Channel Intersections Research Articles

Sensitivity analysis of the ECAE process via 2k experiments design

In this work the theoretical solutions based upon the upper-bound theorem recently proposed by Perez and Luri [Mech. Mater. 40 (2008) 617] for the equal channel angular extrusion process (ECAE) are analyzed by performing a 25 central composite factorial analysis. The uniaxial mechanical properties of commercial pure aluminium are considered by assuming isotropic nonlinear work-hardening combined to von Mises and Drucker isotropic yield criteria to predict the ECAE load and the effective plastic strain. From the proposed 25 factorial analysis, the main parameters affecting the ECAE pressure may be ranked as: (1) Friction factor, (2) die channels intersection angle, (3) outer and (4) inner die corners fillet radii and lastly, (5) plunger velocity. Alternatively, the effective plastic strain is mainly controlled by the die channels intersection angle and, in a less extent, by the outer and inner die corners fillet radii.

Pump‐free and low‐cost negative pressure sampling device for rapid sample loading in MCE

A pump-free and low-cost negative pressure sampling device for injecting well-defined non-biased sample plugs into the separation channel of MCE was developed. It was composed of a pipet bulb, a 3-way electromagnetic valve and a single voltage supply at constant voltage. A sub-atmospheric pressure was created by hand-pressing air out of the pipet bulb and retained in it by switching the 3-way electromagnetic valve at cutoff position. During the sample loading stage, the sub-atmospheric pressure in the pipet bulb was applied via a 3-way electromagnetic valve to the headspace of the sealed sample waste reservoir (SW). A pinched sample plug was formed at the channel intersection in less than 0.5 s. Once the 3-way electromagnetic valve was switched to connect SW to ambient atmosphere to release the vacuum in SW, electrophoresis separation was consequently activated under the electric potentials applied. Experimental results demonstrated the pump-free negative pressure sampling device worked well in a wide vacuum degree ranged from -250 to -30 mbar with a satisfactory analytical precision. The sample consumption for each cycle was calculated to be 51-12 nL under the sampling pressure. Theoretical deduction indicates that the volume of the pipet bulb can be further reduced to 1 mL, which is critical for minimizing the sampling device for MCE.

Detailed Determination of the Tl+ Positions in Zeolite Tl−ZSM-5. Single-Crystal Structures of Fully Dehydrated Tl−ZSM-5 and H−ZSM-5 (MFI, Si/Al = 29). Additional Evidence for a Nonrandom Distribution of Framework Aluminum

The structures of the fully exchanged, fully dehydrated zeolites Tl−ZSM-5 (a = 20.064(1), b = 19.946(1), c = 13.416(1) A) and H−ZSM-5 (a = 20.079(1), b = 19.948(1), c = 13.419(1) A) have been determined crystallographically using modestly twinned single crystals and synchrotron X-radiation. They were refined in the orthorhombic space group Pnma to R1 = 0.071 and 0.066 with 3962 and 4278 reflections, respectively, for which Fo > 4σ(Fo). The geometry of the zeolite framework in both crystals (MFI, Al3.2Si92.8O192, Si/Al = 29) is very similar to that in earlier determinations. The ZSM-5 framework and Tl+ positions are described using the four nonequivalent partially overlapping 10-rings (R), the two channel systems (C), the channel intersection volume, and the cove of the ZC. The latter two comprise the conventionally defined cavity. The zigzag (sinusoidal) channel (ZC) passes through R1, R3, and R4; the straight channel (SC) passes through R2. A total of 3.3(2) Tl+ ions per unit cell were found scattered am...

Molecular Simulations of Water and Paracresol in MFI Zeolite - A Monte Carlo Study

Paracresol is a protein-bound toxin that is not efficiently eliminated by the hemodialysis method. Monte Carlo simulations in grand-canonical (GCMC) and canonical ensembles were performed to investigate the adsorption of paracresol and water in silicalite-1 zeolite. GCMC simulations using a configurational-biased algorithm show that four paracresol molecules are adsorbed at the channel intersections per unit cell of silicalite-1. The adsorption isotherms of water with and without the presence of paracresol at the intersections were investigated. A cooperative phenomenon in the process of coadsorption has been observed: at very low chemical potential, paracresol facilitates the penetration of water into silicalite-1. This mechanism is interpreted in terms of the properties of the zeolite and paracresol molecules. A thermodynamic cycle is used to calculate the adsorption energy of paracresol in silicalite-1. The calculated adsorption energy reasonably agrees with the experimental data.

Mapping vortex-like hydrodynamic flow in microfluidic networks using fluorescence correlation spectroscopy

The ability to quickly measure flow parameters in microfluidic devices is critical for micro total analysis system (μTAS) applications. Macrofluidic methods to assess flow suffer from limitations that have made conventional methods unsuitable for the flow behavior profiling. Single molecule fluorescence correlation spectroscopy (FCS) has been employed in our study to characterize the fluidic vortex generating at a T-shape junction of microscale channels. Due to its high spatial and temporal resolution, the corresponding magnitudes relative to different flow rates in the main channel can be quantitatively differentiated using flow time ( τ F) measurements of dye molecules traversing the detection volume in buffer solution. Despite the parabolic flow in the channel upstream, a heterogeneous distribution of flow has been detected across the channel intersection. In addition, our current observations also confirmed the aspect of vortex-shaped flow in low-shear design that was developed previously for cell culture. This approach not only overcomes many technical barriers for examining hydrodynamic vortices and movements in miniature structures without physically integrating any probes, but it is also especially useful for the hydrodynamic studies in polymer-glass based micro -reactor and -mixer.

Grafting of antibodies inside integrated microfluidic–microoptic devices by means of automated microcontact printing

A novel approach to integrating biochip and microfluidic devices is reported in which microcontact printing is a key fabrication technique. The process is performed using an automated microcontact printer that has been developed as an application-specific tool. As proof-of-concept the instrument is used to consecutively and selectively graft patterns of antibodies at the bottom of a glass channel for use in microfluidic immunoassays. Importantly, feature collapse due to over compression of the PDMS stamp is avoided by fine control of the stamp's compression during contact. The precise alignment of biomolecules at the intersection of microfluidic channel and integrated optical waveguides has been achieved, with antigen detection performed via fluorescence excitation. Thus, it has been demonstrated that this technology permits sequential microcontact printing of isolated features consisting of functional biomolecules at any position along a microfluidic channel and also that it is possible to precisely align these features with existing components.

Rapid and efficient isotachophoretic preconcentration in free solution coupled with gel electrophoresis separation on a microchip using a negative pressure sampling technique

We present a novel isotachophoresis–gel electrophoresis (ITP–GE) microchip system designed for rapid and efficient isotachophoretic preconcentration coupled with gel electrophoresis separation by using a negative pressure sampling technique. The overall ITP–GE procedure involves only three steps: sample loading, ITP preconcentration and GE separation and was controlled by a simple and compact negative pressure sampling device, which is composed of a vacuum vessel, a three-way electromagnetic valve and a single high voltage power supply. During the sample loading stage, a negative pressure was applied via a three-way electromagnetic valve in headspace of the two sealed sample waste reservoirs (SWs). A sandwiched sample zone between a leading and a terminating electrolyte zone was formed in the channel intersection in less than 1 s. Once the three-way electromagnetic valve was switched to connect SWs to ambient atmosphere to release vacuum in SWs, ITP preconcentration in free solution and GE separation in the 4% hydroxyethylcellulose (HEC) sieving material were consequently activated under the electric potentials applied. The performance of present approach was evaluated by using DNA fragments as model analytes. Compared to conventional cross microchip GE using electrokinetic pinched injection, an average signal enhancement of 185-fold was obtained with satisfactory resolution. The results demonstrated the ITP–GE approach possessing an exciting potential of high sensitivity and short sampling time with significant simplification in operation and instrumentation.

Adsorption into the MFI zeolite of aromatic molecule of biological relevance. Investigations by Monte Carlo simulations

Adsorption of paracresol and water into the silicalite-1 (MFI) zeolite has been investigated using canonical and grand-canonical Monte Carlo simulations. The most stable sites of adsorption of paracresol are found to be located at the channel intersections. Grand-canonical simulations have shown that at low loading, water molecules adsorb preferably at the vicinity of paracresol molecules, whereas they are also located in the sinusoidal channels as the loading increases. In order to explain the experimental adsorption isotherm observed for the coadsorption of water and paracresol in the MFI zeolite we propose a new concept of apparent adsorption enthalpy that varies with the concentration of the solution. The mathematical expression for the apparent enthalpy is introduced in an adsorption isotherm model. We shall refer to this theoretical isotherm as a non-langmuirian isotherm. The non-linear expression for the apparent adsorption enthalpy accounts for a variable accessibility of the sites of adsorption with respect to the concentration of the solution.

Incorporation and electron transfer of anthracene in pores of ZSM-5 zeolites. Effect of Brønsted acid site density

The sorption course of anthracene (ACENE-3) into Brønsted-acidic medium pore MFI zeolites was monitored by in situ EPR and diffuse reflectance UV-visible absorption over one year. Weighed amounts of solid ACENE-3 were merely exposed to H(n)ZSM-5 (H(n)(AlO(2))(n)(SiO(2))(96-n)), with the following Brønsted acid site (BAS) densities, n = 0.0, 0.17, 0.57, 0.95, 2.0, 3.4, 6.6, dehydrated at 623 K under argon. The weighed amounts correspond to 1 ACENE-3 per zeolite unit cell. ACENE-3 is found to be incorporated as intact molecules in purely siliceous MFI (silicalite-1). Monte Carlo simulations indicate that ACENE-3 lies in the intersection of straight and zigzag channels. In contrast, the presence of BASs on the inner surface of channels induces spontaneous ionization of ACENE-3 (ionization potential = 7.44 eV). The charge separation as ACENE-3*(+)@H(n)ZSM-5*(-) is caused by the strong Coulombic field gradient of Si-O(-)(H(+))-Al BAS in the absence of any Lewis acid site. The rate and yield of ionization are found to increase dramatically with BAS density increase. The stabilization of ACENE-3*(+)@H(n)ZSM-5*(-) is explained by the tight fit between the rod-shape ACENE-3 and the channel dimensions and especially by the compartmentalization of ejected electrons as AlO(4)H*(-) centers away from the initial site of ionization. The final charge recombination occurs after more than one year and leads to ACENE-3 occluded in the straight channel in close proximity to BAS without any protonation of ACENE-3 (pK(a) = -13.5).

Exploitation of a microfluidic device capable of generating size-tunable droplets for gene delivery

This study presents a new microfluidic chip that generates micro-scale emulsion droplets for gene delivery applications. Compared with conventional methods of droplet formation, the proposed chip can create uniform droplets (size variation <7.1%) and hence enhance the efficiency of the subsequent gene delivery. A new microfluidic chip was developed in this study, which used a new design with a pneumatic membrane chamber integrated into a T-junction microchannel. Traditionally, the size of droplets was controlled by the flow rate ratio of the continuous and disperse phase flows, which can be controlled by syringe pumps. In this study, a pneumatic chamber near the intersection of the T-junction channel was designed to locally change the flow velocity and the shear force. When the upper air chamber was filled with compressed air, the membrane was deflected and then the droplet size could be fine-tuned accordingly. Experimental data showed that using the new design, the higher the air pressure applied to the active tunable membrane, the smaller the droplet size. Finally, droplets were used as carriers for DNA to be transfected into the Cos-7 cells. It was also experimentally found that the size of the emulsion droplets plays an important role on the efficiency of the gene delivery.

Microstructures and recrystallization behavior of severely hot-deformed tungsten

When coarse-grained (CG) tungsten (W) is heavily worked by equal-channel angular extrusion (ECAE), the grain size is reduced to the ultrafine-grained/nanocrystalline regimes (UFG/NC) and the strength and ductility increase. Because of the brittle nature of CG W, the material must be hot-extruded, and, if the temperatures are near the recrystallization temperature ( T rc), gains in properties may not be maximized. In this study, the recrystallization behavior of ECAE-processed CG W is examined as a function of the imparted strain (i.e., number of extrusions) and the hot-working extrusion temperature. Up to four ECAE passes were performed in tooling with a 90° channel intersection, and at temperatures of 1000 °C or 1200 °C. Subsequent 60 min annealing of the worked material to 1600 °C allowed for the determination of T rc. Vickers microhardness measurements and scanning electron microscopy, were used to characterize the microstructures in the as-worked and recrystallized states. The ECAE-processed W shows increased microstructural break-up and refinement with increasing strain and decreasing hot-working temperature in the fully worked state. T rc was determined to be ∼1400 °C, which is nearly independent of the number of extrusions and the working temperature. These results show that if ECAE is accomplished below 1400 °C (i.e., at 1000 °C or lower) the attractive properties of the UFG/NC-worked W may be retained. Specifically, below 1000 °C, with increasing strain imparted to the material, high hardness values with a concomitant grain size refinement (∼350 nm) could be expected.

Molecular Interplay of Cations and Nonpolar/Polar Sorbates in Titanosilicate ETS-10

Molecular simulations are performed to investigate the interplay of the nonframework Na + cations and the nonpolar (CH 4 )/polar (H 2 O) sorbates separately in titanosilicate ETS-10. Five types of Na + cations are identified in the ETS-10 framework based on the different geometric positions and site energies. Located in the 12-ring channels and with the lowest site energy, type V cations show substantially greater mobility than type I-IV cations that remain essentially static in the 7-ring channels and the 7- and 12-ring channel intersections. The predicted adsorption isotherms of both CH 4 and H 2 O in Na-ETS-10 agree well with the literature data. Two and three adsorption sites are observed for CH4 and H 2 O, respectively. Compared to CH 4 , H 2 O exhibits a greater extent of adsorption and a much smaller diffusivity. Diffusion of CH 4 drops monotonically as loading increases due to the steric hindrance. The interplay between Na + and CH 4 is not pronounced because of the weak van der Waals interactions, and the number of each type of Na + ion does not change appreciably upon the adsorption of CH4. However, the interplay is remarkable between Na + and H 2 O as a consequence of strong electrostatic interactions. Redistribution of Na + ions is observed upon the adsorption of H 2 O, in which the number of type V cations increases while other types slightly decrease. As the loading increases, diffusion of H 2 O initially rises and then drops as largely determined by H 2 O in the 12-ring channels. The mobility of Na + follows H 2 O in the 7- and 12-ring channel intersections due to the formation of Na + -H 2 O complex.

Droplet Formation Utilizing Controllable Moving-Wall Structures for Double-Emulsion Applications

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> The formation of microscale single- and double-emulsion droplets with various sizes is crucial for a variety of industrial applications. In this paper, we report a new microfluidic device which can actively fine-tune the size of single- and doubleemulsion droplets in liquids by utilizing controllable movingwall structures. Moreover, various sizes of external and internal droplets for double emulsions are also successfully formed by using this device. Three pneumatic side chambers are placed at a T-junction and flow-focusing channels to construct the controllable moving-wall structures. When compressed air is applied to the pneumatic side chambers, the controllable moving-wall structures are activated, thus physically changing the width of the microchannels. The size of the internal droplets at the intersection of the T-junction channel is then fine-tuned due to the increase in the shear force. Then, the internal droplets are focused into a narrow stream hydrodynamically and finally chopped into double-emulsion droplets using another pair of moving-wall structures downstream. For single emulsions, oil-in-water droplets can be actively fine-tuned from 50.07 to 21.80 <formula formulatype="inline"><tex>$\mu\hbox{m}$</tex> </formula> under applied air pressures from 10 to 25 psi with a variation of less than 3.53%. For a water-in-oil single emulsion, droplets range from 50.32 to 14.76 <formula formulatype="inline"><tex>$\mu\hbox{m}$</tex></formula> with a variation of less than 4.62% under the same applied air pressures. For double emulsions, the sizes of the external and internal droplets can be fine-tuned with external/internal droplet diameter ratios ranging from 1.69 to 2.75. The development of this microfluidic device is promising for a variety of applications in the pharmaceutical, cosmetics, and food industries. <formula formulatype="inline"><tex>$\hfill$</tex></formula>[2007-0230] </para>

Computer Simulation of Kinematics of Plastic Flow and the Deformed Condition of Metal at Processes Equal-Channel Angular Pressing

Object of researches in the given paper is the technological process of obtaining from carbon steel method equal-channel angular extrusion (ECAE) on one pass. The purpose of theoretical research is the working of recomdations on projection of the process with the help of a designed technique of simulation of process ECAE in CAE systems. Calculations were done under variable conditions ECAE over the range changes of parameters: a corner of intersection of channels Ф from 90 up to 150 grades, speed of driving press from 0,05 m/s up to 0,2 m/s, temperature from 20°С up to 600°С. As a result quantitative links of local parameters (stresses, strains and temperature) are established with geometrical and technological ECAE parameters to one separate pass. Regularities of change of parameters to ECAE process of cylindrical preforms in diameter of 20 mm and 30 mm are established (steel 0,15%С), are investigated; character of change of a tension in the instrument and power conditions of the process was studied.

MTBE adsorption and diffusion in silicalite-1

Vapor phase adsorption isotherms of methyl tertiary butyl ether (MTBE) in silicalite-1 at temperatures in the range of 298–600K were measured using a gravimetric analysis system. A maximum saturation loading of 4mol/u.c. was measured. The diffusion coefficients as a function of loading at each temperature were calculated from the differential adsorption uptake data. Diffusivities were observed to increase with loading up to about 1mol/u.c., possibly due to significant adsorption on external surfaces of the particles. Above this value, diffusivities became independent of loading. Additionally, Grand Canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations were carried out to estimate the adsorption isotherms and the diffusion coefficients, and the results were compared to those of the experiments. The GCMC simulation results were in reasonable agreement with the experimental data, especially at higher pressures and lower temperatures, where the contribution of interparticle and surface adsorption became marginal. From the MD simulations, MTBE molecules were seen to move very slowly inside the crystal since they spend time at the channel intersections. These simulations were also extended to loadings higher than 4mol/u.c., in order to shed light on the higher adsorption capacities from aqueous solutions previously reported in the literature. The mobility of the MTBE molecules was observed to increase with loading beyond the value of 4mol/u.c., which deserves further investigation.

The role of the friction during the equal channel angular pressing of an IF-steel billet

It is well known that high levels of friction induce adherence effects in materials processed by equal channel angular pressing (ECAP) promoting some degree of heterogeneity along the deformation zone. In the present paper, the role of the friction in relation of die geometry considering frictionless, ideal lubrication and severe friction conditions of an interstitial free (IF) steel deformed by ECAP technique using plane strain finite element models was investigated in details. The analysis of adherence at the billet–die contact region during only one pass of deformation was carried out in a quasi-static form at room temperature. Independent of the die channels intersection angle (90° or 120°) analyzed an adherence phenomenon was observed under determined friction conditions. It can be concluded that it is necessary to establish an upper limit to the friction coefficient in order to avoid the adherence effect in two-dimensional finite element simulations.

Solute Transport in Porous Media. Media with Capillaries as Voids

We study solute transport in porous media with periodic microstructures consisting of interconnected thin channels. We discuss a local physical mechanism that occurs at the intersections of channels and promotes mixing of the solute with the solvent (i.e., the host liquid). We identify the parameter regime, where this mechanism is the dominant cause of dispersion, and obtain the effective or macroscopic transport equation that the concentration of solute satisfies when the medium is subjected to a time periodic applied pressure gradient. We conclude with illustrative examples.

Solid−State NMR Determination of the Zeolite ZSM-5/ortho-Xylene Host−Guest Crystal Structure

Solid-state NMR spectroscopy has been used to successfully determine the complete three-dimensional structure of the ortho-xylene−ZSM-5 zeolite complex, using complexes of three different specifically deuterated ortho-xylene molecules. The structures determined from these, at two different temperatures, using both cross polarization (CP) and CP drain experiments all agree. The ortho-xylene molecule is located at the channel intersection with one ring carbon−methyl carbon bond oriented along the straight channel while the other ring carbon−methyl carbon bond points toward the zigzag channel.

A micropillar‐integrated smart microfluidic device for specific capture and sorting of cells

An integrated smart microfluidic device consisting of nickel micropillars, microvalves, and microchannels was developed for specific capture and sorting of cells. A regular hexagonal array of nickel micropillars was integrated on the bottom of a microchannel by standard photolithography, which can generate strong induced magnetic field gradients under an external magnetic field to efficiently trap superparamagnetic beads (SPMBs) in a flowing stream, forming a bed with sufficient magnetic beads as a capture zone. Fluids could be manipulated by programmed controlling the integrated air-pressure-actuated microvalves, based on which in situ bio-functionalization of SPMBs trapped in the capture zone was realized by covalent attachment of specific proteins directly to their surface on the integrated microfluidic device. In this case, only small volumes of protein solutions (62.5 nL in the capture zone; 375 nL in total volume needed to fill the device from inlet A to the intersection of outlet channels F and G) can meet the need for protein! The newly designed microfluidic device reduced greatly chemical and biological reagent consumption and simplified drastically tedious manual handling. Based on the specific interaction between wheat germ agglutinin (WGA) and N-acetylglucosamine on the cell membrane, A549 cancer cells were effectively captured and sorted on the microfluidic device. Capture efficiency ranged from 62 to 74%. The integrated microfluidic device provides a reliable technique for cell sorting.

A SANDWICH-INJECTION METHOD FOR MICROCHIP ELECTROPHORESIS

In microchip electrophoresis (μ-CE), sample injection is generally achieved through cross, double-T, or T-form injector structures. In these reported approaches, the separation efficiency and detection sensitivity of μ-CE is significantly influenced by the shape and size of the sample plug introduced into the separation channel or sample leakage in separation phase. Here, we present a sandwich-injection method for controlling discrete sample injection in μ-CE. This method involves four accessory arm channels in which symmetrical potentials are loaded to form a unique parallel electric field distribution at the intersection of sample and separation channels. The parallel electric field effectuate a virtual wall to confine the shape of a sample plug and depress the spreading of the sample plug at the junction of sample and separation channels, and also prevent sample leakage during separation step. The key features of this method are the ability to inject well-defined sample plugs at the original sample concentration and the ability to control the sample plug size. The virtues of the novel injection technique were demonstrated with numerical models and validated with fluorescence visualizations of electrophoretic experiments.