Nantakan Muensit

Effects of copper filler sizes on the dielectric properties and the energy harvesting capability of nonpercolated polyurethane composites

Nonpercolated composites based on polyurethane (PU) filled with low concentrations copper (Cu) powders of varying sizes were studied as electrostrictive materials for mechanical energy harvesting. The dispersion of the fillers within the polymeric matrix was investigated by scanning electron microscopy, and results showed a relatively homogeneous dispersion for the microsized fillers and the existence of agglomerates for their nanosized counterparts. Differential scanning calorimetry measurements displayed that there occurred no interaction between the polymeric matrix and the microsized fillers whereas the nanosized fillers slightly enhanced the glass transition of the soft segments of PU and significantly affected the recrystallization temperature. The dependence of the dielectric properties of the composites as a function of the filler volume fraction and filler size was investigated over a broad range of frequencies, showing an increase in the permittivity when fillers were used. This increase was more pronounced for the composites containing nanosized fillers. The measurement of the harvested current and of the harvested power also demonstrated an enhancement of the energy harvesting capability when nanofillers were employed. From the experimental data, it appeared that the electrostrictive coefficient Q was not proportional to the inverse ratio of the permittivity and the Young modulus for the studied composites. Finally, analytical modeling of the harvested current and of the harvested energy offered an accurate description of the experimental data.

Design and performance testing of an ultrasonic linear motor with dual piezoelectric actuators

In this work, design and performance testing of an ultrasonic linear motor with dual piezoelectric actuator patches are studied. The motor system consists of a linear stator, a pre-load weight, and two piezoelectric actuator patches. The piezoelectric actuators are bonded with the linear elastic stator at specific locations. The stator generates propagating waves when the piezoelectric actuators are subjected to harmonic excitations. Vibration characteristics of the linear stator are analyzed and compared with finite element and experimental results. The analytical, finite element, and experimental results show agreement. In the experiments, performance of the ultrasonic linear motor is tested. Relationships between velocity and pre-load weight, velocity and applied voltage, driving force and applied voltage, and velocity and driving force are reported. The design of the dual piezoelectric actuators yields a simpler structure with a smaller number of actuators and lower stator stiffness compared with a conventional design of an ultrasonic linear motor with fully laminated piezoelectric actuators.

Influence of Copper Nanoparticles Concentration on the Properties of Poly(vinylidene fluoride)/Cu Nanoparticles Nanocomposite Films

In this study, the nanocomposite films of polyvinylidene fluoride/copper nanoparticles were prepared by mixing of copper nanoparticles in a solution of dimethylformamide and polyvinylidene fluoride. The prepared nanocomposites were investigated by fourier transform infrared spectroscopy and X-ray diffraction techniques, showed an obvious α- to β-phase transformation compared to pure PVDF. Scanning electron microscope micrographs showed spherulitic crystal structure of PVDF. The spherulitic morphology of the pure PVDF is maintained for the PVDF nanocomposites; the size of the spherulites decreased by increasing weight fraction of copper nanoparticles. The optical band gap values deduced from the UV–Visible absorption spectra were found to reduce from 4.77xa0eV in pure PVDF to 3.2xa0eV after embedding 1xa0wt% of copper nanoparticles. The surface resistivity values were decreased with increasing copper nanoparticles content. Thermal stability of the nanocomposites was studied by thermogravimetric analysis (TGA). TGA curves showed that nanocomposite films have higher resistance to thermal degradation compared to pure PVDF.

Micropower energy harvesting using poly(vinylidene fluoride hexafluoropropylene)

This work explores applications for poly(vinylidene fluoride hexafluoropropylene) or P(VDF-HFP). The P(VDF-HFP) with a 10u2009wt. % HFP can be prepared to exhibit the piezoelectricity and energy conversion ability. This was achieved by determining the nanostructural parameters by the Small Angle X-Ray Scattering. The unpoled sample gained linear crystallinity with drawing rate. The optimal conditions for poling process were 60 MV/m at 90u2009°C. The piezoelectric coefficient d31 of 28.7 pC/N and FoM of 8.8u2009×u200910−12 m2/N were obtained from the poled sample drawn at 45u2009mm/min. The piezoelectric P(VDF-HFP) was proven to deliver a microwatt energy essential for powering small-scale electronics.

Interface Polarization Effect on Dielectric and Electrical Properties of Polyurethane (PU)/Polyaniline (PANI) Polymer Composites

In this study conductive polymer composites of polyurethane (PU)/polyaniline (PANI) below the percolation threshold were prepared by using solution casting. The dispersion of the conductive PANI fillers within the PU matrix was investigated by scanning electron microscopy (SEM). The SEM results showed a relatively homogeneous dispersion of the PANI fillers within the polymeric matrix. The effects of filler concentration on the dielectric and electrical conductivity depend upon the interface between conductive filler and matrix. Dielectric properties and ac conductivity of polymer composites have been investigated at different frequencies (102 - 105 Hz). The results show that the dielectric constant, dielectric loss and the electrical conductivity are strongly dependent on the frequency. The dielectric constant and dielectric loss decreased, whereas electrical conductivity increased with increasing frequency. In addition, the dielectric constant and conductivity increase when concentration of PANI increased. Differential scanning calorimetry (DSC) presented an enhanced the glass transition temperature (Tg) of the polymer composite with increasing PANI fillers. A correlation of Tg and the interface polarization between the PANI fillers and PU matrix on dielectric properties was proposed.

Effect of Micro- and Nano-Particle Fillers at Low Percolation Threshold on the Dielectric and Mechanical Properties of Polyurethane/Copper Composites

Polymeric composites based on polyurethane (PU) as the matrix and copper (Cu) particles as the filler were prepared by using solution casting. The effects of micro- and nano-particles size and content on the dielectric and mechanical properties depend upon the interface between metal filler and polymeric matrix. The dispersion of the fillers within the polymeric matrix was investigated by scanning electron microscopy (SEM). The SEM results showed a relatively homogeneous dispersion for the micro-particle size and the existence of the aggregation and poor compatibility for the nano-particle size. Differential scanning calorimetric measurements showed that the glass transition temperature (Tg) in case of micro-particles is quite similar to that of the neat PU, but the increase in Tg was observed when nano-particles were used. The dielectric properties of the composites as a function of the filler concentration and filler size was investigated in the frequency range of 100xa0Hz–10xa0kHz, showing an increase in dielectric constant with increasing filler content. This increase was more significant when using the nano-particles. The mechanical properties of the composites were obtained by using a tensile tester (ASTM D412). The tensile modulus generally increased with increasing Cu content, but the extent of increase was lower in case of micro-particles. The tensile strength of composite filled with nano-particle slowly decreased when filler content increased, while there was a significant in case of micro-particle as fillers. In addition, the elongation at break decreased with increasing Cu content, but the effect was more significant when micro-particle were employed. AFM image was used to investigate a topology of the tensile fractured surface, showing the mechanism of failure of the composites.

Electrostrictive Energy Conversion of Polyurethane with Different Hard Segment Aggregations

This work reported the electrostriction of polyurethane (PU) with different aggregations of hard segments (HS) controlled by dissimilar solvents: N,N-dimethylformamide (DMF) and a mixture of dimethyl sulfoxide and acetone denoted as DMSOA. By using atomic force microscopy and differential scanning calorimetry, the PU/DMSOA was observed to have larger HS domains and smoother surface when compared to those of the PU/DMF. The increase of HS domain formation led to the increase of transition temperature, enthalpy of transition, and dielectric constant (0.1u2009Hz). For the applied electric field below 4u2009MV/m, the PU/DMSOA had higher electric-field-induced strain and it was opposite otherwise. Dielectric constant and Young’s modulus for all the samples were measured. It was found that PU/DMF had less dielectric constant, leading to its lower electrostrictive coefficient at low frequency. At higher frequencies the electrostrictive coefficient was independent of the solvent type. Consequently, their figure of merit and power harvesting density were similar. However, the energy conversion was well exhibited for low frequency range and low electric field. The PU/DMSOA should, therefore, be promoted because of high vaporizing temperature of the DMSOA, good electrostriction for low frequency, and high induced strain for low applied electric field.

Extreme Wetting-Resistant Multiscale Nano-/Microstructured Surfaces for Viscoelastic Liquid Repellence

We demonstrate exceptional wetting-resistant surfaces capable of repelling low surface tension, non-Newtonian, and highly viscoelastic liquids. Theoretical analysis and experimental result confirm that a higher level of multiscale roughness topography composed of at least three structural length scales, ranging from nanometer to supermicron sizes, is crucial for the reduction of liquid-solid adhesion hysteresis. With Cassie-Baxter nonwetting state satisfied at all roughness length scales, the surface has been proven to effectively repel even highly adhesive liquid. Practically, this high-level hierarchical structure can be achieved through fractal-like structures of silica aggregates induced by siloxane oligomer interparticle bridges. The induced aggregation and surface functionalization of the silica particles can be performed simultaneously within a single reaction step, by utilizing trifunctional fluoroalkylsilane precursors that largely form a disordered fluoroalkylsiloxane grafting layer under the presence of sufficient native moisture preadsorbed at the silica surface. Spray-coating deposition of a particle surface layer on a precoated primer layer ensures facile processability and scalability of the fabrication method. The resulting low-surface-energy multiscale roughness exhibits outstanding liquid repellent properties, generating equivalent lotus effect for highly viscous and adhesive natural latex concentrate, with apparent contact angles greater than 160&#-80;, and very small roll-off angles of less than 3&#-80;.

Electrostriction of Natural Rubber Latex/Carbon Black Nanocomposites

The purpose of this paper is to investigate an electrostrictive behavior of natural rubber (NR) and NR composites filled with carbon black (CB) nanopowders below percolation threshold. These NR elastomers present advantageous features such as a high productivity, elasticity, and ease of processing. In addition, such materials also exhibit the high induced strain and low young modulus for electrostrictive materials that can be used as actuators and energy harvesting. The NR and all composites were prepared by using solution casting method. The electrostrictive property of the composites was evaluated at low electric field (E 5 MV/m) by measuring the electric field induced strain Sz with the photonic displacement apparatus. The surface morphology of the samples was observed by the atomic force microscopy (AFM) and their electrical properties were analyzed as function of concentration and frequency in a range of 102105 Hz. The results show that the dielectric constant and the dielectric loss decrease when the frequency was increased. Moreover, the dielectric constant and the electrical conductivity strongly increase with increasing the CB contents, relate to interfacial charge distribution. While the dielectric loss slightly increases with increasing filler concentration. The electrostriction coefficient tended to increase with a higher CB loading. In comparison at CB 1 wt%, it was found that the electrostriction coefficient of NR composites is approximately 7 times larger than the pure NR. The NR nanocomposites thus seem to be very attractive for low frequency electromechanical applications.

Synthesis, Characterization and Optical Properties of La-Doped ZnO Nanoparticles Prepared by Precipitation Method

ZnO and La-doped ZnO nanoparticles were synthesized by precipitation method by using Zn (CH3COO)22H2O, (CH2)6N4, (PEO)128-(PPO)54-(PEO)128 and LaCl3H2O as zinc source, precipitating agent, capping agent and dopant, respectively. The calcined samples exhibited a hexagonal wurtzite structure. The smallest particle size of pure ZnO nanoparticles of about 88 nm was obtained when 0.7 mmol (PEO)128-(PPO)54-(PEO)128 was used. The particle size of La-doped ZnO nanoparticles increased when La concentrations increased. The La-doped ZnO nanoparticles showed the energy band gap between 3.159-3.222 eV.