"In and out diffusion" hypothesis of exponential multilayer film buildup revisited.

A hypothesis concerning the exponential buildup of polyelectrolyte multilayer films prepared by layer-by-layer assembly has become widely accepted in the scientific community. This model was first introduced with experimental data in Langmuir. It was subsequently described in Proceedings of the National Academy of Sciences and extended and amended in papers in Langmuir and other journals. According to the "in and out diffusion" hypothesis, as it is called, or "common rule" of exponential multilayer film buildup, as it is widely regarded, "a diffusion-based buildup mechanism ... explains most of the exponential-like growth process of polyelectrolyte multilayers reported in the literature." The present work offers an alternative viewpoint to specific elements of the hypothesis and the model as a whole.