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Printed circuit antennas have been used for the detection of electromagnetic radiation at a wide range of frequencies that go from radio frequencies (RF) up to optical frequencies. The design of printed antennas at optical frequencies has been done by using design rules derived from the radio frequency domain which do not take into account the dispersion of material parameters at optical frequencies. This can make traditional RF antenna design not suitable for optical antenna design. This work presents the results of using a genetic algorithm (GA) for obtaining an optimized geometry (unconventional geometries) that may be used as optical regime antennas to capture electromagnetic waves. The radiation patterns and optical properties of the GA generated geometries were compared with the conventional dipole geometry. The characterizations were conducted via finite element method (FEM) computational simulations.

Seebeck nanoantennas, which are based on the thermoelectric effect, have been proposed for electromagnetic energy harvesting and infrared detection. The responsivity and frequency dependence of three types of Seebeck nanoantennas is obtained by electromagnetic simulation for different materials. Results show that the square spiral antenna has the widest bandwidth and the highest induced current of the three analyzed geometries. However, the geometry that presented the highest temperature gradient was the bowtie antenna, which favors the thermoelectric effect in a Seebeck nanoantenna. The results also show that these types of devices can present a voltage responsivity as high as 36 μV/W36 μV/W for titanium–nickel dipoles resonant at far-infrared wavelengths.

The field of plasmonics, an optics discipline that studies the interaction of light with matter for structures with dimensions similar to the wavelength of the electromagnetic radiation affecting them, has been further developed with the support of computational technologies that are capable of performing calculations with large volumes of data to solve the complex problems of this discipline. Some of the problems in plasmonics require the use of algorithmic techniques that can simultaneously handle more than one function that tend not to present their maximum or minimum at the same point, i.e., their optimal performances conflict with each other. In this paper, we present the results of the use of a multi-objective genetic algorithm to obtain the maximum plasmonic resonance in nanoparticles assuming three relevant factors: geometry, current density, and electric field, which are, in turn, the three objective functions for the proposed algorithm. The method used for the characterization of the nanoparticles was a numerical simulation using the finite element method. To verify the results, the electromagnetic radiation patterns and other optical properties of the obtained nanoparticles were compared with those of nanoparticles reported in the literature. Possible applications and work in progress are also discussed.

The synthesis of poly(acrylonitrile-butadiene-styrene) (ABS) was carried out using the mass-suspension process, high cis polybutadiene (PB), benzoyl peroxide (BPO) as the initiator and modified and unmodified nanoparticles of zinc oxide (nano-ZnO). X-ray diffraction (XRD) and Fourier transform infrared (FTIR) were used to characterize the ZnO nanoparticles. A Universal tensiometer, Brokfield viscosimeter and transmission electronic microscopy (TEM) were used to characterize ABS. The employment of nano-ZnO induced an impressive morphologic modification and transformed the highly occluded salame morphology of poly(styrene-acrylonitrile) (SAN) to a highly dispersed one in its matrix. During the reaction, a decrease in the total production of SAN was observed due to the interaction between radicals produced by the initiator and nano-ZnO, causing a molecular weight increase of SAN. The nano-ZnO also induced a decline in the phase inversion and extended the period of occurrence. ABS without nano-ZnO yielded higher mechanical properties than one without any nanoparticles.

Different high impact polystyrenes were synthesized using styrene/butadiene copolymers (SB) with PS/PB composition: 30/70 and 20/80 as the precursor rubber, benzoyl peroxide (BPO) as the initiator, and ter-dodecyl mercaptane (TDM) as the chain transfer agent. During the polymerization, several samples were taken and analyzed under different techniques to evaluate the phase inversion (PI) phenomenon. The PI was determined through transmission electron microscopy (TEM) and through dynamic oscillatory behavior, where the PI takes places when the relaxation process presents the lower value of activation energy. Finally, the Choi and Schowalter emulsion model was employed to elucidate the PI, and relevant information was revealed about the interfacial tension in the PI. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

The bulk copolymerization of styrene and acrylonitrile in the presence of SB using BPO as initiator was investigated. Reactions were carried out at 80°C with different initial SB concentrations. Global variables, such as conversion and cumulative grafting efficiency of SAN, were determined during the prepolymerization. The isolated non-grafted SAN was also analyzed to determine its average molar masses and composition. A mathematical model was developed, and theoretical predictions were compared with experimental data. A good agreement between measurements and simulations was obtained from a heterogeneous model when BPO was evenly distributed between phases.

Équipe 101 : Nanomagnétisme et électronique de spin; International audience; Arrays of metallic thermocouples in the shape of spiral nanoantennas are proposed as infrared detectors, which use the thermoelectric properties of the metallic interfaces to generate electrical DC signals. The responsivity of these types of antennas is evaluated from both theoretical and numerical perspectives pointing out its potential as infrared sensors. Moreover, the same structures can be used to characterize the state of polarization of the optical near fields with a spatial resolution comparable to the wavelength.

In recent years, synthetic rubbers nanocomposites have captured and held the attention of scientists because are the materials for the future, which have improved resistance to thermal degradation and stability of the nanocomposite. Commonly fillers like layered silicates, carbonaceous nanofillers (carbon nanotubes, carbon naanofibers and exfoliated nanographite), spherical particles (Silica, TiO2, ZnO, CaSO4, CaCO3, ZnFe2O4) and polyhedral oligomeric silsesquioxane (POSS) are used for reinforcing elastomers. This new materials exhibit enhanced properties at very low filler level, usually ≤5 wt%. The properties of rubber nanocomposites strongly depend on the dispersion state of fillers and method of preparation. The effect to different nanoparticles on rubber properties is studied with thermal stability. This is mainly studied using TGA, TGA-MS, TGA-FTIR and other techniques. The thermal degradation mechanism of the rubber synthetic nanocomposites is generally considered to be related to the kind of used nanoparticles and its amount, the interactions between inorganic nanoparticles and polymer reactive group. Rubber synthetic nanocomposites play an important role in engineering, automotive, aerospace, construction, packaging and medical devices applications due to is possible to design new materials with unprecedented and improvements in their physical properties, particularly from the perspective of applications.

High impact polystyrene(HIPS) was repeatedly coextruded at 220°C, maintaining a constant composition of 70 wt% of virgin HIPS and 30 wt% of recycled HIPS. The gel content (GC), grafting degree (GD), swell index (SI), morphology of the rubber phase, and average molecular weight of the polystyrene (PS) matrix (w) were characterized after each processing cycle. The effect of these parameters on the melt flow index (MFI), the shear viscosity (η), the power law index (n), the Izod impact, and the stress at break were evaluated. The results demonstrated that the rheological properties changed with the number of processing cycles, e.g. the MFI decreased in the first cycle from 2.8 to 1.7 g/10 min, while from the second to the sixth cycle increased to 3.4 ± 0.2 g/10 min. The power law index increased from n = 0.29, after the first processing cycle, to n = 0.34 in the sixth cycle. The changes in MFI and n were attributed to changes in the physical structure of the rubber phase and to chain scissions in the PS matrix, caused by the recycling. Finally, the impact strength decreased with the increasing number of processing cycles, while the tensile stress at break remained constant. POLYM. ENG. SCI., 46:1698–1705, 2006. © 2006 Society of Plastics Engineers

High impact polystyrene was extruded repeatedly at 220°C and thermoformed under different heat time (Ht), plug assist time (PAt), mold time (Mt), and mold temperature (MT). The optimum thermoforming process conditions were determined for a material processed in one cycle, using an experimental design of the four variables mentioned before at two levels. Mt has no influence on the coefficient of wall thickness variation (CV), while the rest of the variables present a noticeable influence on CV, and they can be modified to obtain lower values of CV (i.e. CV = 1.3, using Ht = 46 s, PAt = 2.5 s, and MT = 80°C). These conditions were then employed for a material processed under six cycles, resulting in an increase in the CV value to 3.5. The normalized thickness (NT) of HIPS with one and six processing cycles was also evaluated. It depends on Ht, Mt, and PAt. With the values of the calculated parameters for CV, it was possible to obtain NT values close to 1, using a material processed one cycle. The NT value obtained for six cycles processed HIPS was far from unity. The changes on thermoforming variables' responses are a consequence of the changes occurred in HIPS inner structure. POLYM. ENG. SCI. 46:503–509, 2006. © 2006 Society of Plastics Engineers.

Chitosan-coated magnetic nanoparticles (CMNP) were prepared in one-step by precipitation in a high-aqueous phase content reverse microemulsion in the presence of chitosan. The high-aqueous phase concentration led to productivities close to 0.49 g CMNP/100 g microemulsion; much higher than those characteristic of precipitation in reverse microemulsions for preparing magnetic nanoparticles. The obtained nanoparticles present a narrow particle size distribution with an average diameter of 4.5 nm; appearing to be formed of a single crystallite; furthermore they present superparamagnetism and high magnetization values; close to 49 emu/g. Characterization of CMNP suggests that chitosan is present as a non-homogeneous very thin layer; which explains the slight reduction in the magnetization value of CMNP in comparison with that of uncoated magnetic nanoparticles. The prepared nanoparticles show high heavy ion removal capability; as demonstrated by their use in the treatment of Pb2+ aqueous solutions; from which lead ions were completely removed within 10 min.

Thermoplastic vulcanizates (TPVs) based on high-density polyethylene (HDPE), ethylene–propylene–diene terpolymer (EPDM), and ground tire rubber (GTR) were dynamically vulcanized with dicumyl peroxide (DCP). The polymer blend was composed of 40% HDPE, 30% EPDM, and 30% GTR, and the concentration of DCP was varied from 0.3 to 3.6 parts per hundred rubber (phr). The properties of the TPVs were determined by evaluation of the gel fraction content and the mechanical properties. In addition, IR spectroscopy and differential scanning calorimetry analysis were performed as a function of the DCP content. Decreases in the Young's modulus of the blends and the crystallinity of HDPE were observed when the content of DCP was greater than 1.8 phr. The results regarding the gel content indicate that the presence of DCP promoted the crosslinking of the thermoplastic matrix, and optimal properties were obtained with 1.5% DCP. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39901.

Nanoantennas have been fabricated by scaling down traditional antenna designs using nanolithographic techniques and testing them at different optical wavelengths, these particular nanoantennas have shown responses in a broad range of frequencies going from visible wavelengths to the range of the terahertz. Some self-assembled nanostructures exist that exhibit similar shapes and properties to those of traditional antenna structures. In this work the emission and absorption properties of self-assembled nanostructures made of zinc oxide nanorods on silver nanowires, which resemble traditional dipole antennas, were measured and simulated in order to test their antenna performance. These structures show resonant properties in the 10-120 THz range, with the main resonance at 60 THz. The radiation pattern of these nanostructures was also obtained by numerical simulations, and it is shown that it can be tailored to increase or decrease its directivity as a function of the location of the energy source of excitation. Experimental measurements were performed by Raman spectroscopy and Fourier Transform Infrared Spectroscopy (FTIR) in order to show existing vibrational frequencies at the resonant frequencies of the nanostructures, measurements were made from ~9 to 103 THz and the results were in agreement with the simulations. These characteristics make these metal-semiconductor Ag/ZnO nanostructures useful as self-assembled nanoantennas in applications such as terahertz spectroscopy and sensing at terahertz frequencies.

The mechanical properties of different high impact polystyrene (HIPS) were determined by means of impact and tensile tests. Impact strength (IS), yield stress (σy) and Young’s modulus (E) were evaluated as a function of the rubber phase morphological features such as type and particle size (Dp), volume fraction (Φ) and interparticle distance (IPD). In order to evaluate the changes produced in the rubber phase, the initiator, chain transfer agent (CTA), and type and concentration of SB copolymer were varied during the synthesis of HIPS. Transmission electron microscopy was used to analyze the materials’ morphology and the data obtained reveal that the Dp and Φ increases mainly with an increase in the PB content and/or with the use of CTA and decreases with an increase in initiator concentration. In addition, E and yield stress diminishes when increasing the dimensions of the rubber phase (Dp and Φ), contrary to the IS. The IPD/Dp ratio also indicates the dependency of the mechanical properties with respect to the rubber phase features. An increase in IPD/Dp provokes an increases in E and σy, whereas IS diminishes.