Modeling the Buildup of Polyelectrolyte Multilayer Films Having Exponential Growth

Two types of polyelectrolyte multilayer films have been reported in the literature. These are (i) films whose mass and thickness increase linearly as the number of deposited bilayers increases and (ii) films that grow exponentially. We present a model for the buildup of exponentially growing films that allows a discussion of the behavior of them in a unified manner. This model is based on the diffusion both in and out the whole film of part of the chains of at least one of the polyelectrolytes constituting the multilayer. In short, the film is brought into contact with the solution of polyelectrolytes that are able to diffuse into the film. Inside of the film, chains of this polyelectrolyte constitute the “free” chains. At the subsequent rinsing step, some of them diffuse outward from the film. The remaining chains leave the film as it is brought into contact further with the polyelectrolyte solution of opposite charge. As the “free” chains reach the film/solution interface, they are complexed by the poly...