Energy harvesting technologies have been explored by researchers for more than two decades as an alternative to conventional power sources (e.g. batteries) for small-sized and low-power electronic ...devices. The limited life-time and necessity for periodic recharging or replacement of batteries has been a consistent issue in portable, remote, and implantable devices. Ambient energy can usually be found in the form of solar energy, thermal energy, and vibration energy. Amongst these energy sources, vibration energy presents a persistent presence in nature and manmade structures. Various materials and transduction mechanisms have the ability to convert vibratory energy to useful electrical energy, such as piezoelectric, electromagnetic, and electrostatic generators. Piezoelectric transducers, with their inherent electromechanical coupling and high power density compared to electromagnetic and electrostatic transducers, have been widely explored to generate power from vibration energy sources. A topical review of piezoelectric energy harvesting methods was carried out and published in this journal by the authors in 2007. Since 2007, countless researchers have introduced novel materials, transduction mechanisms, electrical circuits, and analytical models to improve various aspects of piezoelectric energy harvesting devices. Additionally, many researchers have also reported novel applications of piezoelectric energy harvesting technology in the past decade. While the body of literature in the field of piezoelectric energy harvesting has grown significantly since 2007, this paper presents an update to the authors' previous review paper by summarizing the notable developments in the field of piezoelectric energy harvesting through the past decade.
Nanocomposites combining a high breakdown strength polymer and high dielectric permittivity ceramic filler have shown great potential for pulsed power applications. However, while current ...nanocomposites improve the dielectric permittivity of the capacitor, the gains come at the expense of the breakdown strength, which limits the ultimate performance of the capacitor. Here, we develop a new synthesis method for the growth of barium strontium titanate nanowires and demonstrate their use in ultra high energy density nanocomposites. This new synthesis process provides a facile approach to the growth of high aspect ratio nanowires with high yield and control over the stoichiometry of the solid solution. The nanowires are grown in the cubic phase with a Ba0.2Sr0.8TiO3 composition and have not been demonstrated prior to this report. The poly(vinylidene fluoride) nanocomposites resulting from this approach have high breakdown strength and high dielectric permittivity which results from the use of high aspect ratio fillers rather than equiaxial particles. The nanocomposites are shown to have an ultra high energy density of 14.86 J/cc at 450 MV/m and provide microsecond discharge time quicker than commercial biaxial oriented polypropylene capacitors. The energy density of our nanocomposites exceeds those reported in the literature for ceramic/polymer composites and is 1138% greater than the reported commercial capacitor with energy density of 1.2 J/cc at 640 MV/m for the current state of the art biaxial oriented polypropylene.
Two new thermoresponsive self‐healing polyurethanes (1DA1T and 1.5DA1T) based on the Diels–Alder (DA) reaction between furan and maleimide moieties are developed that use the shape‐memory effect to ...bring crack faces into intimate contact such that healing can take place. Unlike other self‐healing polymers, these polymers do not require external forces to close cracks but rather they use the shape‐memory effect to autonomously close the crack. Both polyurethanes have a stable polymer structure and comparable mechanical properties to commercial epoxies. A differential scanning calorimeter is employed to check the glass transition temperature of the polymers as well as the DA and retro‐DA (rDA) reaction temperatures. These DA and rDA reactions are confirmed with variable‐temperature proton nuclear magnetic resonance. Healing efficiency is calculated using a measurement of the failure load from compact tension testing. The results show that the shape‐memory effect can replace external forces to close two crack surfaces and the DA reaction can be repeatedly employed to heal the cracks.
Thermo‐responsive self‐healing polyurethanes that can be healed repeatedly without the application of external forces are developed. Instead, these polymers use the shape‐memory effect to autonomously bring the two crack surfaces together during the healing process.
High energy density capacitors are critically important in advanced electronic devices and power systems since they can reduce the weight, size and cost required to meet a desired application. ...Nanocomposites hold strong potential for increasing the performance of high power energy sources; however, the energy density of most nanocomposites is still low compared to commercial capacitors and neat polymers. Here, we develop a new synthesis method for the growth of high aspect ratio barium titanate nanowires (BaTiO3) nanowires (NWs) with high yield. High energy density nanocomposite capacitors are fabricated using surface‐functionalized high aspect ratio BaTiO3 NWs in a poly(vinylidene fluoride‐trifluoroethylene‐chlorofluoroethylene) (P(VDF‐TrFE‐CFE)) matrix. At a 17.5% volume fraction, the nanocomposites show more than 45.3% increase in energy density above that of the pure P(VDF‐TrFE‐CFE) polymer (10.48 J/cc compared to 7.21 J/cc) at electric field 300 MV/m. This value is significant and exceeds those reported for the conventional polymer‐ceramic nanocomposites; it is also more than seven times larger than high performance commercial polypropylene capacitor (1.2 J/cc at 640 MV/m). In addition, our nanocomposite capacitor has a maximum power density as high as 1.2 MW/cc occurring only 1.52 μs after the start of discharge. The findings of this research could lead to enhanced interest in nanowires based nanocomposites due to their potential for achieving next generation energy storage devices.
High energy density nanocomposite capacitors are fabricated using surface‐functionalized high aspect ratio barium titanate (BaTiO3) nanowires in a poly(vinylidene fluoride‐trifluoroethylene‐chlorofluoroethylene) (P(VDF‐TrFE‐CFE)) matrix. These nanocomposites show a high energy density of 10.48 J/cc and a maximum power density as high as 1.2 MW/cc, occurring only 1.52 μs after the start of discharge.
Aramid fibers are well-known for their excellent tensile properties and low density but are limited in composite applications due to their inert surface which leads to poor interfacial properties. ...One method that has shown promise in recent years is the application of nanoscale reinforcements to the surface of the fibers to improve mechanical interaction with the matrix. With aramid fibers, it is ideal to perform an interfacial reinforcement utilizing the dense hydrogen bonding which is responsible for the fibers strength. Here, it is demonstrated that recently developed aramid nanofibers (ANFs) can adsorb onto the surface of macroscale aramid fibers to enhance the interfacial properties through mechanical interlocking with the matrix. A simple and rapid dip-coating process is used to deposit the ANFs on the aramid fiber surface. These ANFs bond with the fiber through physisorption and hydrogen bonding, yielding a 70.27% increase in interfacial shear strength and a 25.6% increase in short beam shear strength in composites prepared by dip-coating unidirectional tape into a solution of ANFs. Notably, the interfacial gains are made while fully preserving the strength of the aramid fiber following the treatment, therefore ensuring in-plane properties of the composite are maintained. This work shows that the introduction of an ANF interphase may present a novel and convenient method to improve the interfacial strength of aramid reinforced composites, enabling cost-effective and simplified production of stronger structural materials.
Thermosetting polymers have been demonstrated to exhibit improved mechanical properties when nanofillers are introduced. These improvements can be further increased through the introduction of ...covalent linkages between the polymer matrix and nanofillers that enhances the chemical interaction. Here, aramid nanofibers (ANFs) are functionalized using a glycidyl ether silane coupling agent and their effect on the mechanical properties of epoxy are investigated. The results show that Young's modulus and tensile strength of 1 wt % epoxy functionalized ANFs (EANFs) reinforced nanocomposites increase by 16.8% and 14.0%, respectively, and fracture toughness increases by 4.4 times with the addition of 1.5 wt % EANFs. Additionally, both an increase in storage modulus and glass transition temperature are observed during dynamic mechanical analysis with increasing percentage of EANFs. Thus, this work demonstrates that the EANFs can further enhance the mechanical properties of epoxy nanocomposites through chemical crosslinking between the epoxy matrix and ANFs.
Display omitted
•Aramid nanofibers (ANFs) are functionalized using a glycidyl ether silane coupling agent.•The effect of epoxy functionalized ANFs (EANFs) on the properties of epoxy nanocomposites is investigated.•The mechanical and viscoelastic properties of EANF reinforced epoxy nanocomposites are improved.•The chemical crosslinking between the polymer and ANFs further enhances the mechanical properties.
A configuration that shows great promise in sensing applications is vertically aligned piezoelectric nanowire arrays that allow facile interfacing with electrical interconnects. ...Nano-electromechanical systems developed using piezoelectric nanowires have gained interest primarily for their potential in energy harvesting applications, because they are able to convert several different sources of mechanical energy into useful electrical power. To date, no results have demonstrated the capability to use aligned piezoelectric nanowire arrays as a highly accurate nano-electromechanical system based dynamic sensor with a wide operating bandwidth and unity coherence. Here we report the growth of vertically aligned (~45 μm long) barium titanate nanowire arrays, realized through a two-step hydrothermal synthesis approach, and demonstrate their use as an accurate accelerometer. High sensitivity of up to 50 mV g(-1) is observed from the sensor composed of vertically aligned barium titanate nanowire arrays, thus providing performance comparable to many of the commercial accelerometer systems.
Spatial control over the wetting properties of graphene surfaces is a desired feature in numerous applications. Traditionally, this is achieved using time consuming chemical treatment processes that ...lack spatial tuning. Here, we demonstrate the use of laser induced graphene for the direct, spatial printing of surfaces with either superhydrophilic or superhydrophobic character through simple and convenient control over graphene array morphology, and without the need for chemical surface modification. The wetting properties of the graphene surfaces range from superhydrophilic (0°) for sheet-like structures, to superhydrophobic (>150°) for micro-pillar and hemispherical structures. By varying the induction parameters of the CO2 laser, we demonstrate the ability to write patterns with spatially tailored wettability to enable liquid micro-patterning and channeling of flow. Furthermore, we study solid-liquid interactions for such surfaces using viscosity measurements, where a “petal effect” is observed in the graphene material, thus revealing the parahydrophobicity of the surface.
Display omitted
The design of nanocomposite capacitors poses certain challenges due to the reduced dielectric strength resulting from the integration of typically high dielectric fillers into the polymer. In prior ...efforts it was demonstrated that increasing of the filler could lead to energy‐storage densities up to 19.3% above the neat polymer. To further enhance the energy density, a novel strategy is developed to align nanowires in a thermoplastic matrix by uniaxial stretching assembly. It is demonstrated that the energy‐storage capability of the nanocomposite can be enhanced through the alignment of lead zirconate titanate (PZT) nanowires (NWs) in the direction of the applied electric field compared to randomly oriented samples. The maximum energy density of the nanocomposites is as high as 1.28 J cm−3 at a volume fraction of 40% PZT NWs (aspect ratio around 14) with axis of alignment in the direction of the electric field. The findings of this research could lead to broader interest due to development of the piezoceramic nanocomposites with enhanced dielectric properties for use in next‐generation energy‐storage and conversion devices.
Nanocomposites with aligned PZT nanowires are prepared by uniaxial strain assembly. It is demonstrated that the nanocomposites with nanowires aligned along the axis of the electric field have higher energy densities than samples with randomly dispersed nanowires. These results show that control of the orientation of the filler could be used to improve the energy density of nanocomposites.
While aramid fibers have been innovative for ballistic protection because of their high energy absorption, minimal usage has been applied to continuous fiber reinforced polymer (CFRP) composites in ...structural applications. One of the challenges with aramid fibers results from their processing, which yields smooth and chemically inert surfaces that limit the ability of the fibers to adhere to polymeric matrices. Here, it is shown that aramid nanofibers can adhere to the surface of macroscale aramid reinforcements to improve the strength of the composite interface and reinforce the matrix as well. Aramid nanofibers are formed through the dissolution of aramid fibers followed by isolation and dispersion into an epoxy matrix. When employed in CFRP, aramid nanofibers prove to be effective reinforcement agents through improvement in both matrix properties as well as modifying the interfacial shear strength, which leads to improved interlaminar shear strength and fracture toughness. The interface enhancements are attributed to hydrogen bonding and π-π coordination between the aramid nanofibers and the macro fibers providing improved transfer load from the fiber to the matrix. This work demonstrates that aramid nanofibers may provide the robust mechanical properties that are necessary for structural applications while utilizing a cost-effective and convenient nanoscale building block.
PDF
