Determination of Intrinsic Viscosity

The shape factor can be estimated by measuring the time t required for a solution of macromolecules to flow through a capillary. If this is measured 

By calculating the intrinsic viscosity of a macromolecule using Equation (4.2) we can determine how the viscosity is affected. For instance, the shape of the red blood cell influences the viscosity of blood. If the shape of the red blood cell changes from a disc to a prolate ellipsoid the viscosity of the blood will increase as will the energy required to pump blood through the capillaries. This occurs in sickle cell anemia when the disclike red blood cell changes in shape as a result blood flow and oxygen absorption are impaired. 

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Chee K.K. A critical evaluation of the single-point determination of intrinsic viscosity. Journal of Applied Polymer Science 34, 3 (1987) 891-899. 

Maron, Samuel H.. Determination of intrinsic viscosity from one-point measurements. Journal of Applied Polymer Science 5,15 (1961) 282-284. 

Ram Mohan Rao M. V., Yaseen M. Determination of intrinsic viscosity by single specific viscosity measurement. Journal of Applied Polymer Science 31, 8 (1986) 2501-2508. 

It is also in agreement with the data obtained from the determination of intrinsic viscosities of the polymers (,46). In Fig. 29 the reciprocals of the intrinsic viscosities (raised to 1.35) of the polymers obtained by operating at different pressures and with the same Al/Ti ratio, are plotted vs. the square root of the alkylaluminum concentration in the catal3dic system. For a given Al/Ti ratio, the lines which correspond to different pressures are almost parallel between themselves according to the fact that can be represented by the relationship... 

Figure 4.2. Determination of intrinsic viscosity. Intrinsic viscosity is determined by extrapolation of the reduced specific viscosity (r sr) to zero concentration. The reduced specific viscosity is calculated by taking the difference between the flow time in a capillary for polymer in a solvent and that of the pure solvent and dividing the difference by the flow time of the pure solvent times the polymer weight concentration. Data are shown for hyaluronan for various fractions isolated from bovine vitreous.

Numerous empirical equations have been proposed to express the vis cosities as a function of concentrations for the determination of intrinsic viscosity. These equations have been tabulated in several textbooks (see, for example, Philippoff, 1942), but many of them have only limited applications and are already obsolete. Here we will only mention three commonly used ones. For dilute solutions the well-known Huggins equation (1942) can be written as... 

As stated in Chapter 1, for the determination of intrinsic viscosity, [ ], of a polymer, viscosity values of several dilute solutions, when the relative viscosities ( / s) of the dispersions are from about 1.2 to 2.0, are determined. To facilitate such measurements, the so called Ubbelohde glass capillary viscometer is used that has a large reservoir to permit several successive dilutions of a polymer solution (Figure 3-19). Because intrinsic viscosity measurement is important, the test procedure for using the Ubbelohde viscometer is outlined here in brief (Cannon Instrument Co., 1982). 

In earlier studies on solutions of synthetic polymers (Ferry, 1980), the zero-shear viscosity was found to be related to the molecular weight of the polymers. Plots of log r] versus log M often resulted in two straight lines with the lower M section having a slope of about one and the upper M section having a slope of about 3.4. Because the apparent viscosity also increases with concentration of a specific polymer, the roles of both molecular size and concentration of polymer need to be understood. In polymer dispersions of moderate concentration, the viscosity is controlled primarily by the extent to which the polymer chains interpenetrate that is characterized by the coil overlap parameter c[r] (Graessley, 1980). Determination of intrinsic viscosity [r]] and its relation to molecular weight were discussed in Chapter 1. The product c[jj] is dimensionless and indicates the volume occupied by the polymer molecule in the solution. 

After determination of monomer conversions, the polymers were dissolved in benzene and reprecipitated two additional times prior to determination of intrinsic viscosities ([r]]) and specific activities. Intrinsic viscosities were obtained in benzene at 30°C with a no. 1 Ubbelohde viscometer (solvent flow times were 69.1 - 0.1 sec). Number average molecular weights (S n) were calculated from the expression [ri] =8.69 X 10" (13). Specific activities were determined by ... 

Nishida, K., Kaji, K., Kanaya, T, and Fanjat, N., Determination of intrinsic viscosity of polyelecirolyte solutions. Polymer, 43, 1295-13(X) (2002). 

The addition of low-molecular salts to a polyelectrolyte solution compensates the effects of the osmotic pressure as well as the coulomb forces by shielding the dissociated ionic groups as shown in Fig. 5.16. The addition of these salts allows for an extrapolation of the reduced viscosity to c O and a determination of an intrinsic viscosity. This is not possible for the salt free polyelectrolyte solution as can clearly be seen in Fig. 5.16. Although the addition of salt enables the determination of intrinsic viscosities, these values do not reflect the coil expansion in the salt free solution. 

Polyelectrolytes with flexible chains and high charge density are more expanded in water than nonionic polymers, especially at low ionic strength. Determination of intrinsic viscosity is difficult in this regime (Fig. 5c). Electrostatic repulsions not only cause increases in hydrodynamic volume but also increases in shear sensitivity or non-Newtonian behavior. 

It was proved that for molecular weights above 400,000 the shear effects becomes important even to the usual concentrations for the determination of intrinsic viscosity, [tj], at the specific shear gradients of capillary viscometers. The shear effects are higher in the case of polyelectrolytes solutions in good solvents and also in solutions containing rigid macromolecules. 

This was shown to good effect in an experiment [22] carried out to prepare a series of cationic acrylamide copolymers (60/40 weight ratio) as inverse emulsion polymers using identical polymerisation conditions, in which only the concentration of cross-linking monomer was varied. Subsequent determination of intrinsic viscosity values for this set of polymers showed the results in Table 3.1. 

Shroff RN (1965) Single-point determination of intrinsic viscosity. J Appl Polym Sci 9 1547-1551... 

Figure 3.4. Determination of intrinsic viscosity for a xanthan sample using the same laboratory data plotted as reduced and inherent viscosity versus concentration (unpublished data).

Pavlov, G. M., Gubarev, A. S., Zaitseva, I. L, and Sibileva, M. A. 2006. Determination of intrinsic viscosity of polyelectrolytes in salt-free solutions. Russ. J. Appl. Chem. 79 1407-1412. 

Ghimici, L. and Popescu, E. 1998. Determination of intrinsic viscosity for some cationic polyelectrolytes by Eedors method. Eur. Polym. J. 34 13-16. 

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