Multi-stimuli Responsiveness Research Articles

Toward synergistic reinforced graphene nanoplatelets composite hydrogels with self-healing and multi-stimuli responses

Although many effects to design smart self-healing sustainable hydrogels with sensitivity to multi-environmental stimuli have been documented, a facile fabrication of stimuli-responsive hydrogels with improved mechanical properties remains challenging. Here, smart self-healing sustainable hydrogels containing soy protein polymer (SPP) and/or graphene nanoplatelets (GNP) were fabricated using “slime” chemistry. The composites hydrogels exhibited impressive self-healing behavior and high ductility under mechanical stimuli, pH-modulation, and thermo sensitivity. An unexpected synergistic reinforcing effect was achieved via combination of SPP and GNP (ternary composite); while the usage of mere SPP and GNP (binary composite) even weakened the gel modulus. Surprisingly improved resistance to gel flowability caused by external heat stimuli was also achieved in the same system. The reinforcing mechanism was attributed to the interactions between SPP and GNP to restore the crosslinking structures. This character also offered merits to the higher viscosity of ternary composite system and thereby resulted in improved heat resistance.

Multi-stimuli-response programmable soft actuators with site-specific and anisotropic deformation behavior

Biological systems with the capabilities of multi-stimuli response and delicate structural changes have inspired the design of soft actuators and robots by either creating anisotropic elements within actuators or patterning site-specific elements on layered actuators. However, introducing these two strategies into one soft actuator has not been well investigated. Here, we present a fast and reliable strategy for constructing programmable graphene oxide (GO)/wax actuators to achieve this goal by printing designable wax patterns composed of oriented wax fibrils onto GO paper. The anisotropic behavior of fabricated GO/wax actuators are proved to be related with the orientation of wax fibrils, so wax patterns consisting of wax fibrils with single and multiple orientations are controlled to print onto one and two sides of GO papers to achieve the diversity, complexity and spatial freedom of their structural changes. The GO/wax actuator with black wax exhibits excellent actuating performance stimulated by infrared light, humidity and heat. Printed programmable actuators are further applied as humidity-driven shape-adaptation gripping, heat-driven autonomous crawling robot and light-driven steerable robot. Certainly, we expect more versatile applications can be achieved by rationally designing corresponding actuators. • Designable Wax patterns composed of wax fibrils are printed onto GO papers for programmable actuators. • The anisotropic behavior of wax fibrils are demonstrated. • Integrated anisotropic and site-specific actuations in one actuator system. • Autonomous crawling robots and steerable soft robots are achieved.

Vitrimer-based soft actuators with multiple responsiveness and self-healing ability triggered by multiple stimuli

<h2>Summary</h2> Soft actuators are highly desirable in soft robots, electronic devices, wearable devices, etc. Both multi-stimuli responsiveness and multichannel self-healing ability are essential for soft actuators to be used in different circumstances. However, to date, research on soft actuators with multi-stimuli response or multichannel self-healing ability is scarce, and there is none on actuators with both multi-stimuli abilities. Here, we show that simply hot-pressing carbonized silk fabrics into the surface of vitrimers results in a thermosetting soft actuator that can be efficiently and repeatedly self-healed by five stimuli (light, electricity, electromagnetic wave, solvent, and heat) and can respond to four stimuli (light, electricity, heat, and solvent) simultaneously. Moreover, due to the nature of vitrimer, it is robust, sustainable, recyclable, and reprocessable. This soft actuator may greatly broaden its applications, as it is hopefully healed and actuated by a handy and facile tool when it is used in different environmental circumstances.

Nanohybrids as Protein-Polymer Conjugate Multimodal Therapeutics.

Protein therapeutic formulations are being widely explored as multifunctional nanotherapeutics. Challenges in ensuring susceptibility and efficacy of nanoformulation still prevail owing to various interactions with biological fluids before reaching the target site. Smart polymers with the capability of masking drugs, ease of chemical modification, and multi-stimuli responsiveness can assist controlled delivery. An active moiety like therapeutic protein has started to be known as an important biological formulation with a diverse medicinal prospect. The delivery of proteins and peptides with high target specificity has however been tedious, due to their tendency to aggregate formation in different environmental conditions. Proteins due to high chemical reactivity and poor bioavailability are being researched widely in the field of nanomedicine. Clinically, multiple nano-based formulations have been explored for delivering protein with different carrier systems. A biocompatible and non-toxic polymer-based delivery system serves to tailor the polymer or drug better. Polymers not only aid delivery to the target site but are also responsible for proper stearic orientation of proteins thus protecting them from internal hindrances. Polymers have been shown to conjugate with proteins through covalent linkage rendering stability and enhancing therapeutic efficacy prominently when dealing with the systemic route. Here, we present the recent developments in polymer-protein/drug-linked systems. We aim to address questions by assessing the properties of the conjugate system and optimized delivery approaches. Since thorough characterization is the key aspect for technology to enter into the market, correlating laboratory research with commercially available formulations will also be presented in this review. By examining characteristics including morphology, surface properties, and functionalization, we will expand different hybrid applications from a biomaterial stance applied in in vivo complex biological conditions. Further, we explore understanding related to design criteria and strategies for polymer-protein smart nanomedicines with their potential prophylactic theranostic applications. Overall, we intend to highlight protein-drug delivery through multifunctional smart polymers.

Phase changing poly(ionic liquid) with electrolytic functionality for a single-layer ionogel-based smart window with multi-stimuli response

Functional materials play a crucial role in the design of smart windows that can provide a more comfortable indoor environment for people to enjoy a better lifestyle. A traditional smart window material tends to have only a single feature wherein the color change is led by solar energy input. It was known that different color tones have a significant influence on people's emotions. Herein, our group has adopted a strategy to combine the properties of an electro- and thermo-chromic in a single layer (all-in-one) ionogel. In this work, 3-chloro-N-isopropylacetamide containing thermo-responsive poly [VNIm][TFSI] based electroactive has been synthesized for multi-responsive device. Ionogel, consisting of MBV [TFSI], ferrocene, and poly [VNIm][TFSI], was utilized to construct a single layer (all-in-one) device (with and without water). The proposed ionogel based device 1 (with water) that could offer a useful response to surrounding environments by switching between opaque and transparent in the aqueous condition through a temperature change. This kind of device 1 can be utilized as an individual privacy smart windows, under specific conditions. On the other hand, the ionogel based device 2 (without water) exhibits remarkable electrochromic performance through a reversible color change between colorless to purple color once 1.8 V was applied at 25 °C (below UCST) and gave a high (ΔT) of 74.9% and a coloration efficiency (CE) of 229.03 cm2 C−1 with coloration and bleaching times of 10.2 s and 100 s, respectively, while the tone changes from purple to blue when the device 2 is above UCST (52 °C). These phenomena are caused by the synergetic effect of its electrochromic reaction and thermochromic behavior. The device 2 maintained its switching stability for >2000 cycles. This novel strategy of integrating thermo- and electrochromic materials into a single device will lead to the development of the next generation of multifunctional smart windows.

Multistimuli Responsive Solid-State Emission of a Zinc(II) Complex with Multicolour Switching.

The development of smart luminescent materials, especially those stimulus-responsive fluorescent materials that can switch between different colors repeatedly under external stimulation based on a single molecule, is of great significance but a challenge. In this work, a novel zinc(II)-Schiff base complex (ZnL2) was obtained and characterized. Upon exposure to the HCl and NH3 vapors, it displayed remarkable tricolor acidochromic behavior with high contrast and rapid response under the ambient light as well as UV light (365 nm). The XPS analyses of ZnL2 crystals before and after HCl/NH3 fuming show that the acidochromism originates principally from the adsorption of vapor and the gas-solid reaction equilibrium on the crystal surface. The reddish-brown color of the HCl-fumigated ZnL2 crystals could be attributed to the generation of HL at the surface of ZnL2, and red-shifted emission could be ascribed to the self-absorption effect. The single crystal X-ray diffraction data indicate that these processes cause slight changes in the molecular conformation and crystal packing. ZnL2 shows reversible mechanochromic luminescence behavior between yellow and orange emission during the grinding-fuming/heating cycles due to the modulation between amorphous and crystalline states. Moreover, ZnL2 was successfully made into test paper for the rapid detection of HCl/NH3 vapors and mechanical stimuli.

A tripodal stimuli responsive self-assembly system and its application for detecting of organic amines, acids and Cu2+ ions aqueous solution

A novel fluorescent tripodal low-molecular weight gelator (LMWG) with the triaminoguanidinium cation unit as the center and triphenylamine groups modifying was designed and synthesized. The unique gelators (X) formed microfibers with different size and distribution characteristics in different solvents, which was closely crucial to the stability of gels. The self-assembly structures were performed characterization analyses by scanning electron microscope (SEM), powder X-ray diffraction (XRD), rheology, transmission electron microscope (TEM) and atomic force microscope (AFM). It was found that the most stable gel XMG was formed in DMSO-CH3OH (1:9, v/v), which had the gelation-induced fluorescence enhancement characteristic and the fibers with small and thick structure features, uniform dispersion as well as high distribution density. In addition, XMG can be used as a multi-stimulus response fluorescent gel material to make special responses to copper ions, TEA and TFA directly and indirectly. The lowest limit of quantitation (LOQ) for TEA and TFA as well as the minimum limit of detection (LOD) for Cu2+ were in the range of 8.24 × 10−10, 9.75 × 10−10 and 5.39 × 10−10 M respectively. The gelator possesses the potential of application in the field of detection chemical, environmental and biological samples.

Van der Waals epitaxy for high-quality flexible VO2 film on mica substrate

Vanadium dioxide (VO2) has wide application prospects in the electronics industry because of its rapid, reversible, and multi-stimulus response phase transition behavior. The development of flexible VO2 films and devices can further promote the development of flexible electronic materials and may play an important role in the next generation of wearable electronics. Here, we directly fabricated flexible VO2 films on mica via a pulsed-laser deposition system. By selection and optimization of the deposited condition, a high-quality flexible VO2 film with excellent metal to insulator (MI) transition properties of about a 3 order resistance variation in magnitude is successfully prepared. The growth competitions with different phases and different epitaxial orientations in the selection of deposited conditions verify the van der Waals (vdW) epitaxial growth mechanism of VO2 films on mica substrates. The invariable sheet resistance of VO2 films under different bending radii and bending cycles indicate their excellent mechanical flexibility and bending stability. Moreover, benefiting from the vdW epitaxy, a millimeter-scale, totally free-standing and transferable VO2 film is further obtained by a simple wet method and it is expected to be integrated into conventional silicon electronics and other systems. The high-quality, flexible, and peelable VO2 film prepared in our work lays a solid foundation for the application of VO2 films in wearable and integrated electronics.

Insight into the Properties of Heteroleptic Metal Dithiolenes: Multistimuli Responsive Luminescence, Chromism, and Nonlinear Optics.

A comprehensive investigation of the functional properties of heteroleptic donor-M-acceptor dithiolene complexes Bu4N[MII(L1)(L2)] is presented (M = Pd, Pt). The acceptor L1 consists of the chiral (R)-(+)α-methylbenzyldithiooxamidate ((R)-α-MBAdto), the donor L2 is 2-thioxo-1,3-dithiole-4,5-dithiolato (dmit) in 1 (Pd) and 2 (Pt), 1,2-dicarbomethoxyethylenedithiolate (ddmet) in 3 (Pd) and 4 (Pt), or [4',5':5,6][1,4]dithiino[2,3-b]quinoxaline-1',3'-dithiolato (quinoxdt) in 5 (Pd) and 6 (Pt). L1 is capable of undergoing proton exchange and promoting crystal formation in noncentrosymmetric space groups. L2 has different molecular structures while it maintains similar electron-donating capabilities. Thanks to the synergy of the ligands, 1-6 behave as H+ and Ag+ switchable linear chromophores. Moreover, the compounds exhibit a H+-switchable second-order NLO response in solution, which is maintained in the bulk for 1, 3, and 4 when they are embedded into a PMMA poled matrix. 5 and 6 show unique anti-Kasha H+ and Ag+ tunable colored emission originating from the quinoxdt ligand. A correlation between the electronic structure and properties is shown through density functional theory (DFT) and time-dependent DFT calculations.

Bioinspired Multi-Stimuli Responsive Actuators with Synergistic Color- and Morphing-Change Abilities.

The combination of complex perception, defense, and camouflage mechanisms is a pivotal instinctive ability that equips organisms with survival advantages. The simulations of such fascinating multi‐stimuli responsiveness, including thigmotropism, bioluminescence, color‐changing ability, and so on, are of great significance for scientists to develop novel biomimetic smart materials. However, most biomimetic color‐changing or luminescence materials can only realize a single stimulus‐response, hence the design and fabrication of multi‐stimuli responsive materials with synergistic color‐changing are still on the way. Here, a bioinspired multi‐stimuli responsive actuator with color‐ and morphing‐change abilities is developed by taking advantage of the assembled cellulose nanocrystals‐based cholesteric liquid crystal structure and its water/temperature response behaviors. The actuator exhibits superfast, reversible bi‐directional humidity and near‐infrared (NIR) light actuating ability (humidity: 9 s; NIR light: 16 s), accompanying with synergistic iridescent appearance which provides a visual cue for the movement of actuators. This work paves the way for biomimetic multi‐stimuli responsive materials and will have a wide range of applications such as optical anti‐counterfeiting devices, information storage materials, and smart soft robots.

Bio-Inspired Bicomponent Fiber with Multistimuli Response to Infrared Light and Humidity for Smart Actuators

Bio-Inspired Bicomponent Fiber with Multistimuli Response to Infrared Light and Humidity for Smart Actuators

Synthesis and Properties of Multistimuli Responsive Shape Memory Polyurethane Bioinspired from α‐Keratin Hair

AbstractHerein, a multistimuli responsive shape memory polyurethane (multiresponsive SMPU) containing disulfide bonds (–S–S–), bioinspired from α‐keratin hair component, was synthesized using a two‐step reaction and activated via four‐varied stimuli, including water, heat, redox agent, and UV‐light. First, the prepolymer was prepared by the reaction between the comonomers of hexamethylene diisocyanate and polycaprolactone‐2000, and once ended, 1,4‐butylene glycol and 3‐mercapto‐1,2‐propanediol (C3H8O2S) have been appended to the prepolymer to initiate the chain‐extension reaction. The chemical structure and properties of the multi‐responsive SMPU were decoded by FT‐IR, XRD, DSC, and Raman spectra. The correlation between microstructure, dynamic‐mechanical‐analysis, and shape‐memory properties of the multi‐responsive SMPU were systemically discussed. As a primary clue, the opening/closing of H‐bonds and disulfide bonds approved that they dictated the shape memory performance. The clear‐cut results clarified that the multiresponsive SMPU endowed composition‐dependent stress relaxation, and its reversible variation of storage modulus was examined by changing temperature. Owing to such molecular switches, the strip pieces were able to represent a multistimuli responsive shape memory effect —induced by water, heat, redox agent (NaHSO3‐H2O2 solutions), and UV‐light. This research paves a feasible road to prepare a novel multistimuli responsive shape memory actuator with high potential features in flexible sensor and robotic applications.

Effect of conjugation on the optoelectronic properties of pyrazine-based push-pull chromophores: Aggregation-induced emission, solvatochromism, and acidochromism

A series of pyrazine-based bipodal D-π-A-π-D and D-π-A-π-A molecules with multi-stimuli response have been synthesized via Suzuki and Sonogashira cross-coupling reactions. We present a joint theoretical and experimental study to elucidate structure-property relationship of these push-pull chromophores. The modification of the end-capped donor-acceptor units and the extension of π-conjugation are key factors in tuning their optical, thermal and electrochemical properties. Depending on the different electron-donating substituents, the chromophores emit blue to orange fluorescence. The solvent dependent emission was observed and their Dimroth-Reichardt plots show a linear correlation. The aggregation-induced study shows enhanced emission in aggregates. Our work has elucidated that these small structural isomers can be utilized to develop a promising multi-stimuli responsive fluorescent materials.

π-stacked donor-acceptor molecule to realize hybridized local and charge-transfer excited state emission with multi-stimulus response

• The HLCT property based on the ISCT emitter is presented. • The HLCT&ISCT emitter enables multi-stimulus response properties. • High efficiency and exciton utilization in OLEDs are achieved. Organic materials with multi-stimulus response (MSR) properties have magnificent application prospects in the optoelectronics field. Herein, a new asymmetric donor-spiro-acceptor type hybridized local and charge-transfer excited state (HLCT) compound based on benzothiadiazole derivative (2P-BT) moiety, Spiro-2P-BT-TPA , was designed and synthesized. The fluorene unit has a rigid linker to position the acceptor and donor subunit in close vicinity with control over their spacing and molecular structure and to achieve MSR properties, such as quasi-aggregation-induced emission (quasi-AIE), mechanochromic and solvatochromic. Moreover, Spiro-2P-BT-TPA possesses a high photoluminescence quantum yield (PLQY) of 80.9% when it is incorporated in a solid matrix, owing to spatial confined D/A stacked structure, multi-inter/intramolecular interactions as well as quasi-AIE properties. OLEDs based on Spiro-2P-BT-TPA achieve an EQE of 6.6% and the exciton utilization is 40%. To the best of our knowledge, this is a novel example for HLCT materials based on intramolecular spatial charge transfer as well as MSR properties.

Tailoring Multistimuli Responsive Micropatterns Activated by Various Mechanical Modes

AbstractA versatile wrinkle‐based micropatterned system with a film‐substrate structure is proposed, which contains a hydrophilic film of polyvinyl alcohol or its composite with laponite and a hydrophobic substrate of polydimethylsiloxane or its composite with carbon black. The wrinkled system features high design flexibility and multistimuli responsiveness, which can be activated by various mechanical methods, including vertical press or scratch, gentle stretch‐and‐release, bend, or analogous magneto‐mechanical and electro‐mechanical modes. The resultant wrinkles possess 1) instantaneous and reversible strain/moisture/light responsive optical modulation; 2) tunable dynamics for the aforementioned strain/moisture/light response;3) tailorable amplitude/wavelength; 4) unique surface morphologies from the coupling of wrinkles and cracks; 5) excellent reversibility and durability. A variety of applications are demonstrated based on this system, including 1) a moisture erasable highly sensitive pressure responsive device and pattern replicator with a high fidelity; 2) a moisture erasable scratch/magneto‐mechanical re‐writable tablet; 3) an electro‐mechanical controllable smart window with an ultra‐sensitive strain responsive transmittance modulation and a low operating voltage; 4) various types of strain responsive, moisture erasable, and laser writable information recording/encryption devices. This work provides new routes for designing innovative wrinkled systems triggered by diverse mechanical fashions and can decode multiple environmental stimuli into optical signals for widespread application.

Synthesis of Anthracene-Based Cyclic π-Clusters and Elucidation of their Properties Originating from Congested Aromatic Planes.

Synthesis and properties of anthracene-based cyclic π-clusters which possess two and four anthracene units are discussed. The optimal cyclization conditions were determined based on a nickel(0)-mediated reaction that afforded a cyclic anthracene dimer as the major product. Bringing two anthracene planes in close proximity in a face-to-face manner resulted in red-shifted absorption owing to the narrowing of the HOMO-LUMO gap. The cyclic anthracene dimer exhibits multi-stimuli responsiveness due to high π-congestion. For example, photoirradiation on the anthracene dimer affords its photoisomer having C-C bonds that are longer than 1.65 Å, which can undergo thermal reversion under gentle heating. This enabled mechanochromism of the photoisomer (colorless) to the original anthracene dimer (red). Photoisomerization was also observed in the crystalline state, accompanied by crystal jumping or collapsing, that is, the photosalient effect.

Novel self-healing and multi-stimuli-responsive supramolecular gel based on d-sorbitol diacetal for multifunctional applications.

A simple-structured super gelator with self-healability and multi-stimuli responses was reported herein, which exhibited multiple visual molecular recognition abilities. Multifunctional applications such as effective lubricants, safe fuels, high-efficient propellants, dyes adsorbents, enhanced fluorescence emission and separation of aldehydes from aqueous solutions are integrated into a single organogelator, which was rarely reported.

Tunable dual-emission luminescence from Cu(i)-cluster-based MOFs for multi-stimuli responsive materials

Through filling guest molecules in cages, two Cu(i)-cluster-based MOFs with distinct luminescence at room temperature were obtained. They show multi-stimuli responses to VOCs, temperature and nitro-compounds.

Molecular structure controlled self-assembly of pyridine appended fluorophores: multi-stimuli fluorescence responses and fabricating rewritable/self-erasable fluorescent platforms

Pyridine appended structural isomers showed a planar or propeller conformation dependent molecular self-assembly, fluorescent polymorphs, stimuli-responsive fluorescence switching and halochromism.

Dynamic coordination of metal–alanine to control the multi-stimuli responsiveness of self-powered polymer hydrogels

A new design of self-powered metallo-hydrogels with intriguing electrical-signal responses to multiple stimuli.