Fabrication Of Robust Layer By Layer Nanometric Thin Films By Post-Infiltration And A Subsequent Photo-Cross-Linking Strategy

The layer-by-layer (LbL) self-assembly technique has been proven to be a convenient method of constructing nanothin films with tailored composites, structures and surface properties. The LbL multilayers are usually fabricated under ambient conditions without affected by substrate. However, the driving forces for construction LbL multilayers are generally weak supramolecular interactions the assembled multilayers are unstable in certain situations, such as in solutions with high/low pH values, in solutions of high ionic strength, in good solvents of the employed polyelectrolytes, or in solutions with disturbances, like under sonication. The insufficient stability of the traditional LbL multilayers posed pressing challenges for the application of LbL multilayers. To address this challenge, chemists have developed strategies to convert the interlayer forces from weak supramolecular interactions to strong covalent bonds.Our group has developed a facile method for fabrication of robust LbL multilayers by post-photo-cross-linking of azido groups. After multilayers were constructed employing the LbL technique,4,4’-diazostilbene-2,2’-disulfonic acid disodium salt (DAS) was post-infiltrated into the multilayers and subsequent photochemical cross-linking was completed under UV irradiation. The negative charges would presumably improve its compatibility with the polyelectrolyte multilayers, and the azido groups were able to generate a highly reactive nitrene intermediates under UV irradiation. Nitrene was expected to insert into its adjacent C-H, N-H or O-H bond unselectively. We have prepared robust polyelectrolytes multilayers such as PAH/PAA and PAH/PSS by using this method. In this thesis, we applied this method to prepare stable LbL multilayers incorporating nanoparticles. Furthermore, we fabricated robust surface molecular imprinting in layer-by-layer (SMI-LbL) devices by using this strategy.A series of data show that the stability of multilayers with Fe3O4NPs and Au NPs were both improved significantly, and less than15%of the nanoparticles were lost from the multilayers after an intensive agitation. Meanwhile, a robust SMI-LbL device with high fatigue-resistance was achieved. The preparation conditions have been optimized to achieve repeated unloading and rebinding of the targeting molecule with high fidelity. We demonstrated that’post-infiltration and subsequent photochemical cross-linking’was a facile and efficient strategy to significantly stabilize LbL multilayers. Considering the widespread applications of layer-by-layer technique, it is anticipated that this line of research, which can be used to stabilize multilayers, will have promising applications in various functional systems.