Void volume membrane

Porous membranes have been prepared by leaching an additive from films and tubes of PCL (64,72). The procedure involves extrusion or casting blends of PCL and Pluronic F68, the latter being an FDA-approved oxyethylene-co-oxypropylene triblock copolymer. Treatment of the phase-separated blend with aqueous acetone or aqueous alcohols causes both swelling of the polymer and extraction of the Pluronic F68. The induced pore size and void volume may be controlled by the time, temperature, and solvent composition. 

The lowest theoretical interparticular volume of perfectly packed uniformly sized spherical beads is calculated to be about 26% of the total available volume. In practice, even the best packed columns still contain about 30-40% void volume in addition to the internal porosity of the beads. The problem of interparticular volume does not exist in systems in which a membrane is used as the separation medium. Both theoretical calculations and experimental results clearly document that membrane systems can be operated in a dead-end filtration... 

Although Tyrann-M/E and even conventional membranes are superior to the new polyamide and polyfvinylidene fluoride) membranes with respect to flow rates and filtration capacities, the latter two are more suitable for filtration of most (but not all) organic solvents and, partially as a result of their lower void volumes (Table IV) exhibit mechanical and thermal properties which are generally superior to those of the cellulosics. It should also be noted that in the special case of fiber-reinforced membranes, the mechanical properties are predominantly functions of the embedded fibers rather than of the membrane structu reverse. 

The device will have to hold within its volume a colony of hepatic cells and perhaps a hydrogel membrane and still have enough void volume to allow physiologically correct blood flow. Hepatic diameters spheroids are about 100 pm." In order for a scaffold to contain a significant number of hepatic cells and still be able to handle the flow rates required, it must have a large void volume. 

The extent of contact between the reactant(s) and the catalyst is often believed to be very important in the reactor performance but is difficult to determine. This problem is complicated by several factors. In gas/vapor reactions, the volumetric flow rate may change as the reaction proceeds. Furthermore, the true void volume of the catalyst bed or membrane pores (and therefore, the void fraction of the reactor) is not easy to measure. 

The introduction of the IonPac AS5 separator column significantly facilitated the analysis of polarizable anions. Reducing the hydrophobicity of the functional groups bonded to the latex beads makes it possible to elute polarizable anions using a standard mixture of sodium bicarbonate and sodium carbonate. To minimize adsorption phenomena, some p-cyanophenol is added to the eluent mixture. The influence of this species on the peak form is evident in Fig. 3-18. The peak broadening could also be greatly reduced because of the compatibility of the eluent with commercial membrane suppressors and the reduction in the void volume. 

The simple Donnan model has limitations that are comparable to those of the GC model. The assumption that d,D = 0 just outside the hypothetical membrane is reasonable as long as the particle size is much larger than For particle sizes that are of the order of the hypothetical membrane can be thought at about a distance from the particle surface to incorporate the diffuse layer ions in the Donnan phase [25]. Ultimately this leads to a value of Vd that is larger than the void volume inside the particles and an average Donnan potential that is somewhat lower than the potential without this correction. The magnitude of the differences will depend on... 

Annealing a porous membrane (particularly one which contains a nonsolvent capable of functioning as a plasticizer) produces a decrease in void volume and permeability and, because pore size is... 

A continuous effect is the decrease in water content and void volume with Increasing temperature. Water is lost from the primary gel during annealing, both because of the formation of virtual crosslinks and because of the decrease in hydrogen bonding and cluster size in the water Itself. An example of a discontinuous effect is the dramatic increase in permselectivity (salt rejection) observed when cellulose acetate membranes are heated above the glass transition temperature 68.6 C. In fact, not one but two... 

Whereas heating causes shrinkage in three dimensions, the application of pressure causes shrinkage primarily in one dimension that is, in the plane perpendicular to the surface. Two stages may be distinguished in the shrinkage of porous membranes under pressure (1) the rapid loss of void volume in the porous... 

Gas adsorption (N2, Kr) can be used to estimate the relative quantity of zeolite deposited on the support (BET- or Langmuir equation). When a dense substrate is used, ellipsometry gives the film thickness and void volume fraction. Absorption spectroscopies such as FTIR, are adapted to study the membrane material short range structure. 

In some experiments vesicle membranes treated with phospholipase A and control vesicles were separated from the ACh in the suspension medium by gelfiltration on a Sephadex G-50 column. Vesicles or enzyme-treated vesicles were identified by protein analysis and came out with the void volume. After acid boiling it was found by bioassay that the enzyme-treated vesicles contained less ACh than the controls. 

The main difference between the three flow FFF systems is the channel dimensions, given in Table I. Although systems Flow I and II were constructed with 254-/zm spacers, the protrusion of the compressible membrane material into the channel space reduced the thickness w below this value. The w values reported in Table I are back-calculated from void volume measurements and subsequently confirmed by polystyrene standards. Flow I, with an initial w of 181 /zm, was reassembled at one point, after which w was found to be 152 /zm. This variation in w due to membrane compressibility was not observed when the thin polypropylene (25 /zm) membrane was used in Flow III. In this case, the channel thickness equals the spacer thickness. Thus the measured and geometric void volumes are in good agreement. 

The porosity (e) of the membrane is the same as the void volume of the membrane and may be determined by measuring the difference between the wet and dry weights of the membrane. Since... 

There are two common types of membrane material-, microporous and homogeneous. Microporous mate-riiils are manufactured from hydrophobic polymers such as polytetrafluoroethylene or polypropylene, which have a prtrosity (void volume) of about 70% and a pore size of less than I pm. Because of the nonpolar, water-repellent properties of the film, water molecules and electrolyte ions are excluded frrrm the pores gaseous molecules, on the other hand, are free to move in and out of the pores by affusion and thus across this barrier. Typically, the thickness of microporous membranes is about 0.1 mm. 

FIGURE 28 23 A micromembrane suppressor. Eluent flows through a narrow channel that contains a plastic screen that reduces the void volume and appeeirs to increase mass-transfer rates. The eluent is separated from the suppressor solution by 50-pm exchange membranes. Regenerant flow is in Ihe direction opposite to eluent flow (Courtesy ol Dionex Corporation. Sunnyvale. CA.)... 

Procedures. Americium transfer behavior was studied using hollow fiber membrane modules assembled In the laboratory. Each module consisted of two Armak Accurel hollow fibers, each 11.5 cm long and 0.15 cm l.d. with a 0.1 cm wall thickness, sealed Into a glass tube 14 cm long x 0.8 cm l.d. by using RTV silicone adhesive. The hollow fibers have a nominal void volume of 75Z. The glass tube Is equipped with side Inlet and outlet ports. 

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