Abstract Spin-casting is a widely used technique for fabricating uniform polymer thin films; however, the final film thickness is highly sensitive to processing parameters such as acceleration and polymer solution concentration. Here, we systematically investigate these effects through experiments and numerical simulations. A critical acceleration threshold is identified, below which the final thickness deviates markedly from conventional trends because of an “acceleration effect.” This effect arises from insufficient solvent spreading during the initial acceleration stage, resulting in residual film thickening. It becomes particularly pronounced at high spinning speeds, low polymer concentrations, low molecular weights, and under rapid solvent evaporation, when centrifugal thinning is suppressed, and evaporation dominates the thickness evolution. We further show that increasing the polymer concentration or molecular weight leads to a nonlinear increase in film thickness, which is attributed to enhanced chain entanglements and a rapid increase in solution viscosity that hinders hydrodynamic thinning and alters the evaporation profile. To rationalize these observations, we develop an improved mathematical model that incorporates time-dependent viscosity and concentration changes associated with solvent evaporation and polymer diffusion. The model successfully reproduces the observed nonlinearities and transition thresholds, providing a deeper mechanistic insight into thickness formation during spin-casting.
Iino et al. (Fri,) studied this question.