Construction Of Free-standing Film With Double Network Structure By Layer-by-layer Self Assembly

Free-standing multilayer films with poor mechanical properties which is the main problem of multilayer films has limited the application of layer-by-layers method. Although you can peel off multilayer films from the substrate or fabricate multilayer films by fast-growing layer-by-layer self assembly, even select high-performance assembly components, there are still many problems in these methods. Recently fabricating free-standing ultra-thin multilayer film with good mechanical properties has attracted a lot of attention from scientists. Getting inspiration of excellent mechanical properties of double network, we construct multilayer with double network structure from electrostatic layer-by-layer self assembly and post-processing. Exploration on the regulation of the internal structure of multilayer films not only enhances the mechanical properties of multilayer films, but also provides a new approach to rich the functionalities of multilayer.1. Construction of double network free-standing film through the diffusion of small molecule. By testing the diffusion effects of the monomer, crosslinker, especially the initiator with different outermost layer of the (PEI9.0/PAA2.85)n multilayer through QCM-D, PEI outmost layer of the multilayer is beneficial to the diffusion of negatively charged initiator. XPS data show that the components of upper and bottom surface of multilayer proved the formation of double network multilayer but not the hydorgel coating on the multilayer surface. Immersed the (PEI9.0/PAA2.85)12-PEI multilayer film in a solution consist of monomer, initiator, and crosslinker, after a photopolymerization crosslinking and thermal cross-linking, free-standing film can be formed. Additionally, the Young's modulus and Ultimate strain of free-standing film were 0.04MPa,2.7%. Finally, without changing the thickness of the multilayers, this method can improve the resilience of the multilayer and fabricate the free-standing film.2. pH response, the light reversible cross-linking of double network multilayer. Using random copolymerization to synthesize poly(acrylic acid-random-coumarin methacrylate). This amphiphilic copolymer molecules has pH response, light reversible crosslinking groups and forms micelles in aqueous solution easily. Uncrosslinked P(AA-r-CMA) assembled with PEI in the solid-liquid interface can gain pH amplified exponential growth, but the use of light crosslinked P (AA-r-CMA) assembled with PEI multilayer film only shows linear growth. Uncrosslinked and crosslinked P(AA-r-CMA)/PEI multilayer films correspond to the interludes and the internal structure respectively. The multilayer film with interspersed internal structure loading drugs by post-diffusion method, crosslinking can promote the drug release; and multilayer film with layered internal structure loading drugs by pre-loading method, uncross-linking can promote the drug release. In addition to reversible cross-linking, multilayer films with different internal structure showes a completely different drug release behavior, and interspersed internal structure multilayer films with double network structure formed even by light and thermal cross-linking can still be maintained intact, enhancing the mechanical properties of multilayer film.