Second viscosity

KINEMATIC VISCOSITY-STOKES REDWOOD VISCOSITY-SECONDS... 

Now in some cases a direct study of a polymer under 0 conditions is not feasible or, more frequently, not desired. The need to work under 0 conditions when determining unperturbed chain dimensions might be circumvented if one could rely on theories connecting accurately measurable quantities such as intrinsic viscosity, second virial coefficient etc. obtained in good solvents, with the chain expansion factor. 

The significant improvement in flow properties of resin IV vs. V is evident from the data. First, the torque from Brabender mixing indicates that resin IV is an easier-flowing material (Table II). The lower torque values for IV indicate the necessity of a lower-energy input to mix the polymer melt. This lower rotational force therefore indicates the polymer melt has a lower melt viscosity. Secondly, injection-molding conditions demonstrate the improved processability of resin IV (Table III) in comparison with resin V. At the same injection cylinder temperatures, the injection pressure for the tensile bar and Izod/heat distortion bar molds is lowered by 300 psi and 250 psi, respectively. 

The rheological parameters of primary scientific and practical concern are the static and dynamic shear modulus, the yield stress, and the shear rate-dependent viscosity. The aim is to understand and predict how these depend on the system parameters. In order to accomplish this with any hope of success, there are two areas that need to be emphasized. First, the systems studied must be characterized as accurately as possible in terms of the volume fraction of the dispersed phase, the mean drop size and drop size distribution, the interfacial tension, and the two bulk-phase viscosities. Second, the rheological evaluation must be carried out as reliably as possible. 

MI Briceno, M Ramirez, J Bullon, JL Salager. Customizing drop size distribution to change emulsion viscosity. Second World Congress on Emulsion, Bordeaux, France, 1997, Proceedings Vol 2, paper 2-1-094-01/05. 

Dynamic viscosity of the liquid carrier Shear spin viscosity Second coefficient of viscosity Bulk spin viscosity... 

Resonance structures can be drawn that show that the polymer backbone from triphenylantimony dichloride and p-benzoquinone dioxime is quite stiff. The product had a low viscosity (6mL/g) but a molecular weight of about 7 x 10 with a LVN/weight average molecular weight of 0.09 x 10". In comparison, polystyrene has a LVN/M of 8 x lO" or about 100 times the antimony product. Polyethylene has a LVN/M value of 35 x 10 or a value about 400 times that of the antimony polymer. Becanse of this stiffness, it is possible that the stiff chain is caught between flow planes rather than residing within a number of flow planes as modest flow occurs. This would result in a greatly decreased viscosity. Second, errors exist because of the possibility that such polymers fluorescence. Thus, this same polymer showed a of 1.5 x 10 before correction for fluorescence. After correction, the was reduced to 7 x 10. Third, anomalous scatter may result from color or absorption. This was tested for the antimony polymer and not found to be a factor. 

The concept of low-molecular-weight imide prepolymers can be viewed as an alternative route to enhanced processability. The development of such systems has been conducted on the basis of three fundamental requirements. First, the prepolymers should be of low molecular weight, allowing for the possibility of a low melting point and low viscosity. Second, imide groups should be present in the prepolymer so as to remove the particularly troublesome polyamic acid to imide conversion process mentioned previously. Third, the prepolymers should have reactive terminal groups capable of reaction by an addition mechanism so as to convert the molten prepolymer to a cross-linked polymer without the harmful evolution of volatiles. 

The simple extruder design analyzed here would not be implemented in practice because of obvious mechanical problems, but, as we shall see subsequently, it is sufficiently close to the description of a true single-screw extruder that the calculations done here are all relevant. There are three weaknesses in the analysis. First, we have considered only a Newtonian fluid, while most real polymers have highly shear-dependent viscosities. Second, our heat transfer analysis is inadequate, both because we have considered temperature- and pressure-independent physical properties and because we have been able to obtain explicit solutions only for certain limiting cases. Finally, we have not dealt with the flow in the neighborhood of the transition from the extruder channel to the die. All of these restrictions can be relaxed, as we shall see, but to do so for the latter two generally requires the use of numerical algorithms to solve the full equation set. We shall address this topic in Chapter 8. 

The preceding development assumed that solute molecules were present in each pore. The pore size distribution of porous membrane may be such that the solute molecules can enter only pores larger than the solute molecule. This has two effects. First, the development of the solvent flux expression (3.4.86) assumed no effects due to any solute molecules in reality, the solute molecules increase the solvent viscosity. Second, the solute flux expressed by (3.4.91c) may have to be corrected if all of the membrane pores are not available to solute molecules. Simplified analysis of such a case has been provided by Harriott (1973). 

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