Getting inspiration of excellent mechanical properties of double network hydrogels

we explored to prepare a free-standing multilayer film with double network structure.The diffusion of the monomer

crosslinker

especially the initiator into the multilayer with different outermost layer was investigated by quartz crystal microbalance (QCM).The positive charged outmost layer of polyethylenimine (PEI) was proved to be beneficial to the diffusion of negatively charged initiator into the multilayer.A free-standing film can be formed by immersing the (PEI/PAA)12-PEI multilayer film in a solution consisting of monomer

initiator and crosslinker

following with a double crosslink process via photo and thermal polymerization.XPS data show that the upper and bottom surfaces of multilayers have similar components.Instead of a top hydorgel coating on the multilayer surface

the data proved the formation of a double network multilayer.The Young's modulus and ultimate strain of the free-standing film were 0.04 MPa and 2.7%

respectively.This method provides a facile method to improve the resilience of the multilayer and fabricate the free-standing film without changing the thickness of the multilayers.