Development Of Smart Materials Research Articles

Polymer Free Volume‐Controlled Molecular Clock and Emitter for Multicolored Transient Data Display in Advanced Photonic Cryptography

The booming demand on data security has aroused great interest for developing smart materials with temporal display feature and dynamic multicolor fluorescence. However, it remains challenging to implement both features on most responsive molecules. Herein, we construct a polymer free volume‐controlled “molecular clock and emitter” via covalently embedding a multi‐stimuli responsive molecular switch (i.e., spiropyran) into a polymer network (i.e., poly(pentafluorophenyl acrylate)) with programmable crosslink density and free volume. By the aminolysis of pentafluorophenyl ester with different amount of diamine crosslinkers, pPFPA‐co‐SP networks with controllable crosslink densities are generated, which have different confinement effects on the rate constant of SP/MC isomerization, thus leading to time‐dependent photochromism. In addition, PTF1, a fluorescent probe that is sensitive to polymer rigidity, is introduced to further endow pPFPA‐co‐SP system with phototunable dynamic full‐color emission. Therefore, relying on their synergistical responses to the rigidity of the polymer network, we have successfully developed a versatile molecular clock and emitter via an “one stone two birds” manner, which shows time‐dependent data display along with dynamic multicolor fluorescence switching, providing great potential for advanced encryption and anticounterfeiting with a high security level.

Shape Programming of Porous Bilayer Hydrogel Structures

Abstract Shape-programmable materials have garnered significant attention for their ability to morph into complex three-dimensional (3D) configurations under external stimuli, with critical applications in the fields of biomedical engineering, soft robotics, and sensing technologies. A current challenge lies in determining the geometric parameters of the initial two-dimensional (2D) structure and the intensity of the external stimulus required to achieve a target 3D shape. In this work, we introduce a novel inverse design strategy based on hole pattern engineering. Utilizing a temperature-sensitive bilayer hydrogel with differing coefficients of thermal expansion in each layer, we achieve controlled bending deformations by varying the porosity distribution in one of the layers. Drawing on the Timoshenko theory on bimetallic beam, we establish a quantitative relationship between porosity and curvature, allowing for the hole distribution of the initial structure to be tailored to the desired curvature. We demonstrate the efficacy of our inverse design approach with several prototypical 3D structures, including variable-curvature strip and ellipsoidal surface, validated through finite element simulations and experimental trials. This strategy paves the way for advanced fabrication techniques in developing smart materials and devices with programmable shapes.

Development of smart materials with versatile bending capabilities using microcellular foaming process: influence of foaming and desorption time

Abstract Herein, a smart material with versatile bending capability is developed using a microcellular foaming process (MCPs). In contrast to previous hydrogel-based approaches, the bi-layered smart material is fabricated using typical thermoplastics, polyethylene terephthalate glycol (PETG) and polymethyl methacrylate (PMMA), to achieve shape deformation in response to thermal stimuli. Further, the theoretical model for bi-layered smart materials based on the modified Timoshenko’s model is employed to predict and comprehend this thermal response phenomenon. Due to the distinct foaming characteristics of the two polymers, a reversal in the bending direction is achieved by manipulating the foaming and desorption time. The length variation after foaming differs depending on the desorption time for each polymer. PMMA decreases in length after foaming, measuring 56.25 mm at a desorption time of 40 min and 53.16 mm at 80 min. On the other hand, PETG shows an increase in length after foaming, measuring 53.33 mm at 40 min and 58.25 mm at 80 min. Consequently, when the two polymers are bonded and foamed, bending occurs depending on the desorption time, and a reversal in the bending direction is observed at the critical desorption time of around 60 min. Based on this result, the folding direction of a five-leafed flower-shaped object is successfully altered under thermal stimuli. This innovative approach extends the category of smart materials beyond the hydrogels and showcases the potential of the MCPs for the creation of smart materials for various applications that require versatile shape changes in response to temperature.

Recent Insights into Glucose-Responsive Concanavalin A-Based Smart Hydrogels for Controlled Insulin Delivery.

Many efforts are continuously undertaken to develop glucose-sensitive biomaterials able of controlling glucose levels in the body and self-regulating insulin delivery. Hydrogels that swell or shrink as a function of the environmental free glucose content are suitable systems for monitoring blood glucose, delivering insulin doses adapted to the glucose concentration. In this context, the development of sensors based on reversible binding to glucose molecules represents a continuous challenge. Concanavalin A (Con A) is a bioactive protein isolated from sword bean plants (Canavalia ensiformis) and contains four sugar-binding sites. The high affinity for reversibly and specifically binding glucose and mannose makes Con A as a suitable natural receptor for the development of smart glucose-responsive materials. During the last few years, Con A was used to develop smart materials, such as hydrogels, microgels, nanoparticles and films, for producing glucose biosensors or drug delivery devices. This review is focused on Con A-based materials suitable in the diagnosis and therapeutics of diabetes. A brief outlook on glucose-derived theranostics of cancer is also presented.

Multi-stimuli-responsive shape memory flexible composites based on magnetic melamine/polydopamine/phosphorene complex foams and polyethylene glycol

We have developed a novel type of flexible multi-stimuli-responsive shape memory composite system based on a melamine/polydopamine (PDA)/Fe3O4/phosphorene (PR) complex foam and poly(ethylene glycol) (PEG). The system was constructed through coating PDA on the skeleton of the melamine foam and then decorating the PDA layer with Fe3O4 and PR nanosheets, followed by vacuum impregnation of PEG. The resultant composites exhibit an intrinsic thermal-driven shape memory behavior with a high shape recovery ratio of around 100% thanks to their high latent heat capacity derived from the loaded PEG. The introduction of magnetic Fe3O4 nanoparticles and PR nanosheets not only enhances the thermal conductance of the composites but also generates good magnetic and photothermal responsiveness. This enables the composites to obtain good light- and magnetic-driven shape memory capabilities in a shorter shape recovery period. This study offers a new strategy for developing smart materials with multiple and effective response to light, heat, and magnetism.

Self-indicating polymers: a pathway to intelligent materials.

Self-indicating polymers have emerged as a promising class of smart materials that possess the unique ability to undergo detectable variations in their physical or chemical properties in response to various stimuli. This article presents an overview of the most important mechanisms through which these materials exhibit self-indication, including aggregation, phase transition, covalent and non-covalent bond cleavage, isomerization, charge transfer, and energy transfer. Aggregation is a prevalent mechanism observed in self-indicating polymers, where changes in the degree of molecular organization result in variations in optical or electrical properties. Phase transition-induced self-indication relies on the transformation between different phases, such as liquid-to-solid or crystalline-to-amorphous transitions, leading to observable changes in color or conductivity. Covalent bond cleavage-based self-indicating polymers undergo controlled degradation or fragmentation upon exposure to specific triggers, resulting in noticeable variations in their structural or mechanical properties. Isomerization is another crucial mechanism exploited in self-indicating polymers, where the reversible transformation between the different isomeric forms induces detectable changes in fluorescence or absorption spectra. Charge transfer-based self-indicating polymers rely on the modulation of electron or hole transfer within the polymer backbone, manifesting as changes in electrical conductivity or redox properties. Energy transfer is an essential mechanism utilized by certain self-indicating polymers, where energy transfer between chromophores or fluorophores leads to variations in the emission characteristics. Furthermore, this review article highlights the diverse range of applications for self-indicating polymers. These materials find particular use in sensing and monitoring applications, where their responsive nature enables them to act as sensors for specific analytes, environmental parameters, or mechanical stress. Self-indicating polymers have also been used in the development of smart materials, including stimuli-responsive coatings, drug delivery systems, food sensors, wearable devices, and molecular switches. The unique combination of tunable properties and responsiveness makes self-indicating polymers highly promising for future advancements in the fields of biotechnology, materials science, and electronics.

Stimuli-fluorochromic smart organic materials.

Smart materials based on stimuli-fluorochromic π-conjugated solids (SFCSs) have aroused significant interest due to their versatile and exciting properties, leading to advanced applications. In this review, we highlight the recent developments in SFCS-based smart materials, expanding beyond organometallic compounds and light-responsive organic luminescent materials, with a discussion on the design strategies, exciting properties and stimuli-fluorochromic mechanisms along with their potential applications in the exciting fields of encryption, sensors, data storage, display, green printing, etc. The review comprehensively covers single-component and multi-component SFCSs as well as their stimuli-fluorochromic behaviors under external stimuli. We also provide insights into current achievements, limitations, and major challenges as well as future opportunities, aiming to inspire further investigation in this field in the near future. We expect this review to inspire more innovative research on SFCSs and their advanced applications so as to promote further development of smart materials and devices.

Luminescent switching behavior achieved by adjusting cocrystal charge transfer excitons under acid stimulation

This study presents acid stimuli responsive cocrystal systems with dynamically controllable luminous characteristics, demonstrating highly sensitive fluorescence switching, offering a successful method for developing smart materials.

Unraveling Dynamic Helicity Inversion and Chirality Transfer through the Synthesis of Discrete Azobenzene Oligomers by an Iterative Exponential Growth Strategy.

Unraveling the chirality transfer mechanism of polymer assemblies and controlling their handedness is beneficial for exploring the origin of hierarchical chirality and developing smart materials with desired chiroptical activities. However, polydisperse polymers often lead to an ambiguous or statistical evaluation of the structure-property relationship, and it remains unclear how the iterative number of repeating units function in the helicity inversion of polymer assemblies. Herein, we report the macroscopic helicity and dynamic manipulation of the chiroptical activity of supramolecular assemblies from discrete azobenzene-containing oligomers (azooligomers), together with the helicity inversion and morphological transition achieved solely by changing the iterative chain lengths. The corresponding assemblies also differ from their polydisperse counterparts in terms of thermodynamic properties, chiroptical activities, and morphological control.

Unraveling Dynamic Helicity Inversion and Chirality Transfer through the Synthesis of Discrete Azobenzene Oligomers by an Iterative Exponential Growth Strategy

AbstractUnraveling the chirality transfer mechanism of polymer assemblies and controlling their handedness is beneficial for exploring the origin of hierarchical chirality and developing smart materials with desired chiroptical activities. However, polydisperse polymers often lead to an ambiguous or statistical evaluation of the structure–property relationship, and it remains unclear how the iterative number of repeating units function in the helicity inversion of polymer assemblies. Herein, we report the macroscopic helicity and dynamic manipulation of the chiroptical activity of supramolecular assemblies from discrete azobenzene‐containing oligomers (azooligomers), together with the helicity inversion and morphological transition achieved solely by changing the iterative chain lengths. The corresponding assemblies also differ from their polydisperse counterparts in terms of thermodynamic properties, chiroptical activities, and morphological control.

Hydro-Photo-Thermo-Responsive Multicolor Luminescence Switching of a Ternary MOF Hybrid for Advanced Information Anticounterfeiting.

Developing smart materials capable of solid-state multicolor photoluminescence (PL) switching in response to multistimuli is highly desirable for advanced anticounterfeiting. Here, a ternary MOF hybrid showing hydro-photo-thermo-responsive multicolor PL switching in the solid state is presented. This hybrid is constructed by co-immobilizing Eu3+ and methyl viologen (MV) cations within an anionic MOF via the cation-exchange approach. The confined guest cations are well arranged in the framework channels, facilitating the synergistic realization of stimuli-responsive multiple PL color-switching through intermolecular coupling. The hybrid undergoes a rapid and reversible PL color-switching from red to blue upon water simulation, which is achieved by activating the blue emission of the framework linker while simultaneously quenching the Eu3+ emission. Furthermore, the hybrid displays photo-thermo-responsive PL switching from red to dark. UV-light irradiation or heating triggers the chromic conversion of MV to its colored radical form, which exhibits perfect spectral overlap with Eu3+, thus activating Förster resonance energy transfer (FRET) from Eu3+ to MV radicals and quenching the Eu3+ emission. Inspired by these results, PL morse patterns are designed and fabricated using a novel triple-level encryption strategy, showcasing the exciting potential of this hybrid in advanced anticounterfeiting applications.

Self‐Healing Concrete Due the Use of on Demand opening Core‐Shell Capsules

AbstractIncreasing the durability of concrete is one of the major challenges in terms of environmentally friendly concrete. To achieve this, it is necessary to develop smart materials, which are superior to the current materials in term of multi‐field requirements. These materials are characterized by their ability to detect starting damages and the ability to initialize the self‐healing process. Self‐healing concrete is subject of current research and performed in different ways. In terms of this work autonomous self‐healing due to the use of an epoxy‐resin, encapsulated in a core‐shell capsule is investigated. The opening of the capsules should be realized by irradiation with microwaves. Therefore, the shell of the capsules was functionalized with trigger materials. The on demand opening of the capsules was investigated with sub‐μ‐CT. According to the tomography a 3‐dimensional model of the pore system was calculated. Based on this model a pore size distribution was calculated to get insight in the opening of the capsules. These investigations showed a successful release of the active agent.

Coating of Felt Fibers with Carbon Nanotubes and PEDOT with Different Counterions: Temperature and Electrical Field Effects.

The use of wearable devices has promoted new ways of integrating these devices, one of which is through the development of smart textiles. Smart textiles must possess the mechanical and electrical properties necessary for their functionality. This study explores the impact of polymer-felt microstructure variations on their morphology, electrical, and mechanical properties. The application of thermal treatment, along with an electric field, leads to a substantial structural reorganization of the molecular chains within pristine felt. This results in a system of nanofibrils coated with MWCNT-PEDOT, characterized by highly ordered counterions that facilitate the flow of charge carriers. Both temperature and an electric field induce reversible microstructural changes in pristine felt and irreversible changes in coated felt samples. Furthermore, electropolymerization of PEDOT significantly enhances electrical conductivity, with PEDOT:BTFMSI-coated fabric exhibiting the highest conductivity.

Alkyne-to-alkene conversion in graphdiyne driving instant reversible deformation of whole carbon film.

The emerging field of soft robotics demands the core actuators and related responsive functional materials with rapid responsiveness and controllable accurate deformation. Here, we developed an alkyne-to-alkene chemical bond conversion way as the driving force to control ultrasensitive and instant reversible deformation of 2D carbon graphdiyne (GDY) film with an asymmetric interface design. The alkyne-to-alkene chemical bond conversion was triggered by acetone through the fast binding and release process. The as-fabricated GDY-based deformation modulator was exhibited to rapidly change shape (within 0.15 seconds) while dipped in an acetone vapor atmosphere and recover to its original form when exposed to air (recovery time < 0.01 seconds), with outstanding properties like large curvature, quick recovery time, excellent stability, and repeatability. It could mimic the movement of mosquito larvae, displaying great promise as micro bionic soft robots. Our results suggest alkyne-to-alkene bond conversion as a unique driving force for developing smart materials for areas like intelligent robotics and bionics.

Advancing Smart Textiles: Structural Evolution of Knitted Piezoresistive Strain Sensors for Enabling Precise Motion Capture.

Recently, there has been remarkable progress in the development of smart textiles, especially knitted strain sensors, to achieve reliable sensor signals. Stable and reliable electro-mechanical properties of sensors are essential for using textile-based sensors in medical applications. However, the challenges associated with significant hysteresis and low gauge factor (GF) values remain for using strain sensors for motion capture. To evaluate these issues, a comprehensive investigation of the cyclic electro-mechanical properties of weft-knitted strain sensors was conducted in the present study to develop a drift-free elastic strain sensor with a robust sensor signal for motion capture for medical devices. Several variables are considered in the study, including the variation of the basic knit pattern, the incorporation of the electrically conductive yarn, and the size of the strain sensor. The effectiveness and feasibility of the developed knitted strain sensors are demonstrated through an experimental evaluation, by determining the gauge factor, its nonlinearity, hysteresis, and drift. The developed knitted piezoresistive strain sensors have a GF of 2.4, a calculated drift of 50%, 12.5% hysteresis, and 0.3% nonlinearity in parts.

Erasable, Rewritable, And Reprogrammable Dual Information Encryption Based on Photoluminescent Supramolecular Host-Guest Recognition And Hydrogel Shape Memory.

Information encryption technologies are very important for security, health, commodity, and communications, etc. Novel information encryption mechanisms and materials are desired to achieve multi-mode and re-programmable encryption. Here, wedemonstrate a supramolecular strategy to achieve multi-modal, erasable, reprogrammable, and reusable information encryption by reversibly modulating fluorescence. A butyl-naphthalimide with flexible ethylenediamine functionalized β-cyclodextrin (N-CD) is utilized as fluorescent responsive ink for printing or patterning information on polymer brushes with dangling adamantane group grafted on responsive hydrogels. The photoluminescent naphthalimide moiety is bonded to β-CD and entrapped in the cavity. Its fluorescence is highly weakened in β-CD cavity and recovers after being expelled from the cavity by a competing guest molecule to emit bright green photoluminescence under UV. Experiments and theoretical calculations suggest π-π stacking and ICT as the primary mechanism for the naphthalimides assembly and fluorescence, which can be quenched through insertion of conjugated molecules and recover by removing the insert. Such reversible quenching and recovering are used to achieve repeated writing, erasing, and re-writing of information. Wefurther combine supramolecular recognition and hydrogel shape memory to achieve reversible dual-encryption. This study provides a novel strategy to develop smart materials with improved information security for broad applications. This article is protected by copyright. All rights reserved.

Thermoresistivity of Carbon Nanostructures and their Polymeric Nanocomposites

AbstractCarbon nanostructures such as carbon nanotubes, graphene, and its multi‐layer derivatives exhiibit temperature‐dependent electrical conductivity. They can form percolated networks inside polymers, which render electrical conductivity to nanocomposites. Upon the formation of a percolated network, thermal energy applied to the material drives structural changes of the network, which manifest as changes in electrical conductivity. This principle is used to develop smart materials with self‐sensing temperature capabilities. This critical review covers past and present research on the electrical response to temperature (thermoresistivity) of carbon nanostructures and their polymeric nanocomposites. It covers few‐ and multi‐layer graphene, carbon nanotubes, carbon‐nanostructured arrays and fibers (yarns). The mechanisms driving the thermoresistive response of individual nanostructures, their arrays, and of their polymeric nanocomposites are addressed. The role of the nanostructured filler on the thermoresistivity of polymer nanocomposites depends on its morphology and concentration. For low filler concentrations, thermal expansion of the polymer may dominate over the inherent thermoresistivity of the filler. For high filler concentrations, or for densely packed arrays of carbon nanostructures, the inherent (quantum) thermoresistive response of the nanostructures becomes dominant. The review addresses recent progress in the field, highlights current issues, synthesizes published data, and provides outlooks and insights into future directions.

Multifunctional Magnetoelectric Sensing and Bending Actuator Response of Polymer-Based Hybrid Materials with Magnetic Ionic Liquids.

With the evolution of the digital society, the demand for miniaturized multifunctional devices has been increasing, particularly for sensors and actuators. These technological translators allow successful interaction between the physical and digital worlds. In particular, the development of smart materials with magnetoelectric (ME) properties, capable of wirelessly generating electrical signals in response to external magnetic fields, represents a suitable approach for the development of magnetic field sensors and actuators due to their ME coupling, flexibility, robustness and easy fabrication, compatible with additive manufacturing technologies. This work demonstrates the suitability of magnetoelectric (ME) responsive materials based on the magnetic ionic liquid (MIL) 1-butyl-3-methylimidazolium tetrachloroferrate ([Bmim][FeCl4]) and the polymer poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE) for magnetic sensing and actuation device development. The developed sensor works in the AC magnetic field and has frequency-dependent sensitivity. The materials show voltage responses in the mV range, suitable for the development of magnetic field sensors with a highest sensitivity (s) of 76 mV·Oe-1. The high ME response (maximum ME voltage coefficient of 15 V·cm-1·Oe-1) and magnetic bending actuation (2.1 mm) capability are explained by the magnetoionic (MI) interaction and the morphology of the composites.

Relaxor-antiferroelectric hybrids for pyroelectric energy conversion from low-grade heat using flexible PVDF-TrFE-CTFE-NaNbO3 nanocomposite films

Nowadays, researchers focus more on developing smart materials that respond to different stimuli for harvesting energy output. In this paper, the pyroelectric energy harvesting capabilities of smart terpolymer poly(vinylidene-fluoride-trifluoroethylene-chlorotrifluoroethylene) [PVDF-TrFE-CTFE]-based nanocomposites have been investigated. Sodium niobate (NaNbO3) from the perovskite family is selected as the filler. The Sol-gel method is used to synthesise NaNbO3 nanoparticles, and solvent-cast films for different weight fractions (0–20%) of fillers have been fabricated. Structural, morphological, and dielectric properties of the polymer nanocomposite samples were done at room temperature. The ferroelectric properties of the terpolymer is improved with filler addition. The thermal stability of composite films was confirmed using differential scanning calorimetric (DSC) studies. The thermodynamic Olsen cycle was applied to nanocomposites for calculating the harvested energy output. Maximum energy density is obtained for higher filler loading (20 wt % sodium niobate). The operating temperatures were selected at 303 K and 333 K with an applied field of 130 kV/cm. The results show that including NaNbO3 in the relaxor terpolymer matrix considerably enhances the energy harvesting density of the nanocomposites, indicating that they are promising materials for designing thermally stable energy harvesting systems.

Light-responsive rotaxane-based materials: inducing motion in the solid state.

Light-responsive rotaxane-based solid-state materials are ideal scaffolds in order to develop smart materials due to the properties provided by the mechanical bond, such as control over the dynamics of the components upon application of external stimuli. This perspective aims to highlight the relevance of these materials, by pointing out recent examples of photoresponsive materials prepared from a rotaxanated architecture in which motion of the counterparts and/or macroscopic motion of the interlocked materials are achieved. Although further development is needed, these materials are envisioned as privileged scaffolds which will be used for different advanced applications in the area of molecular machinery.