Design And Layer-by-Layer Assembly Of A Polymer Multilayer Film Based On Halogen Bonding

The fabrication of structurally regulated organic ultrathin films by simple and convenient methods has gained a lot of attention in the fields of materials science and interface science, and ultrathin film through layer-by-layer(LbL) assembly has become one of the most active fields because of its strong potential in buildup of new materials. In order to develop the species and functionality of multilayer films, several intermolecular interactions, such as electrostatic interaction, hydrogen bonding, host-guest interaction,Ï€-Ï€stacking, coordination and so on, have been proved to be driving forces of multilayer films. Halogen bonding, which has done excellent performance in the field of supramolecular assembly, is a kind of noncovalent interaction involving a halogen(halogen bonding donor, normally iodine or bromine) and a Lewis base(halogen bonding acceptor, often an amine or pyridine derivative). It exhibits similar characteristics to hydrogen bonding in directionality and strength. It was exciting to see that halogen bonding prevailed over hydrogen bonding in a competitive recognition process. This observation suggested to us a new possible driving fore for LbL assembly. In this thesis, we attempted to develop a new kind of method to fabricate multilayer film on the basis of halogen bonding. It will give us inspiration of polymer design and synthesis as well as show us a new way to adjust and control the structure and quality of multilayer film.In chapter 2, we realized the 4-iodo-2,3,5,6-tetrafluorophenoxy group was a perfect group to forming strong halogen bonding because of the iodine atom's strong electron-accepting ability and the fluorin atom's strong electron-attracting ability.Thus we designed and synthesized a polymer poly(4-(4-iodo-2,3,5,6-tetra -fluorophenoxy)-butylacrylate)(PIPBA).In the chapter 3, we used the PIPBA and poly(4-vinylpyridine) (P4VPy) to fabricate a polymer multilayer film based on halogen bonding. The successful assembly of two polymer was confirmed by the linearly increasing process, and the mass of two polymers in each bilayer was calculated to be about 255 ng/cm~2. The surface of the multilayer film is flat, and the thickness of one bilayer is about 1.3 nm. Molecular weight of polymers and steric hindrance have effect on the fabrication of multilayer film. We also compared the stability of a halogen-bonded film in methanol with that of a hydrogen-bonded film. Furthermore, we fabricated a hydrogen/halogen-bonded hybrid film which was much more stable than the halogen-bonded film.chapter 4 gives us a view on our future halogen-bonding-related studies. On one hand, in order to promote the wide application of the halogen-bonding layer-by-layer assembly, we will continue to design and synthesize polymers with different halogen bonding donor/acceptor side-chain to fabricate new types of polymer films based on halogen bonding with different strength. On the other hand, we will directly detect the halogen-bonding based polymer adsorption force using single molecule force spectroscopy. It's helpful for understanding the halogen-bonding-based layer-by-layer assembly on molecular level.