| Polyelectrolyte multilayers (PEMs) present a new class of nanostructured materials obtained through alternating self-assembly of water-soluble polymers at solid-liquid interfaces. The use of weak polyelectrolytes for the multilayers construction offers the advantage to engineer pH-responsive coatings of controllable film structure and thickness. A variety of potential applications in, for example, drug delivery and tissue engineering urge a better understanding of the fundamentals of the self-assembly and post-assembly response.; We present new fundamental insights into the stability regimes of multilayers made of weak polyelectrolyte (wPEMs) and into the ability of these films to controllably load and release functional molecules. We study two related classes of wPEMs where interactions between adjacent layers are controlled by either electrostatic or by hydrogen-bonding forces. Specifically, by applying in situ Fourier transform infrared spectroscopy in attenuated total reflection mode (FTIR-ATR) and ellipsometry we quantified amount adsorbed of multilayer constituents and showed that pH-induced film response is controlled by charge imbalance and by the strength of intermolecular interactions. Neutron reflectivity was employed to probe the degree of layer interpenetration at assembly and post-assembly steps.; With electrostatically assembled films, apart from the two conventional regimes of film pH-response---compositional stability or disintegration---we find a new regime in which a weak polyelectrolyte is selectively released from the film. Release is driven by the charge imbalance within the film, and is accompanied by dramatic randomization of layered film structure. With hydrogen-bonded multilayers, we observed a correlation between the strength of interlayer adhesion and the pH at which these films become unstable. By involving temperature-responsive polymers in hydrogen-bonding self-assembly, we broaden the pH-range of film stability and provide multilayers with temperature responsiveness. When deposited onto porous support membranes, such multilayers exhibit temperature-responsive control of small molecule permeability. Hydrogen-bonded films are also converted into polyacid surface hydrogels via chemical crosslinking, and they show reversible pH-triggered loading and release of functional molecules such as dyes and proteins. Our results demonstrate that WPEMs exhibit a close correlation between their structure and properties, which is essential for various applications. |
