Viscosimetry calculations

The characteristic ratio of atactic polylferf.-butyl vinyl ketone) is determined from light scattering and viscosimetry measurements, and at 300 K in benzene the dipole moment ratio and its temperature coefficient are measured. Calculations of Ca and Da based on a two-state RIS model, with parameters independently derived from a previously developed semiempirical potential energy surface and from epimerization equilibrium measurements for dimeric and trimeric oligomers, are in excellent agreement with the experimental results. The predicted temperature coefficient is positive but lower in magnitude than that observed. 

An expression of this swelling as a function of the parameters z, g, and h has not been calculated yet (in 1988), and for this reason we cannot precisely determine the value of z which, for the viscosity swelling, corresponds to the quasi-Brownian structure of chains of area S. Consequently, the temperature at which the chains have a quasi-Brownian behaviour cannot be determined rigorously by viscosimetry. 

However, in viscosimetry using a capillary viscosimeter normally the viscosity is not calculated from the maximum shear rate and the shear stress but rather from the Hagen-Poiseuille-Law (Eq. 3.1). 

A theoretical approach for the determination of a I Q-M-relationships is possible from the viscosimetry, if vis calculated from the exponent a of the [q]-M-rela-tionship according to Eq. (8.26) and the constant Krq according to the Fox-Flory theory via Eq. (8.42) from the constant K[j y... 

Viscosimetry is a cheap technique and is very convenient for comparing gelators in terms of their ability to self-assemble in solution. Nevertheless, it should be restricted to Newtonian liquids (that is, liquids for which the viscosity does not depend on the shear rate (Section 2.4)), because from the capillary wall to its center the shear rate is not constant. For non-Newtonian fluids, proper viscosity calculations require corrections of the raw data once the dependency of their viscosity with the shear rate is known (Section 3.2). Unfortunately, for a given viscosimeter, the range of accessible shear rates is rather limited and it is often difficult to run measurements at very low shear rates where diluted solutions are usually expected to present a Newtonian plateau. 

Characteristic viscosities of unmodified and modified samples were determined by the method of viscosimetry with viscosimeter Ubbelode at 25 0.1 °C and for initial samples was calculated by the Mark-Kun-Hawink... 

To determine the constants in Maik-Houwink equation it is necessary to calculate values of the initial velocity of the enzymatic destruction of the Eq. (1), CHT sample was fractionated into 10 fractions of molecular weight ranging from 20,000 to 150,000 Daltons. The absolute value of the molecular weight fractions of CHT were determined by a combination methods sedimentation velocity and viscosimetry. 

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