mineral in the soils in tropical and Subtropical regions, and its dissolution has an influence on a variety of soil properties. In this work, kaolinite dissolution induced by three kinds of low-molecular-weight organic acid, i.e., citric, oxalic, and malic acids, was evaluated under far-from-equilibrium conditions. The rates of kaolinite dissolution depended on the kind and concentration of organic acids, with the sequence R-oxalate > R-citrate > R-malate. Chemical calculation showed the change in concentration of organic ligand relative to change in concentration of organic acid in suspensions of kaolinite and organic acid. The effect of organic acid on kaolinite dissolution was modeled by species of organic anionic ligand. For oxalic acid, L-oxalic(2-) and HLoxalic- jointly enhanced the dissolution of kaolinite, but for malic and citric acids, HLmalic- and H2Lcitric- made a higher contribution to the total dissolution rate of kaolinite than L-malic(2-) and L-citric(3-), respectively. For oxalic acid, the proposed model was R-Si = 1.89 x 10(-12) x [(25x)/(1+25x)] + 1.93 x 10(-12) x [(1990x(1))/(1+1990x(1))] (R-2 = 0.9763), where x and x(1) denote the concentrations of HLoxalic and L-oxalic, respectively, and x(1) = 10(-3.81) x x/[H+]. For malic acid, the model was R-Si =4.79 x 10(-12) x [(328-v)/(1+328x)] + 1.67 x 10(-13) x [(1149x(1))/(1+1149x(1))] (R-2 =0.9452), where x and x(1) denote the concentrations of HLmalic and L-malic, respectively, and x(1) = 10(-5.11) x x/[H+], and for citric acid, the model was R-Si = 4.73 x 10(-12) x [(845x)/(1+845x)] +4.68 x 10(-12) x [(2855x(1))/(1+2855x(1))] (R-2 =0.9682), where x and x(1) denote the concentrations of H2Lcitric and L-citric, respectively, and x(1) = 10(-11.16) x x/[H+](2). (c) 2005 Elsevier Inc. All rights reserved.

Marine species of Ainudrilus and Heterodrilus (Oligochaeta : Tubificidae : Rhyacodrilinae) from Hainan Island in southern China

Six species of Rhyacodrilinae (Oligochaeta: Tubificidae) are reported from intertidal and shallow water subtidal habitats around Hainan Island in southern China. Four species are new to science: Ainudrilus pauciseta n. sp., Heterodrilus chenianus n. sp., Heterodrilus nudus n. sp., and Heterodrilus uniformis n. sp. Japanese material of Ainudrilus lutulentus (Erseus, 1984) is also briefly described. Hitherto, 27 species belonging to Tubificidae have been recorded from Hainan.

Numerical simulations of interrupted and conventional microchannel heat sinks

We provide three-dimensional numerical simulations of conjugate heat transfer in conventional and the newly proposed interrupted microchannel heat sinks. The new microchannel heat sink consists of a set of separated zones adjoining shortened parallel microchannels and transverse microchambers. Multi-channel effect, physical property variations, and axial thermal conduction are considered. It is found that flow rate variations in different channels can be neglected, while heat received by different channels accounts for 2% deviations from the averaged value when the heat flux at the back surface of the silicon chip reaches 100 W/cm(2). The computed hydraulic and thermal boundary layers are redeveloping in each separated zone due to shortened flow length for the interrupted microchannel heat sink. The periodic thermal developing flow is responsible for the significant heat transfer enhancement. Two effects influence pressure drops across the newly proposed microchannel heat sink. The first one is the pressure recovery effect in the microchamber, while the second one is the head loss when liquid leaves the microchamber and enters the next zone. The first effect compensates or suppresses the second one, leading to similar or decreased pressure drop than that for the conventional microchannel heat sink, with the fluid Prandtl number larger than unity.

Stability and demulsification of emulsions stabilized by asphaltenes or resins

Experimental data are presented to show the influence of asphaltenes and resins on the stability and demulsification of emulsions. It was found that emulsion stability was related to the concentrations of the asphaltene and resin in the crude oil, and the state of dispersion of the asphaltenes and resins (molecular vs colloidal) was critical to the strength or rigidity of interfacial films and hence to the stability of the emulsions. Based on this research, a possible emulsion minimization approach in refineries, which can be implemented utilizing microwave radiation, is also suggested. Comparing with conventional heating, microwave radiation can enhance the demulsification rate by an order of magnitude. The demulsification efficiency reaches 100% in a very short time under microwave radiation. (C) 2003 Elsevier Inc. All rights reserved.