결정 및 준-비정질 구조를 바탕으로 한 자극 감응형 포토닉 물질의 연구

Abstract

Polyelectrolyte hydrogels and colloidal nanoparticle assembly are responsive to the various stimuli, and which have been widely utilized for many applications including actuators, displays and sensors. Recently, there have been increasing research efforts of combining hydrogels or nanoparticles with other functional materials to extend their potential applications. For example, the photonic materials consisting of hydrogels or nanoparticles exhibit unique tunable photonic bandgaps (PBGs) in response to the various stimuli including pH, solvent, electric field, high-energy radiation etc. Volume transition of polystyrene-b-(quaternized-poly-2-vinylpyridine) (PS-b-QP2VP) lamellae by a selective swelling is useful for PBGs materials with large tunability. Charge driven nanoparticles assembly of quasi-amorphous photonic solution (QAPS) is also a great platform for optoelectric materials. In this thesis, I’ll address the responsive photonic mesostructured exhibiting strong reflective multi-colors in the visible regime modulated by physical and chemical stimuli. This thesis reports photosensitivity of photonic hydrogel and chemically and/or physically driven tunable PBGs properties of colloidal nanoparticles. In Chapter I, photoresponsive block copolymer photonic crystals exhibiting structural multi-colors in response to UV radiation energy will be presented. Block copolymer photonic gels reflect broad range of visible colors by controlling their swelling ratio. UV generates radicals on the polymer chain and induce crosslinking inside the blocks which decreases swelling ratio. Since the properties polyelectrolyte hydrogel is strongly dependent on ion-pair species, 2-vinylpyridine blocks of PS-b-P2VP block copolymer are quaternized with 1-methyl iodide and counter anions are exchanged with various kinds of ions. In this case, photosensitivity of our block copolymer photonic gels can be accelerated or decelerated by species of ion-pairs. The photo-reactive anion such as acetate, phenoxide and catecholate generate the reactive radicals effectively upon irradiation of UV, and then which can be quickly propagated to polymer chains by hydrogen abstraction process. However, radical generation can be retarded by using electron withdrawing groups such as trifluoroacetate and halogen anions. In other words, the photosensitivity of block copolymer photonic gel can be tuned by varying counter-anions and all of these results can be visualized by large PSB shifts against the exposure of UV. Chapter II shows colloidal glassy photonic solutions exhibiting high color saturation and color gamut. Colloidal SiO2 nanoparticles doped with small amount of light absorbing particles are used for our experiments. Polydopamine (PDA) is selected as a model dopant of absorbing light due to its broad absorption range. SiO2 quasi-amorphous photonic solution (SiO2-QAPS) doped with PDA exhibits unusual photonic responses. SiO2-QAPS doped with PDA shows strong enhancement of photonic reflectance and color contrast. The photonic color enhancement by PDA dopping is explained by interplay of absorption by dopants with periodicity in photonic structures. Chapter III reports fabrication method of double emulsion micro-capsules exhibiting photonic colors fabricated on a two-stage consecutive flow-focusing microfluidic chip and an in situ UV polymerization technique. Three immiscible fluids were employed to create double emulsion such as polydopamine modified SiO2 quasi-amorphous photonic solution (SiO2@PDA-QAPS) for the core material, organic UV curable monomers for the shell and silicon oil as the carrier solution. Photonic droplets form at the first focusing junction, and then double emulsion structure is developed as passing through the second focusing junction. The size of microcapsule was controlled by changing the flow rate of the fluids. The flow rate of SiO2@PDA-QAPS and UV curable monomers are optimized at 0.08 and 0.1 mL/h respectively, and the shell thickness of the microcapsule is controlled from 8.8 to 22.1 μm by adjusting by the flow rate of silicon oil. The colors of fabricated photonic capsules are controlled by changing the size of nanoparticles. The last part, Chapter IV reports dielectrophoresis (DEP) induced photonic inks encapsulated in eccentric core-shell microcapsules form glassy photonic structures under an electric field. The microcapsules are prepared on two-stage consecutive flow-focusing microfluidic chip as mentioned in Chapter III, but the photonic solution is changed from SiO2@PDA-QAPS to SiO2@QAPS. Also, the microcapsules were designed to have eccentric core-shell geometry where one part of the shell has thicker than that of the other so that our SiO2 dielectric particles are easily response to a non-uniform electric field. The microcapsules dispersed in N-methylpyrrolidone (NMP) were deposited between two ITO glasses for electro-tuning experiments. SiO2-QAPS turned into blue color at the thinner-shell region within a second when the bias was applied upon E = 250 V/cm. The electric field profile and the particle trajactory are simulated by COMSOL Multiphysics so that we can figure out the electric field intensity and surmise particle movement. In addition, by using of the simulation, the property of the photonic inks exhibiting various photonic colors depending on the strength of local electric field has been utilized for measuring the electric field gradients by reading hue distances. |본 연구에서는 블록공중합체 및 콜로이드입자를 이용하여 자기조립을 통한 광밴드갭을 갖는 주기성/비주기성 구조를 제조하고 광결정 센서, 디스플레이 등 기술적으로 높은 잠재성을 가지는 새로운 물질 또는 물리/화학적 특성을 발견 제시하고자 한다. 외부 물리/화학적 자극에 쉽게 감응하는 블록공중합체 광결정은 광밴드갭의 변화를 쉽게 유도할 수 있으며 이를 통한 색 변화 센서응용이 가능하다. 콜로이드입자의 자기조립을 통한 비주기성, 유사비정질 구조 형성은 시야각에 무관한 광밴드갭을 형성하여 넓은 시야각을 통해 시각적 디스플레이 응용에 용이하고, 간단한 처리만으로 색재현율을 높이는 것이 가능하다. 콜로이드의 특성상 캡슐화를 통해 안정적인 픽셀을 만드는 것이 가능하며 내부 물리적 변화연구 역시 능동적으로 진행할 수 있다. 1장에서는 자외선 에너지 조사량을 통해 광밴드갭을 조절가능한 블록공중합체 광결정의 제조에 대해 논의하고자 한다. 1차원 층상구조 블록공중합체 광결정 (PS-b-QP2VP)은 용매에 의한 quaternized poly(2-vinylpyridine) (QP2VP) 블록의 팽윤을 통해 광범위한 영역에서 광밴드갭을 보여준다. 수화젤의 팽윤율은 PS-b-QP2VP 내의 QP2VP 블록의 가교율에 따라 달라지게 된다. 에너지가 높은 자외선 에너지가 블록공중합체에 가해지게 되면 고분자 사슬에 라디칼이 생성되고, 생성된 활성라디칼에 의해 QP2VP블록 내 서로 다른 고분자 사슬간의 임의 가교가 진행된다. 더 높은 에너지에 의해 가교율이 높아진 경우 팽윤율의 감소로 이어지게 되며 광밴드갭은 단파장으로 이동하게 된다. 수화젤은 이온쌍의 종류에 따라 특성이 많은 달라지는 것을 보여왔는데, 특히 본 연구에서 사용된 PS-b-QP2VP 수화젤의 경우 QP2VP 양이온과 쌍을 이루고 있는 음이온의 종류에 따라 상당히 다른 광감응도를 보였고 이는 광밴드갭의 변화를 통해 확인할 수 있었다. 광감응도가 높은 음이온으로는 acetate, phenoxide, chatecholate 등으로, QP2VP와 이온쌍을 이룰 경우 수소 떼기 반응을 통해 QP2VP 고분자 사슬 위에 활성라디칼을 유도하여 상당히 높은 광감응도를 보였고, 이것은 강한 광밴드갭 변화로 나타났다. 반면, 광감응도가 낮은 음이온으로는 전기음성도가 높거나 전자끌기에 능한 작용기가 존재하는 할로겐 이온이나 trifluoroacetate 이온의 경우 라디칼이 이러한 이온에 의해 안정화되어 고분자 사슬위에 활성라디칼 형성을 막게 된다. 따라서 QP2VP 의 가교는 일어나지 않게 되고 광밴드갭 변화는 일어나지 않게 된다. 이와 같이, 본 연구에서 개발한 자외선 감응 블록공중합체는 이온쌍 변화를 통해 감응도를 조절할 수 있으며 이러한 결과는 광밴드갭의 변화를 통해 확인할 수 있다. 2장에서는 높은 색재현율과 반사율을 가지는 준비정질 콜로이드 광결정에 대하여 발표하고자 한다. SiO2로 이루어진 콜로이드 광결정 속에 광밴드갭과 유사한 흡광범위를 갖는 미세량의 흡광제를 넣어 줌으로써 시스템을 완성하였다. 가시광선의 넓은 영역에서 높은 흡광계수를 가지로 있는 polydopamine (PDA)을 SiO2 나노입자 수용액 광결정 (SiO2-QAPS) 용액에 소량 첨부 할 경우 색재현율과 반사율의 높은 증가를 보여주었다. 이러한 광결정의 광특성 증가는 흡광제에 의한 빛의 흡수와 주기성을 지닌 광결정의 광반사의 상호작용에 따른 결과로 예측할 수 있다. 3장에서는 준비정질 콜로이드 광결정 수용액을 중심부에 지니고 있는 이중액적 마이크로캡슐 제조방법에 대해 설명하고자 한다. 연속적인 2단계의 흐름-집중 접합 구조를 가지고 있는 미세유동칩 속에 세 가지 섞이지 않는 액체를 차례로 각각 주입하여 이중액적 마이크로캡슐을 제조할 수 있다. PDA가 코팅되어 있는 SiO2 나노입자로 구성된 준비정질 콜로이드 광결정 용액 (SiO2@PDA-QAPS)을 중심으로 하고, UV에 의해 빠른 시간 안에 가교 및 고분자를 형성하는 UV감응 단분자를 껍질 물질로 정하고 마지막으로 실리콘오일을 생성된 이중액적 방울의 이동상으로 사용하였다. 광결정 용액 방울은 첫 번째 접합지점에서 생성이 되고, 두 번째 접합지점에서 이중액적 구조가 완성된다. UV 조사를 통해 최종 고정된 껍질로의 마이크로캡슐 제조가 완료된다. 마이크로캡슐의 전체 사이즈 및 껍질의 두께는 SiO2@PDA-QAPS 용액과 UV감응 단분자의 흐름속도의 상대적 변화에 따라 최소 8.8 μm 에서 최대 22.1 μm까지 조절이 가능하다. 4장에서는 콜로이드 나노입자의 유전이동(dielectrophoresis)을 통해 준비정질 콜로이드 광결정 용액을 중심에 포함하고 있는 마이크로캡슐 내부의 전기장 변화를 시각적으로 확인할 수 있는 방법에 대해 논의하고자 한다. 3장에서 논의했던 것과 마찬가지로 마이크로캡슐을 같은 방법으로 제조하되, SiO2 나노입자를 준비정질 콜로이드 광결정 용액으로 사용하였다. 마이크로캡슐 내부에 전기장 기울기를 발생시키기 위해 캡슐은 비대칭적 구조를 갖도록 제조하였다. 생성된 캡슐은 N-methylpyrolidone (NMP) 용액에 분산되었고, 두 ITO 전극 사이에 놓여지도록 하였다. E = 250 V/cm 에 해당하는 전기장을 두 ITO 전극 사이에 발생시킬 경우 캡슐 내부의SiO2@QAPS는 유전이동에 의해 광밴드갭을 형성하게 된다. 캡슐 내부의 전기장의 세기와 나노입자의 움직임은 COMSOL Multiphysics 시뮬레이션을 통해 예측 가능하였고 이는 실험결과와 일치하였다. 유전이동의 원리에 의해 국부전기장의 세기에 따라 나노입자의 농도가 달라지게 된다. 캡슐 내부 국부전기장의 세기 차이는 광밴드갭 형성의 결과로 나타나는 색 차이로 구별 가능하다. 이 시스템을 통해 수 μm 크기의 범위 안에서 측정장비의 제약 없이 전기장 세기의 차이를 색으로 손쉽게 구별 가능하다.; Polyelectrolyte hydrogels and colloidal nanoparticle assembly are responsive to the various stimuli, and which have been widely utilized for many applications including actuators, displays and sensors. Recently, there have been increasing research efforts of combining hydrogels or nanoparticles with other functional materials to extend their potential applications. For example, the photonic materials consisting of hydrogels or nanoparticles exhibit unique tunable photonic bandgaps (PBGs) in response to the various stimuli including pH, solvent, electric field, high-energy radiation etc. Volume transition of polystyrene-b-(quaternized-poly-2-vinylpyridine) (PS-b-QP2VP) lamellae by a selective swelling is useful for PBGs materials with large tunability. Charge driven nanoparticles assembly of quasi-amorphous photonic solution (QAPS) is also a great platform for optoelectric materials. In this thesis, I’ll address the responsive photonic mesostructured exhibiting strong reflective multi-colors in the visible regime modulated by physical and chemical stimuli. This thesis reports photosensitivity of photonic hydrogel and chemically and/or physically driven tunable PBGs properties of colloidal nanoparticles. In Chapter I, photoresponsive block copolymer photonic crystals exhibiting structural multi-colors in response to UV radiation energy will be presented. Block copolymer photonic gels reflect broad range of visible colors by controlling their swelling ratio. UV generates radicals on the polymer chain and induce crosslinking inside the blocks which decreases swelling ratio. Since the properties polyelectrolyte hydrogel is strongly dependent on ion-pair species, 2-vinylpyridine blocks of PS-b-P2VP block copolymer are quaternized with 1-methyl iodide and counter anions are exchanged with various kinds of ions. In this case, photosensitivity of our block copolymer photonic gels can be accelerated or decelerated by species of ion-pairs. The photo-reactive anion such as acetate, phenoxide and catecholate generate the reactive radicals effectively upon irradiation of UV, and then which can be quickly propagated to polymer chains by hydrogen abstraction process. However, radical generation can be retarded by using electron withdrawing groups such as trifluoroacetate and halogen anions. In other words, the photosensitivity of block copolymer photonic gel can be tuned by varying counter-anions and all of these results can be visualized by large PSB shifts against the exposure of UV. Chapter II shows colloidal glassy photonic solutions exhibiting high color saturation and color gamut. Colloidal SiO2 nanoparticles doped with small amount of light absorbing particles are used for our experiments. Polydopamine (PDA) is selected as a model dopant of absorbing light due to its broad absorption range. SiO2 quasi-amorphous photonic solution (SiO2-QAPS) doped with PDA exhibits unusual photonic responses. SiO2-QAPS doped with PDA shows strong enhancement of photonic reflectance and color contrast. The photonic color enhancement by PDA dopping is explained by interplay of absorption by dopants with periodicity in photonic structures. Chapter III reports fabrication method of double emulsion micro-capsules exhibiting photonic colors fabricated on a two-stage consecutive flow-focusing microfluidic chip and an in situ UV polymerization technique. Three immiscible fluids were employed to create double emulsion such as polydopamine modified SiO2 quasi-amorphous photonic solution (SiO2@PDA-QAPS) for the core material, organic UV curable monomers for the shell and silicon oil as the carrier solution. Photonic droplets form at the first focusing junction, and then double emulsion structure is developed as passing through the second focusing junction. The size of microcapsule was controlled by changing the flow rate of the fluids. The flow rate of SiO2@PDA-QAPS and UV curable monomers are optimized at 0.08 and 0.1 mL/h respectively, and the shell thickness of the microcapsule is controlled from 8.8 to 22.1 μm by adjusting by the flow rate of silicon oil. The colors of fabricated photonic capsules are controlled by changing the size of nanoparticles. The last part, Chapter IV reports dielectrophoresis (DEP) induced photonic inks encapsulated in eccentric core-shell microcapsules form glassy photonic structures under an electric field. The microcapsules are prepared on two-stage consecutive flow-focusing microfluidic chip as mentioned in Chapter III, but the photonic solution is changed from SiO2@PDA-QAPS to SiO2@QAPS. Also, the microcapsules were designed to have eccentric core-shell geometry where one part of the shell has thicker than that of the other so that our SiO2 dielectric particles are easily response to a non-uniform electric field. The microcapsules dispersed in N-methylpyrrolidone (NMP) were deposited between two ITO glasses for electro-tuning experiments. SiO2-QAPS turned into blue color at the thinner-shell region within a second when the bias was applied upon E = 250 V/cm. The electric field profile and the particle trajactory are simulated by COMSOL Multiphysics so that we can figure out the electric field intensity and surmise particle movement. In addition, by using of the simulation, the property of the photonic inks exhibiting various photonic colors depending on the strength of local electric field has been utilized for measuring the electric field gradients by reading hue distances.