Viscosimetric measurement

It is possible to indicate by thermodynamic considerations 24,25,27>, by spectroscopic methods (IR28), Raman29 , NMR30,31 ), by dielectric 32> and viscosimetric measurements 26), that the mobility of water molecules in the hydration shell differs from the mobility in pure water, so justifying the classification of solutes in the water structure breaker and maker, as mentioned above. 

Figure 2.11. Evolution of the experimental characteristic distance X (deduced from the best Ht to the data using Eq. (2.19)) as a function of the polymer coil hydrod5mamic radius Rg (deduced from viscosimetric measurements) for the PVA-Vac polymer. ( ) Air-water interface ( ) Oil-water interface. (Adapted from [31].)...

Absolute Viscosimetric Method for the Determination of Endocellulase Activities. Experimental Setup of the Viscosimetric Measurements. The substrate, buffer, and enzyme solutions are prepared in the same manner as described in the section on light scattering. However, no clarification of the substrate solution by pressure filtration is needed. 

The final concentration of the buffered HEC was about 2.5 X 10"3 g/mL and the enzyme concentration about 3 X 10 4 FIP units/mL. The FIP (F6d6xation Internationale Pharmaceutique) unit is a unit of endocellulase activity (49) calculated from capillary viscosimetric measurements. 

As with the alkylated polysaccharides, the physicochemical properties of hydroxyalkylated polysaccharides have continued to be investigated, particularly those of commercial value. The general characteristics of 0-(2-hydroxyethyl)cellulose have been described, together with pro-cedmes for the viscosimetric measurement of solutions of the polymer, and the macromolecular properties of the polymer in solution, described earlier, have been reviewed. The effect of increasing the substitution of both water-soluble 0-(2-hydroxyethyl)- and 0-(2-hydroxypropyl)-cellulose is to decrease their afiBnities for water. Water-soluble 0-(2-hy-droxypropyl) cellulose can be fractionated in a way analogous to that for O-methylcellulose by utilizing solvent—nonsolvent mixtures. For polysac-... 

Kuehn AV, Ozegowski J-H, Peschel G, Neubert RHH. Complementary exploration of the action pattern of hyaluronate lyase from Streptococcus agalactiae using capillary electrophoresis, gel-permeation chromatography and viscosimetric measurements. Carbohydr Res 2004 339 2541-2547. 

A reversible transition from a swollen to unperturbed coil and further to a more compact globule-like conformation of polystyrene on cooling its diluted solutions in cyclohexane below the -temperature is well documented by viscosimetric measurements [142, 144], determination of... 

Figure 2.1 Typical graph illustrating distribution of molecular weight of polymers after synthesis by chemical methods. M molecular weight of a given species M , number-average molecular weight M molecular weight as determined from viscosimetric measurements weight-average...

In the course of the processing the sample underwent considerable changes. The powder turned into a monolithic pill which crushing for further research required some effort. Viscosimetric measurements showed that... 

For efificient viscosimetric measurements, only ISO cups (ISO 2431) should be used. The length of the capillary is 20 mm. The shear rates lie—for efflux times f=30-100 s—between y=60 and 1500 s" They depend on the capillary radius Ry which can be varied through interchangeable outlet nozzles. The calculation of the mean shear rate is made using the Hagen-Poiseuille-Law ... 

The most commonly used type of viscosimeter for the determination of the intrinsic viscosity or for single point measurements is the capillary viscosimeter. As the reproducibility with this type of viscosimeter depends on the clean execution of the measurement, a detailed description of the proceedings for a viscosimetric measurement is given below. 

For viscosimetric measurements to have a good reproducibility, a clean preparation of the sample is very important (Fig. 3.12). The preparation must be identical for every polymer solution that has to be measured, so that a reliable comparison of the measurements is assured. 

Right before the viscosimetric measurement the sample should be filtered to avoid a pollution of the viscosimeter with dirt particles. Solutions with a low viscosity should be filtered with a glass filter of a porosity of 2-4 (equals a pore diameter of approx. 10-100 pm) higher viscous solutions should be filtrated with filters of mesh size 0,3 mm (see DIN 4188). 

For the execution of exact viscosimetric measurements with good reproducibility, a clean viscosimeter is of crucial importance. Even the smallest dust particles on a microscopic scale lead to a deviation of the running times of several percent. The dust particles that adhere to the wall of the capillary lead to a longer running time. 

For the determination of the intrinsic viscosity [q] of the particular polymer-solvent system, the specific viscosity /jsp can be evaluated from the relative viscosity r j. via Eq. (2.11). With the specific viscosity and known concentrations of the solutions, the evaluation can be directly started according to Eq. (4.9) in Determination of the intrinsic viscosity by viscosimetric measurements in the next chapter. With the determined intrinsic viscosity [q], the critical concentration of the viscosimetry can be evaluated according Eq. (7.7). 

Viscosimetric measurements of surface-active samples in capillary viscosimeters are often hindered by vesication. In addition to a variation of the running times by bubbles of air in the reservoir and the no longer existing laminar flow profile in the capillary, an exact determination of the running times is not possible, because the foam formation on the fluid meniscus interface is particularly strong. Especially fully automated viscosimeter systems with light barriers at the marks Mi and M2 provide no exact data in this case. 

Via the determined viscosities, useful information can be obtained about molecular structure and chemical constitution. For example, the knowledge of the viscosity is of crucial importance for the beer brewing process. A beer with a viscosity above 1,7 mPa s is hard to filtrate, which leads to a declining capacity. On the other hand, a higher viscosity has a positive effect on the wholeheartedness and the stability of the foam of the beer. For this reason the main aim of viscosimetric measurements here is the optimization of filtration methods and the quality control of malt, flavor and beer [42]. 

Single point measurements are commonly used to determine the intrinsic viscosity via the so-called Fikentscher K-value. This method is, as shown in Determination of the intrinsic viscosity by viscosimetric measurements in Chap. 4, only applicable under very special conditions and should not be used anymore. Generally, single point measurements only serve for the determination of a viscosity value. 

The number of parameters that have influence on the flow behavior of a polymer solution is, as will be shown in the upcoming chapters, enormous and makes it difficult to interpret the viscosimetric measurements. For this reason, viscosimetric measurements are carried out with dilute sample solutions to minimize the interactions of the single polymer molecules. In this case, only the interactions between the polymer and the solvent are determined. The dilute state of solution is shown in Fig. 4.1. 

The unit of the reduced viscosity is defined via the used concentration unit, which is usually [g ml" ] for viscosimetric measurements. With this, the unit for the reduced viscosity is [ml g" ]. 

However, the reduced viscosity is also not totally independent of the concentration. Even though viscosimetric measurements are performed in the range of dilute solutions (below the critical concentration c where the single polymer coils start to interpenetrate), small polymer interactions (that are decreasing with a decreasing concentration) have to be considered. The true viscosity enhancing properties of a polymer is therefore the reduced viscosity extrapolated to c—>0 ... 

The intrinsic viscosity [q] represents the most relevant variable to describe the viscous behavior of a polymer solution and most viscosimetric measurements have the aim of its determination. Therefore, in the upcoming chapters the focus will be on a detailed description of the determination of the intrinsic viscosity, the influence parameters on the intrinsic viscosity and the establishment of structure-property-relationships with the intrinsic viscosity. 

Fig. 4.3. Viscosity q ed a function of the concentration c for carboxymethyl cellulose (CMC) of different molar masses in 0.1 mol/l NaNOj solution with 200 ppm NaNj at 7=25 °C.The degree of substitution with carboxymethyl groups is constant at DS. In addition the relative viscosity range of qr=. 2-2.5 is shown In which the data points for a good viscosimetric measurement should lie...

---