The mechanisms of flow of a face-centred cubic micellar phase were investigated using small-angle X-ray scattering (SAXS)
for samples under either steady or oscillatory shear in two different geometries: Couette cell and planar shear sandwich.
The system studied was a gel formed by a poly(oxyethylene)–poly(oxypropylene) diblock copolymer in water. SAXS indicated that
under steady shear in a Couette cell, flow occurs via sliding of hexagonal close-packed (hcp) layers with a close-packed [110]
direction along the shear direction. Under oscillatory shear in the planar shear sandwich, coexistence between this orientation
and one in which the hcp layers are rotated by 30° (and flow is in a [211] direction) was observed; however, when subject
to oscillatory shear in the Couette cell, flow only occurred along a [110] direction. This observation of flow in a non-close-packed
direction may be due to alignment induced by the walls of the shear sandwich.
Received: 24 February 2001 Accepted: 21 March 2001 相似文献
The migration of emulsion droplets under shear flow remains a largely unexplored area of study, despite the existence of an extensive literature on the analogous problem of solid particle migration. A novel methodology is presented to track the shear-induced migration of emulsion droplets based on magnetic resonance imaging (MRI). The work is in three parts: first, single droplets of one Newtonian fluid are suspended in a second Newtonian fluid (water in silicone oil (PDMS)) and are tracked as they migrate within a Couette cell; second, the migration of emulsion droplets in Poiseuille flow is considered; third, water-in-silicone oil emulsions are sheared in a Couette cell. The effect of (a) rotational speed of the Couette, (b) the continuous phase viscosity, and (c) the droplet phase concentration are considered. The equilibrium extent of migration and rate of migration increase with rotational speed for two different emulsion systems and increased continuous phase viscosity, leads to a greater equilibrium extent of migration. The relationship between the droplet phase concentration and migration is however complex. These results for semi-concentrated emulsion systems and wide-gap Couette cells are not well described by existing models of emulsion droplet migration. 相似文献
A transition from a body-centred cubic structure at room temperature to a face-centred cubic structure at higher temperature
has been observed in a solution of a poly(oxyethylene)-poly(oxybutylene) diblock copolymer. The ordered micellar structures
were confirmed using small-angle X-ray scattering by preparing oriented domains via steady shearing in a Couette cell. The
effect of shear in generating highly oriented, twinned cubic domains is discussed.
Received: 13 January 1998 Accepted: 22 January 1998 相似文献
In this paper, the ordering in concentrated charge stabilized colloidal dispersions is considered. Despite the impressive Bragg reflections obtained for shear ordered dispersions by light (LS), small-angle neutron (SANS), and small-angle X-ray scattering (SAXS), a number of open questions remain. Sheared dispersions are usually ordered in layers. For such systems, two questions arise: (1) What is the structure in a layer? (2) What is the stacking structure perpendicular to the layers? The second question requires a method to determine the structure perpendicular to the layers. Although originally interested only in structural aspects, we were forced to consider different methods. Two methods are treated both applicable to neutron and X-ray scattering from concentrated dispersions. One has been used by physicists and chemists for many years to determine the structure of crystals by sample rotation. In colloid science, we have used it previously in neutron and X-ray scattering. A second method is treated here which can be applied in small-angle scattering from a Couette cell. It gives the scattering intensity in a certain direction without sample rotation. Although very useful with the Couette cell, it cannot be found in any of the well-known references on colloid science. A theoretical explanation and experimental examples obtained by synchrotron X-ray scattering from a Couette cell are given in the paper. 相似文献
Experiments of flow birefringence have been performed on a concentrated solution of CTAB submitted to shear in a Couette cell. Qualitative observations of the flow in the annular gap of the Couette device let us clearly see that the flow is divided into two layers when the shear rate exceeds a critical value. This shear banding structure is shown on a set of photographs. The extinction angle and the retardation were measured as a function of the shear rate
for different temperatures. The results are in agreement with the predictions of the shear banding theory. 相似文献
This article presents a new design of flow-orientation device for the study of bio-macromolecules, including DNA and protein complexes, as well as aggregates such as amyloid fibrils and liposome membranes, using Linear Dichroism (LD) spectroscopy. The design provides a number of technical advantages that should make the device inexpensive to manufacture, easier to use and more reliable than existing techniques. The degree of orientation achieved is of the same order of magnitude as that of the commonly used concentric cylinders Couette flow cell, however, since the device exploits a set of flat strain-free quartz plates, a number of problems associated with refraction and birefringence of light are eliminated, increasing the sensitivity and accuracy of measurement. The device provides similar shear rates to those of the Couette cell but is superior in that the shear rate is constant across the gap. Other major advantages of the design is the possibility to change parts and vary sample volume and path length easily and at a low cost. 相似文献
The structure and flow behaviour of a micellar “cubic” phase is studied, using small-angle X-ray scattering (SAXS) and constant
stress rheometry on a poly(oxyphenylethylene)–poly(oxyethylene) diblock copolymer in water. The predominant structure is a
face-centred cubic (fcc) array of spherical micelles, which under shear undergoes layer sliding to give a scattering pattern
from stacked hexagonal close-packed layers. A detailed analysis of the SAXS data indicates the presence of a fraction of grains
with a structure distorted from a fcc phase. The additional reflections that characterize this structure can be indexed to
a rhombohedral unit cell, space group R3ˉm, with the same volume as the fcc unit cell. The rhombohedral unit cell corresponds to a cubic cell that has been “stretched”
along a [111] direction, and it is suggested that such a structure results from the gradient in shear velocity in the Couette
cell employed. Shearing at high shear rates leads to a “smearing out” of the reflections, but upon cessation of shear under
these conditions a highly oriented SAXS pattern is obtained, which confirms the persistence of rhombohedral ordering. The
shear-induced changes in orientation are correlated to a plateau observed in the stress plotted against shear rate, such a
plateau being a sign of inhomogeneous flow.
Received: 8 September 2000 Accepted: 29 November 2000 相似文献
The behavior of Couette flow of nanofluids composed of negatively-charged nanoparticles dispersed in aqueous NaCl solutions is studied theoretically. The equation for calculating the Couette flow velocity profiles is derived. The induced electric fields and velocity profiles are calculated as a function of key parameters including nanoparticle size and volume fraction. We have found for the first time that the velocity profile of nanofluids containing charged nanoparticles deviates significantly from the classical linear velocity profile for Couette flow. This previously unseen flow phenomenon is attributed to the dominance of the electric field strength induced by the flow of charged nanoparticles. This new mechanism of nanoparticle-induced microfluidic transport could lead to novel microfluidic and tribological applications. 相似文献
Bicelles are excellent membrane-mimicking hosts for a dynamic and structural study of solutes with NMR, but the magnetic fields required for their alignment are hard to apply to optical conditions. Here we demonstrate that bicellar mixtures can be aligned by shear forces in a Couette flow cell, to provide orientation of membrane-bound retinoic acid, pyrene and cytochrome c (cyt c) protein, conveniently studied with linear dichroism spectroscopy. 相似文献
The dynamic viscosity of six anhydrous silicate melts, obtained by fusing rocks collected from the Department of Energy's Nevada Test Site, has been measured from 1120 to 1688°C under atmospheric pressure using a rotational cup viscometer of the Couette type. The melts exhibit Newtonian behavior in this temperature interval. Melt viscosities decrease in the order: tuff >; alluvium 2; basalt. Activation energy for viscous flow in the interval 1120–1688°C ranges from 268 to 393 kJ. 相似文献
Long molecules such as fibrous proteins are particularly difficult to characterise structurally. We have recently designed a microvolume Couette flow linear dichroism (LD) cell whose sample volume is only 20-40 microL in contrast to previous cells where the volume of sample required has typically been of the order of 1000-2000 microL. This brings the sample requirements of LD to a level where it can be used for biological samples. Since LD is the difference in absorption of light polarised parallel to an orientation direction and perpendicular to that direction, it is the ideal technique for determining relative orientations of subunits of e.g. fibrous proteins, DNA-drug systems, etc. For solution phase samples, Couette flow orientation, whereby the sample is sandwiched between two cylinders, one of which rotates, has proved to be the optimal technique for LD experiments in many laboratories. Our capillary microvolume LD cell has been designed using extruded quartz rods and capillaries and focusing and collecting lenses. We have developed applications with PCR products, fibrous proteins, liposome-bound membrane proteins, as well as DNA-dye systems. Despite this range of applications, to date there is nothing reported in the literature to enable one to validate the performance of Couette flow LD cells. In this paper we establish validation criteria and show that the data from the microvolume cells are reproducible, vary by less than 1% with sample reloading, follow the Beer-Lambert law, and have signals linear in voltage over a wide voltage range. The microvolume cell data are consistent with those from the large-volume cells for DNA samples. Surprisingly, upon extending the wavelength range by adding the intercalator ethidium bromide, the spectra in the microvolume and large-volume cells differ by a wavelength dependent orientation parameter. This wavelength variation was concluded to be the result of Taylor-vortices in the large-volume cells which have inner rotating cylinders in our laboratory. Thus the microvolume LD cells can be concluded to provide better data than our large-volume LD cells, though the latter are still to be preferred for titration series as it is extremely difficult to add sample to the capillary cells without introducing artefacts. 相似文献
Summary: Shear‐induced phase behavior of poly(ethylene oxide‐b‐(DL ‐lactic acid‐co‐glycolic acid)‐b‐ethylene oxide) (PEO‐PLGA‐PEO) triblock copolymers in water is investigated using rheology and small‐angle neutron scattering equipped with an in situ Couette shear cell. For gels formed by the macroscopic phase separation, the steady shear experiment reveals that the flow‐induced anisotropy on a nanometer length scale at a critical shear rate and the phase separation on a larger length scale are successively induced with a further increase in the shear rate. In particular, the hard gels show a memory effect inscribed by a pre‐high shear in contrast to the soft gels.
2D SANS patterns clearly show the memory effect of the hard gels at a pre‐high shear. 相似文献
Well-defined triolein emulsions of low polydispersity were prepared by shearing a crude emulsion in a modified Couette cell, resulting in radii in the range of 300 to 900 nm. These emulsions were used as synthetic substrates for lipoprotein lipase, a key enzyme for the hydrolysis of serum triacylglycerols. The change in radius with time was studied with on-line static light scattering at 37 degrees C. An optimum radius of about 750 nm was found for this reaction. 相似文献
The aim of this study was to develop a chromatographic method, as a substitute for enzyme-linked immunosorbent assays, for the rapid and simultaneous detection of IgG, insulin, and transferrin present in a cell culture medium. Conjoint liquid chromatography (conjoint LC) using monolithic disks was applied for this purpose. An anion-exchange disk was combined with a Protein G affinity disk in a preparative HPLC system. IgG bound to the Protein G disk, whereas transferrin and insulin were captured on the quaternary ammonium (QA) disk. Using this method, it was possible to simultaneously determine the concentrations of IgG, transferrin, and insulin in the cell culture medium. Thus, conjoint LC could be used for the rapid and simultaneous detection of different proteins present in a cell culture medium. 相似文献
The possibility of preconcentrating vanadium, chromium, copper, and nickel by the simultaneous adsorption in a flow-through
mode on a two-layer adsorbent and the determination of metal ions by diffuse reflectance spectroscopy was studied. The adsorbent
was made of a polyacrylonitrile fiber, one layer of which was filled with an AV-17 anion exchanger (PANV-AV-17), while another
layer, with a KU-2 cation exchanger (PANV-KU-2). The procedure was based on the simultaneous preconcentration of vanadium
and chromium on the first disk and nickel and copper on the second disk, by pumping the analyzed solution through both disks
in a flow-through cell. Then, vanadium was determined on the disk of PANV-AV-17 with 8-hydroxyquinoline-5-sulfonic acid in
0.1 M HCl; next, chromium was determined with 1,5-diphenylcarbazide; the complex of vanadium was decomposed by 0.5 M H2SO4 and ascorbic acid. In the PANV-KU-2 disk, nickel was determined with dimethylglyoxime and then copper was analyzed with sodium
diethyldithiocarbamate; the complex of nickel was decomposed with 1 M HCl. The selectivity factors were determined. A procedure
was developed for the dynamic adsorption-spectroscopic determination of the following elements present simultaneously (μg/mL):
V, 0.01–0.05; Cr, 0.002–0.015; Ni, 0.02–0.10; and Cu, 0.02–0.15. The results of analysis of model solutions are presented
for different component ratios, RSD < 20%. 相似文献
The sensor is based on silver and platinum electrodes with an intervening silver iodide disk as a solid electrolyte. The small disk (13 mm diameter) is easily made by pressing (7000 kg cm-2) silver powder, silver iodide and a platinum gauze in layers in a die. The detector cell containing the disk is thermostated at 120 ± 0.1°C. When sample gas at 30 ml min-1 impinges on the platinum cathode, the current flowing in the external circuit is linearly related to the concentration of ozone and/or nitrogen dioxide up to 0.5 ppm from the detection limit of 0.5 ppb for ozone or 1 ppb for nitrogen dioxide. 相似文献
Abstract The application of a rotating disk working electrode to controlled potential coulometry and the electroreduction of copper(II) at a copper disk electrode are described. The electrode has the advantages of reproducible and calculable mass transfer conditions and electrolysis currents which are relatively free of stirring noise. The evaluation of the diffusion coefficient of the electroactive species from the coulometric current-time curve and the fabrication of the electrolysis cell and electrode are also described. 相似文献
The determination of three elements from a single sample on a two-layer support in the flow mode was studied. One layer is a disk of a fiber material filled with the AV-17 anion exchanger, and the other is a disk of a material filled with the KU-2 cation exchanger. The method is based on the simultaneous preconcentration of elements by pumping a test sample through two disks in a flow cell, the separation of layers, and subsequent detection of chromium on the support filled with AV-17 using 1,5-diphenylcarbazide. The support filled with KU-2 is used for the sequential determination of nickel with dimethylglyoxime and copper with sodium diethyldithiocarbamate in 1 M HCl. The nickel dimethylglyoximate is decomposed under the action of 1 M HCl; its 10-fold amounts do not interfere with the determination of copper. This method provides the determination of chromium, copper, and nickel at a level below the maximum permissible concentration for potable water; at the ratio Cr : Ni : Cu = 1 : 10 : 20, RSD is lower than 10%. The time of the determination of the three elements from a single sample is 25–30 min. 相似文献