Reversible Molecular Memory and pH-Switchable Swelling Transitions in Polyelectrolyte Multilayers

Abstract

The systematic design of materials that alter their macroscopic properties in response to environmental stimuli continues to provide a basis for stimuli-responsive applications in biomaterials and microelectronics. We report discrete volume phase transitions in ultrathin polyelectrolyte multilayers (PEMs) driven by changes in environmental pH of the post-assembled film. These films exhibit a history-dependent swelling behavior and molecular conformational memory. We illustrate that the same two polymerspoly(allylamine hydrochloride)/poly(styrenesulfonic acid) (PAH/SPS)can be incorporated into a multilayer film with specifically designed molecular architectures (by virtue of assembly pH conditions) that enable them to be either virtually insensitive or highly responsive to small changes in post-assembly pH. We thus provide a general design strategy for PEMs that exhibit multiple conformational states and related phenomena. We further demonstrate the ability to spatially regulate the affinity of molecular species to PEMSspecifically, by virtue of pH-triggered conformational changes in the PEM. Finally, we show the potential of these materials for sustained molecular release.