Cell lysis inside the capillary facilitated by transverse diffusion of laminar flow profiles (TDLFP)

Chemical cytometry studies the molecular composition of individual cells by means of capillary electrophoresis or capillary chromatography. In one of its realizations an intact cell is injected inside the capillary, the plasma membrane is disrupted to release the cellular contents into the separation buffer, and, finally, the molecules of interest are separated and detected. The solubilization of the plasma membrane with a surfactant is a simple and efficient way of achieving cell lysis inside the capillary. To facilitate cell lysis by a surfactant the cell has to be contacted with the surfactant inside the capillary. We recently introduced a generic method for mixing solutions inside the capillary termed transverse diffusion of laminar flow profiles (TDLFP). In this work, we propose that TDLFP can facilitate efficient cell lysis inside the capillary. Conceptually, a short plug of the surfactant is injected by pressure prior to cell injection. The cell is then injected by pressure wizthin a plug of the physiological buffer. Due to the parabolic profiles of pressure-driven laminar flows the interface between the plug of the surfactant and that of the physiological buffer is predominantly longitudinal. Transverse diffusion mixes the surfactant with the physiological buffer, which leads to surfactant’s contact with the cell and subsequent cell lysis. Here, we demonstrate that the proposed concept is valid. TDLFP-facilitated cell lysis by a short plug of the surfactant allows us to exclude the surfactant from the run buffer, and, hence, facilitates modes of separation, which are incompatible with the surfactant’s presence in the run buffer. In addition to cell lysis, TDLFP will be used to mix the cellular components with labeling reactants, affinity probes, inhibitors, etc. We foresee that the generic nature and enabling capabilities of TDLFP will speed up the maturation of chemical cytometry into a practical bioanalytical tool.     

Fragmentation of diffusion zone in high-temperature oxidation of copper

Using thermogravimetry, microscopy and X-ray diffraction, high-temperature (600-900 °C) oxidation of copper wires and plates has been studied. An abrupt decrease in reaction rate after complete consumption of metal phase but long before reaching equilibrium has been observed. This phenomenon is connected to an irregular character of the development of the reaction diffusion zone. In contrast to the usually applied layer model, initially formed oxide layers separate into numerous aggregates of Cu₂O crystals chaotically scattered throughout the zone between thinner layers of CuO grains. Such fragmentation of the diffusion zone is induced by macro- and microcracks formed in copper scale under influence of mechanical stresses at metal-oxide phase boundary due to the difference in molar volume between copper and its oxides. The pattern of cracks provides channels of fast diffusion and maintains the reaction rate at high level but only until the source of crack formation remains in action.     

Stabilization of two-phase octanol/water flows inside poly(dimethylsiloxane) microchannels using polymer coatings

In this paper we present our first results on the realization of stable water/octanol, two-phase flows inside poly(dimethylsiloxane) (PDMS) microchannels. Native PDMS microchannels were coated with high molecular weight polymers to change the surface properties of the microchannels and thus stabilize the laminar flow profile. The polymers poly(2-hydroxyethyl methacrylate), poly(vinyl pyrrolidone), poly(ethylene oxide), poly(ethylene glycol), and poly(vinyl alcohol) were assessed for their quality as stabilization coatings after deposition from flowing and stationary solutions. Additionally, the influence of coating the microchannels homogeneously with a single kind of polymer or heterogeneously with two different polymers was investigated. From the experimental observations, it can be concluded that homogeneous polymer coatings with poly(2-hydroxyethyl methacrylate) and poly(vinyl pyrrolidone) led to the effective stabilization of laminar water/octanol flows. Furthermore, heterogeneous coatings led to two-phase flows which had a better-defined and more stable interface over long distances (i.e., 40-mm-long microchannels). Finally, the partitioning of fuchsin dye in the coated microchannels was demonstrated, establishing the feasibility of the use of the polymer-coated PDMS microchannels for determination of logP values in laminar octanol/water flows.     

Stopped-flow injection analysis. The influence of diffusion on dispersion of normal and reverse flow injection

A relationship is derived to enable the comparison of the dispersion heights of normal and reverse flow injection analysis (FIA). A single channel flow system is employed in the absence of a chemical reaction. The stopped-flow injection method is used to probe the influence of molecular diffusion on the overall dispersion of normal and reverse FIA, which appeared to demonstrate fundamentally different diffusion behaviors. Small discrepancies are observed between the dispersion heights, which are enhanced by the stopped-flow period, especially when unmatched matrix ionic compositions of the indicator and counter solutions were involved. For these conditions, the diffusion flux rate is enhanced considerably, displaying a peak, in addition to the transient, for both methods. The influence of diffusion on the dispersion characteristics of normal and reverse FIA is discussed theoretically. Diffusion in the proposed model is postulated to oppose dispersion by convection. The latter initiates concentration gradients in the injection zone and propagates it with flow time over the dispersion zone profile. The diffusion flux then reacts in order to confine the indicator dispersion for normal FIA and to enhance it for reverse FIA. This model is consistent with the experimental results and accounts for most of the phenomena encountered. Probably owing to the influence of secondary flow phenomena, the use of coiled tubes has suppressed the effects of diffusion on the overall dispersion behavior.Part of the experimental work was performed at IMI Institute for Research and Development, Haifa, Israel.     

Impact of Taylor‐Aris diffusivity on analyte and system zone dispersion in CZE assessed by computer simulation and experimental validation

Application of pressure‐driven laminar flow has an impact on zone and boundary dispersion in open tubular CE. The GENTRANS dynamic simulator for electrophoresis was extended with Taylor‐Aris diffusivity which accounts for dispersion due to the parabolic flow profile associated with pressure‐driven flow. Effective diffusivity of analyte and system zones as functions of the capillary diameter and the amount of flow in comparison to molecular diffusion alone were studied for configurations with concomitant action of imposed hydrodynamic flow and electroosmosis. For selected examples under realistic experimental conditions, simulation data are compared with those monitored experimentally using modular CE setups featuring both capacitively coupled contactless conductivity and UV absorbance detection along a 50 μm id fused‐silica capillary of 90 cm total length. The data presented indicate that inclusion of flow profile based Taylor‐Aris diffusivity provides realistic simulation data for analyte and system peaks, particularly those monitored in CE with conductivity detection.     

Modeling of combined electroosmotic and capillary flow in microchannels

In the present study, theoretical model for the transient response of a capillary flow under the combined effects of electroosmotic and capillary forces at low Reynolds number is presented. The governing equation is derived based on the balance among the electrokinetic, surface, viscous and gravity forces. A non-dimensional transient governing equation for the penetration depth as a function of time is obtained by normalizing the viscous, gravity and electroosmotic forces with surface tension force. A new non-dimensional group for the electroosmotic force, E_o, is obtained through the non-dimensional analysis. This new non-dimensional group is a representation of combined electroosmosis and surface tension, i.e., capillarity. The numerical solution of governing equation is obtained to study the effect of different operating parameters on the flow front transport. In a combined flow, it is observed that the flow with positive and low negative magnitude E_o numbers, the attainment of equilibrium penetration depth is similar to a capillary flow. In case of high negative magnitude E_o numbers, complete filling of the channel is observed. The electrolyte with lower permittivity delays the progress of the flow front whereas a large EDL transports the electrolyte quickly. Higher viscous and gravity forces also delay the transport process in the combined flow. This model suggests that in combined flow the electrokinetic parameters also play an important role on the capillary flow and experiments are required to confirm this electrokinetic effect on capillary transport.     

Influence of the convective term in the Nernst-Planck equation on properties of ion transport through a layer of solution or membrane

The one-dimensional boundary-value problem of steady-state ion transport, which takes into account the convective component, is formulated and solved in terms of the Nernst-Planck model. This problem is investigated in connection with the diffusion layer, which is understood in a broad sense. This can be the diffusion layer as it is usually understood, i.e., located adjacent to a hydraulically permeable membrane. In another context it can be regarded as a capillary connecting two reservoirs filled with solutions of different concentration or as an uncharged macropore permeating the membrane and separating two solutions. Finally, the solution to the problem is applied to the membrane itself, which is represented as a quasi-homogeneous gel. In the latter case, a virtual electroneutral solution in local equilibrium with a small volume of membrane is considered. The problem is investigated in dimensionless form as a function of the Peclet number. It is shown that the Peclet number is numerically equal to the absolute value of the dimensionless convection velocity. The limiting current, concentration profiles, distributions of the field strength and potential, and effective transport numbers are analyzed as functions of the convective component.     

Effective intraparticle diffusion coefficients of CoCl2 in mesoporous functionalized silica adsorbents

The scope of this work is to determine the effective intraparticle diffusion coefficient of CoCl₂ over mesoporous functionalized silica. Silica is selected as a carrier of the functionalized groups for its rigid structure which excludes troublesome swelling, often found in polymeric adsorbents. 2-(2-pyridyl)ethyl-functionalized silica is selected as a promising affinity adsorbent for the reversible adsorption of CoCl₂. The adsorption kinetics is investigated with the Zero Length Column (ZLC) method. Initially, experiments were performed at different flow rates to eliminate the effect of external mass transfer. The effect of pore size (60 Å and 90 Å), particle size (40?10^?6 m–1000?10^?6 m) and initial CoCl₂ concentration (1 mol/m³–2.0 mol/m³) on the mass transfer was investigated. A model was developed to determine the pore diffusion coefficient of CoCl₂ by fitting the experimental data to the model. The pore diffusion coefficients determined for two different pore sizes of silica are D _p (60 Å) =1.95?10^?10 [m²/s] and D _p (90 Å) =5.8?10^?10 [m²/s]. The particle size and the initial CoCl₂ concentration do not have an influence on the value of diffusion coefficient. However, particle size has an influence on the diffusion time constant. In comparison with polymer adsorbents, silica based adsorbents have higher values of diffusion coefficients, as well as a more uniform and stable pore structure.     

The conjugation of ionic flows in the diffusion layers of electrodialysis systems

Fundamental regularities of the ion interference in diffusion layers of electrodialysis systems are revealed, as well as their effect on the electrical field strength, through which the ionic flows in their turn affect each other.     

Characterization of chemiluminescence from singlet oxygen under laminar flow conditions in a micro-channel and its quenching with beverages

Singlet oxygen was generated by reaction of sodium hypochlorite and hydrogen peroxide in a micro-channel. The two reagent solutions were delivered into the micro-channel by a syringe pump, providing a laminar flow liquid-liquid interface. The chemiluminescence from the singlet oxygen was emitted in the collapse of the interface due to molecular diffusion under laminar flow conditions. The chemiluminescence intensity was observed continuously and stably for each combination of reagents fed into the micro-channel; while, in the normal batch-type reactor the chemiluminescence peaks from singlet oxygen were observed within ca. 5 s. The features of the chemiluminescence emitted under laminar flow conditions were examined by changing the concentrations of sodium hypochlorite and hydrogen peroxide; the concentrations of 2.5 mM sodium hypochlorite and 7.5 mM hydrogen peroxide provided highest chemiluminescence intensities without bubble formation. Also, the effects of beverages, such as green tea, coffee, white wine, red wine, and sake (rice wine), on the chemiluminescence intensity as well as the concentrations of sodium hypochlorite and hydrogen peroxide were examined. The chemiluminescence intensities observed with addition of the beverages to the reagents decreased in the following orders; green tea > coffee > red wine > rice wine > white wine (being added to sodium hypochlorite); coffee > white wine > green tea > red wine > rice wine (being added to hydrogen peroxide). It was found that coffee decreased the chemiluminescence intensity (ca. 33% chemiluminescence decrease) without altering the concentrations of sodium hypochlorite or hydrogen peroxide. The cause of the decrease in chemiluminescence with coffee is discussed.     

Study on the flow resistance of the dispersion system of deformable preformed particle gel in porous media using LBM-DEM-IMB method

After being injected into the porous media, the dispersion system of preformed particle gel (PPG) tends to enter high permeability regions and block water channeling passages, which forces the subsequent water to turn to the low permeability regions and thus increases sweep efficiency and enhances oil recovery. However, it is still unclear about the influence factors and the mechanisms how PPG increases water flow resistance, which limits the application of PPG in more oilfields. Therefore, the paper combines the lattice Boltzmann method (LBM), the discrete element method (DEM) and the improved immersed moving boundary (IMB) method to simulate the migration of deformable PPG in porous media. On the basis, the paper quantitatively analyzes the variation law of displacement pressure across the porous media and discusses the influence factors such as the PPG diameter, elasticity modulus and the number concentration. Results indicate that, because of the friction and retention of PPG in pore-throat, the displacement pressure across the porous media during PPG flooding is much higher than that during water flooding. In other words, the existence of PPG increases the flow resistance of injected water. Besides, the displacement pressure is always fluctuant resulting from the continuous process of PPG migration, retention, deformation and remigration. Influence factor analysis shows that the incremental value and fluctuation degree of flow resistance increase with the PPG diameter, elasticity modulus and the number concentration. The study not only provides useful reference for future PPG flooding, but also benefits the development of deformable particle flow theory.     

Effect of molecular association on solubility,diffusion, and permeability in polymeric membranes

The filling‐type membrane is composed of grafted polymer and solvent‐resistant substrate; the calculation of solubility, diffusivity and swelling‐suppression effect by the substrate permits the prediction of solvent permeability. As noted in our previous article, the use of this approach, called membrane design, resulted in accurate prediction of the permeability of aromatic compounds. In this study, the influence of hydrogen bonding on solubility and diffusivity is investigated both theoretically and experimentally. The solubility of chloroform and dichloromethane in poly(acrylate)s increases, and their diffusivity decreases, compared with that estimated without considering the hydrogen‐bonding effect. Solubilities predicted by the lattice‐fluid hydrogen‐bonding (LFHB) model show good agreement with the results of vapor sorption. Comparison of diffusion coefficients measured by vapor permeation with those predicted from free volume theory reveals that the decrease of solvent diffusion coefficient is approximately proportional to the fraction of associated molecules. Fluxes of chloroform and dichloromethane were measured by vapor permeation experiments through filling‐type acrylate membranes, and predictions agree well with experiments. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 171–181, 2000     

内扩散行为对F-T合成反应过程影响的研究

选用Co/ZrO2催化剂,通过改变催化剂颗粒径,在积分固定床反应器上研究了内扩散行为对F-T合成反应过程的影响。以表观活化能、烯/烷比的变化等为依据,考察了内扩散行为对F-T合成反应历程、催化剂活性及产物选择性的影响。催化剂颗粒径不同,内扩散限制程度会发生相应变化。实验结果表明,不同程度的内扩散限制条件下,F-T合成反应历程会有较大差异。当反应开始后,颗粒内孔从"干"到"湿",不同粒径的催化剂颗粒上气态烯/烷比变化均呈"U"型趋势。在固定床反应器上,增加空速通常会有CH4选择性升高、气态烯/烷比略有增加的现象,这是由于内扩散限制未完全消除的缘故。     

Evaluation on dispersion behavior of the aqueous copper nano-suspensions

This paper presents a procedure for preparing a nanofluid which is solid-liquid composite material consisting of solid nanoparticles with sizes typically of 1-100 nm suspended in liquid. By means of the procedure, Cu-H(2)O nanofluids with and without dispersant were prepared, whose sediment photographs and particle size distribution were given to illustrate the stability and evenness of suspension with dispersant. Aiming at the dispersion of nano-Cu is regarded as the guide of heat transfer enhancement, the dispersion behavior of Cu nanoparticles in water were studied under different pH values, different dispersant types and concentration by the method of zeta potential, absorbency and sedimentation photographs. The results show that zeta potential has good corresponding relation with absorbency, and the higher absolute value of zeta potential and the absorbency are, the better dispersion and stability in system is. The absolute value of zeta potential and the absorbency are higher at pH 9.5. Hexadecyl trimethyl ammonium bromide (CTAB) [corrected] and sodium dodecylbenzenesulfonate (SDBS) can significantly increase the absolute value of zeta potential of particle surfaces by electrostatic repulsions, and polyoxyethylene (10) nonyl phenyl ether (TX-10) can form a thick hydration layer on the particle surfaces by steric interference, which leads to the enhancement of the stability for Cu suspensions. In the 0.1% copper nano-suspensions, the optimizing concentrations for TX-10, CTAB [corrected] and SDBS are 0.43, 0.05, and 0.07%, respectively, which have the best dispersion results.     

Temperature effect on the lithium diffusion rate in graphite

The temperature influence on the diffusion coefficient for lithium in graphite is investigated. The activation energy for lithium diffusion in graphite is calculated. Its value is 35 kJ mol^?1.     

Influence of varying electroosmotic flow on the effective diffusion in electric field gradient separations

Recently the use electric field gradient focusing (EFGF) to enhance focusing of proteins has been proposed and explored to provide significant improvement in separation resolution. The objective of EFGF is to focus proteins of specific electrophoretic mobilities at distinct stationary locations in a column or channel. This can be accomplished in a capillary by allowing the electric potential to vary in the streamwise direction. Because the electric field is varying, so also is the electrokinetic force exerted on the proteins and the electroosmotic velocity of the buffer solution. Due to the varying electric field, the Taylor diffusion characteristics will also vary along the column, causing a degradation of peak widths of some proteins, dependent on their equilibrium positions and local velocity distributions. The focus of this paper is an analysis that allows characterization of the local Taylor diffusion and resulting protein band peak width as a function of the local magnitude of the EOF relative to the average fluid velocity for both cylindrical and rectangular channels. In general the analysis shows that as the ratio of the local electroosmotic velocity to the average velocity deviates from unity, the effective diffusion increases significantly. The effectiveness of EFGF devices over a range of protein diffusivities, capillary diameters, flow velocities, and electric field gradient is discussed.     

Effect of dry density on 125I diffusion in GMZ bentonite

Gaomiaozi(GMZ) bentonite is regarded as the favorable candidate backfilling material for a potential repository in China.It is important to understand the diffusion behavior of 125 I in GMZ bentonite and compare the diffusion behavior in GMZ and other types of bentonite like MX-80,Avonlea,etc.Therefore,through-and out-diffusion experiments were conducted to obtain the effective diffusion coefficient(D e) and distribution coefficient(K d).A computer code named Fitting for diffusion coefficient(FDP) was used for the experimental data processing and theoretical modeling.At the dry density of GMZ bentonite from 1600-2000 kg/m 3,the D e values of 125 I were(2.4-20.4) × 10-12 m 2 /s and K d values were constants.At dry density above 1800 kg/m 3,the diffusion behaviors were almost the same,indicating that the anion exclusion was ineffective.Out-diffusion results showed that the species of 125 I may be changed during the diffusion processing.It was probably caused by some organic matters or reducing substances in GMZ bentonite.Since the main composition of bentonite is montmorillonite,similar diffusion parameters were obtained in GMZ and other types of bentonite.The relationship of D e and accessible porosity(acc) could be described by Archie’s law with exponent n = 1.2-2.8 for 125 I diffusion in bentonite,whereas n = 2.0 in GMZ bentonite.Furthermore,bentonite with the dry density of 1800 kg/m 3 was proposed as the backfilling materials used in the construction of high level radioactivity waste repository.     

Numerical investigation of the solute dispersion in finite-length microchannels with the interphase transport

This paper utilizes a combined approach of the convection-diffusion theory and the moment analysis to conduct a comprehensive investigation of the solute dispersion under the influence of the interphase transport in finitely long inner coated microchannels. The present work has threefold novel contributions: (1) The 2D solute concentration contours in the stationary phase are calculated for the first time to facilitate the understanding the role of the interphase transport in the solute dispersion in the mobile phase. (2) The skewness of the elution curves is investigated to guide the control of solute band shape at the channel outlet. (3) The 2D diffusion-convection theory and zero-dimensional (0D) moment analysis complement each other to present a characterization of the solute dispersion behaviors more comprehensive than that by either of the two methods alone. Parametric studies are performed to clarify the effects of four major parameters related to the interphase transport (i.e., stationary phase Péclet number, interphase transport rate, partition coefficient, and stationary phase thickness) on the solute dispersion characteristics. The results from this study provide a straightforward understanding of the effects of interphase transport on the solute dispersion in finitely long microchannels and are of potential relevance to the design and operation of the microfluidics-based analytical devices.     

Microscopic spacial effect on the dispersion polymerization in scCO2

We report for the first time the microscopic spacial effect on the dispersion polymerization of methyl methacrylate (MMA) in supercritical carbon dioxide (scCO₂). A variety of different-sized high-pressure vessels including microstructured holey optical fiber were employed to conduct the polymerization reactions. The molecular weights of the polymer products indicate that the function of the stabilizer and the process of chain growth are not significantly influenced. However, the SEM images show a gradual loss of the controlled morphology for the polymer products in reactors of dimension less than 1 mm under the same reaction conditions. This study provides a better understanding of the mechanism of the dispersion polymerization progress and gives a very important caution on the performance of microreactors.