Chemically driven deformation of polymer glasses is important in a variety of electronic packaging applications ranging from stripping of photoresists to diffusion of processing liquids into printed circuit boards. The swelling of such glasses by small molecules requires the deformation of polymer chains, a deformation that can be modelled as driven by an osmotic pressure. Equations governing the rate of this process are developed and the predictions are compared with the results of experiments in which the volume fraction φ of iodohexane (IOH) sorbed at the surface of polystyrene is measured as a function of exposure time. Once a critical φ is reached, a diffusion front develops and moves into the polymer at a constant velocity. The velocity V of this front can be predicted quantitatively from
$V=D(φm)a′(φm)a(φm)∂φ∂tφm$
where D is the diffusion coefficient of the IOH in the glass, a, and a are the activity of IOH and its derivative with respect to φ and the subscript m signifies that the quantities are evaluated at the volume fraction of the maximum osmotic pressure ahead of the front. The φ(t) and V predicted by a pressure dependent viscous swelling model for ∂φ/∂t are in good agreement with the experimental results at low IOH activities.
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