Viscosity measurement techniques

Procedures for determining the ash content and moisture level, solution preparation, and viscosity measurement techniques are given in the manufacturer s hterature (50). 

Viscosity Measuring Techniques and Their Usual Range... 

This monograph provides an introduction to scanning ther-moanalytical techniques such as differential thermal analysis (DTA), differential scanning calorimetry (DSC), dilatometry, and thermogravimetric analysis (TG). Elevated temperature pyrometry, as well as thermal conductivity/diffusivity and glass viscosity measurement techniques, described in later chapters, round out the topics related to thermal analysis. Ceramic materials are used predominantly as examples, yet the principles developed should be general to all materials. 

Numerous methods for measuring fluid viscosity exist, for example, capillary tube flow methods (Ostwald viscometer), Zahn cup method, falling sphere methods, vibrational methods, and rotational methods. Rotational viscometers measure the torque required to turn an object immersed or in contact with a fluid this torque is related to the fluid s viscosity. A well-known example of this type of system is the Couette viscometer. However, it should be noted that as some CMP slurries may be non-Newtonian fluids, the viscosity may be a function of the rotation rate (shear rate). An example of this is the dilatant behavior (increasing viscosity unda increasing shear) of precipitated slurries that have symmetrical particles [33]. Furthermore, the CMP polisher can be thought of as a large rotational plate viscometer where shear rates can exceed 10 s and possibly affect changes to the apparoit viscosity. The reader can refer to the comprehensive review of viscosity measurement techniques in the book by Viswanath et aL [34]. 

The measurement techniques most frequently used are derived from Raoult s and Van t Hoff s laws applied to cryometry, ebulliometry, osmometry, etc. They are not very accurate with errors on the order of ten per cent. Consequently, the molecular weight is often replaced by correlated properties. The mean average temperature or viscosity can thus replace molecular weight in methods derived from ndM. 

Viscosity can also be determined from the rising rate of an air bubble through a Hquid. This simple technique is widely used for routine viscosity measurements of Newtonian fluids. A bubble tube viscometer consists of a glass tube of a certain size to which Hquid is added until a small air space remains at the top. The tube is then capped. When it is inverted, the air bubble rises through the Hquid. The rise time in seconds may be taken as a measure of viscosity, or an approximate viscosity in mm /s may be calculated from it. In an older method that is commonly used, the rate of rise is matched to that of a member of a series of standards, eg, with that of the Gardner-Holdt bubble tubes. Unfortunately, this technique employs a nonlinear scale of letter designations and may be difficult to interpret. 

It turns out that in low-viscosity blending the acdual result does depend upon the measuring technique used to measure blend time. Two common techniques, wliich do not exhaust the possibilities in reported studies, are to use an acid-base indicator and inject an acid or base into the system that will result in a color change. One can also put a dye into the tank and measure the time for color to arrive at uniformity. Another system is to put in a conductivity probe and injecl a salt or other electrolyte into the system. With any given impeller type at constant power, the circulation time will increase with the D/T ratio of the impeller. Figure 18-18 shows that both circulation time and blend time decrease as D/T increases. The same is true for impeller speed. As impeller speed is increased with any impeller, blend time and circulation time are decreased (Fig. 18-19). 

Intrinsic Viscosity Measurements were made by standard techniques in dimethyl formamide (DMF) at 30 C. Weight average molecular weights were calculated from the following relationship ... 

In principle all methods except viscosity measurement can be used to obtain absolute values of molar mass. Viscosity methods, by contrast, do not give absolute values, but rely on prior calibration using standards of known molar mass. The relationship between polymer solution viscosity and molar mass is merely empirical but the techniques are widely used because of their simplicity. All of the absolute methods are time-consuming and laborious and are not used on a routine basis. As well as the techniques already mentioned, there is the size-exclusion method of chromatography known as Gel-Permeation Chromatography (GPC). All of these methods are discussed in detail in the sections that follow. 

In addition to the measurement of the viscosity, this technique also allows the yield stress to be estimated. For a typical yield stress type material, there is a critical shear stress below which the material does not deform and above which it flows. In pipe flow, the shear stress is linear with the radius, being zero at the center and a maximum at the wall. Hence, the material would be expected to yield at some intermediate position, where the stress exceeds the yield stress. The difficulty with this method is in the determination of the point at which yielding occurs and, indeed, whether the material is appropriately modeled as having a yield stress or is... 

Characterization. The series of poly(alkyl/arylphosphazenes) (1-6) was studied by a variety of standard dilute solution techniques including viscosity measurements, membrane os-... 

In many applications a capiiiary viscometer is used to measure the viscosity of poiymer soiutions of differing concentrations, and then the data are piotted to obtain the intrinsic viscosity. Severai techniques have been used to determine intrinsic viscosity from soiution. One is the Huggins equation for intrinsic viscosity [1] ... 

J. Allouche, E. Tyrode, V. Sadtler, L. Choplin, and J.L. Salager Simultaneous Conductivity and Viscosity Measurements as a Technique to Track Emulsion Inversion by the Phase-Inversion-Temperature Method. Langmuir 20, 2134 (2004). 

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