Viscometric methods

Eor production use, once an accurate determination of monomeric, dimeric, and higher oligomeric dimer acids has been estabHshed for a specific process and feedstock s oligomerization, subsequent reaction extent can be estimated rapidly by a viscometric method (80). 

For determination of Molecular weights by these methods we need complicated apparatus and the methods are time consuming. In laboratory generally the viscometric method is used. 

The procedures used for styrene and benzene purification are given elsewhere (15) as is the technique used to study the association states U The viscometric method relies on the fact... 

Nowadays it is established that confocal microscopy observation can be a more sensitive method to assess die phase state of mixed biopolymer systems than the traditional centrifugation or viscometric methods (Alves et al., 1999, 2001 Vega et al., 2005). Indeed, microscopy can demonstrate that a system may be already phase-separated at compositions well below the apparent binodal line (as determined by these other methods). The report of Alves et al. (2001) demonstrates the relationship between specific compositional points in the phase diagram (Figure 7.1) and the observed microstructure (Figures 7.2 and 7.3) for water + gelatin + locust bean gum (LBG). The white areas in Figures 7.2 and 7.3 corre-... 

Gusakov, A.V., Markov, A.V., Grishutin, S.G., Semenova, M.V., Kondratyeva, E.G., and Sinitsyn, A.P. 2002. Viscometric method for assaying of total endodepolymerase activity of pectinases. Biochemistry (Moscow) 67 676-682. 

Post effects have not been examined in detail in homogeneous systems. On yon (109) attempted to use the viscometric method, but the data did not vary in accordance with theory and did not allow accurate determination of individual rate constants. 

The viscometric method relies on the relation (in the entanglement regime) ... 

Carpenter, D. K., and Westerman, L. (1975). Viscometric methods of studying molecular weight and molecular weight distribution. In Polymer Molecular Weights, Slade, P. E., Jr. (Ed.), Vol. 2, p. 388. Dekker, New York. 

Characterization of molecular weight distributions by a viscometric method. Nature (Lond.) 183, 1670 (1959). 

Demeester, J., Bracke, M., and Lauwers, A., Absolute viscometric method for the determination of endocellu-lase (Cx) activities based upon light-scattering interpretations of gel chromatographic fractionation data. Adv. Chem. Ser. 1979, 181, 91-125. 

A third technique for determination of alpha-amylase is the viscometric method. This is the most sensitive method for studying the initial attack on amylose, but it is too time-consuming to be used as a routine method for enzymic assay. If the relation between viscosity and molecular weight is known for the substrate, an estimate of the rate of bond scission may be made. (This estimation would be valid only if completely random attack were occurring.)... 

In a large number of investigations the possibility of the formation of polymer-polymer complexes with the participation of alternating and random copolymers has been shown. So, using the viscometric method the complex formation of iso-PMAA and methyl methacrylate and methacrylic add copolymer has been reported. The stability of the stereocomplex decreases with increasing add content in the copolymer. 

Additional in vitro methods include adhesion weight, fluorescent probe, " flow channel,mechanical spectroscopic, falling film, colloidal gold staining, viscometric method, thumb test, ... 

Circular dichroism and viscometric methods have been used successfully to determine the degree of acetylation and the MW of chitin and chitosan, respectively (Zhang and Neau, 2001). The DD has no effect on the acidbinding properties of chitosan (Scheruhn et al., 1999). Chitosans have a relatively high DD and strongly enhance fibroblast proliferation, whereas chitosans with lower levels of deacetylation show less activity. The MW and polymer chain length were of little importance (Howling et al., 2001). 

Evaluation of paints and paint ingredients can be done with conventional viscometers, in which the material is sheared between two mating surfaces. Constant shear rates or known frequencies of oscillation may be used. Raw materials are evaluated and formulation changes are monitored by conventional viscometric methods. 

The Commission on Enzymes states that, wherever possible, enzyme assays should be based on measurements of initial rates of reaction. A viscometric assay method should be especially suitable for this purpose since the mean molecular weight of a polymer can be rapidly determined by such methods. A useful viscometric method has been worked out by Almin et al. (3,4, 5). 

The influence of DS and DP was not found to be so clear-cut that conversion factors could be predicted from these parameters alone. In addition to DS and DP there is some other structural characteristic of the CMC samples influencing the enzyme-substrate reaction. These conversion factors interrelating activity, obtained with different CMC preparations, must be empirically determined. The accuracy obtained in the A determinations by the viscometric method outlined above is reflected by the coefficient of variation which was found to be approximately 0.2. 

The degree of polymerization (DP) of cellulose (i.e., the number of anhydroglucose units per chain) varies widely (Table 2) and depends on the source of the cellulose, the extent of cell development within that source, and the meAods used for isolation of the cellulose. Cellulose is poly disperse the DPs reported in Table 2 are weight-average degrees of polymerization (DP J that were determined by viscometric methods (assumes DP , - DP J. 

Cellulose standards for use in calibration, especially by the peak position method, can be obtained by a number of methods. The most straightforward method is to utilize a series of celluloses from a variety of sources (eg., pulps, yarns, and avicel) that have a wide range of DPs (15,26). In a second method, celluloses of different DPs are obtained from a single cellulosic source (e.g., cotton) by controlled, acid-catalyzed depolymerization (93). Another method uses fractional precipitation of the appropriate cellulose derivative (10,29). Once obtained, the DP of each cellulose standard can be determined by osmotic and viscometric methods. The SEC calibration curve obtained with these standards is then adjusted numerically until a best fit with the DPs of each of the standards is obtained (93). 

Houwink R (1940) Relation between the polymerization degree determined by osmotic and viscometric methods. J Prakt Chem 157 15-18... 

The viscosity of CM-chitosan can be determined by the viscometric method with an Ubbelohde capillary viscometer. A One-Point method equation was used to calculate the intrinsic viscosity (Fan et al. 2002) ... 

In the case of polymer blends, refractometric and viscometric methods are used to study the polymer-solvent and polymer-polymer miscibility. It is clear that... 

We now briefly describe some common viscometric methods to characterize the shear flow in capillary viscometers used frequently for observing the die extrusion behavior of most polymer systems. Detailed descriptions of these techniques and the other theoreticals may be found in some well-organized textbooks and monographs [32-38,41 5]. 

Kita, Y., Masumoto, S., and Yonezawa, D., 1977a, Viscometric method for estimating the stabiUty ofw/oAv multiple-phase emulsions, J. Colloid Interface Sci. 62 745-751. 

Swelling Kinetics Methods. Swelling kinetics for superabsorbent polymers may be measured by a viscometric method (37), based on the dependence of suspension viscosity on the volume fraction of the suspended particles. However, the swelling rate is most often measured by determining the speciflc absorbency as a function of time, for example, by means of the centrifuge capacity analysis. An absorption rate may also be obtained from data of swelling vs time using the demand absorbency method (38). 

A solubility-structure study has been made together with viscosity studies on poIy(amic acids).The flexibility of aromatic polyimides and poly(amic acids) has also been studied theoretically and investigated by viscometric methods for the poly(amic acids).The data obtained on these systems was used to justify the theoretical approach to flexibility studies on the insoluble polyimides. 

Viscometric Methods.—Dilute Solution Viscosity [ij]. Ubbelohde and Fica automatic viscometers are among the apparatus which are frequently used to obtain thermodjmamic data from dilute solution viscosity measurements. The method suffers from vagaries of interpretation in... 

There are many relative viscometric methods, i.e., those which require calibration with a fluid of known viscosity. Although they may be useful for viscometry of Newtonian fluids and for process and product control, the relative methods are inappropriate for adhesive materials, since concentrated colloidal dispersions and concentrated solutions of macromolecules show non-Newtonian behavior. While macromolecular systems usually exhibit viscoelasticity, colloidal dispersions can often be considered to be purely viscous. Non-Newtonian behavior can be characterized in steady shear, and is usually expressed as the functional dependence of shear stress on shear rate, or of viscosity on shear rate. 

FIGURE 3. Data obtained on non-Newtonian viscosity of an aqueous solution of hexylethylcellulose by four different viscometric methods capillary rheometry, concentric cylinder, cone-plate and parallel disk. 

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