Fabrication of porous hierarchical multilevel composite thin films by combining different self-assembly processes
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Kemian tekniikan korkeakoulu |
Master's thesis
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Authors
Date
2020-10-20
Department
Major/Subject
Functional Materials
Mcode
CHEM3025
Degree programme
Master's Programme in Chemical, Biochemical and Materials Engineering
Language
en
Pages
114
Series
Abstract
In nature, directed self-assembly on multiple length scales is commonly used to create superior structural and functional materials. Such control over different levels of patterning would also be of great interest for many advanced devices. By now, it remains challenging to fabricate such hierarchical structures. The spontaneous self-organization of block copolymers can further be used as a bottom-up self-assembly technique creating patterns with a 10-100 nm period. The formed pattern can be used to organize nanoparticles. Another self-assembly technique is the condensation of water onto drying polymer films, which can lead to highly ordered honeycomb like patterns, called breath figures, with pores of up to 20 µm in diameter. The pores can be utilized to selectively incorporate nanoparticles into the film. The combination of block copolymer (BCP) assembly and breath figure formation with the incorporation of different nanoparticles into the respective patterns should lead to a multi-hierarchical composite material allowing for unique property combinations and the independent tunability of each level of hierarchy. Using dip-coating for film formation will also allow to create such patterns on an industrial scale. In this thesis, an extensive literature review of the relevant mechanisms is presented. Polymer thin films were created via dip-coating and the complexity of the system increased stepwise. Poly(styrene) was chosen as preliminary cheap model polymer. Breath figures were induced by dispersing water droplets containing sucrose in the solution. Solution and synthesis parameters were optimized, and small ordered pores were mainly found at the bottom of the substrates, among some bigger ones. TiO2 nanoparticles were successfully introduced to assemble at the pores. Replacing poly(styrene) with poly(styrene)-block-poly(4-vinylpyridine) lead to multi-level polymer patterns, with breath figure induced micropores of 1-50 µm diameter, and BCP induced nanopores of 10-80 nm between. The nanoparticles presumably dissolved in the poly(4-vinylpyridine) block. Future directions of this research are discussed, including the continuation with a second type of nanoparticle to reach the desired organisation of different nanoparticles at different length scales.Description
Supervisor
Vapaavuori, JaanaThesis advisor
Nguyen, HoangKeywords
thin film, self-assembly, breath figures, block copolymer, nanoparticles, Pickering emulsion