Layer-by-Layer Assembled Multifunctional Adhesive Films

Water-based adhesives which have strong adhesion and can simplify the adhesionprocess, endow the adhesives with desired functions are important for variousapplications. Adhesives can be either pastes or films based on their physical forms.Compared with pastes, adhesive films have the advantages of convenience in storage andhandling, and conformal adhesion due to their homogeneous thickness. Traditionaladhesive films composed of thermoplastic polymers usually require thermal treatments ororganic solvents in the adhesive process, which make the adhesion process complicatedand environmentally unfriendly. The layer-by-layer (LbL) assembly, which involves thealternate deposition of species with complementary interactions, is currently a powerfulmeans for fabricating composite films with precisely controlled film structure andcomposition. Previous studies show that LbL assembled polyelectrolyte films arepromising as adhesives. However, considering the wealth of functions of LbL assembledpolyelectrolyte films, their functions as adhesive films have not been fully exploredbecause no other functions have been integrated into the LbL assembled adhesive films.In chapter1, we briefly introduced the recent development of the LbL assembly,theories of adhesion and film adhesives. Although LbL assembled polyelectrolyte filmshave been used as adhesive films, their potential as bioadhesives, conductive adhesives,and so forth are far more being explored.In chapter2, water-based highly adhesive films with satisfactory electricalconductivity are constructed by sandwitching AgNWs into LbL assembled branchedpoly(ethylenimine)/poly(acrylic acid)(bPEI/PAA) films. The electrical conductivity of the adhesive films is ca.0.1S m-1.Confocal laser scanning microscope (CLSM)measurements disclose that the strong adhesion originates from the intermixing ofpolyelectrolytes at the interface of two contacted adhesive films. Strong adhesion as highas～7MPa can be achieved when ITO glass substrates deposited with LbL assembledelectrically conductive adhesive films are slightly pressed together, which means that theglued conductive adhesive films with an area of1cm2can hold a weight of approximate70kg. Poly(allylamine hydrochloride)-carbon nanotube (CNT) complexes were also LbLassembled with a blend of poly(acrylic acid) and CNT to produce electrically conductiveadhesive films.The thin nature of the adhesive films and the incorporated conductivefillers such as AgNWs and CNTs endow the adhesive films with satisfactory electricalconductivity.In chapter3, water-based highly adhesive films with drug delivery ability arefabricated by LbL assembly of chemically cross-linked poly(allylaminehydrochloride)-dextran (PAH-D) microgels and hyaluronic acid (HA). Strong adhesion ashigh as6.95±0.92MPa can be achieved when glass substrates deposited with LbLassembled PAH-D/HA films are slightly pressed together. Free-standing PAH-D/HAfilms can use directly as adhesives because PAH-D microgels have strong interactionswith various surfaces. PAH-D/HA adhesive films can load negatively charged drugs suchas ibuprofen based on electrostatic interaction between PAH-D microgels and ibuprofenmolecules and release them in physiological conditions. Ibuprofen-loaded PAH-D/HAfree-standing films can strongly glue periostea, promising their potential application asbioadhesives capable of accelerating the healing of damaged tissues or organs.In chapter4, cathnol/dopamine-grafted oppositely charged polyelectrolytes wereLbL assembled to fabricate waterproof adhesive films. These adhesive films can worknot only in an environment of100%relative humidity, but also in water. A lap shearstrength more than1MPa can be achieved in an environment of100%relative humidity.Moreover, the present design of waterproof adhesives can be extended to the fabrication of biocompatible adhesive films by using biopolymers as building blocks. It is expectedthat the waterproof adhesive films are potentially useful in tissue engineering.