fabrication and analysis study

학위논문(박사) -- 서울대학교대학원 : 공과대학 기계공학부, 2022. 8. 안성훈.Azobenzene incorporated liquid crystalline elastomers (azo-LCEs) is contains azobenzene in there molecule network, and it occur photo-isomerization when PRP-LCEs irradiated UV-light. Azo-LCEs can potentially be used in diverse applications, such as soft robot, sensors, and actuators, because of their reversibility, remote-controllability, and immediateness of the response. However, real world applications of azo-LCEs are lacking because of the strains generated by irradiation of light are not so large, and the work capacity is not suitable to apply. Here, we report an azo-LCEs constructed with thiol-click Michael addition reaction. Azo LCEs shows dual stimuli shape memory cycle triggered by force/heat and light. In particular during photo deformation process, azo LCEs shows not only huge actuation (up to 26%) under the stress condition but also shows the higher work capacity than mammalian muscle (up to 77J/Kg). To better understand, we control the molecule structure system by using change of crosslinker concentration and sequential polymerization process. When azobenzene in the molecules network occur photo-isomerization, not only the isomerization effect of the azobenzene itself but also influence of tuned nematic-isotropic transition temperature of azo-LCEs molecule network contribute to make immediately huge actuation. Since the photo-isomerization of azobenzene and the external loading force applied to azo-LCEs have a complex effect on this transition temperature shifting, we constructed an in-situ experimental system to better understand this phenomenon. Our azo-LCE has not only shown that it has conditions that can be used in various applications including artificial muscles, but is also expected to be used importantly in various fields for future actuators and their mechanism studies.광반응 탄성체 소재의 분자 네트워크 내부에 가교되어 있는 아조벤젠은 특정 파장대의 빛이 조사 될 경우 광 이성질화를 일으킵니다. 이러한 광 이성질화는 아조벤젠 그 자체의 구조 및 물성변화뿐 아니라, 분자배열 전체에 변화를 야기하여 결과적으로 물성변화와 거동을 발생시킵니다. 광반응 탄성체 소재의 이러한 가역성, 원격제어 가능성 및 그 응답이 즉각적이라는 특성으로 인해 소프트로봇, 정밀 센서 및 액츄에이터와 같은 다양한 활용이 기대되고 있습니다. 그러나 광반응 탄성체의 광변형 거동 시 그 변형의 크기가 충분하지 않고 발생하는 일의 크기가 제한적이라는 특성으로 인해 실질적인 활용에는 어려움을 겪고 있습니다. 이러한 한계점들을 해결하기 위해 본 연구에서는 Michael addition thiol-click 가교반응을 사용하여 액정 단량체, 아조벤젠 단량체, thiol 작용기를 지닌 가교제로 이루어진 광반응 탄성체 소재를 합성하였습니다. 외력에 의해 일시적인 배향성을 만들고 열을 통해 지울 수 있으며, 빛에 의해서도 형상기억사이클을 발생시키는 해당 광반응 탄성체는 외력하에서 26% 이상의 광반응 대변형을 발생시키며, 포유류근육이상의 일률을 발생시킬 수 있음을 확인하였습니다. 이 후 가교제의 조성비를 제어하는 것과 촉매와 작용기를 설정해주는 방식을 이용한 순차적 중합과정을 이용한 가교과정 제어를 통해 가교율을 통제하였고, 가교율의 변화에 따른 물성의 변화를 연구하였습니다. 또한 광반응에 따른 물성변화를 실시간으로 관측할 수 있는 실험환경을 구축하여, 광반응 거동 및 물성변화의 메커니즘을 규명하였습니다. 본 연구에서 소개한 광반응 탄성체 소재는 인공근육을 비롯한 다양한 응용분야에서 사용될 수 있는 조건을 가지고 있음을 보여주었을 뿐만 아니라, 향후 액츄에이터 및 그 메커니즘 연구를 위한 다양한 분야에서 중요하게 활용될 것으로 기대됩니다.Chapter 1. Introduction 1 1.1 Multi-functional polymer-based smart actuator 1 1.2 Liquid crystalline polymer 3 1.3 Azobenzene incorporated liquid crystalline elastomers 8 1.4 Polymer alignment under the preloading force 14 1.5 Sequential polymerization 17 1.6 Scope and aim 21 1.7 Outline of dissertation 22 Chapter 2. Synthesis and characterization 24 2.1 Synthesis of bi-acrylic azobenzene monomer 24 2.2 Synthesis of unsymetric-functionalized azobenzene monomer 28 2.3 Synthesis of azobenzene incorporated liquid crystalline elastomers (Azo-LCEs) 40 2.4 Onepot method based on two-step sequential thiol-ene reaction 44 Chapter 3. Methodology and sample properties 49 3.1 Experimental method for photo-actuation test of the azo-LCEs actuator 49 3.2 Experimental method for in-situ test of the azo-LCEs actuator 53 3.3 Mechanical/ thermal properties of the azo-LCEs actuator 55 3.4 Controlled polymerization effect on properties of azo-LCEs 59 Chapter 4. Photo-triggered actuation of the azo-LCEs based actuator 64 4.1 Characteristics of the actuation 64 4.2 Effect of crosslinking density under the loading condition change 66 4.3 Effect of the sequential polymerization 73 4.4 Azo-LCEs actuator as an artificial muscle 77 Chapter 5. Actuation mechanism 79 5.1 Study of the catalyst 79 5.2 Real time in-situ test to know the thermal properties change under the photo-isomerization 94 Chapter 6. Conclusion 97 국문 요약 98 Bibliography 101박

Adaptive optics for laser processing

The overall aim of the work presented in this thesis is to develop an adaptive optics (AO) technique for application to laser-based manufacturing processes. The Gaussian beam shape typically coming from a laser is not always ideal for laser machining. Wavefront modulators, such as deformable mirrors (DM) and liquid crystal spatial light modulators (SLM), enable the generation of a variety of beam shapes and furthermore offer the ability to alter the beam shape during the actual process. The benefits of modifying the Gaussian beam shape by means of a deformable mirror towards a square flat top profile for nanosecond laser marking and towards a ring shape intensity distribution for millisecond laser drilling are presented. Limitations of the beam shaping capabilities of DM are discussed. The application of a spatial light modulator to nanosecond laser micromachining is demonstrated for the first time. Heat sinking is introduced to increase the power handling capabilities. Controllable complex beam shapes can be generated with sufficient intensity for direct laser marking. Conventional SLM devices suffer from flickering and hence a process synchronisation is introduced to compensate for its impact on the laser machining result. For alternative SLM devices this novel technique can be beneficial when fast changes of the beam shape during the laser machining are required. The dynamic nature of SLMs is utilised to improve the marking quality by reducing the inherent speckle distribution of the generated beam shape. In addition, adaptive feedback on the intensity distribution can further improve the quality of the laser machining. In general, beam shaping by means of AO devices enables an increased flexibility and an improved process control, and thus has a significant potential to be used in laser materials processing

Exploration of elastomeric and polymeric liquid crystals with photothermal actuation: a review.

Recent research in soft materials is an exhilarating category which has been transcending boundaries for variety of functional applications. This category also stems liquid crystals whose stimuli-responsive feature has fantasized researchers for application arrays in actuators and biomedical. Liquid crystals evince dual characteristics of liquid and solids empowering them to reversibly transit on external actuation. The after-effect of irradiating photons on liquid crystals (LC) facilitate outlying functioning and are engineered with gold nanorods, dyes, graphene and carbon nanotubes among others which greets to incoming stimulus and participates in transference of light energy to perceivable transformation through heat drive. This is progressively explored in medical domain for drug delivery, tissue engineering, cancer treatment, and other disciplines of medicine and bio-mimicking. Additionally, photothermal trigger equips localized punctilious treatment outshining diffusion assisted heating and enables spot treatment. However, LC utilization is burgeoning towards 3D printing, characterizing it as 4D Printing. Present review framework probes LC and its photothermal actuation chemistry in the medical domain. Furthermore, it reflects on LC potential in smart manufacturing in 3D/4D printing, its challenges (limited concentration of filler, its miscibility, and actuation cycle fatigue) and future likelihood

Nanostructured Composites Based on Liquid-Crystalline Elastomers

Liquid-crystalline elastomers (LCEs) are the object of many research investigations due to their reversible and controllable shape deformations, and their high potential for use in the field of soft robots and artificial muscles. This review focuses on recent studies about polymer composites based on LCEs and nanomaterials having different chemistry and morphology, with the aim of instilling new physical properties into LCEs. The synthesis, physico-chemical characterization, actuation properties, and applications of LCE-based composites reported in the literature are reviewed. Several cases are discussed: (1) the addition of various carbon nanomaterials to LCEs, from carbon black to carbon nanotubes, to the recent attempts to include graphene layers to enhance the thermo-mechanic properties of LCEs; (2) the use of various types of nanoparticles, such as ferroelectric ceramics, gold nanoparticles, conductive molybdenum-oxide nanowires, and magnetic iron-oxide nanoparticles, to induce electro-actuation, magnetic-actuation, or photo-actuation into the LCE-based composites; (3) the deposition on LCE surfaces of thin layers of conductive materials (i.e., conductive polymers and gold nanolayers) to produce bending actuation by applying on/off voltage cycles or surface-wrinkling phenomena in view of tunable optical applications. Some future perspectives of this field of soft materials conclude the review. Keywords: liquid-crystal polymers; bilayers; composites; liquid single-crystal elastomers; actuators; artificial muscles; orientational order; NMR; nanoparticles; nanomaterials; photo-actuation; electro-actuation; thermal actuatio

Responsive liquid crystal networks

Responsieve polymeren zijn interessant voor een groot aantal toepassingen, omdat de eigenschappen van deze materialen over een breed bereik ingesteld kunnen worden en het bovendien mogelijk is om ze tegen lage kosten en op grote schaal te fabriceren. Vloeibaar-kristallijne netwerken vormen een platformtechnologie voor deze responsieve materialen. Een groot aantal stimulusgevoelige moleculen kunnen worden toegevoegd om het polymeer gevoelig te maken voor warmte, licht, pH, waterdamp of biologische stimuli. De vloeibaar-kristallijne kernen van het polymere netwerk versterken de stimulus, wat snelle en grote responsies tot gevolg heeft. De responsies kunnen zowel mechanische als optische veranderingen zijn, en zijn naar wens reversibel of irreversibel te maken. In dit werk wordt het gebruik van deze materialen in microsystemen, zoals lab-on-a-chip, onderzocht. Actuatie met licht wordt gekozen omdat dit compatibel is met een natte omgeving en van afstand aangestuurd kan worden.Theoretische en experimentele resultaten laten zien dat door een optimalisatie van de moleculaire ordening in een ‘splaybend’ orientatie, de prestaties van buigende actuatoren sterk verbeterd kan worden. Daarnaast is er theorie ontwikkeld die de beweging van de actuator onder invloed van aansturing met licht beschrijft en deze theorie wordt door experimentele resultaten bevestigd. Voor toepassing in microfluidische systemen worden actuatoren ontworpen die gebaseerd zijn op cilia in natuurlijke organismen. Deze actuatoren kunnen dienen als pompen en mixers, maar daarvoor is het noodzakelijk dat de beweging van de cilia asymmetrisch in de tijd is. Verschillende manieren voor het genereren van deze asymmetrische beweging zijn onderzocht. Eén manier maakt gebruik van actuatoren bestaande uit verschillende delen die elk reageren op een andere kleur licht. Een andere manier maakt gebruik van een gradient in compositie van de actuator door de dikte van het materiaal, waardoor een sterk niet-lineaire responsie ontstaat. Verschillende methodes voor het miniaturiseren van deze actuatoren zijn verkend, waaronder lithografie en inkjet printen. Het is aangetoond dat met inkjet printen, actuatoren kleiner dan een millimeter gemaakt kunnen worden, zonder dat de prestaties van de actuatoren daaronder te leiden heeft. Behalve de toepassing van vloeibaar-kristallijne netwerken als actuatoren is de toepassing als sensor ook onderzocht. Als het materiaal een cholesterische ordening heeft, kan dit een gedeelte van het licht reflecteren. Als de reflectieband in het zichtbare gedeelte van het licht ligt, lijkt het materiaal een kleur te hebben. Net als bij de actuatoren kan het netwerk gedeformeerd worden door de moleculaire ordening te verstoren of door het te laten zwellen of krimpen, hetgeen een zichtbare verschuiving van de reflectieband tot gevolg kan hebben. Het is aangetoond dat door gebruik te maken van waterstofbruggen in het netwerk, cholesterische sensoren kunnen reageren op vluchtige amines, pH of temperatuur. Als alternatief voor de licht gestuurde actuatoren zijn magnetisch gedreven, ferromagnetische systemen onderzocht. Magnetische velden zijn net als licht compatibel met een nat milieu en kunnen van afstand aansturen. Twee methodes zijn onderzocht om kunstmatige magnetische cilia te maken: ‘glancing angle’ depositie van nikkel op PDMS scharnieren en electrolytisch gegroeid nikkel in een membraan. De beste resultaten werden bereikt met electrolytische gegroeide staafjes die vrij in een kanaal ronddreven. Toepassingen van de actuatoren uit dit onderzoek liggen in medische applicaties zoals lab-on-a-chip systemen, maar ook in andere toepassingen zoals mechatronica en textiel. Omdat de materialen in een continu proces aan de lopende band verwerkt kunnen worden, hebben ze de potentie om in goedkope systemen zoals slimme verpakkingen of wegwerp applicaties toegepast te worden

Structured light enables biomimetic swimming and versatile locomotion of photoresponsive soft microrobots.

Microorganisms move in challenging environments by periodic changes in body shape. In contrast, current artificial microrobots cannot actively deform, exhibiting at best passive bending under external fields. Here, by taking advantage of the wireless, scalable and spatiotemporally selective capabilities that light allows, we show that soft microrobots consisting of photoactive liquid-crystal elastomers can be driven by structured monochromatic light to perform sophisticated biomimetic motions. We realize continuum yet selectively addressable artificial microswimmers that generate travelling-wave motions to self-propel without external forces or torques, as well as microrobots capable of versatile locomotion behaviours on demand. Both theoretical predictions and experimental results confirm that multiple gaits, mimicking either symplectic or antiplectic metachrony of ciliate protozoa, can be achieved with single microswimmers. The principle of using structured light can be extended to other applications that require microscale actuation with sophisticated spatiotemporal coordination for advanced microrobotic technologies.This work was in part supported by the European Research Council under the ERC Grant agreements 278213 and 291349, and the DFG as part of the project SPP 1726 (microswimmers, FI 1966/1-1). SP acknowledges support by the Max Planck ETH Center for Learning Systems.This is the author accepted manuscript. The final version is available from Nature Publishing Group via http://dx.doi.org/10.1038/nmat456

Actionneurs en polymère cristallins liquides poreux

Les actionneurs en matériaux souples possèdent des caractéristiques distinctives qui les rendent utiles pour de nombreuses applications. Parmi les matériaux souples à des fins d'actionnement, les élastomères cristallins liquides (LCE - abréviation en anglais) sont particulièrement prometteurs en raison de leur grande déformation réversible, de leur im-portante force mécanique lors de l’actionnement, et de leurs mouvements diversifiés dé-clenchés par des stimuli. Dans ce domaine de recherche, la plupart des efforts ont été con-sacrés à la conception de nouvelles structures moléculaires de LCE, au contrôle de l'ali-gnement LC qui est crucial pour la déformation, et à l'ingénierie des structures ou archi-tectures d'actionneurs. Toutefois, tant pour la recherche fondamentale que pour les appli-cations, il est important de développer de nouvelles approches qui, sans changer les struc-tures du LCE et de l'actionneur et en utilisant le même alignement LC, peuvent donner lieu à de nouvelles fonctions d'actionnement. C’est le but de la présente thèse qui porte sur le développant d’un nouveau type d’actionneurs, à savoir, actionneurs poreux en LCE. Afin de fabriquer des actionneurs LCE poreux, nous avons développé une méthode simple et efficace qui consiste à, successivement, disperser des nanoparticules inorganiques (celles du CaCO3 et du MOF : metal-organic framework) dans un film LCE, préparer l'ac-tionneur par étirement mécanique pour l'alignement des mésogènes et irradiation à la lu-mière UV pour la réticulation du polymère, et enlever les nanoparticules inorganiques de la matrice LCE par voie de gravure chimique. Nos études sur les actionneurs LCE poreux résultants ont non seulement révélé de nouvelles fonctions ou fonctionnalités d'actionne-ment, mais aussi démontré leur potentiel pour des applications. Premièrement, bien que le LCE utilisé soit hydrophobe, son actionneur poreux est capable d’absorber une grande quantité d'eau et gonfler comme un hydrogel. L’étude montre que ce changement de propriété est probablement causé par des ions restants dans l'actionneur gravé, ce qui améliore l'affinité entre les surfaces des pores et les molécules d'eau. Malgré la présence d'eau, l'alignement des mésogènes peut être préservé en grande partie. Par con-séquent, l'actionneur LCE poreux gonflé peut présenter une déformation réversible par changement de volume lors de l'absorption et de la désorption d'eau (comme un hydrogel) ou par une transition de phase ordre-désordre des mésogènes induite thermiquement (une caractéristique de LCE). Des comportements en actionnement particuliers peuvent être obtenus en combinant ces deux mécanismes d'actionnement différents. Cette nouvelle fonctionnalité est abordée dans les chapitres 2 et 4. Deuxièmement, le gonflement important de l’actionneur poreux dans l'eau offre un moyen efficace pour introduire dans l'actionneur un additif dissous dans l’eau, et après séchage, l’additive ainsi encapsulé par les canaux de pores peut doter l’actionneur d'une fonction au-delà de l’actionnement. Nous avons démontré une nouvelle fonctionnalité dite « recon-figurabilité des fonctions » en chargeant, lavant et rechargeant trois différents additifs fonctionnels dans un même actionneur LCE poreux : un liquide ionique (IL) pour la con-ductivité ionique, un colorant photothermique pour le mouvement piloté par la lumière et un fluorophore pour l'émission de couleur. Cette nouvelle fonctionnalité est rapportée au chapitre 2. De plus, nous avons utilisé un actionneur LCE poreux contenant un liquide ionique (PLCE-IL) pour démontrer séparément la détection et l'actionnement qui sont normalement deux fonctions obtenues avec deux classes de matériaux : matériaux défor-mables pour détection par voir électrique et matériaux souples pour actionnement déclen-ché par des stimuli. D'une part, lors de la transition de phase ordre-désordre des méso-gènes alignés, le PLCE-IL se comporte comme un actionneur typique capable de changer sa forme de manière réversible et peut être utilisé pour assembler un robot souple alimenté par la lumière. D'autre part, à des températures en-dessous de la transition de phase, le PLCE-IL est un élastomère qui peut supporter et détecter de grandes déformations de di-vers modes ainsi que des changements de conditions environnementales en signalant la variation de résistance électrique correspondante. L'utilisation collective de ces deux fonc-tions intégrées dans un dispositif a également été montrée. Ce travail est discuté au cha-pitre 3. Finalement, rapporté au chapitre 4, nous avons fait une découverte inattendue en étudiant les actionneurs LCE chargés de MOF (LCE-MOF). Après gravure chimique pour le retrait des cristaux MIL-88A, l'actionneur poreux devient magnétiquement sensible, réagissant à un aimant proche. L’analyse suggère la formation in situ de nanoparticules magnétiques de Fe3O4 due à la gravure chimique et à l'irradiation par la lumière UV. En plus des fonc-tionnalités susmentionnées, un actionneur poreux magnétique peut être dirigé par un ai-mant d’entreprendre des mouvements multidirectionnels à la surface de l'eau. En plus, la présence des nanoparticules de Fe3O4 donne un important effet photothermique qui peut être mis à profit pour obtenir un mouvement efficace de l'actionneur poreux alimenté par la lumière.Abstract: Soft materials-based actuators possess distinctive characteristics making them useful for applications in many fields. Among the soft materials for actuation, liquid crystalline elas-tomers (LCEs) stand out owing to their unique actuation features including large shape deformation, high mechanical forces, and diversiform movements driven by variety of stimuli. In terms of material research in the field of LCE actuators, understandably, most effort has been dedicated to designing new molecular structures of LCE, controlling LC alignment, and engineering actuator structures or architectures. However, it is of funda-mental interest to develop new approaches that, without changing the LCE and actuator structures and using the same LC alignment, can give rise to new actuation functions. The purpose of the present thesis is to address this important issue by developing porous LCE actuators. To fabricate porous LCE actuators, we developed a simple and efficient direct templating method that consists in dispersing inorganic nanoparticles, like CaCO3 and MIL-88A (metal-organic framework, MOF) in LCE film, preparing the actuator through mechanical stretching for alignment of mesogens and UV light irradiation for polymer chain crosslink-ing, and subsequently removing inorganic nanoparticles from the LCE matrix by means of chemical etching. Our studies of porous LCE actuators not only revealed a number of new actuation functions but also demonstrated the potential for applications. First, although the LCE used is hydrophobic, porous LCE actuators can absorb large amounts of water and swell like hydrogel, which is likely due to ions remained in the etched actuator leading to improved affinity between pore surfaces and water molecules. Despite the presence of water, the alignment of mesogens can be preserved to a great extent. Con-sequently, swollen porous LCE actuator can exhibit reversible deformation through either volume change upon water absorption and desorption (like hydrogel) or thermally induced order-disorder phase transition of the mesogens (characteristic of LCE). Unusual actuation behaviors can be obtained by combining these two different actuation mechanisms. This new feature is discussed in Chapters 2 and 4. Secondly, by dissolving a given active additive in water, the large swelling of porous LCE actuator in water provides an effective means to introduce this additive in the actuator and thus endow it with a beyond-actuation function enabled by the additive embedded in pore channels after drying. We demonstrated the new feature of function reconfigurability by loading, washing out and reloading different functional additives in a same porous LCE actuator: an ionic liquid (IL) for ionic conductivity, a photothermal dye for light-driven movement and a fluorophore for color emission. This new feature is reported in Chapter 2. Furthermore, we went on to use porous LCE actuator containing ionic liquid (PLCE-IL) for separate sensing and actuation that are normally two functions obtained with two clas-ses of materials: electrically responsive and deformable materials for sensing and soft ac-tive materials for stimuli-triggered actuation. On one hand, upon the order–disorder phase transition of aligned mesogens, PLCE-IL behaves like a typical actuator capable of reversi-ble shape change and can be used to assemble light-fueled soft robot. On the other hand, at temperatures below the phase transition, PLCE-IL is an elastomer that can sustain and sense large deformations of various modes as well as environmental condition changes by reporting the corresponding electrical resistance variation. The collective use of the two functions integrated in one device was also shown. This work, discussed in Chapter 3, shows that electrically responsive porous LCEs are a potential materials platform that of-fers possibilities for merging deformable electronic and actuation applications. Finally, reported in Chapter 4, we made an unexpected finding in studying MOF-loaded LCE actuators (LCE-MOF). After chemical etching for removal of MIL-88A crystals, the porous LCE-MOF actuator becomes magnetically responsive. The characterization results suggest the in-situ formation of magnetic Fe3O4 nanoparticles due to acid etching and UV light irradiation. In addition to the aforementioned features of porous LCE actuators, with a magnetic LCE actuator, a magnet can be used to drive its multi-directional movement on water surface, and the enhanced photothermal effect due to light absorption of Fe3O4 na-noparticles can be taken advantage to achieve efficient light-driven locomotion of the po-rous actuator