Viscometric studies

Rapidly solidifying compositions used for reactive injection molding place some restrictions on measurement. In the time required to prepare the reaction mixture, place a sample in the measuring cell of an instrument, and achieve a steady state in the sample and the measuring system at a preset temperature, chemical conversion of the material may advance considerably, making viscosity measurements meaningless. The volume of lost information depends on the ratio of the transient time necessary to achieve a steady state in the sample and the characteristic time of the chemical reaction. The sensitivity of the reaction rate to temperature is also important. In order to avoid the necessity to maintain isothermal conditions for the measurements, a non-isothermal scanning method for viscosity measurements was proposed.156 

In this method, the components of a reactive mixture are thermally conditioned and mixed at a low temperature, which retards the reaction during the preparatory stages. The working cell of a viscometer is thermally conditioned at the same temperature. When the sample is placed in the measuring device, a programmed heater controls the temperature changes. In the simplest case, the temperature changes linearly as  

In order to describe changes in the rheological properties of polyurethanes during curing, the following equation was proposed and proved to be correct  

If the measuring (transmitting) circuit of an instrument has linear characteristics (which requires separate experimental validation), the output signal of a linear instrument y(t) is expressed in terms of the input signal x(t) using the integral equation  

To determine the function x(t), it is necessary to find the solution of the integral of Eq. (3.6) for a known h(t) and measured y(t) functions. One proposed method of calculating x(t) assumes that the shape of the function x(t) is known beforehand and that the transfer function h(t) can be experimentally determined.158 A more general solution uses Fourier transforms. If Eq. (3.6) is rewritten with the Fourier transforms of the functions x(t), y(t), and h(t - t), which are denoted by Y, X, and H, then, using the convolution theorem  

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To date, there has been relatively little work reported on the mesophase pitch rheology which takes into account its liquid crystalline nature. However, several researchers have performed classical viscometric studies on pitch samples during and after their transformation to mesophase. While these results provide no information pertaining to the development of texture in mesophase pitch-based carbon fibers, this information is of empirical value in comparing pitches and predicting their spinnability, as well as predicting the approximate temperature at which an untested pitch may be melt-spun. 

The heat of dissociation in hexane solution of lithium polyisoprene, erroneously assumed to be dimeric, was reported in a 1984 review 71) to be 154.7 KJ/mole. This value, taken from the paperl05> published in 1964 by one of its authors, was based on a viscometric study. The reported viscometric data were shown i06) to yield greatly divergent AH values, depending on what value of a, the exponent relating the viscosity p of a concentrated polymer solution to DPW of the polymer (q DP ), is used in calculation. As shown by a recent compilation 1071 the experimental a values vary from 3.3 to 3.5, and another recent paper 108) reports its variation from 3.14 to 4. Even a minute variation of oe results in an enormous change of the computed AH, namely from 104.5 KJ/mole for oe = 3.38 to 209 KJ/mole for oe = 3.42. Hence, the AH = 154.7 KJ/mole, computed for a = 3.40, is meaningless. For the same reasons the value of 99.5 KJ/mole for the dissociation of the dimeric lithium polystyrene reported in the same review and obtained by the viscometric procedure is without foundation. 

Most frequently, SEC with dextran-, pullulan-, or polystyrene calibration standards has been used to characterize the molecular properties of xylans. However, as for viscometric studies [108], a sufficient solvent ionic strength is a prerequisite for useful SEC measurements of charged polysaccharides, including glucuronoxylans [111-113]. An advantage of the SEC technique is that the presence of protein and phenolic components or oxidative changes can be detected by simultaneous ultraviolet (UV) detection. 

Masuelli, Martin Alberto. Viscometric study of pectin. Effect of temperature on the hydrodynamic properties.. International Journal of Biolovical Macromolecules 48 (2011) 286-291. 

Dombrow and Beckmann163 have carried out ultracentrifugal and viscometric studies of several amylose acetates in methyl acetate solution. Their data, shown in Table VI, were interpreted as supporting the idea of a helical configuration in solution. 

Viscometric Studies on Polyisobutene Solutions, P.H. Plesch and P.P Rutherford, Polymer, 1960,1, 271-273. 

Bachman, S., Klimczak, B. and Gasyna, Z. 1980. Non-destructive viscometric studies of enzymic milk coagulation. III. The effect of pH, temperature and Ca-ions concentration on the secondary phase of milk coagulation. Acta Aliment. Pol. 6, 135-143. 

In the original paper n was taken to be four 189) although the burden of evidence suggests (Table 2) two is more likely. This scheme assumes that complexation need not result in disaggregation. Viscometric studies show that poly(butadienyl)lithium aggregates are broken on complexation 152). Calorimetric measurements89 on the interaction of TMEDA with poly(isoprenyl)lithium have yielded data that are not inconsistent with the formation of a complex between one molecule of the former and two of the latter. 

In careful viscometric studies, this pressure drop is never neglected the pressure reading at zero reservoir height, as found by extrapolation, is used for the value of Pq. 

In the course of preparation of this review, we have had the opportunity to read a number of papers on viscometric studies of polymer solutions, and hence to collect the constants of Mark s, Houwink s and Sakurada s empirical relationship,... 

Polymer-solvent interactions have been examined by viscometric studies of polymer-solvent-non-solvent mixtures in dilute solution The Fox-Flory model which... 

Guveli D, Davis SS, Kayes JB. Viscometric studies on surface agent solutions and the examination of hydrophobic interactions. ] Pharm Pharmacol 1974 26 (Supph) 127P-128P. 

Viscometric studies are used to assess the shear robustness or fragility of cells by exposing them (usually for a short, 10-20 min, time period) to the reproducible and well-defined laminar flow of a viscometric device. In contrast, the (usually turbulent) flow in a bioreactor is not well defined and not easily reproducible, unless the same reactor is used. 

Polymer-solvent interactions have been examined by viscometric studies of polymer-solvent-non-solvent mixtures in dilute solution84 86). The Fox-Flory model which relates the molecular parameters of the unperturbed dimension and the linear expansion coefficient to the total sorption parameter has been used. The latter can be obtained by the simultaneous solution of several Equations when the intrinsic viscosities of the mixtures are known. This method is in an early stage of development and pro-... 

Korolczuk, J., and Mahaut, M. (1989). Viscometric studies on acid type cheese texture. J. Text. Stud. 20, 169-178. 

For a review of viscometric studies on the different mesophase types see... 

The viscometric study of the ternary system, that is, polymer A—polymer B—solvent, has been used in order to determine the interaction parameter Xab which characterizes the incompatibility of the couple polymer A—polymer B [60],... 

The viscometric study has also led to a method of estimation of the incompatibility of the polymer without the need to evaluate Xab- This method evaluates the quantity A[t7]ab defined by... 

A VISCOMETRIC STUDY OF THIAZOLE AND THE THIAZOLE-CARBON TETRACHLORIDE AND THIAZOLE-CYCLOHEXANE SYSTEMS. 

VISCOMETRIC STUDY OF INTERACTION IN SOLUTIONS OF BIS/N-METHYLSALICYLALDIMINE/NICKEL/II/. 

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