Viscosity data interpretation

The number and weight average molecular weights were determined for two samples of linear polyethylenes distributed by the Macromolecular Division of IUPAC. The methods used were GPC, osmotic pressure, infrared analysis, melt viscosity and intrinsic viscosity. Data interpretations are discussed for each method. By comparing the results the average molecular weights were obtained for one sample, STN = 10,500 to 11,000 and Mw = 150,000 to 165,000 for another sample, MN = 13,600 to 18,500, and Mw = 40,000 to 48,000. 

A major use of theoretical and computational methods is the prediction or validation of observed experimental data. New applications involving quantitative structure-property relationships (QSPR) and quantitative structure-retention relationships (QSRR) for the prediction of various physicochemical properties have also been reported. A series of allg ltributylphosphonium chloride ionic liquids has been synthesized and their experimental density and viscosity data interpreted using QSPRs and group contribution methods. A QSRR study has also been performed on a series of new phosphoramidic acid derivatives. Their retention factors Id ) were predicted using a model obtained from a set of previously-synthesized phosphoramidic acid derivatives. 

Evidence of the appHcation of computers and expert systems to instmmental data interpretation is found in the new discipline of chemometrics (qv) where the relationship between data and information sought is explored as a problem of mathematics and statistics (7—10). One of the most useful insights provided by chemometrics is the realization that a cluster of measurements of quantities only remotely related to the actual information sought can be used in combination to determine the information desired by inference. Thus, for example, a combination of viscosity, boiling point, and specific gravity data can be used to a characterize the chemical composition of a mixture of solvents (11). The complexity of such a procedure is accommodated by performing a multivariate data analysis. 

Tn the previous papers of this series (1, 2, 3, 4) calibration and repro- ducibility of gel permeation chromatography (GPC) have been extensively examined. This paper describes the application of GPC to two selected samples of linear polyethylenes, one having a narrow molecular weight distribution (NMWD) and another a broad molecular weight distribution (BMWD). These samples were distributed by the Macro-molecular Division of IUPAC (5) for the molecular characterization of commercial polymers. The average molecular weights by GPC are compared with the data obtained from infrared spectroscopy, osmotic pressure, melt viscosity, and intrinsic viscosity. Problems associated with data interpretation are discussed. 

J. Ferguson and N.E. Hudson, The Interpretation of Instantaneous Extensional Viscosity Data, presented at the 2nd Int. Congress on Extensional and Shear Flow of Polymer Fluids, St. Andrews, Scotland, June 19-22,1994. 

Viscosity data for proteins are indeed too numerous to give even a cursory summary. Rather we will consider only a few examples to illustrate the information that can be obtained from viscometry and the limitations in its interpretations in the light of the previous discussions. 

Interpretation of viscosity data for concentrated polymer solutions. J. Chem. Phys. 34. 393 (1961). 

Singh VS, Gaur RC. Dispersion of cholesterol in aqueous surfactant solutions interpretation of viscosity data. ] Disper Sci Technol 1983 4 347-359. 

A very important advantage gained by the rheologist using this system is the ability to rapidly compare up to six viscosity curves on one plot to aid in data interpretation. 

Table 16.5 shows a generic interpretation for kinematic viscosity data for large diesel engines. The matrix indicates the viscosity condition indicator status and potential cause for the various viscosity level and trend statuses. 

Joos data on distearoyl lecithin (DSL)-cholesterol mixed films (35) coincide with data from our DPL-cholesterol system in the sense that cholesterol reduced the viscosity of the lecithin film, and the surface viscosity decreased with increasing cholesterol concentrations. However, the comparison and interpretation of surface viscosity data require caution (2,6). For example, in Joos experiments the lipid was distearoyl lecithin (DSL), the subphase was distilled water, phospholipid and cholesterol were premixed, and viscosity was measured by the rotational surface Couette method. By the torsion oscillation method, at all film pressures... 

As more viscosity data at very low concentrations were obtained, it was suggested that the interpretation given above seems to be too simple and needs to be modified and some theoretical explanations have been proposed [34,35]. Nevertheless, the general nature of the characteristic viscosity behavior of polyelectrolyte solutions is evident, as similar behavior has been observed for a number of systems, both nonaqueous and aqueous. Table 1 summarizes the systems whose viscosity behavior in nonaqueous solutions has been reported. 

The values for xanthan gum were also reported in an earlier work (7). The molecular sizes were obtained by using the Flory relation (8). There are alternate discussions as to what the configuration and the size of xanthan gum molecules in solution are. Whitcomb, Ek, and Macosko have presented an interpretation of the intrinsic viscosity data assuming a cylindrical rod conformation (9). The K-j and a values for Pusher are given by Lynch and Mac-Williams (10). It should be noted that a range of Kj and a values for polyacrylamides can be found in the literature (11). 

These conclusions are supported by the viscosity data plotted in Figure 1. The reduced viscosity of the hexyl copolymer is presented as a function of a in 0.2M solutions of TMACl, NaCl, and LiCl. The polymer concentration of 3.2 X 10"3 monomole/l was low enough to allow interpretation of the results in terms of the molecular dimensions of the polymer molecules. The findings demonstrate strikingly the differences in the effects of the TMA+ ion and the alkali metal ions. Whereas the polyacid showed an enormous expansion with increasing a in the presence of TMA+ ion, this expansion was suppressed almost completely by the alkali metal ions. The difference between the effects of... 

The mode of interaction of such [Ru fphenla] derivatives with DNA has been a matter of some debate. Both intercalation and surface binding in the major groove were initially proposed for each of the enantiomers A and A, with intercalation as the predominant mode of interaction (175) (see also Ref. 176 for an interesting presentation of molecular recognition and chemical reactions in restricted spaces such as micelles, dendrimers, and DNA). However, viscosity data are against a classical intercalation interpretation (177). Additional results obtained by absorbance, fluorescence, and circular dichroism... 

In order to make a molecular interpretation from these data, it is necessary to obtain a plot of intrinsic viscosity versus shear stress. For this purpose the raw viscosity data in Figure 1 were first fitted to a simple equation, the Meter equation, which has four parameters... 

For higher volume fractions, the viscosity data were more recently interpreted by a similar model of aggregating droplets, and such a model is able to account for the experimental data up to volume fractions of 0.4 [65]. 

Mefliods of study and data interpretation still require further work and refinement. Several experimental techniques are used, including microscopy (TEM, SEM) dynamic light scattering " using laser sources, goniometers, and digital correlators spectroscopic methods (UV, CD, fluorescence) fractionation solubility and viscosity measurements and acid-base interaction. "... 

Depending on the viscosity of liquid and its expected flash point range, one of the above methods is chosen as described in detail elsewhere. It should be additionally noted that if the flash point method uses continuous heating, it is not suitable for testing mixtures of flammable substances because their vapor concentrations are not representative of equilibrium eonditions. One of the weaknesses of flash point analysis is that the flame is well above the liquid surface therefore full vapor concentration is not attained. Many cases exist where a flash point cannot be detected but the material does form flammable mixtures. Before a method is chosen and a data interpretation made full information on the test procedure should be studied in detail and the proper authorities should be eonsulted to define safe practices for a particular material. 

For an interpretation of viscosity data of sols obeying Poiseuille s law Kruyt and Bungenberg de Jong took Einstein s equation... 

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