Abstract: Polymer nanocomposites are formed by nanometrical particles embedded in a matrix. Additions of small amounts of nanoparticles of inorganic material in polymer matrixes can greatly improve mechanical properties when compared with the pure polymer. The high specific surface area of the inorganic nanoparticle materials promotes its dispersion in the polymeric matrix and the resulting properties are strongly related to the homogeneity of the dispersion. In the present work, nylon 6.12 nanocomposites with aged pseudoboehmite were obtained using octadecylamine to improve the union between the polymer and the pseudoboehmite. The nanocomposites were characterized by thermal and mechanical test. The pseudoboehmite was characterized by scanning electron microscopy and x-ray diffraction. The nanocomposite was characterized by tensile strength test, 3 points bending test and impact Izod resistance test. The addition of pseudoboehmite promote the increase of the elasticity modulus evidencing the interaction of the pseudoboehmite with the polymeric matrix, probably modifying its crystalline structure. The addition of pseudoboehmite promoted an increase in the HDT an Vicat temperatures of the nanocomposite.
Abstract: Polymeric nanocomposites are hybrid materials, where fillers with nanometric dimensions are dispersed in a polymeric matrix. The fillers have a high surface area, promoting better dispersion in the polymeric matrix and therefore an improvement in physical properties of the composite depending on the homogeneity of the material. In the present work, nanocomposites of polystyrene with different concentrations of pseudoboehmite obtained by a sol-gel process, and treated with octadecylamine were prepared. The nanocomposites were characterized by thermal and mechanical tests. The addition of pseudoboehmite caused a reduction of the melting flow during the production of the composites evidencing the interaction of pseudoboehmite with the polymeric matrix. The addition of pseudoboehmite promoted an increase in the melt flow index, in the the hardness of the nanocomposites obtained, practically does not affect the tensile strength and modulus and the impact strength decreases. The presence of pseudoboehmite causes increase in heat deflection temperature and Vicat softening point and the thermal decomposition occurred at a higher temperature than the pure PS.
Abstract: Unique conversions between stretched and contracted helices of mono-substituted polyacetylenes (SPA)s prepared with an organo rhodium complex-amine catalytic system were demonstrated. The conversions of aromatic SPAs with a drastic color change were caused by polymerization solvents used, substituents in the phenyl ring, and external stimuli like heat- and solvent-treatments which were induced in the solid state. The helices of aliphatic polyacetylenes was oscillating just like spring or coil which was synchronizing with the restricted rotation around the ester O-*C bond in the solution. The oscillation mode was named as an accordion-like helix oscillation “HELIOS”. All the conversions were attributed to the difference of the thermodynamical stability between stretched and contracted helices.
Abstract: The latest our results on triple polymer composites based on graphene nanoplatelets (GNP) covered by copper nanoparticles, iron oxide nanoparticles, and CdSe two-dimensional and spherical nanoparticles are presented and analyzed. It was found that GNP covered by copper nanoparticles results in higher conductivity and film stability increase in PEDOT:PSS than pure GNP. It was revealed that in magnetic field, composites based on GNP with iron oxide nanoparticles have metallic conductivity and form thin films with higher surface while thin films formed without magnetic field are dielectrics and have less surface. Luminescent composite based on CdSe nanoplatelets has been obtained. Two maxima in the luminescence spectra of CdSe nanoplatelets have been found and explained with a model based on efficient absorption of photons between neighbor nanoplatelets. Luminescence of active particles was different in different places of the sample and strongly depends on the graphene type. Stronger luminescence is observed in graphene with less amount of defects.
Abstract: Composite lightweight materials based on a polymeric matrix with embedded magnetic micro-particles have been developed. The application of a magnetic field (MF) during the foaming of samples induced the alignment of magnetic particles along the MF lines, forming reinforcing chain-like structures. The presence of aligned micro-particles imparted an anisotropic mechanical behavior along the particle alignment direction, thus strongly improving mechanical stiffness and strength compared to randomly filled systems. The application of a MF on pre-strained samples during the magneto-mechanical characterization resulted in a direct relationship between the measured variation of the elastic modulus of the foam and the time dependent intensity of the applied MF (also for a magnetic field strength as low as 200 kA/m). In particular, all reinforced samples pre-strained in the linear elastic region of the stress-strain curve exhibited a magneto-strictive response (negative variation of the measured stress). On the contrary, a positive variation of the measured stress (strengthening effect) was detected in samples with aligned particles at pre-strains above the yield point. This behavior has been related to the tendency of chain-like aggregates in buckled cell edges to re-align along the MF lines.
Abstract: The characteristics of the asymmetric artificial muscles, PPy-ClO4/tape, PPy-DBS/tape and PPy-ClO4/PPy-DBS worked in 0.5 M NaClO4 aqueous solutions were discussed by the dynamo-voltammetric responses, coulo-dynamic Evolution responses and the bending angle per unit of consumed charge and the cooperative dynamic effects of PPy-ClO4/PPy-DBS artificial muscles is clarified. In the PPy-ClO4/PPy-DBS asymmetric bilayer artificial muscles, the PPy-ClO4 layer shrinks and PPy-DBS layer swells during reduction and the PPy-ClO4 layer swells and PPy-DBS layer shrinks during oxidation. The artificial muscle originates cooperative dynamic bending actuation of the constituent layers (swelling/shrinking or shrinking/swelling) and achieves the larger bending amplitude than those of the PPy-ClO4/tape and the PPy-DBS/tape. The bending angle per unit of consumed charge on the PPy-ClO4/tape and PPy-DBS/tape is 3.240 and 2.85, respectively, and the cooperative dynamic effect on PPy-ClO4/PPy-DBS is 8.257. In case of NaCl having same level bending angle per unit of consumed charge on PPy-DBS/tape, 2.396, the cooperative dynamic effect on PPy-ClO4/PPy-DBS is just 3.868. Because the bending angle per unit of consumed charge on PPy-ClO4/tape is very low, 0.101. Actually, the cooperative dynamic effect on PPy-ClO4/PPy-DBS in Na2CO3 is 5.184 and is larger than that in NaCl even the bending angle per unit of consumed charge on PPy-DBS is lower than that on NaCl. The expansion and contraction of the PPy-ClO4 film dominates the reaction-driven bending motion and those of the PPy-DBS have a minor influence on the bending actuation.
Abstract: The dielectric elastomer minimum energy structure (DEMES) can realize large angular deformations by a small voltage-induced strain of the dielectric elastomer, so it is a suitable candidate to make a rotary joint for a soft robot. Driven with an alternating electric field, the joint deformation vibrational frequency follows the input voltage frequency. However, the authors find that if the rotational angel over a negative angle during dynamic response, the resonance mode will be different from the traditional, the vibration with the largest amplitude does not occur while the voltage frequency is equal to natural response frequency of the joint. Rather, the vibrational amplitude will be quite large over a range of other frequencies, at which the voltage frequency is greater than one time of the nature frequency and smaller than two times. This phenomenon was analyzed by relationship between the bending angle, applied voltage and bending moment of the film to the frame on a timeline. This new resonance mode can be applied to some biomimetic soft robots that consist of DEMES rotary joint.
Abstract: Fabrication of ionic polymer metal composite (IPMC) on Si substrate and micromachining of IPMC are basic technologies for developing MEMS devices using IPMC. Adhesion of IPMC with the substrate is essential to fabricate IPMC on the substrate. Swelling of IPMC with water makes IPMC peel from the substrate due to the internal stress. To enlarge adhesion force of IPMC with the Si substrate, we have fabricated IPMC on an anodic-oxidized porous Si surface, which dramatically increased adhesion area between the IPMC and the substrate. Fabricated IPMC didn't peel from the Si substrate during the operation in water. Photolithography is a key technology in MEMS fabrication. However, water and organic solvents used in the fabrication process also swell IPMC and lower machining accuracy. We have developed a machining technology of microminiaturized IPMC by mainly using dry processes: reactive ion etching of Nafion film through metal mask, and a selective electrode formation using a plasma irradiation on Nafion and an electroless gold plating. An array of IPMCs with a width of 100 μm was fabricated and their operations in water were confirmed.
Abstract: Electroactive polymer transducers have many features that are desirable for various devices. An especially attractive type of electroactive polymer is dielectric elastomer (DE).
Our recent progress is a DE actuator having only 0.1 g of DE that lifted a weight of 2 kg using carbon system electrodes. We also developed a ribbon form DE actuator having a sensor function that can be used to measure force, or pressure, as well as motion at the same time. This actuator can assist human and robot motions. At the same time, it can work as a motion feedback sensor. We hope that it may be useful for smart rehabilitation equipment for hands, legs, and fingers.
DE has also been shown to operate in reverse as a generator. Experiments have been performed on portable DE generators/wearable generators powered by human motion, ocean wave power harvesters mounted on buoys, solar heat generators, and water turbines. While the power output levels of such demonstration devices is small, the performance of these devices has supported the potential benefits of DE.
We are developing elastomers having larger dielectric constant using barium titanium oxide to produce a “super artificial muscle for energy harvesting devices, actuators & sensors” in the near future.