Concentration measurements, polymer

Various amounts of either ethanol or hexane were added to polystyrene solutions in benzene and r was measured for several concentrations of polymer. The following results were obtainedf (c2 in g liter" Hca/r in mol g M ... 

The viscosity ratio or relative viscosity, Tj p is the ratio of the viscosity of the polymer solution to the viscosity of the pure solvent. In capillary viscometer measurements, the relative viscosity (dimensionless) is the ratio of the flow time for the solution t to the flow time for the solvent /q (Table 2). The specific (sp) viscosity (dimensionless) is also defined in Table 2, as is the viscosity number or reduced (red) viscosity, which has the units of cubic meters per kilogram (m /kg) or deciUters per gram (dL/g). The logarithmic viscosity number or inherent (inh) viscosity likewise has the units m /kg or dL/g. For Tj g and Tj p, the concentration of polymer, is expressed in convenient units, traditionally g/100 cm but kg/m in SI units. The viscosity number and logarithmic viscosity number vary with concentration, but each can be extrapolated (Fig. 9) to zero concentration to give the limiting viscosity number (intrinsic viscosity) (Table 2). 

Three common uses of RBS analysis exist quantitative depth profiling, areal concentration measurements (atoms/cm ), and crystal quality and impurity lattice site analysis. Its primary application is quantitative depth profiling of semiconductor thin films and multilayered structures. It is also used to measure contaminants and to study crystal structures, also primarily in semiconductor materials. Other applications include depth profilii of polymers, high-T superconductors, optical coatings, and catalyst particles. ... 

These tracer and tagged polymer products are very useful for conducting test work such as in the examples given above, but, similar to their application in cooling water, the monitoring system only measures the bulk-water concentration of polymer. This may have little or no relevance to metal surface chemistry and the protective integrity of the magnetite film. 

The most widely used molecular weight characterization method has been GPC, which separates compounds based on hydrodynamic volume. State-of-the-art GPC instruments are equipped with a concentration detector (e.g., differential refractometer, UV, and/or IR) in combination with viscosity or light scattering. A viscosity detector provides in-line solution viscosity data at each elution volume, which in combination with a concentration measurement can be converted to specific viscosity. Since the polymer concentration at each elution volume is quite dilute, the specific viscosity is considered a reasonable approximation for the dilute solution s intrinsic viscosity. The plot of log[r]]M versus elution volume (where [) ] is the intrinsic viscosity) provides a universal calibration curve from which absolute molecular weights of a variety of polymers can be obtained. Unfortunately, many reported analyses for phenolic oligomers and resins are simply based on polystyrene standards and only provide relative molecular weights instead of absolute numbers. 

Utilization of a microfabricated rf coil and gradient set for viscosity measurements has recently been demonstrated [49]. Shown in Figure 4.7.9 is the apparent viscosity of aqueous CMC (carboxymethyl cellulose, sodium salt) solutions with different concentrations and polymer molecular weights as a function of shear rate. These viscosity measurements were made using a microfabricated rf coil and a tube with id = 1.02 mm. The shear stress gradient, established with the flow rate of 1.99 0.03 pL s-1 was sufficient to observe shear thinning behavior of the fluids. 

The analysis of an unknown number of unknown additives in unknown concentration in an unknown polymeric matrix is a demanding task for the analytical chemist for a variety of circumstances (Table 2.1). Primary analytical needs include the identification of the additives, the quantification of the additive levels, and the examination of additive stability. Obviously, the experimental analytical conditions must be such that no measurable polymer degradation or additive loss occurs during analysis. 

Flocculation rate limitation. The adsorption step was rate limiting for the overall flocculation process in this system. Polymer adsorption rate measurements for dispersed systems reported in the literature (2,26) do not lend themselves to direct comparisons with the present work due to lack of information on shear rates, flocculation rates, and particle and polymer sizes. Gregory (12) proposed that the adsorption and coagulation halftimes, tA and t, respectively, should be good indications of whether or not the adsorption step is expected to be rate limiting. The halftimes, tA and t, are defined as the times required to halve the initial concentrations of polymer and particles, respectively. Adsorption should not limit the flocculation rate if... 

Similar measurements and analysis have been carried out for the red solution. In this case the concentration of polymer in the chloroform-hexane solvent is limited to less than 4 x 10 r.u./cm. Therefore, the errors for y t and Y"t are larger than in the case of the yellow solution. In addition, the absorption band of the red solution is shifted to the red with respect to that of the yellow solution. Therefore, 2(i)j can only be extended up to 32 000 cm l. 

Polymer Mole % Acetyl Ti Concentration Measured by XFS (atoms/cm2) ... 

Polymer Ti Concentration Measured by XFS (atoms/cm2 x 1(T15) Before Etching After Etching Rate 0 (A/min) ATi Upon Etching (%)... 

The cell is fitted with windows, and the concentration of polymer along its length is determined by optical methods which are based on measurements of refractive index of absorption solvents to be used for ultracentrifugation experiments must be chosen for difference from the polymer in both density and refractive index. An effort be made to avoid mixed solvents. Low solvent viscosity is also desirable. 

The formation of rr triads Is extremely Improbable, thus explaining the very low concentration measured for such triads In the polymers prepared. 

I, the extremely low concentration of polymer in the fractions collected reduced the precision in the ultraviolet optical density values measured, the influence of which is amplified in the figures in the last column. Therefore, the average styrene content was used as the composition of the peak point to calculate the MW of the polymer by Equation 5. The MW of the styrene homopolymer which is present in small amounts was taken as the MW of the first block, as explained above. In this manner the molecular structure of the polymer was found to be S( 15,000) B(61,000)S( 14,000) the figures given in parentheses being the MW s of the successive blocks. 

Adsorption isotherms are readily determined by measuring polymer concentrations in the bulk solutions before and after adsorption equilibrium has been attained. However, the time required to reach equilibrium is often considerable. 

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