Ionic polymer transducers are soft actuators that perform large bending deflections when voltages on the order of 1–5 V are applied across their thickness. Previous work showed that actuation performance of ionic polymer transducers is strongly correlated with the capacitance due to surface charge accumulation. Increasing the capacitance of the actuator increases the motion of the charges and increases the strain produced under the application of an electric field. Ionomeric transducers consist of an ionomer, such as Nafion (a product of DuPont), sandwiched between two high surface area electrodes. An electric double layer is formed on the interface between the cathode and the adsorbed positive ions. A novel plating technique which was previously developed is used to vary the morphology of the polymer-electrode interface to investigate the parameters of importance to the formation of the electric double layer. Electromechanical transducer tests are performed as a function of electrode morphology to correlate surface charge accumulation with the deflection generated by the transducer.

In this work, a systematic investigation is being carried out on single crystals of Ni47.8Mn27.5Ga24.7 alloy to determine the effect of temperature on the magneto-mechanical behaviour of the Ni-Mn-Ga alloys. Repeated mechanical and magnetic forces have been applied at various temperatures below the martensite finish (MF) temperature. It has been observed that twinning start and finish stresses, critical magnetic field and maximum magnetic-field-induced strain all remain almost constant within about 20K below MF and then change substantially at lower temperatures. Eventually no magnetic-field-induced strain can be observed at temperatures below 262K. It is proposed that although magnetic anisotropy constant increases with decreasing temperature, it is not sufficient to overcome the increasing twinning stresses required for twin boundary motion at lower temperatures.

Fracture tests on poled and depoled lead zirconate titanate (PZT) ceramics indicate that purely electric fields are able to propagate the conductive cracks (notches) and fracture the samples. To understand the fracture behavior of conducting cracks in ferroelectric ceramics, an electric dipole model is proposed, in which a discrete electric dipole is used to represent the local spontaneous polarization and the force couples are used to represent the local strains. The electric dipole model provides basic solutions for microstructural modeling. The microstructural modeling is based on a domain switching mechanism. The domain structure is simulated with a grid of points where polarizations and strains vary with the applied loads. As a first step study, the microstructural modeling is conducted for a dielectric material with a conductive crack. The simulation result explains why the electric fracture toughness is much higher than the mechanical fracture toughness.

Shape memory polymers (SMPs) have the capacity to store and recover relatively large strains when subjected to a unique thermomechanical cycle. In this study, the thermomechanics of strain storage and strain/stress recovery are investigated in a shape memory polymer deformed under uniaxial tension and compression. During heated recovery, three cases of constraint are examined: unconstrained (free) strain recovery, stress recovery under pre-strain constraint, and stress recovery under fixed-strain constraint. Based on the experimental results, a one-dimensional SMP constitutive model is developed, which is motivated by the shape memory mechanism of the polymer network. The foundation of the model is that the entropy change is gradually stored during cooling and released during reheating as free recovery strain or constrained recovery stress. When fit to free strain recovery data, the model can predict the trends of the stress evolution during shape fixation and constrained strain/stress recovery under various thermomechanical conditions.

Electrochemical tuning of single-wall carbon nanotubes has been investigated using in situ Raman spectroscopy. We built a linear actuator from single-wall carbon nanotube mat and studied in several alkali metal (Li, Na, and K) and alkaline earth (Ca) halide solutions. The variation of bonding with electrochemical biasing was monitored using in situ Raman. This is since Raman can detect changes in C-C bond length: the radial breathing mode (RBM) at ∼190 cm−1 varies inversely with the nanotube diameter and the G band at ∼1590 cm−1 varies with the axial bond length. In addition, the intensities of both the modes vary significantly in a nonmonotonic manner pointing at the emptying/depleting or filling of the bonding and anti-bonding states - electrochemical charge injection. We discuss the variation of spectroscopic observables (intensity/frequency) of these modes providing valuable information on the charge transfer dynamics on the single-wall carbon nanotubes mat surface. We found the in-plane compressive strain (∼ -0.25%) and the charge transfer per carbon atom (fc ∼ -0.005) as an upper bound for the electrolytes used i.e. CaCl2. These results can be quantitatively understood in terms of the changes in the energy gaps between the one-dimensional van Hove singularities in the electron density of states arising possibly due to the alterations in the overlap integral of π bonds between the p orbitals of the adjacent carbon atoms. Moreover, the extent of variation of the absolute potential of the Fermi level or alternatively modification of band gap is estimated from modeling Raman intensity to be around 0.1 eV as an upper bound for CaCl2.

Composite films of polypyrrole (PPy) and poly(2-methoxyaniline-5-sulfonic acid) (PMAS) have been electrodeposited from aqueous electrolytes solution consisting of pyrrole and various ratios of dodecylbenzene sulfonic acid (DBS) and PMAS. The obtained PPy(DBS/PMAS) films exhibited different characteristics in water contents, surface morphology and electrochemomechanical deformations (ECMD) depending on the content of PMAS. A film having the content of PPy(95%DBS/5%PMAS) simply showed the large cathodic ECMD with the strain of 6.1% in non-aqueous electrolyte solution of 0.1M tetrabutylammonium chloride/acetonitrile electrolyte. The improvement of cathodic ECMD is conjectured to the large porosity of the composite film. The ECMD behaviors of the films operated in various electrolyte solutions including aqueous solution are also reported.

We examine the shape-memory effect in polymer networks intended for biomedical applications. The polymers were photopolymerized from tert-butyl acrylate (tBA) with polyethyleneglycol dimethacrylate (PEGDMA) acting as a crosslinker. Three-point flexural tests were used to systematically investigate the thermomechanics of shape-storage deformation and shape recovery. The glass transition temperature (Tg) of the polymers varied over a range of 100°C and is dependent on the molecular weight and concentration of the crosslinker. The polymers show 100% strain recovery up to maximum strains of approximately 80% at low and high deformation temperatures (Td). Free strain recovery was determined to depend on the temperature during deformation; lower deformation temperatures (Td < Tg) decreased the temperature required for free strain recovery. Constrained stress recovery shows a complex evolution as a function of temperature and also depends on Td. The thermomechanical results are discussed in light of potential biomedical applications and a prototype stent that can be activated at body temperature is presented.

The objective of this study is to examine the effect of heat treatment on polycrystalline Ti-50.9 at.%Ni subsequent to hot-rolling. In particular we examine microstructure, transformation temperatures and mechanical behavior of deformation processed NiTi. The results constitute a fundamental understanding of the effect of heat treatment on thermal/stress induced martensite, which is critical for optimizing mechanical properties. The high temperature of the hot-rolling process caused recrystallization, recovery, and hindered precipitate formation, essentially solutionizing the NiTi. Subsequent heat treatments were carried out at various temperatures for 1.5 hours. Transmission Electron Microscopy (TEM) observations revealed that Ti3Ni4 precipitates progressively increased in size and changed their interface with the matrix from being coherent to incoherent with increasing heat treatment temperature. Accompanying the changes in precipitate size and interface coherency, transformation temperatures were observed to systematically shift, leading to the occurrence of the R-phase and multiple-stage transformations. Room temperature stress-strain tests illustrated a variety of mechanical responses for the various heat treatments, from pseudoelasticity to shape memory. The changes in stress-strain behavior are interpreted in terms of shifts in the primary martensite transformation temperatures, rather then the occurrence of the R-phase transformation. The results confirm that Ti3Ni4 precipitates can be used to elicit a desired isothermal stress-strain behavior in polycrystalline NiTi.

Giant magnetostrictive thin films deposited on nonmagnetic substrates can constitute effective sensors and actuators for microdevices. In this work, we investigated the effects of a stress-induced anisotropy on the magnetic properties of Tb0.4Fe0.6, Fe0.5Co0.5 single layer films and [Tb0.4Fe0.6/Fe0.5Co0.5]n multilayers deposited on Si substrates. The magnetostrictive thin films were fabricated by means of RF sputtering and were subjected to a post-deposition annealing treatment. The uniaxial magnetic anisotropy was induced by bending the substrate before deposition and then allowing it to resume its original flat shape after depositing the film. The heat treatment was performed in a vacuum system with a vacuum of 10−6 Torr. The magnetic properties of the fabricated specimens were measured using a SQUID. SEM and XRD analyses were performed to ensure that the thermal treatment would relax the internal stresses induced during the deposition process without crystallizing the film. The thickness of the single layer thin films studied was between 300 and 800 nm while multilayer samples consisted of 6 layers with each layer thickness ranged from about 20 to 40 nm. Compared to single layer samples, multilayer samples with stress anneal growth exhibited an improvement in magnetic saturation by a factor of two while maintaining a low coercive field. Manipulations of the magnitude and direction of magnetic anisotropy was observed by introducing various values of tensile and compressive stress into the film.

Superelastic shape memory materials are of special interest in medical applications due to the large obtainable strains, the constant stress level and their biocompatibility. Superelastic NiTi-polymer-composites have the potential to be used for novel applications in orthodontics and medical instrumentation as well as in certain areas of mechanical engineering. Especially, using NiTi thin films these composites have the potential to substantially reduce those forces compared to conventional NiTi wires and tubes. In orthodontic applications lowering the forces during archwire treatment is of special importance due to tooth root resorption, which can be caused by the application of oversized forces. Furthermore, the use of superelastic materials or composites enables the application of constant forces independent of diminutive tooth movements during the therapy due to the superelastic plateau. Superelastic NiTi thin films have been fabricated by magnetron sputtering using extremely pure cast melted targets. Special heat treatments were performed for the adjustment of the superelastic properties and the transformation temperatures. A superelastic strain exceeding 4% at 36°C was obtained. In this paper the fabrication of superelastic NiTi thin walled tubes by magnetron sputtering is presented and their mechanical properties are compared to conventional wires and tubes in view of orthodontic applications.

Two series of Ni-Mn-Ga thin films with two different compositions and various thicknesses in the submicron range are investigated with respect to their structural and magnetic properties. The films are fabricated by sputter deposition on alumina substrates and subsequent heat treatment. The martensitic transformation occurs well above room temperature showing a small thermal hysteresis width of about 6 K. The magnetic properties turn out to be thickness-dependent in the submicron range. In particular, in-plane magnetic susceptibilities increase and critical field strengths for onset of saturation decrease for decreasing thickness down to 0.1 μm by factors of 3–5 depending on the chemical composition. The Curie temperature TC decreases by about 25 K for samples with TC higher than the martensitic transformation.

A mathematical model is developed to predict the changing stiffness of magnetic fibers within a uniform external magnetic field. Magnetite nanoparticles 16nm in diameter were synthesized by an organic route. An ultrafine PMMA fiber containing 16nm magnetite nanoparticles was produced by electrospinning. The magnetic properties of the fibers were also characterized.

A micro-electromechanical diaphragm (MEMD) as micro-sensor platform is introduced. The performance of a MEMD is compared with that of a microcantilever (MC). It is theoretically found that the sensitivity of a MEMD is about 50 times higher than that of a MC. The measured resonance frequencies in air proved the validity of the MEMD design. More importantly, the quality merit factor (Q value) of MEMD is higher than that of MC. The damping effect of liquid medium on a MEMD is much smaller than on a MC. It is experimentally demonstrated that the MEMD works well in both air and liquid.

Thermally actuated shape memory polymers (SMPs) interest, both academically and industrially, due to their ability to memorize a permanent shape that is set during processing and a temporary shape that is later programmed by manipulation above a critical temperature, either Tg or Tm. However, the thermal triggering process for SMPs is usually retarded compared to that of shape memory alloys, because the thermal conductivity of polymers is much lower (<0.30 W/m.K). In the present study, we incorporated a highly thermal conducting filler into a shape memory matrix to increase its thermal conductivity and therefore, shorten the heat transfer progress. A mathematical was worked out that quantitatively relates the material's thermal conductivity with the heat transfer time, τ, also defined as a shape memory induction time. The model fit nicely with our experimental data. In addition, mechanical reinforcement was observed with the addition of this rigid thermal conducting filler.

The giant magnetostrictive films exhibit promising device applications for micro-machines and sensor systems due to high response velocity and huge stress created by the magnetostriction. We developed magnetostrictive bimorph-type Fe70Pd30 or Fe83Ga17 (positive magnetostriction)/Al/Ni(negative magnetostriction) thin films by magnetron sputtering. Magnetostriction of these films measured by a bending cantilever beam method has reached 250–300 ppm in the small magnetic field of 1.0 kOe and exhibits little hysteresis. Moreover, the magnetostrictive characteristics do not change under low alternating magnetic field. The magnetoelastic coefficient of these films is 25∼30 MPa, which is comparable to the coefficient of the PbTiO3-PbZrO3 system. These metallic sensor/actuator materials are useful for applications in magnetostrictive 2D- scanners and remote-interrogated tire sensors.

As the data storage density in cutting edge microelectronic devices continues to increase, the superparamagnetic effect poses a problem for magnetic data storage media. One strategy for overcoming this obstacle is the use of thermomechanical data storage technology. In this approach, data is written by a nanoscale mechanical probe as an indentation on a surface, read by a transducer built into the probe, and then erased by the application of heat. An example of such a device is the IBM millipede, which uses a polymer thin film as the data storage medium. It is also possible, however, to use other kinds of media for thermomechanical data storage, and in the following work, we explore the possibility of using thin film Ni-Ti shape memory alloy (SMA). Previous work has shown that nanometer-scale indentations made in martensite phase Ni-Ti SMA thin films recover substantially upon heating. Issues such as repeated thermomechanical cycling of indentations, indent proximity, and film thickness impact the practicability of this technique. While there are still problems to be solved, the experimental evidence and theoretical predictions show SMA thin films are an appropriate medium for thermomechanical data storage.

In this paper, a novel micro-biosensor platform - magnetostrictive microcantilever (MSMC) - is reported. The resonance behavior and the sensitivity of MSMC as sensor platform were characterized and compared to the theoretical calculation. The detection of yeast cells using the biosensor made of MSMC was reported. The results demonstrate the feasibility of MSMC as a high performance biosensor platform. Compare to current microcantilevers, which is widely considered as the state-of-art sensor platform, the MSMCs have following advantages: 1) remote/wireless driving and sensing; 2) easy to fabricate. More importantly, it is experimentally found that the quality merit factor (Q value) of MSMC can reach more than 250, which is much higher than other cantilevers.

This paper provides a unified modeling framework for ferroelectric, ferromagnetic and ferroelastic materials operating in hysteretic and nonlinear regimes. Whereas the physical mechanisms which produce hysteresis and constitutive nonlinearities in these materials differ at the microscopic level, shared energy relations can be derived at the lattice, or mesoscopic, scale. This yields a class of models which are appropriate for homogeneous, single crystal compounds. Stochastic homogenization techniques are then employed to construct macroscopic models suitable for nonhomogeneous, polycrystalline compounds with variable effective fields or stresses. This unified methodology for quantifying hysteresis and constitutive nonlinearities for a broad class of ferroic compounds facilitates both material characterization and subsequent model-based control design. Attributes of the models are illustrated through comparison with piezoceramic, magnetostrictive and thin film SMA data.

The Phenomenological Theory of Martensite Crystallography, developed fifty years ago, envisages martensitic interfaces to be invariant planes of the shape transformation. This theory has been very successful, but neither incorporates the notion of atomic relaxations at martensitic interfaces, nor explicitly demonstrates that such interfaces are glissile. A new model, called the Topological Model, is proposed that addresses these issues. Predictions of the habit plane and relative orientation of the crystals according to the two models are compared and contrasted.

Argon pressure significantly affects the residual stress in sputter deposited thin films and coatings. In case of W thin films, high residual stresses on the order of 1–2 GPa are quite common. With the rest of sputtering parameters being equal, argon pressure determines the sign and the value of residual stress.

When the amount of stored elastic energy in the film due to the residual stress exceeds the interfacial toughness, fracture normally occurs. Telephone cord buckling delamination blisters are commonly observed in compressed thin films. These mechanically active features form by a loss of adhesion between the film and the substrate due to residual stress relief, and exhibit directional growth under certain conditions. This paper considers telephone cord delamination channels for micro-fluidics applications, as this could to be a valuable, reliable, and inexpensive method of forming open channels.