Vacuum-processed polyethylene as a dielectric for low operating voltage organic field effect transistors

We report on the fabrication and performance of vacuum-processed organic field effect transistors utilizing evaporated low-density polyethylene (LD-PE) as a dielectric layer. With C₆₀ as the organic semiconductor, we demonstrate low operating voltage transistors with field effect mobilities in excess of 4 cm²/Vs. Devices with pentacene showed a mobility of 0.16 cm²/Vs. Devices using tyrian Purple as semiconductor show low-voltage ambipolar operation with equal electron and hole mobilities of ～0.3 cm²/Vs. These devices demonstrate low hysteresis and operational stability over at least several months. Grazing-angle infrared spectroscopy of evaporated thin films shows that the structure of the polyethylene is similar to solution-cast films. We report also on the morphological and dielectric properties of these films. Our experiments demonstrate that polyethylene is a stable dielectric supporting both hole and electron channels.     

Mechanical properties and repair bond strength of polymer-based CAD/CAM restorative materials

Information on the mechanical properties and repairability of computer-aided design/computer-aided manufacturing (CAD/CAM) blocks is scarce. Five CAD/CAM blocks with similar indications were evaluated, including four resin nanoceramics, one polymer-infiltrated ceramic network (PICN), and one feldspathic ceramic. CAD/CAM blocks were sectioned into 4 mm × 1.2 mm × 13 mm bars for flexural strength (FS), and 4 mm thick blocks were prepared for elastic modulus (EM), nanohardness (NH), and microshear bond strength (µSBS) testing. FS of the CAD/CAM blocks was determined using a three-point bending test, whereas EM and NH values were measured using a nanoindenter. The reparability of the tested block materials was determined by the µSBS test. One-way ANOVA was conducted for FS, EM, NH, and µSBS followed by Tukey's pairwise comparison (α < 0.05). FS ranged from 115 to 207 MPa, EM from 8.21 to 44 GPa, NH from 0.76 to 7.24, and µSBS from 24.9 to 30.6 MPa. The findings of the present study revealed that resin nanoceramic blocks exhibited higher FS values than PICN and feldspathic ceramic, and they have acceptable mechanical properties for the fabrication of single-unit restorations according to the ISO 6872:2008. Furthermore, all CAD/CAM blocks tested can be successfully repaired regarding their recommended repair protocol.     

Synthesis and characterization of poly(dimethylsiloxane)–polythiophene composites

The synthesis was performed by the electropolymerization of thiophene on a poly(dimethylsiloxane) (PDMS)‐coated platinum electrode at 2.2 V with tetrabutylammoniumtetrafloroborate (TBAFB) as a supporting electrolyte and with acetonitrile as a solvent. The characterization of the PDMS–polythiophene (Pth) composites was carried out with cyclic voltammetry, Fourier transform infrared (FTIR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis, and conductivity measurements. The observed conductivities of the PDMS composites were 2.2–5.2 S/cm. The conductivity of Pth did not change appreciably with the addition of up to 30% insulating PDMS, but its processability improved. FTIR, SEM, and DSC studies showed the existence of a strong interaction, rather than physical adhesion, between PDMS and Pth. Highly flexible and foldable PDMS–Pth composites were obtained. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2113–2119, 2003     

Preparation and characterization of phosphine oxide containing organosilica hybrid coatings by photopolymerization and sol–gel process

A series of UV-cured organic–inorganic hybrid coating materials containing up to 20 wt.% silica were prepared by sol–gel method from tetraethoxy silane (TEOS) which is used as the primary inorganic precursor, and diallylphenylphosphine oxide monomer (DAPPO), aliphatic urethane diacrylate resin (Ebecryl 210) are employed as the source of the organic components. In addition, methacryloxypropyltrimethoxy silane (MAPTMS) was used as both a secondary inorganic source and a silane-coupling agent to improve the compatibility of the organic and inorganic phases. The DAPPO content in all the coating formulations were from 0 to 20 wt.%. The physical and mechanical properties such as gel content, hardness, adhesion, gloss, contact angle as well as tensile strength were measured. These measurements revealed that all the properties of the hybrid coatings improved effectively, in case of adding the sol–gel precursor and DAPPO monomer content in the hybrid systems. The photo-calorimetric-DSC studies showed that the double bond conversion of the hybrid coatings was faster than the coating materials without silica. The thermal stabilities of the UV-cured hybrid materials were investigated by thermogravimetric analysis. The results showed that the addition of sol–gel precursor and DAPPO into the organic network also improves the thermal-oxidative stability of the hybrid coating materials. The surface morphology was also characterized by scanning electron microscopy (SEM). SEM studies indicated that inorganic particles were dispersed homogenously throughout the organic matrix.     

Characterization and electrical conductivity of poly(ethylene glycol)/polyacrylonitrile/multiwalled carbon nanotube composites

Poly(Lactic acid) (PLA)‐layered silicate nanocomposite films were prepared by solvent casting method. The films were irradiated with Co⁶⁰ radiation facility at dose of 30 kGy. The effect of γ irradiation on mechanical properties of the neat PLA and nanocomposites was evaluated by data obtained from tensile testing measurements. The tensile strength of the irradiated PLA films increased with addition of 1 wt % triallyl cyanurate indicating crosslink formation. Significant ductile behavior was observed in the PLA nanocomposites containing 4 pph of nanoclay. Incorporation of nanoclay particles in the PLA matrix stimulated crystal growth as it was studied by differential scanning calorimetry. The morphology of the nanocomposites characterized by transmission electron microscopy and X‐ray diffraction revealed an exfoliated morphology in the PLA nanocomposite films containing 4 pph of nanoclay. Only very small changes were observed in the chemical structure of the irradiated samples as it was investigated by Fourier transform infrared spectroscopy. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Remote-Controlled Ambidextrous Robot Hand Concept

In the development of robotic limbs, the side of members is of importance to define the shape of artificial limbs and the range of movements. It is mainly significant tbr biomedical applications concerning patients suffering arms or legs injuries, fn this paper, the concept of an ambidextrous design lbr robot hands is introduced. The fingers can curl in one xvay or another, to imitate either a right hand or a left hand. The advantages and inconveniences of different models have been investigated to optimise the range and the maximum force applied by fingers. Besides, a remote control interthce is integrated to the system, allowing both to send comrnands through internet and to display a video streaming of the ambidextrous hand as feedback. Therefore, a robotic prosthesis could be used for the first time in telerehabilitation. The main application areas targeted are physiotherapy alter strokes or management of phantom pains/br amputees by/earning to control the ambidextrous hand. A client application is also accessible on Facehook social network, making the robotic limb easily reachable for the patients. Additionally the ambidextrous hand can be used tbr robotics research as well as artistic performances.     

Efficacy of different surface treatments and universal adhesives on the microtensile bond strength of bulk-fill composite repair

Abstract

The purpose of this in vitro study was to evaluate the influence of different surface treatments and aging on the microtensile bond strength (μTBS) of bulk-fill composite resins. Bulk-fill composites (Filtek One; 3M ESPE) randomly received five different surface treatments: (1) no treatment, control, (2) 37% phosphoric acid etching (PA), (3) 9% hydrofluoric acid etching (HF), (4) air-borne particle abrasion with 50-μm alumina particles (Al₂O₃), (5) tribochemical silica coating (CoJet). Following, the specimens were divided into three subgroups according to universal adhesive applied: Clearfil Universal Bond (CU; Kuraray), Prime&Bond Universal (PBU; Dentsply Sirona), or Single Bond Universal (SBU; 3M ESPE). A nanofill composite (Filtek Ultimate; 3M ESPE) was employed as a repair. Bonded specimens were stored in water for 24?h at 37?°C or thermal aged, then subjected to the μTBS test. Additionally, specimens were analyzed with a contact profilometer and were evaluated with scanning electron microscopy. Control and PA treatments were showed the lowest µTBS (p?<?0.05), and there was no significant difference between these two groups (p?>?0.05). Al₂O₃ and CoJet treatments generally exhibited a similar influence on µTBS values. In addition, a correlation was found between surface roughness and bond strength (r?=?0.831). CoJet resulted in significantly higher repair µTBS values when compared to the other surface treatments. In addition, the use of silane-containing universal adhesive was increased the cohesive failure rate and maintained the repair µTBS values after thermocycling.     

A new approach to evaluate the MODIS annual NPP product (MOD17A3) using forest field data from Turkey

In this study, we present the first evaluation of the MODIS (Moderate Resolution Imaging Spectroradiometer) annual net primary production (NPP) for Turkey’s forest ecosystems using field measurements. Due to lack of country scale field measurements (i.e. flux tower for forest ecosystems), tree DBH (diameter at breast height) data set provided by Ministry of Forest and Water Affairs (MFWA) of Turkey is used to calculate NPP of Turkey’s forest ecosystems. The lack of a reliable NPP data set leads the researchers to use global NPP models such as MODIS annual NPP product. The MODIS MOD17A3 product of vegetation NPP is one of the most highly used data sources for studies of global carbon cycle. However, it is still necessary to test its predictions in multiple biomes, especially for heterogeneous areas in terms of its accuracy and potential bias. Here, we studied a new approach to evaluate coarse scale NPP estimates from the MODIS NPP-MOD17A3 data product, using 2008–2013 field measurements of tree growth throughout Turkey. Three different methods were used to calculate field NPP, including standardized growth coefficients (ministry coefficients [MC]), growth coefficients from North America (Jenkins coefficients [JC]), and annual expected increment (AEI). The average NPP values for all the country is calculated as 2.06 kgC m^–1/5 years (0.412 kgC m^–2 year^–1) (SD = 1.15 kgC m^–1/5 years) from MOD17A3, 0.90 kgC m^–1/5 years (0.18 kgC m^–2 year^–1) (SD = 0.57 kgC m^–1/5 years) with MC, 0.63 kgC m^–1/5 years (0.126 kgC m^–2 year^–1) (SD = 0.37 kgC m^–1/5 years) with JC and 0.58 kgC m^–2 year^–1 (SD = 0.29 kgC m^–1/5 years) with AEI for the studied plots. We found that the MODIS NPP product has a clear relation with both the NPP estimates obtained by using MC (R² = 0.34, root mean square error (RMSE) = 1.51 kgC m^–1/5 years) and JC (R² = 0.32, RMSE = 1.73 kgC m^–1/5 years). In addition to that, the relation between MOD17A3 product and AEI-derived NPP is relatively strong (R² = 0.48, RMSE = 0.26 kgC m^–2 year^–1). We discuss possible reasons for these trade-offs among different methods. This study lays out a new approach to validate coarse scale MODIS product using field data directly, including for highly heterogeneous areas.     

Conducting polymer composites of multiwalled carbon nanotube filled doped polyaniline

A multiwalled carbon nanotube (c‐MWNT)/polyaniline (PANI) composite was synthesized by an in situ chemical oxidative polymerization process. With the carbon nanotube loading increased from 0 to 30 wt %, the conductivity also increased and became weakly temperature‐dependent. Fourier transform infrared spectroscopy studies showed that the synthesis by an in situ process led to effective site‐selective interactions between the quinoid ring of the PANI and the multiwalled nanotubes, facilitating charge‐transfer processes between the two components. The morphological analysis indicated that the c‐MWNTs were well dispersed and isolated, and the tubes became crowded proportionally to the weight percentage of c‐MWNTs used in the composites. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009