Abstract I 中文摘要 II 致謝 III Contents IV List of Scheme VI List of Table VI List of Figures VII 1. Introduction 1 1.1 Preface 1 1.2 Research Motivation 2 2. Literature Review 3 2.1 Introduction of Liquid Crystals 3 2.2 History and Development of LCs 4 2.3 Classification of Liquid Crystal 5 2.3.1 Thermotropic Liquid Crystals 5 2.3.1.1 Nematic Liquid Crystalline Phase 6 2.3.1.2 Cholesteric Liquid Crystalline Phase 7 2.3.1.3 Smectic Liquid Crystalline Phase 11 2.3.2 Lyotropic Liquid Crystals 12 2.4 Anisotropic Property of LCs 13 2.4.1 Birefringence of LCs 14 2.4.2 Dielectric Properties of LCs 16 2.5 Surface Anchoring of Liquid Crystals 17 2.5.1 Physically Induced Alignment 18 2.5.2 Chemically Induced Alignment 19 2.5.3 Photoalignment 21 2.6 Introduction of Liquid Crystalline Actuators 22 2.6.1 Thermally Driven LC Actuators 22 2.6.2 Humidity-sensitive LC Actuators 26 2.6.3 Light-Driven LC Actuators 27 2.7 Structural Color 30 3. Experimental Section 31 3.1 Materials and Instruments 31 3.2 Experimental Process 33 3.2.1 Fabrication of Liquid Crystal Cells 33 3.2.2 Fabrication of Liquid Crystalline Actuators 35 3.2.3 Preparation of LC Films for SEM Observation 38 3.2.4 Therma Properties of LC Films 39 3.2.5 Transmittance Analysis of LC Films 39 3.2.6 Reflective Analysis of LC Films 39 4. Result and Discussion 40 4.1 Characterization of Precursor Mixtures 40 4.1.1 Component of LC Mixtures 40 4.1.2 Thermal Properties of the Precursor Mixtures 41 4.1.3 POM of Precursor Mixtures 42 4.2 Morphology of LC Films 43 4.3 Characterization of Anti-Parallel Films 46 4.3.1 Reflection Band of Anti-Parallel Films 46 4.3.2 Thermal Effect on Anti-Parallel Films 48 4.4 Characterization of Parallel-Perpendicular Films 51 4.4.1 Thermal Property of Parallel-Perpendicular Films 51 4.4.2 Dependence of Bending Angle on Thickness 53 4.4.3 Thermal Effect on Optical Property of LC Films 57 4.5 Thermal Actuation of Parallel-Perpendicular Films 63 4.6 Biomimetic Butterfly-Shaped Actuators 66 5. Conclusions 68 6. Reference 69 List of Scheme Scheme 3-1 Schematic illustration of the fabrication of parallel alignment layer on substrate. 34 Scheme 3-2 Schematic illustration of the fabrication of perpendicular alignment layer on substrates. 34 Scheme 3-3 Schematic illustration of assembly of liquid crystal cell. 35 Scheme 3-4 Schematic process of fabrication of films. 37 Scheme 3-5 Molecular alignment in the anti-parallel cell and parallel-perpendicular alignment. 37 List of Table Table 3.1 List of used material in this research. 31 Table 3.2 Lists instruments used in this study. Hot stage, rubbing machine, hot plate, ultrasonic cleaner, circulator oven, and handheld UV lamp (with 254 nm wavelength) were used to prepare liquid crystalline films. Optical properties of sample were analyzed using polarized optical microscope (POM BH-2), spectrophotometer (LAMBDA 950), and fiber optical spectrometer (SL1 with reflectance accessories). Morphology was investigated by field emission microscope (SU-5000). Thermal properties of liquid crystal mixture and films were analyzed by differential scanning calorimeter (DSC 6000) and thermogravimetric analyzer (TGA 4000). Mechanical properties of films were analyzed by dynamic mechanical analyzer (RSA-G2). Butterfly-shaped actuator was cut by laser cutter engraver (WER-4040). 32 Table 4.1 The recipe of mixtures for three main color fabrication. a 40 List of Figures Figure 2-1 Illustration of phase transition of liquid crystals [1]. 3 Figure 2-2 The timeline of historical evolution of liquid crystals [2]. 4 Figure 2-3 The classification of liquid crystalline molecules. 5 Figure 2-4 (a) Schematic illustration of molecular arrangement in nematic phase and deviation angles between director and molecular axis. (b) Typical schlieren texture in the nematic phase showed four kinds of singularity [6]. 6 Figure 2-5 Schematic illustration of molecular arrangement in cholesteric liquid crystal phase. 8 Figure 2-6 Selective reflection of circular polarized light by right-handed cholesteric liquid crystals in the planar cell [9]. 9 Figure 2-7 (a) Different types of orientation in cholesteric liquid crystal phase showed various optical properties [12]. Typical images of (b1) planar state and (b2) focal conic state under POM [13]. 10 Figure 2-8 (a) Schematic diagram showed various smectic phase from the top view and side view [14]. The POM images show textures of (b) SmA phase and (c) SmC phase [15,16]. 11 Figure 2-9 Various types of lyotropic phases [17]. 12 Figure 2-10 Schematic illustration of anisotropic properties for rod-like liquid crystal. 13 Figure 2-11 The schematic illustration of uniaxial rod-like LCs with positive and negative birefringence. 14 Figure 2-12 (a) Simple illustration of POM. The schematic of illustrations show the optically anisotropy with (a) 0° (b) 45° and (c) 90° rotation. 15 Figure 2-13 The orientation of uniaxial molecules with positive or negative electric anisotropy under the electric field. 16 Figure 2-14 (a) Schematic illustrations of homeotropic, homogeneous, and intermediate surface alignment. (b) Various types of combined surface anchoring induce different molecular arrangement [18]. 17 Figure 2-15 Schematic illustration of rubbing method. 18 Figure 2-16 The sculpted pattern fabricated by diamond pen, ruler, and sandpaper [21]. 19 Figure 2-17 (a) Schematic illustration of LCs oriented by DMOAP. (b) Mechanism of hydrolysis reaction and polymerization of DMOAP. 20 Figure 2-18 Mechanism of photoalignment of (a) isomerization and (b) crosslinking [30,31]. 21 Figure 2-19 Schematic illustration shows reversible shrinkage and recovery of actuator with increased temperature [32]. 23 Figure 2-20 Mechanism of dynamic covalent bond exchanges. (a) Transesterification (b) Boronic-ester exchange reaction (c) Transcarbamoyalation (d) Disulfide bond exchange reaction (e) Allyl sulfide bond exchange reaction [33]. 23 Figure 2-21 (a) Schematic illustration of aligning process. (b) Reversible actuation of doom-shaped actuator by phase transition. (c) The combination of blue sample and opaque sample through boronic ester exchange reaction [34]. 24 Figure 2-22 (a) Schematic illustrations of self-healing. (b) Process of channels fabricated by laser cutter. (c) Injection of hot water made fluid-driven actuator lifted forty-gram counterweight [35]. 25 Figure 2-23 The electrically conducting film exhibited reversible actuation driven by (a) heating and (b) electricity [36]. 26 Figure 2-24 (a) Schematic illustration of mechanism that humidity-sensitive bilayer twisted as moisture absorbed. (b) The rotation angle of bilayer actuator raised with increased relative humidity [37]. 27 Figure 2-25 (a) Strip-like actuator was capable of crawling as repeatedly switching UV light on/off. (b) Wheel-like actuator continuously rolled under UV irradiation [38]. 28 Figure 2-26 Infrared thermal images and diagram showed photothermal effect of a PDA-SMP film under IR irradiation [39]. 29 Figure 2-27 Only PDA-SMP was driven NIR due to photo-thermal effect of PDA [39]. 29 Figure 2-28 Structural color in (a) skin of chameleon, (b) Philepitta castanea, (c) wings of butterfly, and (d) Pollia condensata fruits [40-43]. 30 Figure 3-1 Chemical structure of used compounds. 36 Figure 3-2 Schematic llustration of butterfly-shaped actuator consisting of anti-parallel film, paralel-perpendicular film, and a stick. 38 Figure 4.1 DSC diagram of the precursor mixtures showing clearing points variation. 41 Figure 4.2 POM textures of three sample mixtures filled in (a-c) parallel-parallel and (d-f) parallel-perpendicular cells at 55 °C, and (g-i) showing isotropic state at around 62 °C. 43 Figure 4.3 SEM images of (a) red, (b) green, and (c) blue anti-parallel films showing periodic constructions. 44 Figure 4.4 SEM images of (a) red (b) green, and (c) blue anti-parallel films showing periodic structure. The film thickness is 23 µm. 45 Figure 4.5 UV-vis spectrum of red anti-parallel film. 46 Figure 4.6 UV-vis spectrum of green anti-parallel film. 47 Figure 4.7 UV-vis spectrum of blue anti-parallel film. 47 Figure 4.8 Reflective spectrum of red anti-parallel film showing Bragg reflection. 49 Figure 4.9 Reflective spectrum of green anti-parallel film showing Bragg reflection. 49 Figure 4.10 Reflective spectrum of blue anti-parallel film showing Bragg reflection. 50 Figure 4.11 Photos exhibited the color variations of anti-parallel films at 150 °C and 250 °C. 50 Figure 4.12 TGA diagram shows thermal degradation temperature (Td) of parallel-perpendicular films. 52 Figure 4.13 DSC diagram showed glass transition temperature (Tg) of parallel-perpendicular films in heating cycle. 52 Figure 4.14 Schematic illustration shows the variation of molecular arrangement in heating and cooling cycles. 53 Figure 4.15 Dependence of bending angles on temperature and film thickness for red parallel-perpendicular film. 55 Figure 4.16 Dependence of bending angles on temperature and film thickness for green parallel-perpendicular film. 55 Figure 4.17 Dependence of bending angles on temperature and film thickness for blue parallel-perpendicular film. 56 Figure 4.18 Real images of bending performance of parallel-perpendicular films with different thickness at 150 °C. Sample size was fixed in 2 cm x 4 mm. 56 Figure 4.19 The reflection spectra of top and bottom sides of red parallel-perpendicular films. 57 Figure 4.20 The reflection spectra of top and bottom sides of green parallel-perpendicular films. 58 Figure 4.21 The reflection spectra of top and bottom sides of blue parallel-perpendicular films. 58 Figure 4.22 Dependence of reflective central wavelength of red parallel-perpendicular films on temperature. 59 Figure 4.23 Dependence of reflective central wavelength of green parallel-perpendicular films on temperature. 60 Figure 4.24 Dependence of reflective central wavelength of green parallel-perpendicular films on temperature. 60 Figure 4.25 Shift of central wavelength of red, green, and blue parallel-perpendicular films as temperature increased. 61 Figure 4.26 The reflective intensity of 23 µm green parallel-perpendicular film was reduced as temperature increased. 62 Figure 4.27 Stability of green actuator shows reversible actuation for 100 cycles. 63 Figure 4.28 Real images of 23 µm green actuator shows reversible bending between 50 °C and 150 °C after 1, 50, and 100 cycles. 64 Figure 4.29 (a) Schematic illustration of cutting direction and top view of the film, and (b) real images of reversible U-shape bending of the film via thermal stimuli. 65 Figure 4.30 (a) Schematic illustration of cutting direction and top view of the film, and (b) real images of reversible helical twist of the film via thermal stimuli. 65 Figure 4.31 Angular effect on the synthesized anti-parallel films cut into various shapes. 66 Figure 4.32 Real images shows reversible wing vibrations from (a) side view and (b) top view. 67