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This study investigated the use of quartz fiber as an antenna radome and a dielectric substrate for a patch antenna designed to operate at f=8 GHz. To compare the performance of quartz fiber as an antenna radome, glass fiber is examined for the same antenna. For the substrate case, quartz fiber is compared with the well-known and widely used dielectric substrate, FR-4. The electromagnetic properties of the quartz fiber were examined for different temperature values using a free space measurement setup and a controllable furnace. The complex electrical permittivity (ε) values of glass and quartz fiber are measured using a free-space setup. The antenna parameters, including radiation pattern, gain, return loss, and beamwidth, are investigated and compared in detail for all cases to demonstrate the effects of the use of quartz fiber as a radome and an antenna substrate

In this study, dual-band frequency selective surface (FSS) structures are designed by using 3-D printing technology for antenna radome applications. Four different configurations are studied to find the best candidate for FSS substrate not only for electromagnetic (EM) responses but also for its mechanical properties suitable for radomes. To ease the manufacturing process, a conductive paint is also studied instead of copper microstrip lines. In addition, graphite is also used for the comparison. Different 3-D printed configurations, various thickness values and three different material for conductive part are examined and compared to find the most efficient radome structure.

The effective, high-value reutilization of reclaimed rubber, obtained from end-of-life tires, in the production of new high-performance tires remains an environmental and technological challenge. Cryogenically ground micron-sized rubber particles demonstrate a significant promise to realize satisfactory physical performance measures in reclaimed rubber-based tires. However, the maximum useable content of the cryogenically ground micron-sized rubber particles to be incorporated into tires is strictly limited by their ineffective interfacial chemical interactions with the host pristine rubber matrix during the post-polymerization process. Here, this work presents the non-covalent chemical functionalization of the cryogenically ground micron-sized styrene-butadiene rubber particles with reactive silica particles via a solid-state cryogenic mixing process. The highly-scalable solid-state mixing process enables the sufficiently uniform and near-homogenous distribution of the silica particles on the micron-sized rubber particles. Scanning electron microscope images highlight the micron-sized rubber particles decorated with individual silica particles. Fourier transform infrared and solid-state nuclear magnetic resonance spectra of the functionalized micron-sized rubber particles demonstrate a non-covalent conjugation mechanism between the silica and rubber particles in which the chemical fingerprint of the prime rubber backbone chains remains chemically intact. The chemically functionalized cryogenically ground micron-sized rubber particles possess reactive silica particle sites that are ultimately designed to facilitate the participation of the recycled rubber particles in post-polymerization processes with host matrix which shall allow higher loading levels than the state-of-the-art configurations.

The aromatic thermosetting copolyester (ATSP) was deposited on p-Si substrates by the spin coating method, and the thickness of thin film layer was about 50 nm. It was employed to fabricate metal-polymer-semiconductor (MPS) heterojunctions as interfacial layers between metal contact and p type Si. The morphological properties of the Al/ATSP/p-Si heterojunctions were investigated by Scanning Electron Microscope (SEM) and an Atomic Force Microscope. The electrical characteristics of the heterojunctions were analyzed within a wide temperature range between 100 K and 500 K and frequency range. The current–voltage–temperature (I–V–T) characteristics of the MPS heterojunctions were explained by the Thermionic Emission (TE) theory and Norde function. Critical electrical parameters including leakage current (I0), barrier height (Φb) and ideality factor (n) and series resistance (Rs) were calculated by I–V–T characteristics in dark conditions. The value of n and Φb was obtained as 2.56 and 0.78 eV at 300 K. The n and Φb values were obtained as strong function of the temperature depending on barrier inhomogeneity. The temperature dependent rectification ratios of the Al/ATSP/p-Si heterojunctions were calculated and discussed in the details considering effective operating temperatures. The capacitance–voltage (C–V) and conductance–voltage (G–V) characteristics were measured at 300 K. To obtain Fermi energy (EF), donor concentration (Na), maximum electric field (Em), Φb and interface states (Nss), were performed on the bases of voltage and frequency at 300 K. From the electrical analysis results, it is proposed that the MPS device can be employed in electronic devices at low and high temperatures.

The current trend in the global advanced material market is expeditiously shifting towards more lightweight, multifunctional configurations, considering very recent developments in electrical aircraft, biomedical devices, and autonomous automobiles. Hence, the development of novel polymer nanocomposite materials is critical to advancing the current state-of-the-art of structural material technologies to address the pressing performance demands. Aiming at expanding the existing material design space, we have investigated crosslinkable aromatic polyester matrix nanocomposites. Aromatic polyesters, in the thermosetting form, are a prospective high-performance/high-temperature polymer technology, which is on a par with conventional epoxy-derivative resins and high-performance engineering thermoplastics in the range of their potential applications. The aromatic matrix-based thermosetting nanocomposites manifest greatly enhanced physical properties enabled by a chemistry-favored robust interfacial covalent coupling mechanism developed during the in situ polymerization reaction with various nanofiller particle configurations. Here, we provide a summary review of our recent efforts in developing this novel polymer nanocomposite material system. We highlight the chemical strategy, fabrication approach, and processing techniques developed to obtain various nanocomposite representations for structural, electrical, optical, biomedical, and tribological applications. The unique characteristic features emerging in the nanocomposite morphologies, along with their physicochemical effects on the multifunctional macroscale properties, are demonstrated. This unique matrix configuration introduces superior performance elements to polymer nanocomposite applications towards designing advanced composite materials.

The recent invention of a new processing method for metals and alloys involving the addition of carbon has led to several reports demonstrating an enhancement in the mechanical properties of the materials known as “covetics.” In this work the corrosion behavior and mechanical properties of a 6061 aluminum–carbon covetic are investigated and explained. Covetic samples with carbon added were found to exhibit a corrosion potential 40–70 mV higher than samples processed without the addition of carbon. However, the corrosion current density of the covetic with carbon added relative to samples without carbon added was also increased. Surface characterization following the corrosion testing using scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction revealed significant differences between the covetic with carbon added and the covetic parent material processed without carbon addition. After corrosion, the surface of the covetic with carbon added showed a alloying element rich surface morphology from the parent alloy and exhibited a smaller grain size than the material processed without carbon. Additionally, changes in the mechanical properties of the covetic were observed with both the hardness and the compressive strength of the covetic increasing as a result of carbon addition. The observed change in corrosion behavior and mechanical properties of the covetic with carbon added, along with the physical characterization, are consistent with the formation of a secondary phase in the alloy induced by carbon addition during the process used to make the covetic.

The glass transition is a genuine imprint of temperature‐dependent structural relaxation dynamics of backbone chains in amorphous polymers, which can also reflect features of chemical transformations induced in macromolecular architectures. Optimization of thermophysical properties of polymer nanocomposites beyond the state of the art is contingent on strong interfacial bonding between nanofiller particles and host polymer matrix chains that accordingly modifies glass transition characteristics. Contemporary polymer nanocomposite configurations have demonstrated only marginal glass transition temperature shifts utilizing conventional polymer matrix and functionalized nanofiller combinations. We present nanofiller‐contiguous polymer network with aromatic thermosetting copolyester nanocomposites in which carbon nanofillers covalently conjugate with cure advancing crosslinked backbone chains through functional end‐groups of constituent precursor oligomers upon an in situ polymerization reaction. Via thoroughly transformed backbone chain configuration, the polymer nanocomposites demonstrate unprecedented glass transition peak broadening by about 100 °C along with significant temperature upshift of around 80 °C. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 1595–1603

Aromatic thermosetting copolyester (ATSP) enables high- to low-k tunability as well as providing reliable thermomechanical performance from cryogenic to elevated temperatures, so it is a promising polymer system for silicon-based microelectronics and spacecraft applications. Here we reported on imparting strong photoluminescence to otherwise weak luminescent ATSP matrix by incorporating H-terminated Si nanoparticles (Sinps) to obtain luminescent polymer nanocomposites without degenerating the polymer backbone chain configuration. We employed photoluminescence and ultraviolet-visible (UV-Vis) spectroscopies along with electron microscopy analysis to characterize pre- and post-thermal polymerization processes. In the pre-polymerization stage, a size-dependent convection-like motion was observed in a liquid medium under thermal gradient, which caused the nanocomposites to accumulate and be trapped. Scanning electron microscope (SEM) images revealed the formation of 2-D nanosheets, as small as 50–100 nm, decorated with 10–15 nm size complexes of Sinps and oligomers. The post-polymerization analysis showed that the Sinps homogenously incorporated, with insignificant aggregation, into the polymerization process as a secondary cross-linker neither losing their red-luminescence functionality nor deteriorating the physical properties of the ATSP matrix. Chain relaxation characteristics, measured by dynamic mechanical analysis (DMA), in the glass transition regime likewise indicated the effective conjugation of the Sinps with the cross-linked polymer backbone. The ATSP–Sinps composite structure manifested bandgap imprints of both Sinps and ATSP in the ultraviolet–visible spectral region. Via superb thermomechanical properties enriched with luminescence, the ATSP–Sinps nanocomposite may potentially afford UV shielding to mitigate photo-degradation and enhance operational efficiency for photonics applications.

Aromatic thermosetting copolyester (ATSP) has been recently introduced, which exhibits promising thermal, mechanical, and adhesive properties to address broad range of industrial applications. However, the ATSP resin has not been well described in terms of electronic properties. Hence, we used a thin film of ATSP as an interfacial layer between a metal and a semiconductor to control the properties of the metal-semiconductor contacts. In this study, ATSP oligomers were dissolved in tetrahydrofuran (THF) and multiple layers were deposited on a p-type Si wafer in thin film form by spin-coating technique. To obtain the metal and semiconductor device (Al/ATSP/p-type Si), Al was sputtered on the back surface of Si wafer as an Ohmic contact and the front surface as a rectifying contact. Morphological properties of the ATSP thin film were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Transmittance and band gap values of the ATSP thin film were determined by ultraviolet-visible (UV–Vis) spectrometry. Al/ATSP/p-type Si devices were characterized with I-V measurements under dark condition and with light illumination. These devices can potentially be developed for use as rectifiers and photodiodes.

This paper focuses on the effects of cyclic water immersion and salt spray aging tests on the physical properties of aromatic thermosetting copolyester (ATSP) matrix. Neat and graphene nanoplatelet (GNP) incorporated nanocomposite ATSP foam morphologies are employed to have enhanced surface areas exposed to the surrounding aqueous media, via porous configurations, which deliberately aggravate the extent of the aging on the matrix. The ATSP foams are fabricated through a thermal condensation polymerization process. Upon exposures to the periodic aging conditions, ATSP demonstrates an adsorption-regulated mass uptake mechanism. Contact angle measurements reveal GNP-neutral and hydrophobic characteristics for the ATSP matrix. Microstructural imaging exhibits no substantial physical degeneration in the matrix caused by the accelerated aging conditions. Glass transition temperatures of both neat and nanofiller incorporated ATSP forms display only marginal decreases stemmed from small volumes in the matrix occupied through the hygroscopic swelling. Thermal degradation stability of the ATSP morphology is effectively preserved following the aging processes. Compressive mechanical strengths of the foams lie within the regime of their virgin (not exposed to the aging conditions) counterparts yet show slight reductions. The ATSP matrix demonstrates an outstanding aging resistance to the subjected environments which can potentially address high-performance requirements in cutting-edge industrial applications.

In this study, we present carbon nanoparticle incorporated high-performance aromatic thermosetting copolyester (ATSP) nanocomposite foams. The ATSP nanocomposite foams were fabricated through a facile solid-state mixing method wherein carboxylic acid and acetoxy-functional group oligomers were initially combined with chemically pristine carbon nanofillers separately, while in powder form. The mixtures were then subjected to a thermal condensation polymerization reaction in which the constituent oligomers formed the ester backbone of the ATSP matrix and advanced the molecular weight while acetic acid was emitted as the by-product, and generated a porous nanocomposite morphology. As compared to a neat ATSP foam, the nanocomposite foams exhibited a reduced coefficient of thermal expansion by 25% to 75 × 10 −6 °C −1 . Thermal stability temperature at 5% mass loss was increased by 30 °C exceeding 500 °C. Compressive mechanical strength was enhanced two-fold, reaching 16 MPa along with a nearly doubled fracture strain, which ultimately yielded improved material toughness.

WOS: 000399499000074, In this work, we introduce a three-layer sandwich composite structure having an aromatic thermosetting copolyester (ATSP) foam core with two aluminum foam face layers joined together by an in situ generated foaming mechanism. The ATSP foam core was synthesized on-site between the aluminum foam layers via a heat-induced polycondensation reaction. Upon curing, the ATSP foam core adhered to the aluminum foam layers through an interfacial compatibility-enabled chemical bonding. Lap shear experiments demonstrated that the bond strength clearly surpassed the tensile performance of the bare aluminum foam parts. Drop-weight impact tests showed that the three-layer sandwich structure could absorb four times the impact energy as compared to the bare aluminum foam of the same overall thickness. (C) 2017 Elsevier B. V. All rights reserved., National Science Foundation (NSF) I/UCRC [IIP-1362146], We sincerely thank Dr. David Farrow for helping with the experiments. We gratefully acknowledge funding from the National Science Foundation (NSF) I/UCRC grant (IIP-1362146). The findings, conclusions, and recommendations expressed in this manuscript are those of the authors and do not necessarily reflect the views of the NSF.

In this paper, three types of triply periodic minimal surfaces (TPMS) are utilized to create novel polymeric cellular materials (CM). The TPMS architectures considered are Schwarz Primitive, Schoen IWP, and Neovius. This work investigates experimentally and computationally mechanical properties of these three TPMS-CMs. 3D printing is used to fabricate these polymeric cellular materials and their base material. Their properties are tested to provide inputs and serve as validation for finite element modeling. Two finite deformation elastic/hyperelastic-viscoplastic constitutive models calibrated based on the mechanical response of the base material are used in the computational study of the TPMS-CMs. It is shown that the specimen size of the TPMS-CMs affect their mechanical properties. Moreover, the finite element results agree with the results obtained experimentally. The Neovius-CM and IWP-CM have a similar mechanical response, and it is found that they have higher stiffness and strength than the Primitive-CM. Keywords: Architectured materials, 3D printing, Mechanical testing, Polymeric cellular materials, Finite element analysis

This work presents a unique chemical strategy and a facile fabrication scheme toward development of novel aromatic thermosetting copolyester foams. Designed aromatic-based acetoxy and carboxylic acid end-group oligomers carry out an endothermic condensation polymerization reaction, which self-generates acetic acid blowing agent forming macrocellular porous morphology within cross-linked ester backbone polymer matrix. Herein, we provide a visual insight into the foaming reaction between the constituent oligomer groups via optical micrographs captured at polymerization phase transformation stages; oligomer melt-compounding, bubble nucleation via release of gaseous acetic acid, and subsequently bubble growth at elevated temperatures. Furthermore, we show cure and postcure characteristics of the constituent oligomers in the course of the foaming reaction that the most favorable pair of cure temperature and cure time is determined. Then, combining these outcomes, we design an optimum cure cycle and fabrication...

Development of porous materials consisting of polymer host matrix enriched with bioactive ceramic particles that can initiate the reproduction of cellular organisms while maintaining in vivo mechanical reliability is a long-standing challenge for synthetic bone substitutes. We present hydroxyapatite (HA) reinforced aromatic thermosetting copolyester (ATSP) matrix bionanocomposite as a potential reconfigurable bone replacement material. The nanocomposite is fabricated by solid-state mixing a matching set of precursor oligomers with biocompatible pristine HA particles. During endothermic condensation polymerization reaction, the constituent oligomers form a mechanochemically robust crosslinked aromatic backbone while incorporating the HAs into a self-generated cellular structure. The morphological analysis demonstrates near-homogenous distributions of the pristine HAs within the matrix. The HAs behave as a crack-arrester which promotes a more deformation-tolerant formation with relatively enhanced material toughness. Chain relaxation dynamics of the nanocomposite matrix during glass transition is modified via HA-induced segmental immobilization. Chemical characterization of the polymer backbone composition reveals the presence of a hydrogen-advanced covalent interfacial coupling mechanism between the HAs and ATSP matrix. This report lays the groundwork for further studies on aromatic thermosetting copolyester matrix bionanocomposites which may find applications in various artificial bone needs.

Deliberately controlled interfacial interactions between incorporated nanofiller particles and host polymer backbone chains constitute a critical element in the realm of polymer nanocomposites with tailorable multifunctional properties. We demonstrate the physicochemical effects induced by graphene nanoplatelets (GNP) of different sizes on the condensation polymerization reaction of aromatic thermosetting copolyester (ATSP) through the formation of electrically conductive percolating networks as enabled by interfacial interactions. Carboxylic acid and acetoxy-capped precursor oligomers of ATSP are solid-state mixed with chemically pristine GNP particles at various loading levels. Upon in situ endothermic condensation polymerization reaction, crosslinked backbone of the ATSP foam matrix is formed while the carbonaceous nanofillers are incorporated into the polymer network via covalent conjugation with functional end-groups of the oligomers. The controlled GNP size promotes different electrical percolation thresholds and ultimate electrical conductivities. Microstructural analysis demonstrates GNP distributions in the matrix as well as morphological modifications induced by the formation of conductive percolating GNP networks. Cure characteristics reveal the thermochemical changes prompted in the polymerization processes for GNP content above the requirement for percolation formation. Chemical spectroscopy of the ATSP nanocomposite morphology exhibits the formation of a robust interfacial coupling mechanism between the GNPs and ATSP backbone. The findings here may guide the developmental efforts of nanocomposites through better identifying roles of the morphology and content of nanofillers in polymerization processes.

This paper reports the development of microcantilevers capable of self-heating and Lorentz-force actuation, and demonstrates applications to thermal topography imaging. Electrical current passing through a U-shaped cantilever in the presence of a magnetic field induces a Lorentz force on the cantilever free end, resulting in cantilever actuation. This same current flowing through a resistive heater induces a controllable temperature increase. We present cantilevers designed for large actuation forces for a given cantilever temperature increase. We analyze the designs of two new cantilevers, along with a legacy cantilever design. The cantilevers are designed to have a spring constant of about 1.5 N m(-1), a resonant frequency near 100 kHz, and self-heating capability with temperature controllable over the range 25-600 °C. Compared to previous reports on self-heating cantilevers, the Lorentz-thermal cantilevers generate up to seven times as much Lorentz force and two times as much oscillation amplitude. When used for thermal topography imaging, the Lorentz-thermal cantilevers can measure topography with a vertical resolution of 0.2 nm.