Layer-by-layer Assembled Polymeric Films With Stimulus-Responsive And Self-healing Functions

In this dissertation, layer-by-layer (LbL) assembly was used to fabricate the humid-responsive polyelectrolyte films. The convenience of LbL assembly for precisely tailoring film structures allows for the fabrication of humido-responsive actuators and solvent-enabled self-healing films.(1) Although many kinds of stimulus-responsive materials utilizing asymmetric responsive properties of different layers have been fabricated, there are few reports on responsive free-standing films which have the same film composition but different layer structures. Here, by utilizing the strong swelling property of cross-linked poly(acrylic acid)(PAA)/poly(allylamine hydrochloride)(PAH) multilayer films, we fabricated the bilayer films comprising dense and porous layers of PAA/PAH films. After releasing these films from substrates, the bilayer films with asymmetric structures can bend/unbend quickly and reversibly to the variations of environmental humidity(1) Polyurethane (PU) is a polymer with good mechanical property. Because PU is poorly dissolved in water, LbL assembly of negatively charged PU with poly(acrylic acid)(PAA) in aqueous solutions produces PU/PAA films with coiled PU. Such PU/PAA films can heal cuts of several tens of micrometer wide by immersing the film in ethanol. Detailed study shows that the coiled PU in the films is key important for the healing ability of the films as coiled PU chains have more mobility under external stimulus.In contrast, LbL assembled PU/PAA films fabricated from ethanol do not have the self-healing ability because PU adopts extended configuration.