This PDF file contains the front matter associated with SPIE Proceedings Volume 9432, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

Photoresponsive polymers offer novel methods for morphing applications due to its unique ability to control shape spatially and temporally with light. The constitutive behavior of these materials is complicated by the interactions of time-dependent light fields and molecular conformation changes within the polymer network. This requires applications in non-equilibrium thermodynamics, nonlinear photomechanics, and high fidelity numerical simulations using finite difference/finite element methods. The proposed approach utilizes a set of electronic order parameters to represent light driven molecular conformation changes which are coupled to mechanics of a continuum scale polymer network and time-dependent electromagnetics. The model is applied to explain photoisomerization of azobenzene as it deforms a polymer during different types of light excitation. We consider local surface deformation from laser beams including linearly and circularly polarized lights where the azobenzene liquid crystal microstructure couples to affine deformation of the host polymer network. This local deformation from a laser beam is compared to homogeneous polarized light across the surface of a cantilever film. Non-trivial deformation is predicted and the internal mechanisms associated with bending in different directions is discussed.

Mechanochromism of polymer-dye blends can be used to formulate novel pressure sensors for fluid mechanics and hydrology, where the use of traditional electromechanical transducers may be limited by environmental factors. Here, we investigate optomechanical properties of a mechanochromic blend of thermoplastic polyurethane and 0.5 wt% bis(benzoxazolyl)stilbene fluorescent dye. We characterize the response of this soft active material in a stress relaxation test by simultaneous acquisition of the tensile load, the mechanical deformation, and the fluorescence emission.

Polymer matrix composites (PMCs) are ubiquitous in engineering applications due to their superior mechanical properties at low weight. However, they are susceptible to damage due to their low interlaminar mechanical properties and poor heat and charge transport in the transverse direction to the laminate. Moreover, methods to inspect and ensure the reliability of composites are expensive and labor intensive. Recently, mechanophore-based smart polymer has attracted significant attention, especially for self-sensing of matrix damage in PMCs. A cyclobutane-based self-sensing approach using 1,1,1-tris (cinnamoyloxymethyl) ethane (TCE) and poly (vinyl cinnamate) (PVCi) has been studied in this paper. The self-sensing function was investigated at both the polymer level and composite laminate level. Fluorescence emissions were observed on PMC specimens subjected to low cycle fatigue load, indicating the presence of matrix cracks. Results are presented for graphite fiber reinforced composites.

The objective of origami engineering is to combine origami principles with advanced materials to yield active origami shapes, which fold and unfold in response to external stimuli. We are investigating the use of P(VDF-TrFE-CTFE), a relaxor ferroelectric terpolymer, to realize origami-inspired folding and unfolding of structures and to actuate so-called action origami structures. To accomplish these two objectives, we have explored different approaches to the P(VDF-TrFECTFE) polymer actuator construction, ranging from unimorph to multilayered stacks. Electromechanical characterization of the terpolymer-based actuators is conducted with a focus on free strain, force-displacement and blocked force. Moreover dynamic thickness strains of P(VDF-TrFE-CTFE) terpolymer at different frequencies ranging from 0.1Hz to 10Hz is also measured. Quantifying the performance of terpolymer-based actuators is important to the design of action origami structures. Following these studies, action origami prototypes based on catapult, flapping butterfly wings and barking fox are actuated and characterization of these prototypes are conducted by studying impact of various parameters such as electric field magnitude and frequency, number of active layers, and actuator dimensions.

Lead zirconate titanate (PZT) microwires with applications in sensors, actuators, and energy harvesters are produced using hydrothermal synthesis. The synthesized microwires are relatively large with an average length of about 450 microns and an average width of 4 microns. Each of these individual PZT microwires can be integrated in smart systems as an active phase or be used as an independent smart material. In this paper, the synthesis procedure and characterization of these large microwires is demonstrated. The converse piezoelectric properties of the microwires are measured using digital image correlation after clamping and adding electrodes at each end of the microwire. It has been shown in the literature that digital image correlation can be used as a precise tool for rapid characterization of piezoelectric materials. Here, it is demonstrated that this technique can be applied to characterize the actual response of piezoelectric materials at the micron scale.

Carbon Nanotubes (CNTs) were dispersed in a cement-sand-based piezoelectric smart composite as conductive fillers to improve its poling efficiency, leading to a desirable piezoelectric effect. By introducing a small amount of CNTs, continuous electric networks between Lead Zirconate Titanate (PZT) particles were created, thus making the composite poling easier. Specimens were prepared by mixing PZT powders, Portland cement and sand with CNTs, followed by pressing it with a load frame system. The effect of quantity of CNTs ranging from 0 to 1.0 volume percent on properties of the composite, including its piezoelectric coefficient, dielectric constant and loss, and sensing effects, were characterized. It was found that the addition of CNTs facilitated effective poling at room temperature and improved the piezoelectric and dielectric properties of the composite. The composite modified by CNTs achieved optimal properties when the CNTs content was 0.7 vol.%.

In this paper, we present the next generation of polymer based composite foam material fabricated from poly(vinylidene fluoride) (PVDF) and graphene nano-platelets (GNPs) as secondary fillers. We discovered that such composite material has thermoelectric properties and has the potential to be used in energy harvesting applications. The samples were fabricated though melt blending methods, which is a cheaper, simpler process and can be easily scaled up to industrial level for mass production. Our results indicate that melt blending processes can produce either similar or superior results compared to traditional solvent casting methods. In addition, we utilized a novel batch foaming method and successfully created closed-cell structure for the composite material. Our results also show that the thermal conductivity of PVDF/GNP foam samples have approximately an order of magnitude drop compared to solid samples, which is desired for thermoelectric materials. Furthermore, we observed a change in the electrical conductivity threshold of the GNP fillers after foaming. We report a Seebeck coefficient of 217 μV/K for 15 wt% GNP/PVDF foam samples, which is approximately 10 times higher than values reported previously.

Active fiber composites (AFC) are comprised of lead zirconate titanate (PZT) fibers embedded in a polymer. This paper presents an experimental characterization of the PZT fibers and a constitutive model focused on their time-dependent, nonlinear response. The experiments herein focus on characterizing time dependence of various properties by conducting creep, relaxation, mechanical and electric field-cyclic loading at different frequencies. The constitutive model is a time-dependent polarization model that predicts nonlinear polarization and electro-mechanical strain responses of the fibers. The model of PZT fibers is used in the FEM simulation of AFCs and results of the model are compared to experiments for validation.

The uncertainty of a set of phenomenological ferroelectric phase field parameters are determined from a set of density function theory calculations. Bayesian statistics are employed and numerically implemented using the Markov Chain Monte Carlo (MCMC) technique. Computational DFT data for periodic unit cells and domain wall structures is included in the analysis to identify a broader range of phase field material parameters. This allow for determining a Landau-based stored energy function, electrostrictive coupling, and polarization gradient parameters governing domain wall energy and length. We focus on the tetragonal phase ferroelectric lead titanate which may contain 180◦ and 90◦ domains walls. The comparison of the phenomenological phase field model and DFT computations illustrate good correlations and relatively small propagation of error in prediction of the continuum stored energy function. Larger uncertainty is observed in the electrostrictive stress and domain wall predictions. The larger uncertainty in the electrostrictive parameters is reduced by decoupling the stored energy and stress computations. This leads to a factor of three reduction in the standard deviation of the electrostrictive parameters. Challenges in self-consistent prediction of domain structure energies and sizes is also discussed in light of the Bayesian statistical analysis.

Piezoelectric bimorph laminar actuator of tapered width exhibits better performance for out-of-plane deflection compared to the rectangular surface area, while consuming equal surface area. This paper contains electromechanical analysis and modeling of a tapered width piezoelectric bimorph laminar actuator at high electric field in static state. The analysis is based on the second order constitutive equations of piezoelectric material, assuming small strain and large electric field to capture its behavior at high electric field. Analytical expressions are developed for block force, output strain energy, output energy density, input electrical energy, capacitance and energy efficiency at high electric field. The analytical expressions show that for fixed length, thickness, and surface area of the actuator, how the block force and output strain energy gets improved in a tapered surface actuator compared to a rectangular surface. Constant thickness, constant length and constant surface area of the actuator ensure constant mass, and constant electrical capacitance. We consider high electric field in both series and parallel electrical connection for the analysis. Part of the analytical results is validated with the experimental results, which are reported in earlier literature.

1-3 piezocomposites are very attractive materials in underwater and biomedical applications. These materials may be subjected to high electric field (2kV/mm) under continuous operation leading to deterioration in the output parameters such as remnant, saturation polarization and strain. Hence in this work, an experimental study is carried out to understand the fatigue behavior of 1-3 piezocomposites for various fiber volume fraction subjected to cyclic electric field (2kV/mm, 50Hz) up to 10⁶ cycles. A uni-axial micro-mechanical model is developed to predict the fatigue behaviour of 1-3 piezocomposite. The novelty of this model is, the remnant polarization and strain are chosen as internal variables which is also dependent on the damage.The simulated results are compared with the experimental observations, it is observed that the proposed micro-mechanical model is able to predict the material degradation with increase in number of cycles of operation. A parametric study is also conducted for various fiber volume fraction of 1-3 piezocomposite as function of fatigue cycle it shows that the amplitude of dielectric hysteresis and butterfly loop decreases with increase in the number of cycles. The fatigue behavior has a substantial effect in the performance parameters such as coercive field, remnant polarization and the asymmetric strain behavior of 1-3 piezocomposite. This fatigue study explores the utilities of 1-3 piezocomposites in transducer applications by providing insight into the device design.

Since many years, carbon nanotubes (CNTs) have been considered for a wide range of applications due to their outstanding mechanical properties. CNTs are tubular structures, showing a graphene like hexagonal lattice. Our interest in the calculation of the mechanical properties is motivated by several applications which demand the knowledge of the material behavior. One application in which the knowledge of the material behavior is vital is the CNT based fiber. Due to the excellent stiffness and strength of the individual CNTs, these fibers are expected to be a promising successor for state of the art carbon fibers. However, the mechanical properties of the fibers fall back behind the properties of individual CNTs. It is assumed that this gap in the properties is a result of the van-der-Waals interactions of the individual CNTs within the fiber. In order to understand the mechanical behavior of the fibers we apply a molecular mechanics approach.

The mechanical properties of the individual CNTs are investigated by using a modified structural molecular mechanics approach. This is done by calculating the properties of a truss-beam element framework representing the CNT with the help of a chemical force field.

Furthermore, we also investigate the interactions of CNTs arranged in basic CNT assemblies, mimicking the ones in a simple CNT fiber. We consider the van-der-Waals interactions in the structure and calculate the potential surface of the CNT assemblies.

In the fields of smart materials there is still a demand for a material featuring high modulus, low density and large strain. Carbon materials catch enormous scientific attention not only since carbon fibers were used for highperformance composite structures. But more and more the scientific attention moves from the macroscale to the nanoscale. This paper focuses with a adaptive point of view on one of the carbon allotropes: carbon nanotubes (CNTs). Beside excellent electromechanical properties another interesting feature was first mentioned 1999 - the active behavior of paper-like mats (bucky-papers) made of CNTs. CNT-papers are electrically activated using a double-layer interaction of ions provided by an electrolyte and the charged, high specific surface area of the paper formed by carbon nanotubes. Until now the detailed mechanism behind the strain/force generation of CNT-based architectures is unknown. A clarification of this principle reveals the potential of carbon tubes to be or not to be a resilient smart material in order to use their strong covalent carbon bonds instead of weak van der Waals force as tube-linking. This paper presents further investigations about the composition of CNT-papers and their performance in contrast to vertical aligned CNT-arrays using an actuated tensile test set-up. For better comparison the experiments of both specimen-types are carried out in dry, wet and wet/charged conditions. Especially in the case of CNT-arrays it is essential to preload the specimens because the curly CNT-structure superimposes the vertical orientation. While the CNT-paper is tested in an aqueous solution of one molar sodium chloride, the hydrophobic character of CNT-arrays requires an ionic liquid (IL) as electrolyte. It is found that the mechanical properties of CNT-papers drop significantly by wetting and can be controlled by charging what indicates an electrostatic dominated effect. In contrast the CNT-arrays show identical results regardless of the test conditions and furthermore an active, reversible behavior of tube elongation by charging. These results indicate strongly a quantum mechanical effect as reason of a CNT-array actuation.

Magnetoelectric (ME) coupling is an inherent property of only a few crystals exhibiting very low coupling coefficients at low temperatures. On the other hand, these materials are desirable due to many promising applications, e.g. as efficient data storage devices or medical or geophysical sensors. Efficient coupling of magnetic and electric fields in materials can only be achieved in composite structures. Here, ferromagnetic (FM) and ferroelectric (FE) phases are combined e.g. including FM particles in a FE matrix or embedding fibers of the one phase into a matrix of the other. The ME coupling is then accomplished indirectly via strain fields exploiting magnetostrictive and piezoelectric effects. This requires a poling of the composite, where the structure is exposed to both large magnetic and electric fields. The efficiency of ME coupling will strongly depend on the poling process. Besides the alignment of local polarization and magnetization, it is going along with cracking, also being decisive for the coupling properties. Nonlinear ferroelectric and ferromagnetic constitutive equations have been developed and implemented within the framework of a multifield, two-scale FE approach. The models are microphysically motivated, accounting for domain and Bloch wall motions. A second, so called condensed approach is presented which doesn’t require the implementation of a spatial discretisation scheme, however still considering grain interactions and residual stresses. A micromechanically motivated continuum damage model is established to simulate degradation processes. The goal of the simulation tools is to predict the different constitutive behaviors, ME coupling properties and lifetime of smart magnetoelectric devices.

A novel and precise characterization of the constitutive behavior of solid and laminated research-grade, polycrystalline Galfenol (Fe_81:6Ga18:4) under under quasi-static (1 Hz) and dynamic (4 to 1000 Hz) stress loadings was recently conducted by the authors. This paper summarizes the characterization by focusing on the experimental design and the dynamic sensing response of the solid Galfenol specimen. Mechanical loads are applied using a high frequency load frame. The dynamic stress amplitude for minor and major loops is 2.88 and 31.4 MPa, respectively. Dynamic minor and major loops are measured for the bias condition resulting in maximum, quasi-static sensitivity. Three key sources of error in the dynamic measurements are accounted for: (1) electromagnetic noise in strain signals due to Galfenol's magnetic response, (2) error in load signals due to the inertial force of fixturing, and (3) time delays imposed by conditioning electronics. For dynamic characterization, strain error is kept below 1.2 % of full scale by wiring two collocated gauges in series (noise cancellation) and through lead wire weaving. Inertial force error is kept below 0.41 % by measuring the dynamic force in the specimen using a nearly collocated piezoelectric load washer. The phase response of all conditioning electronics is explicitly measured and corrected for. In general, as frequency increases, the sensing response becomes more linear due to an increase in eddy currents. The location of positive and negative saturation is the same at all frequencies. As frequency increases above about 100 Hz, the elbow in the strain versus stress response disappears as the active (soft) regime stiffens toward the passive (hard) regime.

The aerospace, automotive, and energy industries have seen the potential benefits of using shape memory alloys (SMAs) as solid state actuators. Thus far, however, these actuators are generally limited to non-critical components or over-designed due to a lack of understanding regarding how SMAs undergo thermomechanical or actuation fatigue and the inability to accurately predict failure in an actuator during use. The purpose of this study was to characterize the actuation fatigue response of Nickel-Titanium-Hafnium (NiTiHf) axial actuators and, in turn, use this characterization to predict failure and monitor damage in dogbone actuators undergoing various thermomechanical loading paths. Calibration data was collected from constant load, full cycle tests ranging from 200-600MPa. Subsequently, actuator lifetimes were predicted for four additional loading paths. These loading paths consisted of linearly varying load with full transformation (300-500MPa) and step loads which transition from zero stress to 300-400MPa at various martensitic volume fractions. Thermal cycling was achieved via resistive heating and convective cooling and was controlled via a state machine developed in LabVIEW. A previously developed fatigue damage model, which is formulated such that the damage accumulation rate is general in terms of its dependence on current and local stress and actuation strain states, was utilized. This form allows the model to be utilized for specimens undergoing complex loading paths. Agreement between experiments and simulations is discussed.

Due to its outstanding properties of Nitinol, known as shape memory and superelasticity, Nitinol wires have been used as actuators in many medical devices. For the medical applications, it is critical to have a consistent strain response of Nitinol wires. This work focuses on studying the effect of parameters such as biased stress, maximum temperature, and wire diameters that influence the strain response of Nitinol wires. Specifically, Nitinol phase transformations were studied from microstructural point of view. The crystal structures of one-way shape memory Nitinol wires of various diameters under different thermomechanical loading conditions were studied using X-Ray Diffraction (XRD) method. The location and intensity of characteristic peaks were determined prior and after the thermomechanical loading cycles. It was observed that Nitinol wires of diameters less than 0.19 mm exhibit unrecovered strain while heated to the range of 70ºC to 80ºC in a thermal cycle, whereas no unrecovered strains were found in larger wires. The observation was supported by the XRD patterns where the formation of R-phase crystal structure was showed in wire diameters less than 0.19 mm at room temperature.

The recent discovery of a new kind of thermo-active coiled polymeric wires has opened new perspectives for the implementation of a novel class of actuators that can be easily and effectively manufactured using low-cost materials such as sewing threads or finishing lines. These new devices feature large displacements in response to temperature variations and show very promising performance in terms of energy and power densities.

With the aim of providing information and data useful for the future engineering applications of polymeric coiled actuators, a custom experimental test-bench and procedure have been developed and employed to characterise their thermo-mechanical response. Such a test-bench has been designed to run isothermal and isometric tensile tests on a set of sample actuators that are fabricated with a repeatable process.

This paper provides technical details on the manufacturing process of such sample actuators and on the design and operation of the test-bench. Preliminary experimental results are finally reported.

The shape memory hydrogels were synthesized and studied the physical properties. The gels were made by a hydrophilic monomer named N, N-dimethyl acrylamide (DMAAm) and a hydrophobic monomer named stearyl acrylate (SA). The water-swollen hydrogels show well transparency and shape memory property while gels absorb large water content. The properties were characterized by varying the cross-link concentration, whereas the concentration of other chemical components was remained constant. In this study, the DMAAm and the SA ratio was 3:1 to make one mole solution. It is observed that the swelling ratio slightly depends on the cross-link concentration at certain amount. However, mechanical properties strongly depend on the cross-link concentration. Thermal properties were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). DSC spactra of dried samples exhibits complex crystalline nature, while swollen samples show homogeneous crystallinity. A well thermal stability is observed regard less of cross-link concentration.

Polyurea is a type of elastomer with excellent properties and a myriad of applications. Especially, the application in increasing the survivability of structures and buildings under impact loading is more attractive. Recently, modifying the properties of polyurea by mixing micro and nano particles into polyurea is becoming a new research hotspot. However, systematic study of the effect of particles size on the properties of polyurea-based composites has not been reported. Hence, in our present work, glass beads with diameters in the range from 3μm to 250μm were selected and composites with 20% volume fraction of glass beads were prepared. Microstructure of the composites was investigated by Scanning Electron Microscopy (SEM). Dynamic mechanical analysis was conducted using a TA Instruments DMA 2980 over the temperature range from -80°C to 50°C at various frequencies. The storage and loss moduli master curves for these composites were obtained through application of the time-temperature superposition (TTS). Ultrasonic properties were determined by a personal computer (PC) based ultrasonic system at room temperatures. Velocity and attenuation of longitudinal ultrasonic wave were measured. Consequently, complex longitudinal modulus was computed from these measurements. Evaluation of the effect of particle size on the properties of the composites mentioned above was presented.

Carbon nanotube paper (CNP) based multi-functional composite material is an attractive candidate for deicing, flame retardancy, thermal insulation and lighting strike protection due to the excellent conductivity, light weight and thin dimensions. In this article, multi-functional carbon nanotube paper was fabricated successfully by using commercial carbon nanotube. As a deicing composite material, carbon nanotube was used directly without pretreatment in fabricating carbon nanotube paper. The conductivities of the carbon nanotube paper and deicing composite were 77.8S/cm and 64.9S/ respectively. Electrical heating and deicing performance were test by infrared camera with deicing time less than 220s and 450s to melt a certain amount of ice under different ambient condition. CNT was grafted by zirconium (IV) butoxide solution and dimethyl dichlorosilicane to form co-oligomers on the tube surface while oligomers decompose under a certain temperature to develop an inorganic layer of silicon zirconium oxide. The oxidizing temperature of carbon nanotube increases more than 20°C and the weight loss rate decreases 20% than the untreated carbon nanotube. Lightning protection material required high electro conductivity, due to the utmost high current in a short time. Therefore, silver nanoparticles were deposited on the surface of carbon nanotube with the diameter around 100nm. The conductivity increased sharply from 84s/cm to1756s/cm with the mount of 5.9wt% Ag of the modified carbon nanotube paper because the silver nanoparticles deposited on the surface. In addition, the silver modified also can be used as thermal insulation material decreasing the infrared radiation.

Supercapacitor device electrochemical performance characteristics of different nanocomposite materials containing polyaniline (PAni) and graphene nanoplatelets (GnPs) have been evaluated with two-electrode electrochemical setup. The PAni-based nanocomposite electrodes have been fabricated via ultrasonicated in-situ chemical polymerization and solvent casting process. The specific capacitance of the supercapacitor electrode have reached as high as 357.07 F/g at 10mV/s, in the case of 15:1 PAni/GnPs, as a result of graphene nanoparticles’ large surface area providing an ideal template for polymerization to occur. Electrodes under study are namely, pristine GnPs, pristine PAni, and 5:1, 15:1 PAni/GnPs nanocomposites. Material composition has been confirmed via thermal gravimetric analysis (TGA), while scanning electron microscopy (SEM) has been used to characterize the morphologies of the nanostructures. Threedimensional nanocomposite morphology has been observed in the micrographs of these nanocomposites, indicating a relationship between the material surface area and the charge storage ability.

Interfacial properties of Shape Memory Alloy (SMA) reinforced polymer matrix composites can be enhanced by improving the interfacial bonding. This paper focuses on studying the interfacial stresses developed in the SMAepoxy interface due to various laser shot penning conditions. Fiber-pull test-setup is designed to understand the role of mechanical bias stress cycling and thermal actuation cycling. Phase transformation is tracked over mechanical and thermal fatigue cycles. A micromechanics based model developed earlier based on shear lag in SMA and energy based consistent homogenization is extended here to incorporate the stress-temperature phase diagram parameters for modeling fatigue.

One-dimensional nanostructures such as nanowires, nanorods, and nanotubes with piezoelectric properties have gained interest in the fabrication of small scale power harvesting systems. However, the practical applications of the nanoscale materials in structures with true mechanical strengths have not yet been demonstrated. In this paper, piezoelectric ZnO nanowires are integrated into the fiber reinforced polymer composites serving as an active phase to convert the induced strain energy from ambient vibration into electrical energy. Arrays of ZnO nanowires are grown vertically aligned on aramid fibers through a low-cost hydrothermal process. The modified fabrics with ZnO nanowires whiskers are then placed between two carbon fabrics as the top and the bottom electrodes. Finally, vacuum resin transfer molding technique is utilized to fabricate these multiscale composites. The fabricated composites are subjected to a base excitation using a shaker to generate charge due to the direct piezoelectric effect of ZnO nanowires. Measuring the generated potential difference between the two electrodes showed the energy harvesting application of these multiscale composites in addition to their superior mechanical properties. These results propose a new generation of power harvesting systems with enhanced mechanical properties.

Ionic polymer-metal composite (IPMC) electromechanical and mechanoelectrical phenomena for rectangular and tube-shaped IPMC devices have been examined through simulation and experimental investigation. There is a specific focus on investigating the anion and cation effects in actuation versus sensing. Simulations were performed using COMSOL Multiphysics 4.3b. Sample IPMCs were fabricated in lab in the desired geometries by techniques described herein. The sample sizes were roughly 1 mm thick and 20-25 mm in length. Actuation and sensor experiments were performed with the samples and compared to simulation results, which exhibit good agreement for voltage and tip displacement measurements. Fundamental differences in the electromechanical and mechanoelectrical transductions of IPMCs are highlighted in the simulation results. These results display the negligible effect of anion motion in actuation as compared to during sensing. In actuation, the cation motion is dominated by an electric potential flux, and the anions move only slightly in accordance with the deformed polymer membrane. In sensing, the electric potential is induced by the ionic migration in the polymer, and both cation and anion concentration variations are of similar magnitudes.

Gels are a promising class of soft and wet materials with diverse application in tissue engineering and bio-medical purpose. In order to accelerate the development of gels, it is required to synthesize multi-functional gels of high mechanical strength, ultra low surface friction and suitable elastic modulus with a variety of methods and new materials. Among many types of gel ionic gel made from ionic liquids (ILs) could be used for diverse applications in electrochemical devices and in the field of tribology. IL, a promising materials for lubrication, is a salt with a melting point lower than 100 °C. As a lubricant, ILs are characterized by an extremely low vapor pressure, high thermal stability and high ion conductivity. In this work a novel approach of making double network DN ionic gel using IL has been made utilizing photo polymerization process. A hydrophobic monomer Methyl methacrylate (MMA) has been used as a first network and a hydrophobic IL monomer, N,N-diethyl-N-(2-mthacryloylethyl)-N-methylammonium bistrifluoromethylsulfonyl)imide (DEMM-TFSI) has been used as a second network using photo initiator benzophenon and crosslinker triethylene glycol dimethacrylate (TEGDMA). The resulting DN ionic gel shows transparency, flexibility, high thermal stability, good mechanical toughness and low friction coefficient value which can be a potential candidate as a gel slider in different mechanical devices and can open a new area in the field of gel tribology.

The residual stress of electron beam-physical vapor deposition (EB-PVD) thermal barrier coatings (TBC) is complex and difficult to be obtained. In this paper, the interface morphology of TBCs subjected to cyclic heating and cooling was observed by SEM. Based on the thermal elastic-plastic finite method, corresponding interface model of TBCs was established. The residual stress of EB-PVD TBCs with different interface morphologies and TGO thicknesses was calculated using the FE method without regard to the presence of cracks and defects. The result shows that the distribution of residual stress is significantly affected by the interface morphology, and the growth of TGO also has influence on the residual stress of TC and TGO.

Due to their unique optical properties, quantum dots (QDs) have received a great deal of interest for their potential applications, such as in quantum computing, photovoltaic cells, and electronics. With such increased usage, the effect that altering QD concentration has on optical properties of the solution should be explored. Characterization of the emissivity of CdTe QDs as a function of concentration was conducted on three commercially available CdTe QDs. All have optimal absorption around 400-500 nm with peak emission wavelengths at 530 nm, 550 nm, and 570 nm, respectively. The QDs were suspended in an aqueous solution at 13 different concentrations ranging from 0.37 mg/ml to 10 mg/ml. The samples were excited at room temperature by a 50 mW diode laser emitting at a central wavelength of 405 nm and the fluorescence of the QDs was measured with a free-space CCD spectrometer. The measured spectra showed a general redshift in peak emission wavelength with increasing concentration. A +6.12 nm per mg/ml shift for the 530 nm QDs was observed when a linear fit with a coefficient of determination (R-squared) of 0.96 was applied. The 550 nm QDs and the 570 nm QDs showed a +8.70 nm per mg/ml shift (R-squared=0.94) and a +10.27 nm per mg/ml shift (R-squared=0.97), respectively. The redshift is attributed to a Föster resonance energy transfer (FRET) which causes energy transfer between two light-sensitive molecules.

Mussel-inspired catecholamine polymers (polydopamine and polynorepinephrine) were coated on the surface of carbon and glass fibers in order to increase the interfacial shear strength between fibers and polymer matrix, and consequently the interlaminar shear strength of fiber-reinforced composites. By utilizing adhesive characteristic of the catecholamine polymer, fiber-reinforced composites can become mechanically stronger than conventional composites. Since the catecholamine polymer is easily constructed on the surface by the simultaneous polymerization of its monomer under a weak basic circumstance, it can be readily coated on micro-fibers by a simple dipping process without any complex chemical treatments. Also, catecholamines can increase the surface free energy of micro-fibers and therefore, can give better wettability to epoxy resin. Therefore, catecholamine polymers can be used as versatile and effective surface modifiers for both carbon and glass fibers. Here, catecholamine-coated carbon and glass fibers exhibited higher interfacial shear strength (37 and 27% increases, respectively) and their plain woven composites showed improved interlaminar shear strength (13 and 9% increases, respectively) compared to non-coated fibers and composites.