Nuclepore membranes

Adsorption Isotherms. The adsorption isotherms were determined using the serum-replacement adsorption or desorption methods (7). For the adsorption method, the latex samples (50 or 100 cm 2% solids) containing varying amounts of PVA were equilibrated for 36 hours at 25°C, placed in the serum replacement cell equipped with a Nuclepore membrane of the appropriate pore size, and pressurized to separate a small sample of the serum from the latex. For the desorption method, the latex samples (250 cm 2.5% solids) were equilibrated for 36 hours at 25°C and subjected to serum replacement with DDI water at a constant 9-10 cm /hour. The exit stream was monitored using a differential refractometer. The mean residence time of the feed stream was ca. 25 hours. It was assumed that equilibrium between the adsorbed and solute PVA was maintained throughout the serum replacement. For both methods, the PVA concentration was determined using a An-C calibration curve. 

Pores with a very regular, linear shape can be produced by the track-etch method (Quinn et al. 1972). Here a thin layer of a material is bombarded with highly energetic particles from a radioactive source. The track left behind in the material is much more sensitive to an etchant in the direction of the track axis than perpendicular to it. So etching the material results in straight pores of uniform shape and size with pore diameters ranging between 6 nm and 1200 nm. To avoid overlap of pores only 2-5% of the surface can be occupied by the pores. This process has been applied on polymers (e.g. Nuclepore membranes) and on some inorganic systems like mica. Membranes so obtained are attractive as model systems for fundamental studies. 

The Nuclepore membranes used for this work were standard polyester membranes 25 mm in diameter. The pore number, N, is calculated from the pore density and the effective flowing area of... 

In order to estimate the dimensionless parameters D and to in (6.3.9), (6.3.11) assume the following reasonable values for the parameters of the system (for the filter we adopt values characteristic for the Nuclepore membrane employed in [7]-[9]). 

Characterization of Latex Particles with Respect to Carboxyl Distribution. All latex samples were cleaned by the serum replacement technique (10). Diluted latex sample (3% by weight) was placed in the cell confined with a Nuclepore membrane and distilled deionized water was fed into the cell from a reservoir placed at 1.5 meters above the cell. The serum from the cell exit was collected and monitored with conductance measurement. 

Nuclepore membranes of defined pore sizes 400, 200, 100 nm (Sterlitech Corp., Kent, WA, USA or Sterico AG, Wangen, Switzerland). 

The screened broth was then compared with unscreened broth in polishing by the axial filter wrapped with 5 ym Nuclepore membranes. Figure 8 compares the fluxes. Neither are as high as one might hope, though the screened feed values appear... 

B42. Bignold, L. P., Ferrante, A., and Haynes, D. R. Studies of chemotactic, chemotactic movement-inhibiting and random movement-inhibiting effects of interleukin-1 alpha and beta, tumour necrosis factors alpha and beta and interferon gamma on human neutrophils in assays using sparse-pore polycarbonate (Nuclepore) membranes in the Boyden chamber. Int. Arch. Allergy Appl. Immunol. 91, 1-7 (1990). 

Membrane structures for MF include screen filters, which collect retained matter on the surface, and depth filters, which trap particles at constrictions within the membrane. Depth filters have a much sharper cutoff, resulting in enhanced separation factors. For example, a Nuclepore membrane of type 2 can separate a male-determining sperm from a female-determining sperm (Seader and Henley, 2006). Nuclepore MF membranes come in pore sizes from 0.03 to 8.0 microns with water permeate flux rates, at 294 K and a transmembrane pressure difference of 70 kPa, ranging from 15 to 350,000 L/m2-h. 

Sheldon and Sutcliffe (17) and Sheldon (16) used a Coulter Counter to examine the particle retention of nylon and stainless-steel meshes, Whatman glassfiber filters, and Nuclepore and Millipore membranes. With light particle loading and low vacuum (12-13 cm of mercury), the Millipore and glassfiber filters retained particles of much smaller diameter than the manufacturers stated pore size. The meshes and Nuclepore membranes showed 50% retention of particles (by number) at their manufacturers reported pore sizes. 

Cranston and Buckley (18) examined the retention of latex beads, kaolinite clay, dissolved organics, and dissolved inorganics on five different membrane and fiber filters. Their interest was to select filters that gave the best particle retention and the most consistent gravimetric results. The Nuclepore membrane performed best except for retention of dissolved humic materials Nuclepore membranes were particularly good for not retaining dissolved salts from seawater filtration. 

Particle Sizing by Vacuum Membrane Filtration. In the original plan for this research, particle fractionation by sieving, that is, using microscreens (10, 20, or 30 /xm) and Nuclepore membranes, was anticipated to be a viable means for particle sizing. Microscreens are available in both nylon and stainless steel. The Nuclepore membranes are thin polycarbonate sheets with very uniform round holes etched through them available pore diameters decrease in size from 8.0 /xm. 

Figure 7. Solids retention hy Nuclepore membranes loaded with a 100 1 dilution of sludge with sludge filtrate ((D) 1.0 pm (A) 8.0 pm)...

FAissT Particles in Digested Sewage Sludge of Nuclepore Membranes... 

Particle sizing by filtration was unsuccessful because of pore clogging of the Nuclepore membrane. Results of filtration experiments confirm the results of work cited previously and lead to two major conclusions (1) vacuum membrane filtration is not an acceptable means of particle sizing and (2) membranes with pore sizes of 1 /xm or less should be used for suspended-solids analysis. 

There are two general types of membrane, symmetrical and asymmetrical. Both sides of a symmetrical membrane are the same, therefore, either side can be used in filtration. Symmetrical membranes have very uniform pores, such as a Nuclepore membrane. The sides of the asymmetrical membrane, unlike the symmetrical membrane, are very different. One side has very small openings that branch out through the membrane to form a very large opening on the other side the performance of the filtration depends upon which side is used. This membrane has a tendency to load up with solids. 

If a sample is visibly turbid, it must be centrifuged or filtered through a well-rinsed 0.4 pm Nuclepore membrane filter. Samples containing more than lS0 nnol/L of sulphide are treated as follou ... 

Figure 6.4. Using a Nuclepore membrane filter, DeBlois and co-workers made a resistazone counter with an orifice small enough to measure the size of viruses. (Reprinted from [38], John Wiley and Sons.)...

In addition, the orientational distribution of the liquid crystal is affected by surface effects. Deuterium NMR can be applied to study the director field in microcavities [103, 107-110, 112]. Figure 9 shows deu-teron NMR spectra of selectively deuterat-ed 4- -pentyl-4 -cyanobiphenyl confined in parallel polyimide-modified cylindrical pores of a Nuclepore membrane. The suggested models for the director field in such cylindrical pores with parallel anchoring. 

After the MB release study, the sample was removed and air-dried to constant weight. It was then crushed to fine powder and transferred quantitatively into a flask. The volume of the suspension was adjusted to 500 mL, and 1 mL was withdrawn to determine the residual amount of MB, if any, by spectrophotometry. The flask was then warmed to 60 C to dissolve the remaining PVA derivative. The hot suspension was filtered through a Nuclepore membrane (0.2 micron porosity), and the weight of the insoluble PCL was obtained after air-Drying to constant weight. In a control experiment, pellet discs of a known PVA derivative to PCL ratio were assayed. The amount of the dissolved PVA recovered was determined by-evaporating an aliquot of the filtrate to dryness. 

Liabastre and Orr [52] examined graded series of controlled pore glasses and Nuclepore membranes by electron microscope and mercury porosimetry in o er to determine compressibilities and explore the reason for hysteresis. 

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