Viscometry measurements

Capillary viscometry measures the time it takes for the test fluid to flow through a capillary tube. The viscosity is calculated from this time and the calibration constant of the tube. 

Viscometry measurements were made in benzene at 30 °C and in TFE at 50 °C with uncalibrated Cannon-Ubbelohde dilution viscometers which gave solvent times greater than 100 seconds. The viscometers used had centistoke ranges denoted by viscometer sizes of 50 and 75 for benzene and TFE, respectively. Stock solutions were made up on gram solute/100 gram solution basis and converted to gram/deciliter via the solvent density at the temperature of measurement. The solvent densities used were d ene = 0.8686 (11a) and dlra = 1.3429 obtained from pycno-metric measurements (12). The density—temperature relationship for TFE obtained from regression analysis of the experimental pycnometric data is... 

After whipping whippable emulsions obtain more solid-like properties. This means that ordinary viscometry measurements are not useful. 

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... 

In vitro, the presence of physiological salt concentrations causes G-actin to polymerize to form the F-actin helix, which in native thin filaments represents the backbone of the filament. Polymerization of G-actin into F-actin can be followed by measuring lightscattering or by viscometry measurements. As in skeletal muscle, polymerization of smooth muscle actin depends on actin concentration, temperature, and ionic conditions (Strzelecka-Golaszewska et al., 1980). For both gizzard and bovine aortic muscle actin, the polymerization rate is optimal at 100 mM KCl and 1 mM MgCl2 (Cavadore et al., 1985). 

Viscometry measurements were also conducted. The Huggins coefficients increase with increasing molecular weight for the amine-capped polymers. This behavior is consisted with a star-like structure. For the zwitterionic samples constant kn values, around 1.1 were obtained, meaning that rather compact structures exist in solution. 

Viscometry measurements allow the calculation of the Mark-Houwink constants under conditions used for the analysis. The K and a values for PVA over... 

The former is a calibration-dependent procedure, and Mark-Houwink constants for the standards are readily obtained from calibration-viscometry measurements. These have been reported for PEG and PEO (29). For the latter method, however, a simple ratio of the concentration signal to the specific viscosity signal in a viscometry analysis yields the IVD (peak parameters, mass injected, and viscometer inlet pressure must be known). The IVD method is a calibration-indepetident procedure. By inputting the Mark-Houwink values, molecular weights can be calculated using the Mark-Houwink relationship. Because this procedure is calibration independent, it may hold significant value for quality or process control applications (28). 

Another parameter that is sensitive to the macromolecular architecture is the Huggins constant, / h, calculated by dilute solution viscometry measurements. For linear polymers, kn varies between 0.5 and 0.6 in 0-solvents and is equal to 0.3 in good solvents. For star polymers, in both good and 0-solvents, the values of fen increase with inaeasing / from the value obtained for linear polymers and reach values slightly lower than unity, which is the hard sphere limit (Tables 3 and 4). 

Solutions of HEC derivatives were prepared using the dry powder products at different concentrations. The suspensions were stirred gently for at least three days in order to obtain homogeneous solutions prior to viscometry measurements. Brookfield viscometry measurements were carried out at various shear rates using appropriate spindles. The apparent intrinsic viscosity of modified and unmodified HEC were also measured by using Ubbelohde viscometry. 

---