Viscometers single capillary

It is possible to calculate the offsets between detectors from the independent calibration curves. This was done and the results are shown in Figure 6. The calculated offset between the DRI and UV detectors is constant within experimental uncertainty. In contrast, the calculated offset between the viscometer and DRI detectors shows deviations at its extremes. The cause of these deviations is unclear, but they may be a manifestation of flow effects such as those observed in systems with single capillary viscometers (7). 

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... 

From that point, the necessity of continuously measuring viscosity, in addition to polymer concentration, became obvious. Several attempts were made to adapt existing viscometers as GPC detectors, but the problem of internal volume was critical. Ouano [2] published the first design of a single-capillary viscometer which was based on pressure measurement. Several similar designs [3-6] were pubfished and a commercially available instrument, the Waters Model 150CV (Waters Associates, Milford, MA, U.S.A.), based on a design described in Ref. 4, became commercially available. 

The single-capillary viscometer (SCV) is represented in Fig. la. Its design is a direct extrapolation of classical viscometry measurement. It is composed of a small capillary, through which the solvent flows at a constant flow rate, and a differential pressure transducer (DPT), which measures the pressure drop across the capillary. SCV obeys PoiseuiUe s law and the pressure drop AP across the capillary depends on the geometry of the capillary, on flow rate Q, and on viscosity of the fluid 7j according to... 

Another design was described by the Dupont Company [8]. It is represented in Fig. Ic. It is composed of two single-capillary viscometers. The first one (measure) is located as a normal SCV (Fig. la) and measures polymer plus flow. The second one (reference), identical to the first one, is located after a holdup reservoir which is connected after the refractometer and measures only the flow with pure solvent. It is just necessary to obtain the difference between the two signals to obtain the polymer signal with no flow contribution. 

Balke, S.T. Cheung, P. Lew, R. Mourey, T.H. Single-capillary viscometer used for accurate determination of molecular-weights and Mark-Houwink constants. J. Liquid Chromatogr. 1990,13, 2929-2955. 

There are no inherent limitations on which detectors can be used in ACOMP, and detector selection is made according to the needs of each monitoring situation. A standard configuration involves MATS, a differential R1 detector, a UVWIS detector, and a single capillary viscometer. Infrared, fluorescence, and conductivity detectors are other examples of instruments that can be incorporated. 

The physical meaning of viscosity was discussed in Chapter 5. In the online monitoring context, a very simple and robust means of measuring total dilute solution viscosity, rj, is with a single capillary viscometer. With a measurement of the pure solvent viscosity, and knowledge of the polymer concentration, c, the reduced viscosity, is given by... 

Single capillary viscometers are remarkably easy and inexpensive to construct using a modem differential pressure transducer with a double T-network and capillary of given L and/ . 

Fig. 13. Schematic diagram of the single capillary viscometer (a) capillary (6) purge (c) transducer assay (d) pressure transducer, (e) electronic unit...

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