Programming Deformations of 3D Microstructures:Opportunities Enabled by Magnetic Alignment of Liquid Crystalline Elastomers

ConspectusSynthetic structures that undergo controlled movement are crucial building blocks for developing new technologies applicable to robotics, healthcare, and sustainable self-regulated materials. Yet, programming motion is nontrivial, and particularly at the microscale it remains a fundamental challenge. At the macroscale, movement can be controlled by conventional electric, pneumatic, or combustion-based machinery. At the nanoscale, chemistry has taken strides in enabling molecularly fueled movement. Yet in between, at the microscale, top-down fabrication becomes cumbersome and expensive, while bottom-up chemical self-assembly and amplified molecular motion does not reach the necessary sophistication. Hence, new approaches that converge top-down and bottom-up methods and enable motional complexity at the microscale are urgently needed.Synthetic anisotropic materials (e.g., liquid crystalline elastomers, LCEs) with encoded molecular anisotropy that are shaped into arbitrary geometries by top-down fabrication promise new opportunities to implement controlled actuation at the microscale. In such materials, motional complexity is directly linked to the built-in molecular anisotropy that can be “activated” by external stimuli. So far, encoding the desired patterns of molecular directionality has relied mostly on either mechanical or surface alignment techniques, which do not allow the decoupling of molecular and geometric features, severely restricting achievable material shapes and thus limiting attainable actuation patterns, unless complex multimaterial constructs are fabricated. Electromagnetic fields have recently emerged as possible alternatives to provide 3D control over local anisotropy, independent of the geometry of a given 3D object.The combination of magnetic alignment and soft lithography, in particular, provides a powerful platform for the rapid, practical, and facile production of microscale soft actuators with field-defined local anisotropy. Recent work has established the feasibility of this approach with low magnetic field strengths (in the lower mT range) and comparably simple setups used for the fabrication of the microactuators, in which magnetic fields can be engineered through arrangement of permanent magnets. This workflow gives access to microstructures with unusual spatial patterning of molecular alignment and has enabled a multitude of nontrivial deformation types that would not be possible to program by any other means at the micron scale. A range of “activating” stimuli can be used to put these structures in motion, and the type of the trigger plays a key role too: directional and dynamic stimuli (such as light) make it possible to activate the patterned anisotropic material locally and transiently, which enables one to achieve and further program motional complexity and communication in microactuators.In this Account, we will discuss recent advances in magnetic alignment of molecular anisotropy and its use in soft lithography and related fabrication approaches to create LCE microactuators. We will examine how design choices─from the molecular to the fabrication and the operational levels─control and define the achievable LCE deformations. We then address the role of stimuli in realizing the motional complexity and how one can engineer feedback within and communication between microactuator arrays fabricated by soft lithography. Overall, we outline emerging strategies that make possible a completely new approach to designing for desired sets of motions of active, microscale objects.</p

Programming Deformations of 3D Microstructures:Opportunities Enabled by Magnetic Alignment of Liquid Crystalline Elastomers

ConspectusSynthetic structures that undergo controlled movement are crucial building blocks for developing new technologies applicable to robotics, healthcare, and sustainable self-regulated materials. Yet, programming motion is nontrivial, and particularly at the microscale it remains a fundamental challenge. At the macroscale, movement can be controlled by conventional electric, pneumatic, or combustion-based machinery. At the nanoscale, chemistry has taken strides in enabling molecularly fueled movement. Yet in between, at the microscale, top-down fabrication becomes cumbersome and expensive, while bottom-up chemical self-assembly and amplified molecular motion does not reach the necessary sophistication. Hence, new approaches that converge top-down and bottom-up methods and enable motional complexity at the microscale are urgently needed.Synthetic anisotropic materials (e.g., liquid crystalline elastomers, LCEs) with encoded molecular anisotropy that are shaped into arbitrary geometries by top-down fabrication promise new opportunities to implement controlled actuation at the microscale. In such materials, motional complexity is directly linked to the built-in molecular anisotropy that can be “activated” by external stimuli. So far, encoding the desired patterns of molecular directionality has relied mostly on either mechanical or surface alignment techniques, which do not allow the decoupling of molecular and geometric features, severely restricting achievable material shapes and thus limiting attainable actuation patterns, unless complex multimaterial constructs are fabricated. Electromagnetic fields have recently emerged as possible alternatives to provide 3D control over local anisotropy, independent of the geometry of a given 3D object.The combination of magnetic alignment and soft lithography, in particular, provides a powerful platform for the rapid, practical, and facile production of microscale soft actuators with field-defined local anisotropy. Recent work has established the feasibility of this approach with low magnetic field strengths (in the lower mT range) and comparably simple setups used for the fabrication of the microactuators, in which magnetic fields can be engineered through arrangement of permanent magnets. This workflow gives access to microstructures with unusual spatial patterning of molecular alignment and has enabled a multitude of nontrivial deformation types that would not be possible to program by any other means at the micron scale. A range of “activating” stimuli can be used to put these structures in motion, and the type of the trigger plays a key role too: directional and dynamic stimuli (such as light) make it possible to activate the patterned anisotropic material locally and transiently, which enables one to achieve and further program motional complexity and communication in microactuators.In this Account, we will discuss recent advances in magnetic alignment of molecular anisotropy and its use in soft lithography and related fabrication approaches to create LCE microactuators. We will examine how design choices─from the molecular to the fabrication and the operational levels─control and define the achievable LCE deformations. We then address the role of stimuli in realizing the motional complexity and how one can engineer feedback within and communication between microactuator arrays fabricated by soft lithography. Overall, we outline emerging strategies that make possible a completely new approach to designing for desired sets of motions of active, microscale objects.</p

Donor-Acceptor Stenhouse Adducts

Een betere beheersing van nieuwe moleculaire schakelaars opent nieuwe mogelijkheden in de ontwikkeling van materiaalkunde, geneeskunde en moleculaire machines. Materialen geven vorm aan de wereld om ons heen. Wetenschappers in deze eeuw ontwikkelen nieuwe materialen die onze toekomst mogelijkerwijs opnieuw vorm kunnen geven. In plaats van statische materialen te gebruiken teneinde functionele gereedschappen te ontwikkelen zijn het de materialen zelf die responsieve eigenschappen krijgen. Vroege voorbeelden van zulke ontwikkelingen zijn bijvoorbeeld brillen die automatisch donkerder worden wanneer de lichtintensiteit toeneemt, ‘slimme’ oppervlaktes en polymeren die reageren op elektrische signalen. Aan de basis van deze revolutie liggen moleculen die zulke materialen kunnen vormen. Om dit soort moleculen te kunnen maken moeten scheikundigen nieuwe moleculaire eigenschappen ontwikkelen en ze moeten leren hoe ze met deze nieuwe moleculen om moeten gaan. Dit proefschrift draagt bij aan een dieper begrip van de eigenschappen en mogelijke toepassingen van de zogenoemde DASA, een nieuw soort molecuul die drie jaar geleden is ontwikkeld door de onderzoeksgroep van Prof. Read de Alaniz aan de UC Santa Barbara. Deze molecuul, die verandert van structuur zodra er licht op schijnt, kan ingezet worden voor verschillende toepassingen: zo kan het bijvoorbeeld gebruikt worden in de bouw van moleculaire machines of om oppervlaktes te ontwikkelen waarvan de eigenschappen veranderen door invloed van licht. Onder begeleiding van Prof. Feringa en in samenwerking met een internationaal netwerk van wetenschappers hebben onderzoekers aan de Rijksuniversiteit Groningen de processen bestudeerd die in gang worden gezet zodra er licht op deze molecuul valt. Kennis van deze processen kan gebruikt worden voor het aanpassen van de bestaande moleculen zodat de stabiliteit en de kleurvastheid kan worden verbeterd en de algehele kwaliteit en prestatievermogen van de responsive materialen omhoog zullen gaan. Vervolgonderzoek kan de resultaten van dit onderzoek direct omzetten naar de ontwikkeling van nieuwe materialen en toepassingen.A better grip on novel molecular switches opens up new avenues in material science, medicine and molecular machines. Materials shape the world around us. In this century, scientists have started to create novel materials that have the potential to reshape our future. Instead of using static materials to create functional tools, the materials themselves are becoming responsive. Early signs of such approaches are glasses that automatically darken with higher intensity of light, smart surfaces and polymers that can respond to electric signals. At the heart of this revolution are molecules that can form such materials. In order to be successful, chemists need to create new molecules with properties that have never been seen before, and they need to know how to properly handle them. This thesis helps us to better understand and make use of a novel class of molecules that was discovered only three years ago by the group of Prof. Read de Alaniz at UC Santa Barbara: the so-called DASAs. This molecule changes its structure upon illumination, which has enabled the creation of surfaces that can change their properties with light or it helps building molecular machines. Researchers from the University of Groningen, under the guidance of Prof. Feringa and in cooperation with an international network of scientists, have uncovered the processes that happen when light hits the molecule. This knowledge helps modifying the existing molecules in order to reduce decomposition, improve color fastness, and overall quality and performance of these responsive materials. Subsequent research will take the lessons learned from this work and directly translate them to the development of new tools and materials for the future