Molecular Viscosity curve, effect

In a purely mathematical sense, the lower limit of [ij] predicted by Eq. (58) or Eq. (6) is zero at M — 0. But this is physically meaningless and the intrinsic viscosity curve should stop at a finite non-zero value as the molecular weight approaches the monomer weight. As remarked by Sadron and Remmp, this effect can be expressed empirically by the equation1 [t)] = D + K M, (93)... 

Thorpe and Rodger compared viscosities at temperatures where the slope of the curve is the same (d y/d/=const.), i.e. when temperature has the same effect, on the viscosity. The ratio of viscosities measured at two temperatures of equal slope was found to be constant. They also considered the molecular viscosities, r Mv), where (Mv) is the molecular volume, and what they called the molecular viscosity work rj Mv), or the work required to move a surface equal to the molecular viscosity through the specific molecular length MvY at unit velocity. Some general results found for normal liquids were ... 

The medium-molecular povidones and above all the high-molecular grade, povidone K 90 are used as thickeners in oral and topical solutions and suspensions (viscosity curves, see Section 2.2.3). The use of povidone in suspensions is described in Section 2.4.6. The thickening effect can also be used to adjust the viscosity of solutions - oral drops, eye drops, solutions and syrups - to give a particular drip or flow rate. The thickening effect reduces diffusion processes in the solution, improving the stability of some active substances. 

The basic output of a capillary rheometer is the viscosity curve (or flow curve), the viscosity of a test sample expressed as a function of shear rate at a single test temperature. Many things influence the shape of the viscosity curve. Viscosity data can be used to study the effects of temperature, additives, and/or fillers on material processability, and to determine optimum process conditions. Viscosity may also be correlated with other, more difficult to measure properties such as molecular-weight distribution. 

In SEC, universal calibration is often utilized to characterize a molecular weight distribution. For a universal calibration curve, one must determine the product of log(intrinsic viscosity molecular weight), or log([7j] M). The universal calibration method originally described by Benoit et al. (9) employs the hydro-dynamic radius or volume, the product of [tj] M as the separation parameter. The calibration curves for a variety of polymers will converge toward a single curve when plotted as log([7j] M) versus elution volume (VJ, rather than plotted the conventional way as log(M) versus V, (5). Universal calibration behavior is highly dependent on the absence of any secondary separation effects. Most failures of universal calibration are normally due to the absence of a pure size exclusion mechanism. 

Theories based on the uniformly effective medium have the practical advantage that they can be extended quite easily to polydisperse systems (227). Viscosity master curves can be predicted from the molecular weight distribution, for example. The only new assumption is that the entanglement time at equilibrium for a chain of molecular weight M in a polydisperse system has the form suggested by the Rouse theory (15) ... 

If the Mark-Houwink parameters are unknown and there is insufficient data available for their direct generation, molecular weight calibration curves can be generated by (a) an empirical technique based upon the determination of the intrinsic viscosity of each polymer fraction obtained by the GPC syphon counter or (b) using at least two out of three experimental observables, number- and weight-average molecular weights Mn, Mw, and [77] to fit mathematically for effective values of e and K. 

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