The Princess and the Pea Effect: Influence of the first layer on polyelectrolyte multilayer assembly and properties

In many applications of polyelectrolyte multilayers (PEMs), a base polycation layer is adsorbed to promote adhesion of the PEM to the substrate. In this report, the effect of the first polyelectrolyte adsorbed in a PEM was investigated by assembling PEMs with first layer polycations of different chemistries and molecular weights. In this study, quartz crystal microbalance with dissipation monitoring (QCM-D) was used to monitor the PEM assembly process. First layer choice affects the total mass accumulation of the PEM as well as the stoichiometry of the PEM, although linear growth was observed in all cases. PEM thickness was also affected by first layer choice, although not consistent with changes in mass. Combined with the stoichiometry results, these findings indicate that the structure of a PEM is fundamentally different depending on first layer chemistry and molecular weight. PEM topography is also affected by first layer choice. Selection of appropriate first layer material is therefore an important consideration in the design of a PEM, and changing first layer material may be a facile way to tailor the structure and properties of PEMs.