Dynamics of Polymer Decompression: Expansion, Unfolding and Ejection

The dynamics of polymer decompression, i.e., a process from compressed, compact state to the relaxed swoll en conformation, can be formally described as a {\it nonlinear diffusion}. We discuss here two basic examples: (i) the expansion, or unfolding from a compact state, and (ii) the ejection of pressed polymer through a pore. The problem can be solved exactly for the case (i), but not for the latter. Even in such situations, a scheme called {\it uniform approximation} is shown to be useful to get a physical insight involved. Its application to the case (ii) is able to account for conflicting numerical data in a consistent way.