Azobenzene polymer, briefly called as azopolymer, exhibits extraordinary light-matter interaction phenomena, which is ‘photo-fluidization’. This peculiar property gives unprecedented opportunities to fabricate unique 3D micro/nano structures based on directional movement. The azopolymer contains azobenzene groups grafted to the main chain, which undergo a repetitive photo-isomerization between trans- to cis-isomers until the long axis of the azobenzene is perpendicularly aligned to the polarization direction of the incident light. This photo-induced molecular reaction brings about the directional macroscopic motion of the azopolymer following the polarization direction of incident light even under the glass transition temperature (T$_g$) or melting temperature (T$_m$). For example, when linearly polarized light is irradiated to azopolymer, the mass migration only occurs following the polarization direction of incident light. Such polarization-dependent, fluidic behavior of azopolymer can be usefully used in numerous fields including micro/nano structuring. With azopolymer, inspired by living creatures in nature, many blue-prints for new innovations have been given to scientists and engineers in various fields since they have evolved naturally through rigorous competition to survive natural selection over millions of years. Thus, much effort has been given to mimic designs and materials of living creatures, which efficiently adapt to the harshest of environments. Against this backdrop, biomimetic 3D micro/nano structuring through photo-reconfiguration, exploiting azopolymer’s directional photo-fluidization, will be carefully discussed.
This thesis begins with some brief on azobenzene polymer and their behavior of photo-fluidization in Chapter 1; i) light-responsive behavior of azopolymer, ii) basic mechanisms and iii) the relevant application or patterning techniques (i.e. directional photo-fluidization lithography). After that, I describe a facile and pragmatic way of fabricating sub-micron sized bent pillar structure with programmable and systematic morphology controllability in Chapter 2. The fabricated structure in this work further extends to application in uni-directional wetting and directional adhesion. In Chapter 3, producing shark skin-mimetic denticle structure is presented, where interference light of two-incident light is exploited to form slant riblet geometry onto top of azopolymer pillar. The fabricated structure in this work paves a novel way to mimic complex denticle structure and suggests potential in study of structure-fluidic behavior in micro/nano scale. In chapter 4, brief summary of this thesis is presented.
azobenzene 작용기(-N=N-)를 포함하고 있는 고분자인 아조벤젠고분자는 ‘광유체화’라는 특별한 광-물질 상호 작용 현상을 보인다. 독특한 광응답형 특성은 3차원의 마이크로/나노 구조체의 형성에 유용하게 활용될 수 있다. 아조벤젠고분자는 특정 파장의 빛 조사시에 분자의 구조가 바뀌는 반복적인 광이성질화 반응의 결과로, 고유의 물리적/화학적 특성이 변화한다. 그 중, 가장 흥미로운 특성 변화는 조사되는 빛에 편광방향과 나란하게 움직이는 비등방성 이동 현상이다. 이러한 비등방성 광유체화 현상은 고분자의 유리전이온도 (T$_g$)보다 낮은, 상온 근방에서 일어나며, 빛이 조사되는 동안에만 일어난다. 아직까지 이러한 광유체화 현상에 대한 명확한 이유는 밝혀지지 않았으나, 이 현상은 마이크로/나노 패터닝, 나노 광학, 전기전자, 환경, 에너지 등 많은 분야에서 유용하게 사용되어 지고 있다. 본 학위 논문에서는 아조폴리머 특성인 비등방성 광유체화 특성과 더불어 자연계 생물의 구조 혹은 소재에서 모티브를 얻어 공학에 적용시키는 생체모방학의 접근론으로 생체 모사 3차원 미세 구조체의 제작에 대해 이야기한다.
