Polymers uniform fluids

Viscosity measurements on dilute polymer pseudo- solutions can be used to determine the molecular weight of the dissolved polymer. The uniform dispersal of polymer molecules in solvent is ealled a pseudo-solution beeause polymer molecules are so large that cubic nanometer volumes in the fluid that contain a polymer molecule are decidedly different than equal volumes of the fluid that do not contain a polymer. A fluid that has dissolved a polymer is therefore not isotropic and is not a true solution. 

Background on Spin Casting. As early as 1958, Emslie, et al. (A) proposed a theoretical treatment of spin casting for nonvolatile Newtonian fluids. This theory predicted that films formed on a flat rotating disc would have radial thickness uniformity. They predicted that the final film thickness would depend on spin speed (w) and viscosity (ij) as well as other variables such as liquid density and initial film thickness. The dependence of thickness on u> and ij was also recognized by many of the other authors reviewed in this paper, and their proposed relationships are compared in Table I. Acrivos, et al. (5) extended the Emslie treatment to the general case of non-Newtonian fluids, a category into which most polymers fall. Acrivos predicted that non-Newtonian fluids would yield films with non-uniform radial thickness. 

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