Tailorable Polyanion Diffusion Coefficient in LbL Films: The Role of Polycation Molecular Weight and Polymer Conformation

Assembly of oppositely charged macromolecules (proteins, DNA, polyelectrolytes) is often used for surface modification and functionalization. Yet, it remains a challenge to control the position and mobility of the molecules within the assembly. Using polyelectrolyte multilayers as model systems, we study the diffusion constant of the polyanion PSS. DPSS could be varied by 5 orders of magnitude. Two parameters were found to be important: (i) the conformation of the polyelectrolytes and (ii) the molecular weight of the polycation (Mw(PDADMA)); the latter was the dominant parameter. Independent of conformation, by increasing Mw(PDADMA), DPSS decreased by at least 3 orders of magnitude when Mw(PDADMA) increased by a factor of seven. The decrease was stronger than predicted by any scaling law; it was either exponential or abrupt after DPSS was almost constant for low Mw(PDADMA). The polymer conformation was adjusted with the salt concentration in the preparation solution. Flatter and less entangled chains led ...