Showing papers on "Smart material published in 2017"

Graphene-based smart materials

Abstract: The high specific surface area and the excellent mechanical, electrical, optical and thermal properties of graphene make it an attractive component for high-performance stimuli-responsive or ‘smart’ materials. Complementary to these inherent properties, functionalization or hybridization can substantially improve the performance of these materials. Typical graphene-based smart materials include mechanically exfoliated perfect graphene, chemical vapour deposited high-quality graphene, chemically modified graphene (for example, graphene oxide and reduced graphene oxide) and their macroscopic assemblies or composites. These materials are sensitive to a range of stimuli, including gas molecules or biomolecules, pH value, mechanical strain, electrical field, and thermal or optical excitation. In this Review, we outline different graphene-based smart materials and their potential applications in actuators, chemical or strain sensors, self-healing materials, photothermal therapy and controlled drug delivery. We also introduce the working mechanisms of graphene-based smart materials and discuss the challenges facing the realization of their practical applications. Graphene and its macroscopic assemblies and composites are currently enabling a range of high-performance ‘smart’ materials that are responsive to various stimuli. In this Review, different graphene-based smart materials are described, along with their potential applications in actuators, chemical or strain sensors, self-healing materials, photothermal therapy and controlled drug delivery.

Thermo-responsive polymers and their application as smart biomaterials

Abstract: The drastic development of polymeric materials for a wide range of biomedical and biomaterial applications has been explored in the last few decades. Among these materials, a new class of ‘smart’ or ‘intelligent’ biomaterial has been developed, and these materials are highly responsive to slight changes in their environments. Due to their dynamically alterable properties, smart materials allow for smart biomaterials to be developed. This review presents smart thermo-responsive polymers and discusses how they may be used as smart biomaterials. We describe typical thermo-responsive polymers that are either lower critical solution temperature-type, upper critical solution temperature-type, or thermo-induced shape-memory polymers. The basic mechanisms of the thermo-response processes will also be described. The applications of smart biomaterials with various forms, such as smart fibres, surfaces and hydrogels, will also be introduced.

Digital light processing 3D printing of conductive complex structures

Abstract: 3D printing has gained significant research interest recently for directly manufacturing 3D components and structures for use in a variety of applications. In this paper, a digital light processing (DLP®) based 3D printing technique was explored to manufacture electrically conductive objects of polymer nanocomposites. Here, the ink was made of a mixture of photocurable resin with multi-walled carbon nanotubes (MWCNTs). The concentrations of MWCNT as well as the printing parameters were investigated to yield optimal conductivity and printing quality. We found that 0.3 wt% loading of MWCNT in the resin matrix can provide the maximum electrical conductivity of 0.027S/m under the resin viscosity limit that allows high printing quality. With electric conductivity, the printed MWCNT nanocomposites can be used as smart materials and structures with strain sensitivity and shape memory effect. We demonstrate that the printed conductive complex structures as hollow capacitive sensor, electrically activated shape memory composites, stretchable circuits, showing the versatility of DLP® 3D printing for conductive complex structures. In addition, mechanical tests showed that the addition of MWCNT could slightly increase the modulus and ultimate tensile stress while decreasing slightly the ultimate stretch, indicating that the new functionality is not obtained at the price of sacrificing mechanical properties.

Inorganic and Organic Solution-Processed Thin Film Devices

Abstract: Thin films and thin film devices have a ubiquitous presence in numerous conventional and emerging technologies. This is because of the recent advances in nanotechnology, the development of functional and smart materials, conducting polymers, molecular semiconductors, carbon nanotubes, and graphene, and the employment of unique properties of thin films and ultrathin films, such as high surface area, controlled nanostructure for effective charge transfer, and special physical and chemical properties, to develop new thin film devices. This paper is therefore intended to provide a concise critical review and research directions on most thin film devices, including thin film transistors, data storage memory, solar cells, organic light-emitting diodes, thermoelectric devices, smart materials, sensors, and actuators. The thin film devices may consist of organic, inorganic, and composite thin layers, and share similar functionality, properties, and fabrication routes. Therefore, due to the multidisciplinary nature of thin film devices, knowledge and advances already made in one area may be applicable to other similar areas. Owing to the importance of developing low-cost, scalable, and vacuum-free fabrication routes, this paper focuses on thin film devices that may be processed and deposited from solution.

Review of 4D printing materials and their properties

Abstract: Since its introduction, the 3D printing technology has been widely used in fields such as design, rapid prototyping, and biomedical devices, owing to its advantages of inexpensive, facile embodiment of computer 3D files into physical objects. Later, 4D printing was introduced by adding the temporal dimension to 3D. Stimuli such as heat, humidity, pH, and light trigger the actuation of printed objects without motors or wires. Smart materials that respond to external stimuli are good candidates for 4D printing. In this paper, we review the recent research on 4D printing, and categorize it with respect to the activating stimuli. The mechanical properties of 4D printing materials are mentioned as well. Finally, the future of 4D printing is discussed.

Controlled Sol-Gel Transitions by Actuating Molecular Machine Based Supramolecular Polymers.

Abstract: The implementation of artificial molecular machines in polymer science is an important objective that challenges chemists and physicists in order to access an entirely new class of smart materials. To design such systems, the amplification of a mechanical actuation from the nanoscale up to a macroscopic response in the bulk material is a central issue. In this article we show that bistable [c2]daisy chain rotaxanes (i.e., molecular muscles) can be linked into main-chain Upy-based supramolecular polymers. We then reveal by an in depth quantitative study that the pH actuation of the mechanically active rotaxane at the nanoscale influences the physical reticulation of the polymer chains by changing the supramolecular behavior of the Upy units. This nanoactuation within the local structure of the main chain polymer results in a mechanically controlled sol–gel transition at the macroscopic level.

Maximizing the performance of photothermal actuators by combining smart materials with supplementary advantages.

Abstract: The search for higher-performance photothermal microactuators has typically involved unavoidable trade-offs that hinder the demonstration of ubiquitous devices with high energy density, speed, flexibility, efficiency, sensitivity, and multifunctionality. Improving some of these parameters often implies deterioration of others. Photothermal actuators are driven by the conversion of absorbed optical energy into thermal energy, which, by different mechanisms, can produce mechanical displacement of a structure. We present a device that has been strategically designed to show high performance in every metric and respond to optical radiation of selected wavelength bands. The device combines the large energy densities and sensitivity of vanadium dioxide (VO2)-based actuators with the wavelength-selective absorption properties of single-walled carbon nanotube (SWNT) films of different chiralities. SWNT coatings increased the speed of VO2 actuators by a factor of 2 while decreasing the power consumption by approximately 50%. Devices coated with metallic SWNT were found to be 1.57 times more responsive to red light than to near-infrared, whereas semiconducting SWNT coatings resulted in 1.42 times higher responsivities to near-infrared light than to red light. The added functionality establishes a link between optical and mechanical domains of high-performance photoactuators and enables the future development of mechanical logic gates and electronic devices that are triggered by optical radiation from different frequency bands.

Smart responsive materials for water purification: an overview

Abstract: The present era is represented by the use of smart and intelligent materials in almost all spheres of life. The field of water treatment is not an exception to this. This extremely important and crucial research area has been witnessing increased involvement of stimuli-responsive smart materials in the removal of contaminating pollutants hampering the quality of water available for use in our daily life. In fact, the problem of water pollution is one of the most critical issues that the world is encountering currently. In this regard, stimuli-responsive smart materials (mainly adsorbents and filtration membranes) hold extreme promise in providing a solution to this practically persistent concern. These materials exhibit tuneable properties depending on the state of the involved stimulus/stimuli. This has in turn provided enhanced controllability of the process of contaminant removal. This review will report on the utilization of these smart materials in the form of adsorbents and filtration membranes in water treatment applications, and will discuss the various unique attributes that these materials possess.

Recent developments in self-oscillating polymeric systems as smart materials: from polymers to bulk hydrogels

Abstract: As novel functional materials, we developed self-oscillating polymeric materials composed of synthetic polymers coupled with an oscillating chemical reaction, the so-called Belousov–Zhabotinsky (BZ) reaction. These materials are very different from traditional stimuli-responsive polymeric materials in terms of their autonomic, self-regulating, and rhythmically changing functions. In this review, we address recent advances in the field of self-oscillating smart materials from the microscopic scale (linear copolymers and block copolymers) to the macroscopic scale (cross-linked hydrogels). The unique features of self-oscillating materials are analogous to the diverse functions of living organisms. This overview has been prepared to promote the development of innovative self-oscillating materials for novel biomimetic material systems.

Modelling and characterisation for the responsive performance of CF/PLA and CF/PEEK smart materials fabricated by 4D printing

Abstract: 4D printing, which is the combination of 3D printing technology and printable smart materials, provides the potential of automating actuation devices. In this paper, we have used a modified-fused deposition modelling 3D printing technology to fabricate a double-layer laminate smart material, which can be activated by temperature directly or by an electric circuit indirectly. A double-layer laminate mathematical model has been developed to describe the bending behaviour caused by the mismatch strain between the surface layer and the basal layer. The electrocaloric deformation testings were performed to find the different bending rules of this low-cost printed active composite in different physical states. The considerable maximal deformation values and deformation force (7 mm and 100 mN for these carbon fibre (CF)/polylactic acid specimens, and 10 mm and 200 mN for these CF/polyether-ether-ketone specimens in the paper) provide this double-layer smart material and 4D printing method the prospective...

Nanofibrous Smart Fabrics from Twisted Yarns of Electrospun Piezopolymer

Abstract: Smart textiles are envisioned to make a paradigm shift in wearable technologies to directly impart functionality into the fibers rather than integrating sensors and electronics onto conformal substrates or skin in wearable devices. Among smart materials, piezoelectric fabrics have not been widely reported, yet. Piezoelectric smart fabrics can be used for mechanical energy harvesting, for thermal energy harvesting through the pyroelectric effect, for ferroelectric applications, as pressure and force sensors, for motion detection, and for ultrasonic sensing. We report on mechanical and material properties of the plied nanofibrous piezoelectric yarns as a function of postprocessing conditions including thermal annealing and drawing (stretching). In addition, we used a continuous electrospinning setup to directly produce P(VDF-TrFE) nanofibers and convert them into twisted plied yarns, and demonstrated application of these plied yarns in woven piezoelectric fabrics. The results of this work can be an early st...

Bioinspired Smart Materials for Directional Liquid Transport

Abstract: Bioinspired materials capable of driving liquid in a directional manner have wide potential applications in many chemical engineering processes, such as heat transfer, separation, microfluidics, and so on. Numerous natural materials and systems such as spider silk, cactus, shorebirds, desert beetles, butterfly wing, and Nepenthes alata have been serving as a rich source of inspirations in the area. During the last decades, great efforts have been devoted to design bioinspired smart materials for directional liquid transport. In this review, we begin by introducing several natural materials and systems with surface structural features contributing for their directional liquid transport property, followed by the basic concepts and theories about surface wettability, droplet motion, and driving forces with different structural features. Then, we summarize some typical applications of such bioinspired smart materials in industrial processes and chemical engineering, particularly in heat transfer, separation, ...

Dual-Band Modulation of Visible and Near-Infrared Light Transmittance in an All-Solution-Processed Hybrid Micro–Nano Composite Film

Abstract: Smart windows with controllable visible and near-infrared light transmittance can significantly improve the building's energy efficiency and inhabitant comfort. However, most of the current smart window technology cannot achieve the target of ideal solar control. Herein, we present a novel all-solution-processed hybrid micronano composite smart material that have four optical states to separately modulate the visible and NIR light transmittance through voltage and temperature, respectively. This dual-band optical modulation was achieved by constructing a phase-separated polymer framework, which contains the microsized liquid crystals domains with a negative dielectric constant and tungsten-doped vanadium dioxide (W-VO2) nanocrystals (NCs). The film with 2.5 wt % W-VO2 NCs exhibits transparency at normal condition, and the passage of visible light can be reversibly and actively regulated between 60.8% and 1.3% by external applied voltage. Also, the transmittance of NIR light can be reversibly and passively modulated between 59.4% and 41.2% by temperature. Besides, the film also features easy all-solution processability, fast electro-optical (E-O) response time, high mechanical strength, and long-term stability. The as-prepared film provides new opportunities for next-generation smart window technology, and the proposed strategy is conductive to engineering novel hybrid inorganic-organic functional matters.

Design, fabrication, and bending test of shape memory polymer composite hinges for space deployable structures:

Abstract: Shape memory polymers are smart materials characterized by a recoverability memory effect and a large strain, but their mechanical properties such as low stiffness need to be improved for mechanica...

Stiffness control of magnetorheological gels for adaptive tunable vibration absorber

Abstract: In this study, a stiffness feedback control system for magnetorheological (MR) gel—a smart material of variable stiffness—is proposed, toward the design of a tunable vibration absorber that can adaptively tune to a time varying disturbance in real time. A PID controller was designed to track the required stiffness of the MR gel by controlling the magnitude of the target external magnetic field pervading the MR gel. This paper proposes a novel magnetic field generator that could produce a variable magnetic field with low energy consumption. The performance of the MR gel stiffness control was validated through experiments that showed the MR gel absorber system could be automatically tuned from 56 Hz to 67 Hz under a field of 100 mT to minimize the vibration of the primary system.

Smart Materials Meet Multifunctional Biomedical Devices: Current and Prospective Implications for Nanomedicine.

Abstract: With the increasing advances in the fabrication and in monitoring approaches of nanotechnology devices, novel materials are being synthesized and tested for the interaction with biological environments. Among them, smart materials in particular provide versatile and dynamically tunable platforms for the investigation and manipulation of several biological activities with very low invasiveness in hardly accessible anatomical districts. In the following, we will briefly recall recent examples of nanotechnology-based materials that can be remotely activated and controlled through different sources of energy, such as electromagnetic fields or ultrasounds, for their relevance to both basic science investigations and translational nanomedicine. Moreover, we will introduce some examples of hybrid materials showing mutually beneficial components for the development of multifunctional devices, able to simultaneously perform duties like imaging, tissue targeting, drug delivery, and redox state control. Finally, we will highlight challenging perspectives for the development of theranostic agents (merging diagnostic and therapeutic functionalities), underlining open questions for these smart nanotechnology-based devices to be made readily available to the patients in need.

Effects of variable resistance on smart structures of cubic reconnaissance satellites in various thermal and frequency shocking conditions

Abstract: Piezoelectric materials are widely used as smart structures in cubic reconnaissance satellites because of their sensing, actuating, and energy-harvesting abilities. In this study, an analytical model is developed in specific mechanical thermal shocking conditions. A special circuit and apparatus is designed for experimentation on the basis of the inverse piezoelectric effect. An equivalent circuit method is used to establish the relationship between the resistance and peak-to-peak voltage of lead zirconate titanate used as smart materials for cubic reconnaissance satellites. Various frequencies and resistance were applied in different mechanical thermal shocking conditions. Moreover, numerical simulations are conducted in various mechanical loading conditions to determine the accumulative effect. The model provides a novel mechanism to characterize the smart structures in cubic reconnaissance satellites. A rise in temperature increases peak-to-peak voltage; a rise in frequency decreases peak-to-peak voltage; and intensified resistance decreases peak-to-peak voltage. Based on experimentation and simulation, the optimum resistance is predicted for the various frequencies and temperatures. The various conditions may correspond to the different applications of smart structures for cubic reconnaissance satellites. The analytical calculations are in good agreement with experimental and numerical calculations.

A hybrid strain and thermal energy harvester based on an infra-red sensitive Er3+ modified poly(vinylidene fluoride) ferroelectret structure.

Abstract: In this paper, a novel infra-red (IR) sensitive Er3+ modified poly(vinylidene fluoride) (PVDF) (Er-PVDF) film is developed for converting both mechanical and thermal energies into useful electrical power. The addition of Er3+ to PVDF is shown to improve piezoelectric properties due to the formation of a self-polarized ferroelectric β-phase and the creation of an electret-like porous structure. In addition, we demonstrate that Er3+ acts to enhance heat transfer into the Er-PVDF film due to its excellent infrared absorbance, which, leads to rapid and large temperature fluctuations and improved pyroelectric energy transformation. We demonstrate the potential of this novel material for mechanical energy harvesting by creating a durable ferroelectret energy harvester/nanogenerator (FTNG). The high thermal stability of the β-phase enables the FTNG to harvest large temperature fluctuations (ΔT ~ 24 K). Moreover, the superior mechanosensitivity, SM ~ 3.4 VPa−1 of the FTNG enables the design of a wearable self-powered health-care monitoring system by human-machine integration. The combination of rare-earth ion, Er3+ with the ferroelectricity of PVDF provides a new and robust approach for delivering smart materials and structures for self-powered wireless technologies, sensors and Internet of Things (IoT) devices.

Stress-memory polymeric filaments for advanced compression therapy

Abstract: Shape memory polymers are stimulus responsive smart materials that can be applied in several forms such as films, fibers, and foams for a wide range of applications. Novel stress-memory behavior at a fiber level is yet to be uncovered, which would be favorable to control stress in the broad horizon of smart materials for numerous functions. In this work, a semi-crystalline segmented polyurethane was synthesized to prepare filaments/fibres and films. A rational experimental design was established and the stress-memory behavior of both the films and filaments was systematically studied for comparison. Tensile stress-memory programming was performed at three strain levels (20%, 40%, and 60%) to record the memory stress response as a function of temperature with time. The characterization of the thermal and mechanical properties of the stress-memory programmed specimens has objectively proven the reason behind the higher stress response in the filaments than in the films. Melt spinning has induced perfect crystallization with ordered polymer packing and enabled maximum memory stress to be retrieved in the filaments. The evolution of memory stress follows a linear trend with an increase in strain and temperature (r2 = 0.91–1). In addition, pressure related studies were also carried out for smart filament integrative fabrics to realize stress-memory behavior. This unprecedented and novel approach of unveiling the memory behavior specifically at the filament level will enable material scientists to comprehend the fundamental aspects for precise optimization and control of memory stress in smart structures for applications such as compression stockings that require stimuli responsive force.

Ionic Strength Responsive Sulfonated Polystyrene Opals

Abstract: Stimuli-responsive photonic crystals (PCs) represent an intriguing class of smart materials very promising for sensing applications. Here, selective ionic strength responsive polymeric PCs are reported. They are easily fabricated by partial sulfonation of polystyrene opals, without using toxic or expensive monomers and etching steps. The color of the resulting hydrogel-like ordered structures can be continuously shifted over the entire visible range (405–760 nm) by changing the content of ions over an extremely wide range of concentration (from about 70 μM to 4 M). The optical response is completely independent from pH and temperature, and the initial color can be fully recovered by washing the sulfonated opals with pure water. These new smart photonic materials could find important applications as ionic strength sensors for environmental monitoring as well as for healthcare screening.

Control and characterization of a bistable laminate generated with piezoelectricity

Abstract: Extensive research has been conducted on utilizing smart materials such as piezoelectric and shape memory alloy actuators to induce snap through of bistable structures for morphing applications. However, there has only been limited success in initiating snap through from both stable states due to the lack of actuation authority. A novel solution in the form of a piezoelectrically generated bistable laminate consisting of only macro fiber composites (MFC), allowing complete configuration control without any external assistance, is explored in detail here. Specifically, this paper presents the full analytical, computational, and experimental results of the laminate's design, geometry, bifurcation behavior, and snap through capability. By bonding two actuated MFCs in a [0MFC/90MFC]T layup and releasing the voltage post cure, piezoelectric strain anisotropy and the resulting in-plane residual stresses yield two statically stable states that are cylindrically shaped. The analytical model uses the Rayleigh–Ritz minimization of total potential energy and finite element analysis is implemented in MSC Nastran. The [0MFC/90MFC]T laminate is then manufactured and experimentally characterized for model validation. This paper demonstrates the adaptive laminate's unassisted forward and reverse snap through capability enabled by the efficiencies gained from simultaneously being the actuator and the primary structure.