Carbon nanotubes (CNT) represent an effective filler to be incorporated into polymer matrices. Their physical properties allow them to exert a remarkable strengthening effect, while their nano-scale leaves the polymer weight unaltered. Exploiting their high strength-to-weight ratio, CNT/polymer nanocomposites appear to be the ideal materials to be shaped as wires and fibers. In this work, an ad-hoc innovative extrusion process is proposed to fabricate though and ultralong CNT/polymer nanocomposite wires. The process parameters are finely tuned to produce nanocomposite filaments exhibiting optimized mechanical properties. Optical analyses validate the morphological features of the fabricated filaments having an averaged diameter of 350 μm. Monotonic tensile tests are carried out to investigate the mechanical response of wires with CNTs content ranging from 1 wt% to 3 wt%. Young’s modulus and tensile strength registered increments of 47% and 43%, respectively, when comparing the 3 wt% CNT nanocomposite wires with the neat polymer wires. Finally, cyclic tensile tests are employed to investigate the change in damping capacity that accompanies the integration of CNTs into the polymer matrix. Such optimized CNTs nanocomposite wires can be easily integrated into several devices or assembled into ropes and yarns with multifunctional, improved properties.

The buckling characteristics of thin functionally graded (FG) nano-plates subjected to both thermal loads and biaxial linearly varying forces is investigated. Eringen’s nonlocal elasticity theory is employed to account for the nano-scale phenomena in the plates. Hamilton’s principle and the constitutive relations are used to derive the partial differential governing equations of motion for the thin plates that are modeled using Kirchhoff’s plate theory. The mechanical properties of the FG nano-plates are assumed to vary smoothly across the thickness of the plate following a power law. Three types of thermal loads are presented and the spectral collocation method is utilized to solve for the critical buckling loads. The accuracy of the numerical solution of the proposed model is verified by comparing the results with those available in the literature. A comprehensive parametric study is carried out, and the effects of the nonlocal scale parameter, power law index, aspect ratio, slopes of the axial loads, boundary conditions, assumed temperature distributions, and the difference between the ceramic-rich and metal-rich surfaces on the nonlocal critical buckling loads of the nano-plates are examined. The results reveal that these parameters have significant influence on the stability behavior of the FG nano-plates.

In this study, we demonstrate the electric and magnetic manipulation of nanoscale M-type Barium Hexaferrite (nBF) in polydimethylsiloxane (PDMS) to engineer a multifunctional nanocomposite with improved dielectric and magnetic properties. First, we synthesized the single crystal nBF via the hydrothermal synthesis route. The hydrothermal temperature, duration, and surfactant conditions were optimized to improve the magnetic properties of the nBFs, with further improvement achieved by post-annealing. The annealed nBFs were aligned dielectrophoretically (DEP) in the polymer matrices by applying an AC electric field. Under the influence of this electric field, nBFs were observed to rotate, align and form chains within the polymer matrix. Optical microscopy (OM) imaging was used to determine the electrical alignment conditions (duration, magnitude, and frequency) and these parameters were used to fabricate the composites. A Teflon setup with Indium Tin Oxide (ITO) coated Polyethylene Terephthalate (PET) was used, where the ITO coatings act as electrodes for the electric field-manipulation. To simultaneously apply the magnetic field, this Teflon setup is placed between two permanent magnets capable of generating a 0.6 T external magnetic field. Along with electric and magnetic fields, concurrent heating was applied to cure the PDMS and freeze the microstructure formed due to electric and magnetic fields. Upon completion of the curing step, parallel chain formation is observed under OM. The X-Ray Diffraction (XRD) results also confirm that the particles are magnetically oriented in the direction of the magnetic field within the chain. Vibrating Sample Magnetometry (VSM) measurements and dielectric spectroscopy are used to characterize the extent of anisotropy and improvement in dielectric and magnetic properties compared to random composites. We find that simultaneous electric and magnetic field alignment improves the dielectric properties by 12% compared to just magnetic alignment. We also observe 19% improved squareness ratio when both fields are applied. The possibility of simultaneous electrical and magnetic alignment of magnetic nanoparticles will open up new doors to manipulate and design particle-modified polymers for various applications.

Newts display superior attachment and climbing abilities under wet conditions due to the distinct pattern of micro- and nanoscale structures (i.e., polygonal epidermal cells with raised boundaries, and dense nanopillar arrays) on their foot pad surfaces. Inspired by the surface features of newt foot pads, a microstructured surface consisting of structural elements of round pillars surrounded by a closed hexagonal ridge is produced on the polydimethylsiloxane (PDMS) elastomer, and its wet adhesion properties are studied experimentally. A homebuilt adhesion tester is developed to carry out the pull-off experiments, in which the adhesion force of samples can be measured directly. The PDMS sample is fixed on the substrate, and a flat glass cylinder of 10 mm diameter is adopted as indenter. Different amounts of liquid are added to the area of contact by using a micropipette. Influences of preload, retraction speed, area ratio of round pillars, amount of liquid and approach-retraction cycle on wet adhesion of the patterned surface of PDMS samples are investigated. Results show that the pull-off forces of all samples increase with preload and retraction speed. However, the pull-off forces increase slowly when the preload is over 3 N for both dry and wet conditions. The area ratios of round pillars increase the pull-off forces for the dry condition. When a small amount of liquid (0.1 μl) is added, the effect of the area ratios of round pillars on the pull-off force is not consistent with that of dry condition. Effects of amount of liquid on pull-off force for different area ratios of round pillars are various. For a certain amount of liquid, it is observed that the pull-off forces in general show a relatively high value for the first approach-retraction cycle, then decrease to a lower level starting from the second cycle, and suddenly increase and maintain a relatively constant value after several times of approach-retraction cycles. Our results can give insights into the repeated sliding actions of newt foot pads when climbing in wet environments as well as the possible functions of dense nanopillar arrays on newt footpad surface.

The development of novel characterization techniques is critical for understanding the fundamentals of material systems. Bioinspired systems are regularly implemented but poorly defined through quantitative measurement. In an effort to specify the coupling between multiple domains seen in biologically inspired systems, high resolution measurement systems capable of simultaneously measuring various phenomena such as electrical, chemical, mechanical, or optical signals is required. Scanning electrochemical microscopy (SECM) and shear-force (SF) imaging are nanoscale measurement techniques which examine the electrochemical behavior at a liquid-solid or liquid-liquid interface and simultaneously probe morphological features. It is therefore a suitable measurement technique for understanding biological phenomena. SF imaging is a high resolution technique, allowing for nanoscale measurement of extensional actuation in materials with high signal to noise ratio. The sensing capabilities of SECM-SF techniques are dependent on the characteristics of the micro-scale electrodes (ultramicroelectrodes or UMEs) used to investigate surfaces. Current limitations to this technique are due to the fabrication process which introduces structural damping, reducing the signal produced. Additionally, despite the high cost of materials and processing, contemporary processes only produce a 10% yield. This article demonstrates a UME fabrication process with a 60% yield as well as improved amplitude (250% increase) and sensitivity (210% increase) during SF imaging. This process is expected to improve the signal to noise ratio of SF-based measurement systems. With these improvements, SECM-SF could become a more suitable technique for measuring cell or tissue activity, corrosion of materials, or coupled mechanics of synthetic faradaic materials.

Scanning electrochemical microscopy (SECM) is an electrochemical technique used to measure faradaic current changes local to the surface of a sample. The incorporation of shear force (SF) feedback in SECM enables the concurrent acquisition of topographical data of substrates along with electrochemical measurements. Contemporary SECM measurements require a redox mediator such as ferrocene methanol (FcMeOH) for electrochemical measurements; however, this could prove detrimental in the imaging of biological cells. In this article, nanoscale polypyrrole membranes doped with dodecylbenzene sulfonate (PPy(DBS)) are deposited at the tip of an ultra-microelectrode (UME) to demonstrate a novel modification of the contemporary SECM-SF imaging technique that operates in the absence of a redox mediator. The effect of distance from an insulating substrate and bulk electrolyte concentration on sensor response are examined to validate this technique as a tool for correlated topographical imaging and cation flux mapping. Varying the distance of the PPy(DBS) tipped probe from the substrate in a solution containing NaCl causes a localized change in cation concentration within the vicinity of the membrane due to hindered diffusion of ions from the bulk solution to the diffusion field. The cation transport into the membrane in close proximity to the substrate is low as compared to that in the electrolyte bulk and asymptotically approaches the bulk value at the sense length. At a constant height from the base, changing the bulk NaCl concentration from 5 mM to 10 mM increases the filling efficiency from 35% to 70%. Further, the sense length of this modified electrode in NaCl is about 440 nm which is significantly lower as compared to that of a bare electrode in ferrocene methanol (5–20 μm). It is postulated that this novel technique will be capable of producing high resolution maps of surface cation concentrations, thus having a significant impact in the field of biological imaging.

Over the past two decades, numerous research studies have been conducted to explore behavior of self-sensing cementitious composites with different functional fillers. Most of these studies investigated the use of fillers such as carbon nanofiber (CNF), carbon black, and carbon nanotubes (CNTs) in cement composites to develop a multifunctional material. Since its discovery in 2004, graphene has also raised significant attention as 2D nanoscale reinforcement for composite materials. The planar structure of graphene sheets provides more contact area with the host material. However, high cost and dispersion difficulties are among the drawbacks of graphene. More recently, graphene nanoplatelets (GNPs), which have very thin but wide aspect ratio, are drawing the graphene market due to their advantages such as ease of processing and excellent material properties at a very low cost. The application of two-dimensional graphene nanoplatelets in cementitious composites has yet to gain widespread attention. This paper investigates the self-sensing capabilities of GNP-reinforced hydraulic Portland cement composites. In particular, the effects of GNP content on the electrical properties and piezoresistive characteristics of mortar specimens are explored. In addition, a simple fabrication method that does not require special treating procedures such as ultrasonication and chemical (covalent) treatments for the dispersion of GNPs is pursued. The GNPs used in this study have an average thickness of 8 nanometers and a diameter of 25 microns. Standard prismatic mortar specimens containing different GNP concentrations are prepared using three different mixing procedures. The resistivity of the specimens is measured using a four-point probe method. The piezoresistive response of GNP-reinforced cement composites is evaluated under cyclic compressive loads.

This paper builds on previous work done [1, 2] to explore the effective piezoresistive response of polymer bonded explosive (PBX) materials where the polymer medium is reinforced with carbon nanotubes (CNTs). In the present work, the nanocomposite binder is modeled explicitly as a piezoresistive material whose properties are determined from the nanoscale through a micromechanics based 2-scale hierarchical model connecting the nanoscale to the microscale grain structure. Electromechanical cohesive zones are used to model the interface between the grains and nanocomposite binder in order to characterize interface separation and the resulting piezoresistive effect. The overall microscale piezoresistive effect is measured by using the volume averaged properties of the microscale RVE. The hierarchical framework developed here is used to explore key features of the NCBX microstructure such as the effect of grain conductivity, weight percentage of CNTs used and nanocomposite gage factor.

In the current work, the Material Point Method (MPM) is extended to allow for interfacial discontinuities in problems with composite materials using cohesive zone (CZ) techniques. The proposed CZMPM is observed to result in smaller errors in the primary and secondary field variables, especially near the interface, for a given boundary value problem in comparison to the traditional MPM solution. The proposed CZMPM is used to solve an electromechanical test problem with a single fiber in the matrix medium. It is observed that the proposed CZMPM results in smaller local and volume averaged errors. The CZMPM is further used to evaluate the effective piezoresistive response of the nanoscale carbon nanotube (CNT)-polymer composite with electron hopping in between the nanotubes. The observed effective piezoresistive response exhibits features similar to those reported in the literature using finite element techniques for small strains. However, CZMPM allows for large deformations of the nanoscale representative volume element as presented in the current work.

Structural health monitoring of composite materials is limited by the lack of fundamental understanding of early stage damage at the local material level. This includes damage precursor formation on fiber surfaces, within the matrix, and at the fiber-matrix interface/interphase. In this effort, we present a micro-/nano-scale technique for characterizing damage precursor formation on individual carbon fibers exposed to cyclic tensile loads. Nanoindentation and atomic force microscopy (AFM) were used to study the local properties of the individual microfibers before and after global loading events. An AFM image analysis was used to track evolution of topography on the fiber surfaces. The work is a first step toward understanding damage precursor formation in individual microfibers; the work is expected to enable multiscale composites modeling efforts as well as enable the development of future self-sensing materials.

The current work aims to explore the effective piezoresistive response of polymer bonded explosive (PBX) materials where the polymer medium is reinforced with carbon nanotubes (CNTs). The effective piezoresistive response of these nanocomposite bound polymer explosives (NCBX) is evaluated using micromechanics based 2-scale hierarchical model connecting the CNT-polymer nanocomposite scale (nanoscale) to the explosive grain structure scale (microscale). The binding nanocomposite medium is modeled as electromechanical cohesive zones between adjacent explosive grains which are representative of effective electromechanical response of CNT-polymer nanocomposites. The hierarchical framework developed here is used to explore key features of the NCBX microstructure, e.g. ratio of grain to nanocomposite stiffness, ratio of grain to nanocomposite conductivities etc., and related to the NCBX effective piezoresistive response. The results obtained from the current work show dependence of effective NCBX piezoresistive properties on each of these microstructural features with and without interfacial damage between the explosive grains.

Structural health monitoring can enhance reliability, increase safety, and decrease maintenance costs by detecting damage at an early stage. By taking advantage of the electromechanical coupling, piezoelectric materials have the potential to harvest energy from ambient vibration sources to provide low-power electricity for self-powered electronic devices. In comparison with other piezoelectric transducers, zinc oxide (ZnO) nanowires carry the added advantages of structural flexibility, lower cost, compactness, and lighter weight. In this study, the energy harvesting capabilities of nanoscale ZnO piezoelectric nanowires (NW) grown on the surface of glass fiber fabrics are investigated experimentally. A series of cantilevered carbon fiber beams containing a controlled amount of ZnO nanowires is evaluated. The absolute electrical energy dissipation is quantified by measuring the output power over a broad spectrum of known vibratory loads and frequencies. The maximum amount of power extracted is obtained by employing resistive impedance matching. Here, a maximum peak of ∼6.7 mV was generated when the beam containing ZnO nanowires was excited at 2.90g and connected to a 10 MΩ load. At that excitation level, a maximum of 20.0 pW was generated when an optimal resistor of 1 MΩ is connected. A tip mass of ∼0.6 gram added to the sample with ZnO NWs increased the peak-voltage by 2.21 mV and increased the peak-power by 13.3 pW. A series of DC voltage applied to the ZnO sample suggests the equivalence of poling treatment, where the dipole alignment of the ZnO NWs are disrupted. Here, a maximum peak-power of 45 pW is reported, showing promising potential of scaling-up to harvest ambient energy for low-powered electronics.

The current 2-scale computational multiscale micromechanics based exploration of sensing capabilities in carbon nanotube (CNT)-polymer nanocomposites focuses on the macroscale piezoresistive response when the nanocomposite is subjected to cyclic loading conditions. It has been shown that electron hopping at the nanoscale is the primary mechanism behind the observed macroscale piezoresistivity for such nanocomposites. A novel continuum description of the non-continuum electron hopping effect used in the current work enables the use of multiscale continuum micromechanics based approaches to study nanocomposite piezoresistivity. The focus of the current work is on the interfacial separation/damage initiation, evolution and accumulation when subjected to cyclic loading. Interfacial separation/damage is allowed at the nanoscale CNT-polymer interface using electromechanical cohesive zones to account for electron hopping across the separated interface. The mechanical response of the CNT-polymer interface is obtained in terms of normal/tangential traction-separation behavior from atomistic scale Molecular Dynamics based models. The coupled electrostatic response is based on evolving interfacial resistance through the electron hopping induced current density across the separated interface. Such coupled electromechanical description allowing for current density across the separated interface in addition to normal/tangential tractions is unique in its implementation to the best of the authors knowledge. It is observed that the effective macroscale piezoresistive response obtained from the current modeling framework captures interfacial separation/damage state and shows sensitivity to damage accumulation over several cycles. Such exploration of the governing physical mechanisms starting at the smallest scale of influence and transitioning into macroscale effective properties provides key insights into the multiscale problem.

In this study magnetic force microscopy (MFM), piezoresponse force microscopy (PFM), and the newly developed piezomagnetic force microscopy (PmFM) techniques are used to probe the ferroelectric and ferromagnetic properties of BiFeO 3 -LiMn 2 O 4 (BFO-LMO) heterostructures at nano-scale. The PmFM technique is also used to probe the ferromagnetic properties of CoFe 2 O 4 (CFO) as a case study. The PFM and PmFM mappings of the BFO-LMO heterostructures clearly distinguish the BFO matrix and LMO nanopillars while the MFM mapping is ambiguous. The relatively high piezomagnetic response of BFO matrix is believed to be due to the Mn doping while the piezoelectric-like response of LMO nanopillars is due to the ionic activities and the vertical geometry of its heterostructure. Lastly, limitations of the PmFM technique are discussed.

Combining adaptable supporting structure, large compliance, and intricate energy management, skeletal muscle is a natural system that exhibits numerous attractive characteristics. Recent mechanical modeling of muscle suggests some of the intriguing macroscale features are due to the assembly of nanoscale, metastable cross-bridge constituents. Inspired by the multifunctionality and versatility of muscle’s architectural composition, this research investigates a new paradigm of modular structure-material development to achieve significant system adaptivity by utilizing building blocks possessing metastability . The proposed, assembled systems belong to the class of metastructures , a new concept for engineering adaptive structures from basic, functional units in ways such that the systems exhibit unprecedented characteristics resulting from a synergy of their elements. A modular and metastable building block is created to emulate the effective passive functionality of muscle’s cross-bridge. Analytical and experimental results reveal that metastructures assembled from the metastable modules may supply unique changes in reaction force when the end displacement is prescribed, adapting not only the magnitude of force but also the direction, in addition to yielding a multitude of globally stable topologies. The investigations provide clear evidence that a metastructure may realize orders of magnitude change in stiffness for a constant system shape, and also enables the variation in required energy expense to globally deform the system. From these findings, the metastructural design framework represents a major leap forward in adaptive structures and material systems and has the potential to find broad future application.

The formation/disruption of the electron hopping pathways is considered to be one of the dominant mechanisms affecting macroscale effective piezoresistive response of carbon nanotube (CNT)-polymer nanocomposites. In this study, a computational micromechanics model is developed using finite element techniques to capture the effect of electron hopping induced conductive pathways at the nanoscale which contribute to the macroscale piezoresistive response of the CNT-polymer nanocomposites. In addition, damage is allowed to evolve at the CNT-polymer interface through electromechanical cohesive zones resulting in disruption of electron hopping pathways in the direction of applied strain. The impact of the electron hopping mechanism and nanoscale interfacial damage evolution on the effective piezoresistive response is studied through the macroscale effective material properties and gauge factors evaluated using micromechanics techniques based on electrostatic energy equivalence. It is observed that the interfacial damage at the nanoscale results in lower gauge factors as compared to the perfectly bonded interface.

Direct write (DW) technology offers a simple method of rapid manufacturing technology for printing electronic, optoelectronic devices, and complex functional devices. The key component of DW technology is the functional inks, which are colloidal suspensions of functional nanoparticles in various solvents such as aerosol or liquid form. With a DW approach, patterns or structures can be easily deposited on flexible substrates such as paper, plastics, and composites, once the solvent volatilizes or is driven off via conventional, laser, or microwave sintering. In this work, polymer-assisted silver (Ag) nanoinks were synthesized by silver salt and polymer in the water solution at relatively high silver precursor concentrations and relatively low concentration of polymers. The silver nanoparticle dispersion and morphology was examined by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The results showed that the size of Ag nanoparticles was in nanoscale (∼20 nm) with a narrow distribution of Ag nanoparticle sizes. The viscosity and thermal properties of synthesized silver nanoinks were characterized to determine their applicability and the lifetime. It has been shown that the synthesized silver nanoink can be printed on a flexible plastic substrate or glass substrate. The morphology of the Ag nanoink line printed on the substrate was observed by optical microscopy and scanning electron microscopy (SEM) to understand the relationship between the microstructure and wettability. Uniaxial tension tests of silver nanoink line on a Kapton film indicate that the ink can be stretched ∼20% without failure. The resistance of silver nanoink line printed on the Kapton films was also measured by four probe conductivity measurement system to assess the electrical performance. The resistivity is about 7.5 × 10 −5 Ω-cm by thermal treatment at 250°C for 30 min, which is about half that of bulk silver (1.6 × 10 −6 Ω-cm). Overall, the performance of the synthesized silver nanoink is comparable to a commercially available ink with lower Ag weight content at relatively low cost.

The authors had previously theoretically demonstrated that multiferroic nanomagnetic logic can be clocked in ∼1 GHz with few 100 kT/bit power dissipation which is ∼3 orders of magnitude more energy efficient than current CMOS transistor technology that dissipates several 100,000 kT/bit.. In this work, we propose the more novel concept of 4-state logic by numerically demonstrating the feasibity of an ultra low-power 4-state NOR logic gate using multiferroic nanomagnets with biaxial magnetocrystalline anisotropy. Here, the logic bits are encoded in the magnetization orientation of a nanoscale magnetostrictive layer elastically coupled to a piezoelectric layer. The piezoelectric layer can be clocked with a small electrostatic potential (∼0.2 V) to switch the magnetization of the magnetic layer. We also address logic propagation, where the accurate and unidirectional transfer of data from an input nanomagnet along an array of nanomagnets is needed. This is accomplished by devising an effective clocking scheme to the nanomagnet array, which allows for the realization of feasible logic circuits. Ultimately, this technology would enable higher order information processing, such as pattern recognition, to be performed in parallel at very high speeds while consuming extremely low power. Potential applications include high-density logic circuits, associative memory and neuromorphic computing.

This paper presents forced-controlled nanomanipulation utilizing nano-robotic manipulator and nanomechanical cantilever. A three degree of freedom (3 DOF) nanomanipulator with revolute revolute prismatic (RRP) actuator structure, named here MM3A ® , can be utilized for a variety of nanomanipulation tasks. Previous publications of the authors present the mathematical modeling and robust control of manipulator’s tip using fused visual servoing and force sensor feedbacks. Due to lack of position and velocity feedbacks in MM3A ® nanomanipulator, a fused vision/force feedback robust controller has been recently designed by the authors. Previous publications of the authors present the optimal utilization of the visual servoing and force sensor feedbacks for use in the nanomanipulation tasks. More specifically, the visual servoing and force feedback structures are investigated through extensive simulations in order to reveal issues in practical implementation. In modeling the force sensing module of the designed fused feedback controller, previous publications of the authors present a closed-form distributed-parameters based modeling framework for piezoresistive Nanomechanical Cantilever (NMC)-based force sensors used in a variety of cantilever-based nanomanipulation actions. Current modeling practices call for a simple lumped-parameters framework rather than modeling the piezoresistive NMC itself. Due to the widespread applications of such NMCs in nanoscale force sensing or non-contact atomic force microscopy with nano-Newton to pico-Newton force measurement requirements, precise modeling of the piezoresistive microcantilevers is essential. Instead of the previously used lumped-parameters modeling, a distributed-parameters modeling framework is proposed and developed in previous publications of the authors to arrive at the most complete model of the piezoresistive NMC including tip-mass, tip-force and base movement considerations. Here, experimental results are presented to demonstrate the accuracy of the proposed distributed-parameters model when compared with the previously reported lumped-parameters modeling approach. It is shown that by utilizing the distributed-parameters model rather than lumped-parameters approach and by predicting the exact motion of each point on the NMC, the precision of the piezoresistive NMC’s model is significantly enhanced. Such novel modeling framework could pave the pathway towards nanomechanical cantilever-based manipulation and positioning as detailed in the second part.