Membrane viscometer

In response to the above characterization problems and an interest in understanding the topology of intramolecular entanglement a membrane viscometer was developed.(A) In the membrane viscometer a solution is passed through a thin ( 10 )im) membrane with well-defined pores of fixed diameter that are nearly perpendicular to the membrane surface. The important feature is... 

The membrane viscometer must use a membrane with a sufficiently well-defined pore so that the flow of isolated polymer molecules in solution can be analyzed as Poiseuille flow in a long capillary, whose length/diameter is j 10. As such the viscosity, T, of a Newtonian fluid can be determined by measuring the pressure drop across a single pore of the membrane, knowing in advance the thickness, L, and cross section. A, of the membrane, the radius of the pore, Rj., the flow rate per pore, Q,, and the number of pores per unit area. N. The viscosity, the maximum shear stress, cr. and the velocity gradient, y, can be calculated from laboratory measurements of the above instrumental parameters where Qj =... 

The Vel data as a function of flow rate, Q, are shown for a 10 g/mol molecular weight polystyrene in Figure A. Both the Ubbelohde viscometric data and the membrane viscometer data are platted on the same graph for a 0.6 urn pore membrane at a low concentration of 100 ppm. The flow is Newtonian. The actual agreement of the capillary and membrane viscosities at low flow rates is always excellent when << Dj., and the concentration is extremely low. At small pore size, high concentrations, and high shear rates the flow can become non-Newtonian. The latter effects are only briefly discussed in this paper, but it is this effect that offers an oportunity to characterize the shape rather than the overall size. Even for a relatively large pore (0.6, Hi , membrane the shear rates vary from 100 s at E mi/Hr to 10 s at 200... 

Figure 2. Diagram of membrane viscometer with loop system...

Absolute flow rate, calibration, 132 Acrylic polymers, membrane viscometer characterization, 163,165/... 

Daucus carota Couette viscometer laminar regrowth mitochondrial activity membrane integrity cell lysis (cell number) non-growth (sterile) [57, 69]... 

The viscosities of the membrane casting dopes were measured by a Hoeppler viscometer as previously described (6). The solution densities were obtained by the modified Gibson and Loeffler (,9) dllatometer. From these data the solution viscosities at different temperatures were calculated. The activation energies of viscous flow obtained from the logri-1/T plots were corrected by the corresponding values of the solvents used. 

A viscometer has been constructed using membrane pores as capillary viscometers and can be readily adapted to conventional SEC equipment. The viscometer has been shown to give reasonable values of viscosities for solvent flow and intrinsic viscosities for moderate molecular weight polymers of MW approximately 100,000. 

Early measurements in a steady-state flow apparatus showed that the meiTibrane viscometer allows the direct calculation of kinematic viscosities that are in good agreement with independent capillary viscometer measurements under limited conditions. Agreement is excellent when (1) the average polymer diameter is smaller than the membrane hole, that is, < D, and (E) the effluent flow rate or... 

Mod i f 1 ed Mjymbrajne Viscometer Foi- the pulsed system a coil of tubing (the injection loop) was placed after the prefilter and liefore the membrane holder as shown in Figure P. Directional valves at each end of the loop controlled the flow path. Solvent or solution could be pumped directly to the UV to establish baseline absorbance or for calibration. To make P measurements the flow was directed through the membrane and then into the differential UV spectrophotometer. The flow could also be brought to the upstream portion of tlie membrane holder and then to the UV detector in an effort to measure the concentration at the membrane surface. 

Analysis of the C z and C e olefin mixtures by gas chromatography and/or NMR indicated that in both cases the internal isomers were the predominant product. With all the alkylaluminum coinitiators the ratio of internal to terminal olefin was 3 1. Product characterization data are shown in Table 1. Number average molecular weights of polyisobutylenes were determined using a Hewlett-Packard 503 high speed membrane osmometer at 37° C and toluene solvent. Intrinsic viscosities were obtained with a Ubbelohde capillary viscometer at 30° C in cyclohexane solvent. The viscosity average molecular weights were calculated... 

A Waters GPC 150 CV, equipped with the DRI prototype 4 and a single capillary viscometer, was used for this study. A low-angle laser lightscattering (LALLS) detector (Chromatix CMX 100) was inserted between the column set and the GPC 150 CV detectors. Tetrahydrofuran (THF) was used at 40 °C and at a flow rate of 1 mL/mn. THF was filtered on a Millipore membrane-type FH and stabilized by lonol at a concentration of 0.04%. The columns used were a set of Waters Ultrastyragel (103—106 A). The narrow standards used for calibration were a set of polystyrene standards... 

The enzyme-membranes were placed in a well-agitated 1-2 wt % pigskin gelatin (pi — 8.5 where pi is the pH of the isoelectic point of the gelatin) solution at 25°C and also at 37°C. After varying periods of time the reduced viscosity of the solution was measured with a Cannon-Ubbelohde No. 1 capillary viscometer. The decrease in viscosity of the gelatin solutions containing enzyme-membranes was compared to the viscosity decrease of control solutions and solutions to which a known amount of soluble enzyme was added. 

The breakthrough came in the early decades of this century, mainly through the adoption of physical methods, such as improved optical devices like the ultramicroscope, and the application of the ultracentrifuge, of new viscometers, osmometers, diffusion cells, and most of all, through the systematic appUcation of x-ray and electron diffraction to fibers, membranes, and tissues. A decade of intense research on cellulose, proteins, rubber, and starch wound up with the following fimdamental results ... 

The viscosity of the membrane solution in the pores of the support, cannot be measured. Here, the viscosities of amine solutions saturated with pure (ZO2 at latm were measured with an Ostwalds viscometer and these values were taken as the viscosities of the membrane solutions. The viscosities are listed in Table III. This... 

Blood is a non-Newtonian liquid showing a shear-dependent viscosity. At low rates of shear erythrocytes form cylindrical aggregates (rouleaux) which break up when the rate of shear is increased. Calculations show [82] that the shear rate (D) associated with blood flow in a large vessel such as the aorta is about 100 s but for flow in the capillaries it rises to about 10(K) s The flow characteristics of blood are similar to those of emulsions except that, while shear deformation of oil globules can occur with a consequent change in surface tension, no change in membrane tensions occurs on cell deformation. Fig. 9.32 shows the viscosity of blood at low shear rates, measured in a Brookfield LVT micro cone-plate viscometer. 

Silicone oils SO20 (viscosity 0.218 P), SOSO (viscosity 0.554 P), SOlOO (viscosity 1.18 P), and SO500 (viscosity 5.582 P) purchased from Prolabo, Productos para Laboratorios Quimicos, a Spanish company, were used in the spreading experiments. The viscosity of oils were measured using the capillary Engler Viscometer VPG-3 at 20 0.5°C. Cellulose nitrate membrane filters purchased from Sartorius (type 113), with pore size 0.2 and 3 pm (marked by the supplier). 

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