Viscometers capillary bridge

Norwood DP, Reed WF. Comparison of single capillary and bridge viscometers as size exclusion chromatography detectors. Int J Polym Anal Char 1997 4 99-132. 

Online viscometers (single, dual, or four capillary type viscometers with a symmetrical or asymmetrical bridge) These measure the pressure difference between a sample path and a reference path filled with pure solvent. Viscometers are used to measure specific and intrinsic viscosity, molar masses based on Benoit s universal calibration approach [6] and Mark-Houwink coefficients. Mass spectrometry (MS) detectors (see Chapter 10) Different MS methods have been used in macromolec-ular analysis. They are used to determine absolute molar masses for homo- and copolymers and to detect polymer structures. Matrix-assisted laser desorption ionizationtime of flight (MALDI-ToF) and electrospray ionization (ESI) are the most common instruments used in combination with SEC (Section 9.4.2.4). A recent application summary is available [12]. 

Viscometry Detection Although single and dual capillary viscometers are stiU in use, most commercially available detectors offered today are based on the four capillary bridge design originally developed by Haney [17]. 

I = complex impedance, B = conductivity bridge, C = capillary viscometer, P = pycnometer or dilatometer, V = volumetric glassware, I = instrument, U = method unknown... 

A better approach is the use of two capillaries (Cl and C2) in series, each of which is connected to a differential pressure transducer (DPI and DP2), and a sufficiently large holdup reservoir (H) in between. With this approach, the sample viscosity q is measured from the pressure drop across the first capillary, and the solvent viscosity q0 from the pressure drop across the second capillary. Pulsations are eliminated in this setup because they appear in both transducers simultaneously. Another design is the differential viscometer, in which four capillaries are arranged similar to a Wheatstone bridge. In Fig. 10, both designs are shown schematically. 

The first multiple-capillary viscometer was designed by the Viscotek Company (Houston, TX, U.S.A.) [7]. It is represented in Fig. lb. It is composed of four identical capillaries, assembled as a bridge. Here, the difference is generated by the bridge itself as a differential viscometer. The central DPT provides a differential viscosity signal DP and the second, DPT, provides inlet pressure IP. The intrinsic viscosity [17] can be calculated by the formula... 

I = complex impedance, B = conductivity bridge, C = capillary viscometer, P = pycnometer or dilatometer, V = volumetric glassware, I = instrument, U = method unknown (not provided in the reference). a Conductivity at 29 K calculated from VTF parameters given in reference. b Binary composition of 42.0-58.0 mol % [(CH3)3S]Br-HBr. 

Bridge design flow-referenced capillary viscometer. See text for details. (Adapted from Reference 6 and used with permission from John Wiley and Sons, Publishers.)... 

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