Dynamics of polymer film formation during spin coating

Y Mouhamad,P Mokarian-Tabari,R A L Jones,M Geoghegan,N Clarke

doi:10.1063/1.4896674

Y Mouhamad, P Mokarian-Tabari + Show 3 more

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https://doi.org/10.1063/1.4896674

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Abstract

Standard models explaining the spin coating of polymer solutions generally fail to describe the early stages of film formation, when hydrodynamic forces control the solution behavior. Using in situ light scattering alongside theoretical and semi-empirical models, it is shown that inertial forces (which initially cause a vertical gradient in the radial solvent velocity within the film) play a significant role in the rate of thinning of the solution. The development of thickness as a function of time of a solute-free liquid (toluene) and a blend of polystyrene and poly(methyl methacrylate) cast from toluene were fitted to different models as a function of toluene partial pressure. In the case of the formation of the polymer blend film, a concentration-dependent (Huggins) viscosity formula was used to account for changes in viscosity during spin coating. A semi-empirical model is introduced, which permits calculation of the solvent evaporation rate and the temporal evolution of the solute volume fraction and solution viscosity.

Highlights

Spin coating is a technique widely used to make polymer films
The cell has three outlets: the first is for the deposition of the polymer solution, the second is for the ingress of solvent vapor, and the third to exhaust it. 3 l minÀ1 of nitrogen was allowed to flow in a bubbler filled with toluene
To verify that the fits obtained with the RBD model improve with reduced inertial forces, we study the thinning of a toluene at 2000 and 3000 rpm

Summary

Introduction

Spin coating is a technique widely used to make polymer films. A small change in the coating spin speed or on the concentration of the solution can lead to large changes in the final thickness. With the arrival of organic devices, considerable work has gone into controlling the morphology of polymer films. One can adjust the concentration of the solution, the polymer ratio, the spin speed, and, in addition, use thermal or solvent annealing techniques. In this way, it is possible to control the dynamics of film formation, which is intrinsically linked to the final structure of the film

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