Effect of Fiber Sizing Levels on the Mechanical Properties of Carbon Fiber-Reinforced Thermoset Composites.

Fiber sizing is one of the most important components in manufacturing composites by affecting mechanical properties, including strength and stiffness. The sizing of manmade fibers offers many advantages, such as improving fiber/matrix adhesion and bonding properties, protecting fiber surfaces from damage during the processing and weaving stages, and enhancing the surface wettability of polymer matrices. In this work, the influence of fiber sizing levels on carbon fibers' (CFs) mechanical properties is reported at room temperature using single fiber tensile testing (Favimat+), single fiber pullout testing (SFPO), and interfacial elemental analysis by X-ray photoelectron spectroscopy (XPS). Standard modulus CFs (7 ± 0.2 µm in diameter) were sized using two commercially available Michelman sizing formulations. The average solid content for each sizing formulation was 26.3 ± 0.2% and 34.1 ± 0.2%, respectively. HEXION RIMR 135 with curing agent RIMH 137 was used as a model thermoset epoxy matrix during SFPO measurements. A predictive engineering fiber sizing methodology was also developed. Sizing amounts of 0.5, 1, and 2 wt.% on the fiber surface were achieved for both sizing formulations. For each fiber size level, 50 single-fiber tensile testing experiments and 20 single-fiber pull-out tests were conducted. The ultimate tensile strength (σult) of the carbon fibers and the interfacial shear strength (τapp) of the single fiber composite were analyzed. The sizing levels' effect on interfacial shear stress and the O/C (Oxygen/Carbon) surface composition ratio was investigated. Based on our experimental findings, an increase of 6% in fiber performance was recorded for ultimate tensile and interfacial shear strengths. As a result, generalized fiber sizing and characterization methods were established. These developed methods can be used to characterize the strength and interfacial shear strength of manmade fibers with different sizing formulations and solid contents irrespective of the matrix, i.e., thermoset or thermoplastic.

Anomalous Li Storage Capability in Atomically Thin Two-Dimensional Sheets of Nonlayered MoO2.

Since the first exfoliation and identification of graphene in 2004, research on layered ultrathin two-dimensional (2D) nanomaterials has achieved remarkable progress. Realizing the special importance of 2D geometry, we demonstrate that the controlled synthesis of nonlayered nanomaterials in 2D geometry can yield some unique properties that otherwise cannot be achieved in these nonlayered systems. Herein, we report a systematic study involving theoretical and experimental approaches to evaluate the Li-ion storage capability in 2D atomic sheets of nonlayered molybdenum dioxide (MoO2). We develop a novel monomer-assisted reduction process to produce high quality 2D sheets of nonlayered MoO2. When used as lithium-ion battery (LIB) anodes, these ultrathin 2D-MoO2 electrodes demonstrate extraordinary reversible capacity, as high as 1516 mAh g-1 after 100 cycles at the current rate of 100 mA g-1 and 489 mAh g-1 after 1050 cycles at 1000 mA g-1. It is evident that these ultrathin 2D sheets did not follow the normal intercalation-cum-conversion mechanism when used as LIB anodes, which was observed for their bulk analogue. Our ex situ XPS and XRD studies reveal a Li-storage mechanism in these 2D-MoO2 sheets consisting of an intercalation reaction and the formation of metallic Li phase. In addition, the 2D-MoO2 based microsupercapacitors exhibit high areal capacitance (63.1 mF cm-2 at 0.1 mA cm-2), good rate performance (81% retention from 0.1 to 2 mA cm-2), and superior cycle stability (86% retention after 10,000 cycles). We believe that our work identifies a new pathway to make 2D nanostructures from nonlayered compounds, which results in an extremely enhanced energy storage capability.

Photonic crystal fiber for efficient Raman scattering of CdTe quantum dots in aqueous solution.

A novel hollow-core photonic crystal fiber platform was used for the first time to observe clear vibrational modes of the CdTe core, CdS(0.7)Te(0.3) interface, and carboxylate-metal complexes in dilute aqueous CdTe quantum dot (QD) solutions. These modes demonstrate the presence of crystalline cores, defects, and surface passivation responsible for photoluminescent efficiency and stability. In addition, 3-mercaptopropionic acid (MPA)-capped QDs show higher crystallinity and stability than those capped with thioglycolic acid (TGA) and 1-thioglycerol (TG). This detailed, nondestructive characterization was carried out using Raman spectroscopy for solutions with QD concentration of 2 mg/mL, which is similar to their concentration during synthesis process. This platform can be extended to the in situ studies of any colloidal nanoparticles and aqueous solutions of relevant biological samples using Raman spectroscopy.

Influence of nonadiabatic annealing on the morphology and molecular structure of PEDOT-PSS films.

The effect of nonadiabatic annealing on poly(3,4-ethylendioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS) thin films prepared on silicon substrate has been investigated by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). The analysis indicates the formation of an annealing-induced doping in PEDOT structure, suggesting a modification of the polymer electronic structure and the formation of a PEDOT-rich film surface.

Synthesis and characterization of ruthenium bis-bipyridine mono- and disulfinato complexes.

Reaction of cis-Ru(bpy)(2)Cl(2) with 1,2-benzenedithiol afforded a monosulfhydryl-monosulfinate complex, [Ru(bpy)(2)(S.SO(2))] (1). Complex 1 readily undergoes oxidation when treated with 30% H(2)O(2) and also upon exposure to atmospheric O(2) (rapidly in bright light) to afford the disulfinate complex, [Ru(bpy)(2)(SO(2.)SO(2))] (2). Complexes 1 and 2 were studied using various analytical techniques including elemental analysis, UV-vis, mass spectroscopy, NMR, IR spectroscopy, cyclic voltammetry, X-ray crystallography (for 2). Density functional theory computation was employed with extended charge decomposition and natural population analyses. The agreement between the observed electronic spectrum and that predicted by time dependent DFT, and between the observed infrared spectrum and that predicted by DFT, is truly exceptional. These molecules are relevant to the very unusual active site in the metalloenzyme nitrile hydratase.

Chemically stable silver nanoparticle-crosslinked polymer microspheres.

Stabilization of metal nanoparticles (MNP) is a prerequisite for any application in sensor design, optoelectronics, catalysis, spectroscopic labeling, and nanomedicine. However, MNPs produced by most currently available synthetic approaches tend to undergo aggregation into large clusters, thus reducing their accessibility and compromising properties associated with their nanoscale dimensions. To circumvent the agglomeration problem and enhance their chemical and physical stability, we developed an efficient strategy for the preparation of MNP/polymer composites in which silver nanoparticles coated with 4-mercaptomethylstyrene act as crosslinkers in a suspension polymerization. The resulting microspheres were characterized by Raman, SERS and XPS spectroscopies, DSC, SEM and TEM. Their chemical and physical stability was also established.

Nanotemplating for two-dimensional molecular imprinting.

A new 2D molecular imprinting technique based on nanotemplating and soft-lithography techniques is reported. This technique allows the creation of target-specific synthetic recognition sites on different substrates using a uniquely oriented and immobilized template and the attachment of a molecularly imprinted polymer on a substrate. The molecularly imprinted polymer was characterized by AFM, fluorescence microscopy, and ATR-FTIR. We evaluated the rebinding ability of the sites with theophylline (the target molecule). The selectivity of the molecularly imprinted polymer was determined for the theophylline-caffeine couple. The molecularly imprinted polymer exhibited selectivity for theophylline, as revealed by competitive rebinding experiments. Fluorescence microscopy experiments provided complementary proof of the selectivity of the molecularly imprinted polymer surfaces toward theophylline. These selective molecularly imprinted polymers have the potential for chemical sensor applications. Because of its 2D nature, this novel chemical sensor technology can be integrated with many existing high-sensitivity multichannel detection technologies.

The very covalent diammino(o-benzoquinonediimine) dichlororuthenium(II). An example of very strong pi-back-donation.

The syntheses and X-ray structures of the complexes Ru(S-dmso)Cl2(opda) (1) and Ru(NH3)2Cl2(bqdi) (2) are described (opda= o-phenylenediamine, bqdi= o-benzoquinonediimine). Optical absorption and emission, vibrational (resonance Raman), and electrochemical data are discussed. We explore the nature of the ruthenium benzoquinone electronic interaction in species 2 primarily within the framework of density functional theory (DFT) but also using INDO/S to extract Coulombic and exchange integrals. The resonance Raman and emission data were understood in terms of a common set of coupled vibrations localized primarily within the ruthenium metallacycle ring. Experimental and computational data were also compared among a select group of ruthenium bqdi species with other spectator ligands, specifically ammonia, 2,2'-bipyridine, and 2,4-pentanedione. The changes in the electrochemistry, optical spectroscopy, and vibrational spectra with changing spectator ligand donicity were explained within a common theoretical (DFT) model which further provided a detailed analysis of the variation in the molecular orbital descriptions. With the application of an extended charge decomposition analysis (ECDA), a detailed picture emerged of the bonding between the bqdi ligand and the metal atom, illustrating the coupling between the orbitals of each fragment as a function of orbital symmetry and charge transfer between the fragments of the complex. Metal-to-bqdi pi-back-donation is seen to be very important.

Biodegradable open cell foams of telechelic poly(epsilon-caprolactone) macroligand with ruthenium (II) chromophoric subunits via sub-critical CO2 processing.

This work reports on the effect of CO2 at subcritical conditions and the gaseous state on the telechelic poly(epsilon-caprolactone) polymers. The tested polymers are semi-crystalline in nature and thus the effect of functional groups and their overall contribution to foaming and formation of microstructures with open-cell morphollogy is discussed.

Microwave synthesis of polymer-embedded Pt-Ru catalyst for direct methanol fuel cell.

Platinum-ruthenium nanoparticles stabilized within a conductive polymer matrix are prepared using microwave heating. Polypyrrole di(2-ethylhexyl) sulfosuccinate, or PPyDEHS, has been chosen for its known electrical conductivity, thermal stability, and solubility in polar organic solvents. A scalable and quick two-step process is proposed to fabricate alloyed nanoparticles dispersed in PPyDEHS. First a mixture of PPyDEHS and metallic precursors is heated in a microwave under reflux conditions. Then the nanoparticles are extracted by centrifugation. Physical characterization by TEM shows that crystalline and monodisperse alloyed nanoparticles with an average size of 2.8 nm are obtained. Diffraction data show that crystallite size is around 2.0 nm. Methanol electro-oxidation data allow us to propose these novel materials as potential candidates for direct methanol fuel cells (DMFC) application. The observed decrease in sulfur content in the polymer upon incorporation of PtRu nanoparticles may have adversely affected the measured catalytic activity by decreasing the conductivity of PPyDEHS. Higher concentration of polymer leads to lower catalyst activity. Design and synthesis of novel conductive polymers is needed at this point to enhance the catalytic properties of these hybrid materials.