Polymer Micelles As Building Blocks For Layer-by-Layer Assembly: A New Method Of Stepwise Self-Assembly

Layer-by-layer (LbL) assembly has been widely used as a versatile method for fabricating multilayer thin films with tailored structure and composition. Although numerous substances have been assembled successfully into the films, there still exist many functional molecules with special structures that cannot be assembled via conventional LbL methods. To solve this problem, scientists have developed an unconventional LbL method, which involves a process of precursor assembly via a supramolecular interaction and a conventional LbL procedure with the precursor assemblies as building blocks. Until now, several intermolecular interactions, such as host-guest interaction,π-πstacking, coordination, electrostatic interaction, hydrogen bond and so on, have been proved to be driving forces of the formation of the precursor assemblies. In this thesis, we use poly(styrene-b-acrylic acid), an amphiphilic block copolymer, as a model system and attempt to use the block copolymer micelles as matrixes for incorporation of some water-insoluble molecules for LbL assembly. Furthermore, the properties of these functional molecules in the multilayer films are also studied.In chapter 2, we realize the assembly of water-insoluble pyrene molecules into polyelectrolyte multilayer films by the unconventional LbL method. Moreover, we demonstrate that the loaded molecules can be released from the LbL films, which can be controlled by ionic strength as well as influenced by the core-shell structures of the block copolymer micelles. During the incorporating experiments, we can verify the compatibility between the functional molecules and the block copolymers play a predominant role in the procedure of the co-assembly, higher compatibility leads to higher incorporation amount. By this stepwise assembling method, we develop an approach for assembly of hydrophobic molecules into the multilayer films.In chapter 3, we employ the block copolymer micelle as matrixes for the incorporation of azobenzene and then fabricate the multilayer films with PDDA. By this method, azobenzene is assembled into the LbL films, and its photoisomeric behavior in the films is induced by UV-vis irradiation. We find that the photoisomerization of azobenzene in the LbL film is quite similar to its diluted solutions and exhibit a certain fatigue resistance. Moreover, the photoisomerization rates of the azobenzene in the films can also be adjusted by the incorporation amount of azobenzene as well as the core-shell structures of the block copolymer micelles. The application of this method to enhance the optical properties of photochromic species is greatly anticipated.In chapter 4, we perform a micellization at 60℃to increase the compatibility between the azobenzene-containing amphiphile Azo-AOT and the block copolymers, and realize the incorporation of Azo-AOT into the micelles and multilayer films. This method allows us to assemble some functional amphiphiles into LbL films. It is found, interestingly, that the amount and aggregation states of Azo-AOT in the micelles can be tuned by co-assembly with different block copolymers. Thus, Azo-AOT exhibits different photoisomeric rates in different micelles, which is related to the different aggregating states of Azo-AOT in these micelles. These polyelectrolyte/micelle films incorporating functional amphiphiles have great potential in the field of functional thin films.