Supercritical CO2 dyeing of polyester fabric with photochromic dyes to fabricate UV sensing smart textiles

Photochromic molecules are well-established colourants in the manufacturing of niche products, providing reversible colour change effects when irradiated with ultraviolet (UV) light. The high mater ..

Valoon reagoivat atsobentseeniä sisältävät hybridiohutkalvot ALD/MLD-menetelmällä

Photochromic molecules show a change in their absorption spectrum when they are irradiated at a suitable wavelength. The difference is caused by a change in the structure of the molecule and is usually reversible. Such molecules can be used in applications utilizing their optical properties, such as lenses and filters, as well as applications utilizing the changes in their chemical or physical properties, such as optical switches. In this thesis, different photochromic molecules and thin film techniques are compared. In hybrid materials, the efficiency of the photoisomerization reaction depends on the ability of the photochromic molecule to change from one form to another. Free volume around the molecule has a great effect on its photoisomerization. A rigid matrix with a layered structure helps immobilize the molecules and thus improves the photochromic response. As atomic and molecular layer deposition (ALD/MLD) is based on self-limiting reactions by surface saturation, it should provide uniform, conformal thin films with a suitable layered matrix and accurate control of thickness. In the experimental part, the goal was to deposit photoresponsive thin films containing azobenzene using the ALD/MLD method. The organic precursor was azobenzene-4,4’-dicarboxylic acid and the inorganic precursor was trimethylaluminium. Both hybrid and superlattice thin films were deposited on silicon and quartz. The resulting films were amorphous and nearly homogenous, with a slight gradient seen on hybrid films. The growth rate of the hybrid thin films was lower than expected, and the decreased growth rate upon increasing the number of cycles suggested the presence of double surface reactions in the process. The hybrid thin film showed minor irreversible photoresponsivity after UV irradiation. Superlattice films with very thin oxide layers showed absorption bands related to azobenzene, but with increasing oxide thickness the bands disappeared. None of the superlattice films showed any response to UV irradiation. Poor photoresponsivity was attributed to steric hindrance, likely to be partially caused by the double surface reactions. The results were compared to similar hybrid systems found in literature.Fotokromaattisten yhdisteiden absorptiospektri muuttuu, kun niitä säteilytetään sopivalla aallonpituudella. Niiden eroavuus johtuu muutoksessa molekyylin rakenteessa, joka on usein reversiibeli. Kyseisiä yhdisteitä voidaan käyttää sovelluksissa jotka hyödyntävät niiden optisia ominaisuuksia, esimerkiksi linsseissä ja suodattimissa, sekä sovelluksissa jotka hyödyntävät niiden kemiallisia tai fysikaalisia ominaisuuksia, esimerkiksi optisissa kytkimissä. Tässä työssä vertaillaan eri fotokromaattisia yhdisteitä ja ohutkalvotekniikoita. Hybridimateriaaleissa fotoisomerisaation tehokkuus riippuu fotokromaattisen yhdisteen kyvystä muuttua muodosta toiseen. Vapaa tilavuus molekyylin ympärillä vaikuttaa suuressa määrin sen fotoisomerisaatioon. Jäykkä kerrosrakenteinen matriisi auttaa pitämään molekyylit paikallaan ja siten parantaa fotokromaattista vastetta. Atomi- ja molekyylikerroskasvatus (ALD/MLD) perustuu itserajoittuviin reaktioihin, joissa pinnat saturoituvat, joten sillä pitäisi saada kasvatettua tasalaatuisia, pinnan muotoihin mukautuvia ohutkalvoja, joissa on sopiva kerrosrakenteinen matriisi, ja joiden paksuutta voidaan kontrolloida tarkasti. Kokeellisessa osuudessa päämääränä oli kasvattaa atsobentseeniä sisältäviä valoon reagoivia ohutkalvoja käyttäen ALD/MLD-menetelmää. Orgaaninen prekursori oli atsobentseeni-4,4’-dikarboksyylihappo ja epäorgaaninen prekursori oli trimetyylialumiini. Hybridi- ja superhilaohutkalvoja kasvatettiin sekä pii- että kvartsisubstraateille. Kasvatetut kalvot olivat amorfisia ja lähes homogeenisiä. Hybridiohutkalvojen pinnalla nähtiin pieni gradientti. Hybridiohutkalvojen kasvunopeus oli odotettua matalampi, ja pienenevä kasvunopeus syklien määrän kasvaessa viittasi kaksoispintareaktioiden olevan osa kasvuprosessia. Hybridiohutkalvo reagoi UV-säteilytykseen vain hieman ja irreversiibelisti. Superhilaohutkalvoissa, joissa oksidikerrokset olivat hyvin ohuita, nähtiin atsobentseenille ominaiset absorptiovyöt, mutta paksummilla oksidikerroksilla vöitä ei enää nähty. Superhilaohutkalvot eivät reagoineet UV-säteilytykseen lainkaan. Huonon säteilyyn reagoivuuden syyksi epäiltiin steerisiä esteitä, todennäköisesti johtuen osaksi kaksoispintareaktioista. Tuloksia vertailtiin vastaaviin hybridirakenteisiin kirjallisuudessa

Innovative organic electroluminescent devices: diarylethenes as light-responsive switches and emissive graphene quantum dots

The awarding in 2016 of the Nobel Prize in Chemistry to Prof. J. Sauvage, J. F. Stoddart and B. L. Feringa, “for the design and synthesis of molecular machines” proves the interest of the scientific community and high-tech industry towards stimuli-responsive multifunctional materials and devices. In this direction, the research activity described in this thesis is focused on light-responsive emissive devices, which can be controlled remotely and reversibly via irradiation with light of specific wavelengths. A range of photochromic diarylethene derivatives were judiciously selected in combination with commercially available organic semiconductors to generate the light-responsivity in our devices. At first, optically switchable green-emitting OLEDs and micro-OLEDs were investigated achieving the maximum ON/OFF ratio of ~20 and ~90 for current density and luminance, respectively. Additionally, through the studying of the performance of light-responsive single carrier devices, it was demonstrated that electrons are more affected than holes by the switching of the photo-active dopant. The device emissive area was further scaled-down working on the characterization of light-emitting transistors (OLETs) having channel length of 2.5 µm. For the first time such devices covered the whole visible spectrum and a maximum ON/OFF ratio exceed 500 was achieved for both drain current and luminance. Finally, another macro-trend of the display community was addressed, the constant search for innovative chromophores as alternative to poorly stable and highly expensive iridium-based phosphorescent materials or highly toxic cadmium-based colloidal quantum dots. In this direction, air stable and potentially non-toxic red-emitting graphene quantum dots (GQDs) were embedded in electroluminescent devices. The LEDs showed high colour purity (FWHM= 30 nm), maximum luminance of 1300 cd/m2 and EQE of 0.67 % which are among the best performance ever reported for LEDs based on red-emitting GQDs

Exploiting the properties of mesoporous thin films

Questa tesi di dottorato si pone l’obbiettivo di esplorare le potenzialità offerte dai film sottili mesoporosi. Questi sistemi, infatti, offrono la possibilità di modulare molte delle loro caratteristiche più peculiari come la composizione chimica delle pareti dei pori, la struttura dei pori e la loro organizzazione e sono inoltre eccellenti matrici per strutture host-guest. Inizialmente, sono stati svolti diversi esperimenti in-situ durante l’autoorganizzazione dei film per indagare alcuni aspetti fondamentali di tale processo e per studiare le proprietà chimico-fisiche delle pareti dei pori. In seguito, sono state sfruttate le proprietà di questi materiali attraverso la funzionalizzazione delle loro strutture porose con coloranti, molecole organiche fotoattive e complessi inorganici. E’ stata anche testata la possibilità di utilizzare i pori come stampi monodispersi per la sintesi di nanoparticelle metalliche. Grazie all’elevata area superficiale e ad una particolare composizione chimica delle pareti dei pori, sono stati realizzati film mesoporosi a base di ossidi misti con proprietà ottiche modulabili. Infine, si è cercato di indurre più di un grado di auto-organizzazione all’interno dello stesso materiale per realizzare film a porosità gerarchica. Tre diverse strategie sono state impiegate per ottenere simultaneamente una macro- e una meso-porosità: stampaggio diretto con nanoparticelle fluorurate, separazione di fase controllata mediante l’aggiunta di un agente costampante e cristallizzazione controllata di un sale inorganico. I risultati presentati in questa tesi di dottorato dimostrano la versatilità dei sistemi mesoporosi per la realizzazione di materiali avanzati funzionali con un’ampia varietà di proprietà chimiche e morfologiche.Mesoporous materials show the possibility to tailor several of their characteristic features such as pore structure and arrangement, chemical composition of the pore walls, and, in addition, are excellent matrixes for host-guest systems. This doctoral work explores many of the potentialities offered by mesoporous thin films to produce advanced functional materials with a wide range of tunability in terms of properties and morphology. The first aim was to promote a basic study of self-assembly by in-situ experiments to reveal some fundamental aspects of the process and some chemicalphysical properties of the pore walls. Then, a full set of experiments was dedicated to exploit the mesoporous materials by functionalizing their porous structures with dyes, organic photoactive molecules and inorganic complexes. The pores were also used as a nanoreactor for controlled growth of metallic nanoparticles. Mesoporous mixed oxides films with tunable optical properties were obtained by using the high surface area and controlling the chemical composition of the pore walls. Finally, the possibility of inducing more than one degree of self-organization in the same material, to design hierarchical porous films, was also explored. Three different strategies were used to obtain macro- and meso-porosity, which include direct templating with fluorinated nanoparticles, controlled phase separation using a co-templating agent and controlled crystallization of an inorganic salt

액정 기반의 조정 가능한 회절격자 및 편광 의존 렌즈 어레이에 관한 연구

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2015. 8. 이신두.In recent years, as the employment of optical systems such as display, communication, and data storage has expanded explosively, more sophisticated functions are required to these optical systems. Therefore, fundamental optical components playing significant role in the operation of these optical systems including diffraction gratings, lenses, beam splitters, prisms, and optical filters are widely studied in order to assign advanced and particular functions to optical devices. Among various fundamental optical components described above, the diffraction gratings and the lens arrays composed of regularly aligned lenses have been considered as key elements which are studied most widely due to their wide applications and relatively simple operations and realizations. Since the tuning capability is essential for most recent optical systems, it is clearly required for the diffraction grating and the lens array to change the optical properties according to the external stimuli. For several decades, a number of types of tunable diffraction gratings and lens arrays have been suggested, and the optical properties of most of these devices were modulated by the applied electric voltage, the incident electromagnetic wave, or applied pressure. Especially, based on the large electro-optic modulation of liquid crystals (LCs) resulting from the high optical anisotropy and the electrically or optically tuning capability, a variety of tunable diffraction gratings and lens arrays using LC have been suggested. However, LC diffraction gratings suffer from the very limited diffraction pattern due to the difficulty in achieving unconstrained alignment, or the slow and small change in the diffraction characteristics when optically controlled. Furthermore, the applications of LC lens arrays are also limited owing to the sensitivity of LC alignment on the geometrically uneven substrate or the restricted focusing effect compared to other types of lens. This thesis primarily aims to demonstrate new types of LC diffraction gratings and LC lens arrays. It consists of three major categories, first one and the second one of which concern the electrically tunable LC grating, and the optically tunable ferroelectric LC (FLC) grating. The last one concerns the electrically tunable LC square lens array and the LC lenticular lens array. Firstly, a fully continuous LC grating device with the alternating semi-circular alignment which exhibits the switching effect between the diffraction orders independent of the thickness of the LC cell is demonstrated. The continuous phase modulation in the LC grating with the rotational symmetry was achieved on a micro-imprinted surface where the semi-circular alignment of the LC was spontaneously produced. This LC grating device in the hybrid geometry exhibited the perfect continuity of the phase retardation and the switchable diffraction as a function of an applied voltage. It was also found that the symmetry of the input polarization direction with respect to the grating patterns results in the interchange between two symmetric grating configurations. Secondly, an all-optically switchable FLC grating constructed in an alternating binary configuration with different optical properties from domain to domain is demonstrated. A dye-doped FLC is uniformly aligned in one type of domains whereas it is infiltrated into the photo-polymerized networks of reactive mesogens in the other. Compared to conventional nematic LC cases, this FLC-based grating allows more efficient all-optical modulation and faster diffraction switching in subsecond since the optical response associated with the dye molecules in the layered state is less hindered than in the orientationally ordered state. Finally, an LC-based square lens array with two focusing modes according to the polarization state of the input light is demonstrated. The homogeneously aligned LC layer is placed on an array of static square lenses fabricated using a photo-curable polymer whose refractive index is matched with the refractive index of the LC. For the input beam polarized parallel to the easy axis of the LC, the focal length is varied with the applied voltage. For the perpendicularly polarized input beam, the focal length is independent of the applied voltage and remains constant. An LC-based lenticular lens array, having a polarization-dependent focusing effect, fabricated through a simple imprinting process is also demonstrated. The input polarization-dependence of our LC lenticular lens array arises mainly from the index matching scheme between the polymer lenticular lens and the LC on it. In conclusion, throughout this thesis, new types of LC diffraction gratings including electrically tunable LC grating having continuous alignment geometry and optically switchable FLC binary grating with superb switching capability are demonstrated. Moreover, electrically tunable LC square lens array and LC lenticular lens array with perfect polarization-dependence are also described. These advanced fundamental optical devices will be useful for devising a variety of sophisticated optical systems.Contents Abstract i Contents v List of Figures viii Chapter 1. Introduction 1 1.1. Diffraction Gratings and Lens Arrays 1 1.2. Tunable Optical Devices 6 1.2.1. Tunable Diffraction Gratings 6 1.2.2. Tunable Lens Arrays 7 1.3. Outline of Thesis 8 Chapter 2. Theoretical Background 12 2.1. Basic Properties of Liquid Crystals 12 2.1.1. Liquid Crystals 12 2.1.2. Phases of Liquid Crystals 13 2.1.3. Alignment of Liquid Crystals 18 2.2. Reorientation of Liquid Crystals 24 2.2.1. Electric Field-Induced Reorientation 24 2.2.2. Light-Induced Reorientation 26 Chapter 3. Fully Continuous Liquid Crystal Grating 30 3.1. Introduction 30 3.2. Transfer Matrix Formalism for Diffraction 32 3.3. Fabrication Process of Diffraction Grating 35 3.4. Result and Discussion 38 3.4.1. Polarization-Dependent Diffraction Properties 38 3.4.2. Electrically Tunable Diffraction Properties 43 3.5. Summary 45 Chapter 4. Optically Switchable Ferroelectric Liquid Crystal Grating 46 4.1. Introduction 46 4.2. Photoresponse of Dye-Doped Ferroelectric Liquid Crystal 48 4.3. Fabrication Process of Diffraction Grating 54 4.4. Results and Discussion 58 4.5. Summary 61 Chapter 5. Polarization-Dependent Liquid Crystal Lens Arrays 62 5.1. Introduction 62 5.2. Square Liquid Crystal Lens Array 63 5.2.1. Fabrication Process 64 5.2.2. Results and Discussion 67 5.2.3. Polarization-Dependent Image Selection 73 5.3. Lenticular Liquid Crystal Lens Array 76 5.3.1. Fabrication Process 79 5.3.2. Results and Discussion 81 5.3.3. 2- and 3-Dimensional Display Applications 84 5.4. Summary 87 Chapter 6. Concluding Remarks 89 Appendix (acronyms) 92 Bibliography 93 Publications 103 Abstract (Korean) 111Docto

From nanoscopic to macroscopic photo-driven motion in azobenzene-containing materials

AbstractThe illumination of azobenzene molecules with UV/visible light efficiently converts the molecules between trans and cis isomerization states. Isomerization is accompanied by a large photo-induced molecular motion, which is able to significantly affect the physical and chemical properties of the materials in which they are incorporated. In some material systems, the nanoscopic structural movement of the isomerizing azobenzene molecules can be even propagated at macroscopic spatial scales. Reversible large-scale superficial photo-patterning and mechanical photo-actuation are efficiently achieved in azobenzene-containing glassy materials and liquid crystalline elastomers, respectively. This review covers several aspects related to the phenomenology and the applications of the light-driven macroscopic effects observed in these two classes of azomaterials, highlighting many of the possibilities they offer in different fields of science, like photonics, biology, surface engineering and robotics

Chiroptical Properties in Thin Films of π-Conjugated Systems

Chiral π-conjugated molecules provide new materials with outstanding features for current and perspective applications, especially in the field of optoelectronic devices. In thin films, processes such as charge conduction, light absorption, and emission are governed not only by the structure of the individual molecules but also by their supramolecular structures and intermolecular interactions to a large extent. Electronic circular dichroism, ECD, and its emission counterpart, circularly polarized luminescence, CPL, provide tools for studying aggregated states and the key properties to be sought for designing innovative devices. In this review, we shall present a comprehensive coverage of chiroptical properties measured on thin films of organic π-conjugated molecules. In the first part, we shall discuss some general concepts of ECD, CPL, and other chiroptical spectroscopies, with a focus on their applications to thin film samples. In the following, we will overview the existing literature on chiral π-conjugated systems whose thin films have been characterized by ECD and/or CPL, as well other chiroptical spectroscopies. Special emphasis will be put on systems with large dissymmetry factors (gabs and glum) and on the application of ECD and CPL to derive structural information on aggregated states

Fabrication and Actuation of Hierarchically-Patterned Polymer Substrates for Dynamic Surface and Optical Properties

Switchable optical materials, which possess reversible color and transparency change in response to external stimuli, are of wide interest for potential applications such as windows and skylights in architectural and vehicular settings or optical sensors for environmental monitoring. This thesis considers the tuning of optical properties by tailoring and actuating responsive materials. Specifically, we demonstrate the design and fabrication of tilted pillar arrays on wrinkled elastomeric polydimethylsiloxane (PDMS) as a reversibly switchable optical window. While the original PDMS film exhibits angle-dependent colorful reflection due to Bragg diffraction of light from the periodic pillar array, the tilted pillar film appears opaque due to random scattering. Upon re-stretching the film to the original pre-strain, the grating color is restored due to the straightened pillars and transmittance is recovered. Then, we develop a composite film, consisting of a thin layer of quasi-amorphous array of silica nanoparticles (NPs) embedded in bulk elastomeric PDMS, with initial high transparency and angle-independent coloring upon mechanical stretching. The color can be tuned by the silica NP size. The switch between transparency and colored states could be reversibly cycled at least 1000 times without losing the film’s structural and optical integrity. We then consider the micropatterning of nematic liquid crystal elastomers (NLCEs) as micro-actuator materials. Planar surface anchoring of liquid crystal (LC) monomers is achieved with a poly(2-hydroxyethyl methacrylate)-coated PDMS mold, leading to monodomains of vertically aligned LC monomers within the mold. After cross-linking, the resulting NLCE micropillars show a relatively large radial strain when heated above nematic to isotropic transition temperature, which can be recovered upon cooling. Finally, the understanding of liquid crystal surface anchoring under confined boundary conditions is applied to the self-assembly of gold nanorods (AuNRs) driven by LC defect structures and to dynamically tune the surface plasmon resonance (SPR) properties. By exploiting the confinement of the smectic liquid crystal, 4-octyl-4’-cyanobiphenyl (8CB), to patterned pillars treated with homeotropic surface anchoring, topological defects are formed at precise locations around each pillar and can be tuned by varying the aspect ratio of the pillars and the temperature of the system. As a result, the AuNR assemblies and SPR properties can be altered reversibly by heating and cooling between smectic, nematic and isotropic phases

光と熱によって動くメカニカル結晶の創製

早大学位記番号:新8191早稲田大

Micro and nanoactuators based on bistable molecular materials

Les systèmes microélectromécaniques (MEMS) sont des dispositifs de taille micrométrique capables de transformer un signal mécanique en un signal électrique et vice-versa. Ils sont aujourd'hui largement répandus dans notre vie quotidienne pour la détection, la transformation de l'énergie et l'actionnement de dispositifs grâce à leur faible dissipation énergétique, leur réponse ultra-rapide et leur grande sensibilité. Même si depuis plusieurs décennies, les progrès technologiques ont entraîné la miniaturisation des ces dispositifs, il reste nombreux challenges à surmonter dont l'un des plus importantes est l'intégration à l'échelle nanométrique d'actionneurs à base des matériaux dit " intelligents " (à ces dimensions, les matériaux habituellement utilisés perdent leurs propriétés d'actionnement). Dans ce contexte, ce travail de thèse avait pour objectif d'explorer l'utilisation des matériaux moléculaires à transition de spin pour le développement d'actionneurs électromécaniques. Dans ce but, nous avons conçu des microleviers en silicium que nous avons recouvert par différentes molécules à transition de spin soit par sublimation, soit par " spray-coating ". Les MEMS ont été caractérisés à température et pression variables en modes dynamique et statique à l'aide d'un unique dispositif expérimental. Les résultats obtenus démontrent que les molécules à transition de spin peuvent être intégrées, à l'aide de différents procédés de fabrication, dans des dispositifs MEMS et qu'il est possible de réaliser l'actionnement à l'aide d'une source d'énergie thermique (chauffage et refroidissement) et/ou lumineuse. Simultanément, cette étude a également permis d'évaluer les propriétés mécaniques des matériaux à transition de spin (module de Young, coefficient de Poisson) qui restent mal connues.Microelectromechanical systems (MEMS) are micrometric devices able to transform a mechanical signal into an electrical one and vice-versa. In the past years they have been successfully employed in different fields of our everyday life for sensing, transducing different forms of energy and for actuating purposes thanks to their low energy dissipation, fast response and high sensibility. Even if recent technological progress has allowed a considerable miniaturization of these devices, several challenges remain. In particular the integration of smart actuating materials at the nanometric scale remains arduous because in most cases they lose their actuating properties at reduced sizes. In this context, this thesis work aimed for exploring the possibility of using molecular spin crossover materials for the development of electromechanical actuators. To this aim we have conceived silicon microcantilevers, which have been coated by various spin crossover molecules using either thermal evaporation or spray-coating methods. The MEMS have been characterized at variable temperature and pressure both in dynamical and static modes using a single experimental setup. The results prove that spin crossover molecules can be successfully integrated into silicon MEMS devices using different fabrication processes and their actuation can be achieved using either a thermal energy source or light irradiation. In parallel, this work has allowed us to extract relevant mechanical properties of spin crossover materials (Young's modulus, Poisson's ratio), which have been largely unknown previously