| Layer-by-layer (LbL) self-assembly of polymers at surfaces is a powerful technique to modify and functionalize surfaces or prepare free-standing ultrathin films. Due to their numerous advantages there has been growing interest in using LbL films in many applications, including but not limited to fuel cells, photonic devices, tissue engineering, controlled drug delivery and chemical sensing.;This dissertation examines strategies to introduce functionality to hydrogen-bonded (HB) multilayers at near physiological conditions. First, we developed routes to enhance stability of HB multilayers towards pH variations. Specifically, we introduced chemical crosslinking to multilayers of poly(N-vinylpyrrolidone) (PVPON) and poly(methacrylic acid) (PMAA) resulting in hydrogel-like film structure at neutral pH. Crosslinked films showed amphoteric swelling profile and reversibly uptook/released oppositely charged molecules under pH-cycling. We also showed that pH-stability of HB multilayers can be increased up to basic pH without chemical crosslinking, using tannic acid (TA), a polyphenol, as one of the film constituents. Critical dissolution pH of TA multilayers could be modulated in a pH range 7.5≤pH≤10 by changing the nature of neutral polymers. In addition, by using TA, we were able to shift pH window for film deposition up to neutral values.;Second, we developed principles for regulating release of macromolecules from films by constructing hybrid multilayers through incorporation of a highly acidic component into TA multilayers. We found that film components could be selectively dissolved at near-neutral pH and the critical pH and profile of dissolution were highly dependent on film architecture.;Finally, we extended our work to enhancing the loading capacity of HB films for hydrophobic molecules through incorporation of block copolymer micelles. We showed that a dually responsive block copolymer, poly(2-(diethylamino)ethyl methacrylate)-block-poly(N-isopropylacrylamide) (PDEA- b-PNIPAM) could self-assemble into micellar structures with PNIPAM-corona and PDEA-core above pH 7.5 at 25°C. By taking advantage of the neutral corona and the wide pH window for deposition of TA films, we were able to construct HB multilayers of PDEA-b-PNIPAM micelles and TA at pH 7.5. Lowering pH resulted in dissolution of the micellar cores and film restructuring.;Fundamental concept of this dissertation can serve as a model study for designing functional coatings and controlled delivery systems. |
