The coating flow of non-Newtonian fluids on the surface of a flat rotating disk is analyzed with the power-law and Carreau constitutive equations. Numerical solutions using (1) the method of characteristics and (2) numerical integration are obtained for the film thickness profile as a function of spinning time, exhibiting the dynamics of the spin coating process for the deposition of polymer films for microelectronic devices. It is shown that even irregular (sinusoidal, Gaussian) initial fluid film thickness profiles smooth out to uniform films with spinning time for Carreau model flukte, whereas steep film thickness gradients persist for power-law fluids. The results also show the inherent limitation of the power-law model of non-Newtonian fluids in axisymmetlc free surface flow on a rotating disk. The results further show that the film thickness and its uniformity are determined chiefly by the rheological properties of the fluids and not by the initial profile prior to spinning.
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