Browsing by Author "Priimagi, Arri"
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Item All-Optical Emission Control and Lasing in Plasmonic Lattices(ACS Publications, 2020-10-21) Taskinen, Jani; Moilanen, Antti; Rekola, Heikki; Kuntze, Kim; Priimagi, Arri; Törmä, Päivi; Hakala, Tommi; Department of Applied Physics; Quantum Dynamics; Tampere University; University of Eastern FinlandWe report on reversible all-optical emission control and lasing in plasmonic nanoparticle lattices. By incorporating photochromic molecules into the liquid gain medium composed of organic fluorescent molecules, we realize all-optical control over gain and absorption, the two key parameters associated with both conventional and nanoscale lasing. We demonstrate reversible photoswitching between two distinct modes of operation: (1) spontaneous emission to the lattice mode, characterized by broad emission line width, low emission intensity, and large angular distribution; and (2) lasing action, characterized by very narrow (sub-nm) line widths due to the emergence of increased gain and temporal coherence in the system, approximately 3 orders of magnitude increase in emission intensity, and narrow 0.7° angular divergence of the beam. A rate-equation model is employed to describe the operation of the switchable plasmonic laser. Our results provide the first demonstration of optically tunable losses in plasmonic lattice lasers, which is an important milestone for the development of active plasmonics and paves the way for ultrafast all-optical switching of plasmonic nanolasers.Item Associative Learning by Classical Conditioning in Liquid Crystal Network Actuators(ROYAL SOC CHEMISTRY, 2020-01-08) Zeng, Hao; Zhang, Hang; Ikkala, Olli; Priimagi, Arri; Department of Applied Physics; Molecular Materials; Tampere UniversityResponsive and shape-memory materials allow stimuli-driven switching between fixed states. However, their behavior remains unchanged under repeated stimuli exposure, i.e., their properties do not evolve. By contrast, biological materials allow learning in response to past experiences. Classical conditioning is an elementary form of associative learning, which inspires us to explore simplified routes even for inanimate materials to respond to new, initially neutral stimuli. Here, we demonstrate that soft actuators composed of thermoresponsive liquid crystal networks “learn” to respond to light upon a conditioning process where light is associated with heating. We apply the concept to soft microrobotics, demonstrating a locomotive system that “learns to walk” under periodic light stimulus, and gripping devices able to “recognize” irradiation colors. We anticipate that actuators that algorithmically emulate elementary aspects of associative learning and whose sensitivity to new stimuli can be conditioned depending on past experiences may provide new routes toward adaptive, autonomous soft microrobotics.Item A bifacial colour-tunable system via combination of a cholesteric liquid crystal network and hydrogel(ROYAL SOC CHEMISTRY, 2020-08-14) Wani, Owies M.; Schenning, Albertus P. H. J.; Priimagi, Arri; Molecular Materials; Eindhoven University of Technology; Tampere University; Department of Applied PhysicsWe present a colour tunable system obtained by combining a humidity-responsive cholesteric liquid crystal network and hydrogel coatings, in a diligently designed cell-geometry. The design enables sensitive colour tuningviatemperature-induced changes in humidity inside the cell. Uniquely, the system exhibits a bifacial response, causing either a blue- or red-shift in the reflected color when heated from opposite sides.Item Bright and Switchable Whiteness in Macro-Crosslinked Hydrogels(Wiley-VCH Verlag, 2024-04-15) Eklund, Amanda; Hu, Shanming; Fang, Yuhuang; Savolainen, Henri; Pi, Haotian; Zeng, Hao; Priimagi, Arri; Ikkala, Olli; Zhang, Hang; Department of Applied Physics; Center of Excellence in Life-Inspired Hybrid Materials, LIBER; Molecular Materials; Department of Applied Physics; Tampere UniversityBright white color is often achieved in nature by the combination of polydisperse scattering structures and high refractive index contrast between the scatterer and the surrounding medium. Similarly, synthetic systems have commonly utilized inorganic materials as the scattering centers to achieve white color, which, however, lacks the ability to switch the optical properties. While hydrogels capable of scattering light are utilized in applications such as smart windows, their reflection properties have remained limited due to the low refractive index contrast between the polymer and water. As a result, thick layers in the millimeter range are often required to achieve reasonable whiteness. Here a hydrogel consisting of a temperature-responsive poly(N-isopropylacrylamide) (PNIPAm) and chemically modified agarose used as a chemical macro-crosslinker is presented. The hydrogel exhibits high whiteness at temperatures above the phase transition (≈31 °C). The reflectance at 800 nm is four times as high as for standard PNIPAm, and a change in transmittance can be induced by laser pulses as short as 30 ms. The macro-crosslinked structure of this hydrogel provides superior reflectance at a lower thickness compared to reported hydrogel systems, enabling a variety of potential applications including smart windows, responsive displays, optical switches, and camouflage.Item Enhanced photoinduced birefringence in polymer-dye complexes: Hydrogen bonding makes a difference(AIP Publishing, 2007) Priimagi, Arri; Kaivola, Matti; Rodriguez, Francisco J.; Kauranen, Martti; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of ScienceThe authors demonstrate that photoinduced birefringence in azo-dye-doped polymers is strongly enhanced by hydrogen bonding between the guest molecules and the polymer host. The primary mechanism behind the enhancement is the possibility to use high dye doping levels compared to conventional guest-host systems because dye aggregation is restrained by hydrogen bonding. Moreover, hydrogen bonding reduces the mobility of the guest molecules in the polymer host leading to a larger fraction of the induced birefringence to be preserved after the excitation light has been turned off.Item Fast Switching of Bright Whiteness in Channeled Hydrogel Networks(WILEY-VCH VERLAG, 2020-07-01) Eklund, Amanda; Zhang, Hang; Zeng, Hao; Priimagi, Arri; Ikkala, Olli; Department of Applied Physics; Molecular Materials; Tampere UniversityBeside pigment absorption and reflection by periodic photonic structures, natural species often use light scattering to achieve whiteness. Synthetic hydrogels offer opportunities in stimuli-responsive materials and devices; however, they are not conventionally considered as ideal materials to achieve high whiteness by scattering due to the ill-defined porosities and the low refractive index contrast between the polymer and water. Herein, a poly(N-isopropylacrylamide) hydrogel network with percolated empty channels (ch-PNIPAm) is demonstrated to possess switchable bright whiteness upon temperature changes, obtained by removing the physical agarose gel in a semi-interpenetrating network of agarose and PNIPAm. The hydrogel is highly transparent at room temperature and becomes brightly white above 35 °C. Compared to conventional PNIPAm, the ch-PNIPAm hydrogel exhibits 80% higher reflectance at 800 nm and 18 times faster phase transition kinetics. The nanoscopic channels in the ch-PNIPAm facilitate water diffusion upon phase transition, thus enabling the formation of smaller pores and enhanced whiteness in the gel. Furthermore, fast photothermally triggered response down to tens of milliseconds can be achieved. This unique property of the ch-PNIPAm hydrogel to efficiently scatter visible light can be potentially used for, e.g., smart windows, optical switches, and, as demonstrated in this report, thermoresponsive color displays.Item Feedback-controlled hydrogels with homeostatic oscillations and dissipative signal transduction(Nature Publishing Group, 2022-12) Zhang, Hang; Zeng, Hao; Eklund, Amanda; Guo, Hongshuang; Priimagi, Arri; Ikkala, Olli; Department of Applied Physics; Molecular Materials; Center of Excellence in Life-Inspired Hybrid Materials, LIBER; Tampere UniversityDriving systems out of equilibrium under feedback control is characteristic for living systems, where homeostasis and dissipative signal transduction facilitate complex responses. This feature not only inspires dissipative dynamic functionalities in synthetic systems but also poses great challenges in designing novel pathways. Here we report feedback-controlled systems comprising two coupled hydrogels driven by constant light, where the system can be tuned to undergo stable homeostatic self-oscillations or damped steady states of temperature. We demonstrate that stable temperature oscillations can be utilized for dynamic colours and cargo transport, whereas damped steady states enable signal transduction pathways. Here mechanical triggers cause temperature changes that lead to responses such as bending motions inspired by the single-touch mechanoresponse in Mimosa pudica and the frequency-gated snapping motion inspired by the plant arithmetic in the Venus flytrap. The proposed concepts suggest generalizable feedback pathways for dissipative dynamic materials and interactive soft robotics.Item Hierarchical Self-Assembly of Halogen-Bonded Block Copolymer Complexes into Upright Cylindrical Domains(2017-03-09) Milani, Roberto; Houbenov, Nikolay; Fernandez-Palacio, Francisco; Cavallo, Gabriella; Luzio, Alessandro; Haataja, Johannes; Giancane, Gabriele; Saccone, Marco; Priimagi, Arri; Metrangolo, Pierangelo; Ikkala, Olli; Department of Applied Physics; Molecular Materials; VTT Technical Research Centre of Finland; Polytechnic University of Milan; Italian Institute of Technology; University of Salento; Tampere University of TechnologySelf-assembly of block copolymers into well-defined, ordered arrangements of chemically distinct domains is a reliable strategy for preparing tailored nanostructures. Microphase separation results from the system, minimizing repulsive interactions between dissimilar blocks and maximizing attractive interactions between similar blocks. Supramolecular methods have also achieved this separation by introducing small-molecule additives binding specifically to one block by noncovalent interactions. Here, we use halogen bonding as a supramolecular tool that directs the hierarchical self-assembly of low-molecular-weight perfluorinated molecules and diblock copolymers. Microphase separation results in a lamellar-within-cylindrical arrangement and promotes upright cylindrical alignment in films upon rapid casting and without further annealing. Such cylindrical domains with internal lamellar self-assemblies can be cleaved by solvent treatment of bulk films, resulting in separated and segmented cylindrical micelles stabilized by halogen-bond-based supramolecular crosslinks. These features, alongside the reversible nature of halogen bonding, provide a robust modular approach for nanofabrication.Item Light-Fueled Nonreciprocal Self-Oscillators for Fluidic Transportation and Coupling(Wiley-VCH Verlag, 2024-03-21) Deng, Zixuan; Zhang, Hang; Priimagi, Arri; Zeng, Hao; Department of Applied Physics; Center of Excellence in Life-Inspired Hybrid Materials, LIBER; Molecular Materials; Tampere UniversityLight-fueled self-oscillators based on soft actuating materials have triggered novel designs for small-scale robotic constructs that self-sustain their motion at non-equilibrium states and possess bioinspired autonomy and adaptive functions. However, the motions of most self-oscillators are reciprocal, which hinders their use in sophisticated biomimetic functions such as fluidic transportation. Here, an optically powered soft material strip that can perform nonreciprocal, cilia-like, self-sustained oscillation under water is reported. The actuator is made of planar-aligned liquid crystal elastomer responding to visible light. Two laser beams from orthogonal directions allow for piecewise control over the strip deformation, enabling two self-shadowing effects coupled in one single material to yield nonreciprocal strokes. The nonreciprocity, stroke pattern and handedness are connected to the fluidic pumping efficiency, which can be controlled by the excitation conditions. Autonomous microfluidic pumping in clockwise and anticlockwise directions, translocation of a micro-object by liquid propulsion, and coupling between two oscillating strips through liquid medium interaction are demonstrated. The results offer new concepts for non-equilibrium soft actuators that can perform bio-like functions under water.Item Materials Inspired by Living Functions(Wiley-VCH Verlag, 2024-03-19) Kostiainen, Mauri A.; Priimagi, Arri; Timonen, Jaakko V.I.; Ras, Robin H.A.; Sammalkorpi, Maria; Penttilä, Merja; Ikkala, Olli; Linder, Markus B.; Department of Bioproducts and Biosystems; Department of Applied Physics; Department of Chemistry and Materials Science; Center of Excellence in Life-Inspired Hybrid Materials, LIBER; Biohybrid Materials; Active Matter; Soft Matter and Wetting; Soft Materials Modelling; Molecular Materials; Biomolecular MaterialsEngineering or mimicking living materials found in nature has the potential to transform the use of materials. Unlike classic synthetic materials which are typically optimized for static properties, economics, and recently also for sustainability, materials of life are dynamic, feedback-controlled, evolving, and adaptive. Although synthetic materials do not typically exhibit such complicated functionalities, researchers are increasingly challenging this viewpoint and expanding material concepts toward dynamic systems inspired by selected life-like functions. Herein, it is suggested that such materials can be approached from two perspectives: through engineering of biological organisms and their functions to provide the basis for new materials, or by producing synthetic materials with selected rudimentary life-inspired functions. Current advances are discussed from the perspectives of (i) new material features based on built-in memory and associative learning, (ii) emergent structures and self-regulated designs using non-equilibrium systems, and (iii) interfacing living and non-living systems in the form of cellular community control and growth to open new routes for material fabrication. Strategies combining (i)–(iii) provide materials with increasingly life-inspired responses and potential for applications in interactive autonomous devices, helping to realize next-generation sensors, autonomous and interactive soft robots, and external control over the bioproduction of self-organizing structural materials.Item Multiscale Hierarchical Surface Patterns by Coupling Optical Patterning and Thermal Shrinkage(AMERICAN CHEMICAL SOCIETY, 2021-04-07) Daghigh Shirazi, Hamidreza; Dong, Yujiao; Niskanen, Jukka; Fedele, Chiara; Priimagi, Arri; Jokinen, Ville P.; Vapaavuori, Jaana; Department of Chemistry and Materials Science; Multifunctional Materials Design; Tampere University; University of MontrealHerein, a simple hierarchical surface patterning method is presented by effectively combining buckling instability and azopolymer-based surface relief grating inscription. In this technique, submicron patterns are achieved using azopolymers, whereas the microscale patterns are fabricated by subsequent thermal shrinkage. The wetting characterization of various topographically patterned surfaces confirms that the method permits tuning of contact angles and choosing between isotropic and anisotropic wetting. Altogether, this method allows efficient fabrication of hierarchical surfaces over several length scales in relatively large areas, overcoming some limitations of fabricating multiscale roughness in lithography and also methods of creating merely random patterns, such as black silicon processing or wet etching of metals. The demonstrated fine-tuning of the surface patterns may be useful in optimizing surface-related material properties, such as wetting and adhesion, producing substrates that are of potential interest in mechanobiology and tissue engineering.Item Optically Controlled Construction of Three-Dimensional Protein Arrays(WILEY-VCH VERLAG, 2023-07-10) Liu, Qing; Zhou, Yu; Shaukat, Ahmed; Meng, Zhuojun; Kyllönen, Daniella; Seitz, Iris; Langerreiter, Daniel; Kuntze, Kim; Priimagi, Arri; Zheng, Lifei; Kostiainen, Mauri A.; Department of Bioproducts and Biosystems; Biohybrid Materials; Center of Excellence in Life-Inspired Hybrid Materials, LIBER; Department of Bioproducts and Biosystems; Tampere University; University of Chinese Academy of SciencesProtein crystallization is an important tool for structural biology and nanostructure preparation. Here, we report on kinetic pathway-dependent protein crystals that are controlled by light. Photo-responsive crystallites are obtained by complexing the model proteins with cationic azobenzene dyes. The crystalline state is readily switched to a dispersed phase under ultraviolet light and restored by subsequent visible-light illumination. The switching can be reversibly repeated for multiple cycles without noticeable structure deterioration. Importantly, the photo-treatment not only significantly increases the crystallinity, but creates crystallites at conditions where no ordered lattices are observed upon directly mixing the components. Further control over the azobenzene isomerization kinetics produces protein single crystals of up to ≈50 μm. This approach offers an intriguing method to fabricate metamaterials and study optically controlled crystallization.Item Programmable and Self-Healable Liquid Crystal Elastomer Actuators Based on Halogen Bonding(Wiley-VCH Verlag, 2023-10-23) Guo, Hongshuang; Liang, Chen; Ruoko, Tero Petri; Meteling, Henning; Peng, Bo; Zeng, Hao; Priimagi, Arri; Department of Applied Physics; Molecular Materials; Tampere UniversityShape-changing polymeric materials have gained significant attention in the field of bioinspired soft robotics. However, challenges remain in versatilizing the shape-morphing process to suit different tasks and environments, and in designing systems that combine reversible actuation and self-healing ability. Here, we report halogen-bonded liquid crystal elastomers (LCEs) that can be arbitrarily shape-programmed and that self-heal under mild thermal or photothermal stimulation. We incorporate halogen-bond-donating diiodotetrafluorobenzene molecules as dynamic supramolecular crosslinks into the LCEs and show that these relatively weak crosslinks are pertinent for their mechanical programming and self-healing. Utilizing the halogen-bonded LCEs, we demonstrate proof-of-concept soft robotic motions such as crawling and rolling with programmed velocities. Our results showcase halogen bonding as a promising, yet unexplored tool for the preparation of smart supramolecular constructs for the development of advanced soft actuators.Item Programmable responsive hydrogels inspired by classical conditioning algorithm(NATURE PUBLISHING GROUP, 2019-07-22) Zhang, Hang; Zeng, Hao; Priimagi, Arri; Ikkala, Olli; Department of Applied Physics; Molecular Materials; Tampere UniversityLiving systems have inspired research on non-biological dynamic materials and systems chemistry to mimic specific complex biological functions. Upon pursuing ever more complex life-inspired non-biological systems, mimicking even the most elementary aspects of learning is a grand challenge. We demonstrate a programmable hydrogel-based model system, whose behaviour is inspired by associative learning, i.e., conditioning, which is among the simplest forms of learning. Algorithmically, associative learning minimally requires responsivity to two different stimuli and a memory element. Herein, nanoparticles form the memory element, where a photoacid-driven pH-change leads to their chain-like assembly with a modified spectral behaviour. On associating selected light irradiation with heating, the gel starts to melt upon the irradiation, originally a neutral stimulus. A logic diagram describes such an evolution of the material response. Coupled chemical reactions drive the system out-of-equilibrium, allowing forgetting and memory recovery. The findings encourage to search nonbiological materials towards associative and dynamic properties.Item Semi-Crystalline Rubber as a Light-Responsive, Programmable, Resilient Robotic Material(WILEY-VCH VERLAG, 2022-10-10) Yang, Qi; Shahsavan, Hamed; Deng, Zixuan; Guo, Hongshuang; Zhang, Hang; Liu, Heng; Zhang, Chunyu; Priimagi, Arri; Zhang, Xuequan; Zeng, Hao; Department of Applied Physics; Molecular Materials; Qingdao University of Science and Technology; University of Waterloo; Tampere UniversityPolymers with large and reversible light-induced deformation offer a plethora of opportunities for the wireless control of small-scale soft robots. However, their widespread adoption in real-world applications is hindered, mainly due to their intrinsic softening upon illumination. Such limitation has detrimental effects on the achievable stress, durability, and precise positional control of the soft actuators after multiple cycles of use. Here, a synthetic rubber from a polybutadiene-polyethylene copolymer is reported as a durable material for light-controlled soft robots. The rubber can be programmed to exhibit various deformation modes controlled by visible-to-infrared light through a photothermal effect. Semi-crystallinity of polyethylene within the rubbery network provides this material with a remarkable modulus at high temperatures (2.5 MPa at 100–140 °C), deformation repeatability (>90%) and shape-recovery (>98%) after 100 actuation cycles subject to loads ranging from 10 to 10 000 times of its body weight (1.4 kPa–1.4 MPa). Soft robotic applications are demonstrated, such as thermally-driven jumping and photo-driven cargo transport carrying up to 1200 times its own weight. The results expand the portfolio of materials in designing remotely-controlled, robust, and resilient soft robots working at small scales.Item Surface-relief gratings in halogen-bonded polymer-azobenzene complexes: A concentration-dependence study(2017-11-01) Stumpel, Jelle E.; Saccone, Marco; DIchiarante, Valentina; Lehtonen, Ossi; Virkki, Matti; Metrangolo, Pierangelo; Priimagi, Arri; Department of Applied Physics; Optics and Photonics; Polytechnic University of Milan; Tampere University of TechnologyIn recent years, supramolecular complexes comprising a poly(4-vinylpyridine) backbone and azobenzene-based halogen bond donors have emerged as a promising class of materials for the inscription of light-induced surface-relief gratings (SRGs). The studies up to date have focused on building supramolecular hierarchies, i.e., optimizing the polymer-azobenzene noncovalent interaction for efficient surface patterning. They have been conducted using systems with relatively low azobenzene content, and little is known about the concentration dependence of SRG formation in halogen-bonded polymer-azobenzene complexes. Herein, we bridge this gap, and study the concentration dependence of SRG formation using two halogen-bond-donating azobenzene derivatives, one functionalized with a tetrafluoroiodophenyl and the other with an iodoethynylphenyl group. Both have been previously identified as efficient molecules in driving the SRG formation. We cover a broad concentration range, starting from 10 mol % azobenzene content and going all the way up to equimolar degree of complexation. The complexes are studied as spin-coated thin films, and analyzed by optical microscopy, atomic force microscopy, and optical diffraction arising during the SRG formation. We obtained diffraction efficiencies as high as 35%, and modulation depths close to 400 nm, which are significantly higher than the values previously reported for halogen-bonded polymer-azobenzene complexes.Item Viewpoint: Pavlovian Materials—Functional Biomimetics Inspired by Classical Conditioning(WILEY-V C H VERLAG GMBH, 2020-05-01) Zhang, Hang; Zeng, Hao; Priimagi, Arri; Ikkala, Olli; Department of Applied Physics; Molecular Materials; Tampere UniversityHerein, it is discussed whether the complex biological concepts of (associative) learning can inspire responsive artificial materials. It is argued that classical conditioning, being one of the most elementary forms of learning, inspires algorithmic realizations in synthetic materials, to allow stimuli-responsive materials that learn to respond to a new stimulus, to which they are originally insensitive. Two synthetic model systems coined as “Pavlovian materials” are described, whose stimuli-responsiveness algorithmically mimics programmable associative learning, inspired by classical conditioning. The concepts minimally need a stimulus-triggerable memory, in addition to two stimuli, i.e., the unconditioned and the originally neutral stimuli. Importantly, the concept differs conceptually from the classic stimuli-responsive and shape-memory materials, as, upon association, Pavlovian materials obtain a given response using a new stimulus (the originally neutral one); i.e., the system evolves to a new state. This also enables the functionality to be described by a logic diagram. Ample room for generalization to different stimuli and memory combinations is foreseen, and opportunities to develop future adaptive materials with ever-more intelligent functions are expected.
