Saint-Gobain (United States)

Abstract We review the literature concerned with the effect of proximity to a filler surface on the local segmental mobility of polymer chains. This mobility is commonly assessed from either the glass transition temperature, T g , or the segmental relaxation times measured by mechanical, dielectric, or NMR spectroscopy. Published studies report increases, decreases, or no change in T g upon the addition of carbon black, silica, and other reinforcing fillers. Similarly, the segmental relaxation times have been found to increase or be invariant to the presence of nanometer-sized particles. Some of these discrepancies can be ascribed to ambiguous methods of data analysis; others likely reflect the variation in filler-polymer interaction among different systems. There are unequivocal examples of polymers that have segmental dynamics and glass transitions unaffected by nano-particle reinforcement. However, the general principles governing the behavior remain to be clarified, with further work, focusing on the micromechanics at the particle interface, required for resolution of this important aspect of rubber science and technology.

An in-line rheometer has been incorporated into a fused deposition modeling printer for the first time by designing a modified nozzle with a custom pressure transducer and a thermocouple for measuring the processed melt temperature. Additionally, volumetric flow rates and shear rates were monitored by counting the stepper motor pulses as well as the pulses from a custom filament encoder to account for filament slippage and skipped motor steps. The incorporation of the sensors and the design and development of the in-line rheometer are described; and pressures, temperatures, and viscosities within the 3D printing nozzle are presented. The in-line rheometer was validated against traditional, off-line rotational rheology and capillary rheology measurements by analyzing two polymeric materials: polycarbonate and high-impact polystyrene. A variety of rheological corrections were considered for the in-line rheometer, including entrance effects, non-Newtonian corrections, shear heating, pressure effects, and temperature fluctuations/inaccuracies. Excellent agreement was obtained between the in-line and off-line rheometers after applying the most critical corrections, which were found to be entrance effects, non-Newtonian corrections, and temperature inaccuracies. After applying the appropriate corrections, the in-line rheometer provides an accurate viscosity measurement that can be used for real-time monitoring and process control.

Commercially available LaBr3:5% Ce3+ scintillators show with photomultiplier tube readout about 2.7% energy resolution for the detection of 662 keV γ-rays. Here we will show that by co-doping LaBr3:Ce3+ with Sr2+ or Ca2+ the resolution is improved to 2.0%. Such an improvement is attributed to a strong reduction of the scintillation light losses that are due to radiationless recombination of free electrons and holes during the earliest stages (1–10 ps) inside the high free charge carrier density parts of the ionization track.

Recent improvements in the growth and packaging of lanthanum bromide (LaBr/sub 3/), in addition to its superb intrinsic properties of high light output, excellent energy resolution, and fast decay time, make it a viable detection material for a positron emission tomography (PET) scanner based on time-of-flight (TOF). We have utilized theoretical simulations and experimental measurements to investigate the design and performance of pixelated LaBr/sub 3/ Anger-logic detectors suitable for use in a TOF PET scanner. Our results indicate that excellent energy resolution can be obtained from individual as well as multicrystal arrays of LaBr/sub 3/ in a 4 mm/spl times/4 mm /spl times/ 30 mm geometry. Measured energy resolutions (at 511 keV) of 4.1% for a single crystal and an average of 5.1% for an array of 100 crystals have been achieved with our best samples. Both simulations and experimental measurements of an Anger-logic based detector consisting of the LaBr/sub 3/ crystal array coupled to a continuous light guide and seven photomultiplier tubes (PMTs), have resulted in the ability to clearly discriminate 511 keV interactions in each crystal. We have measured coincidence time resolutions for both 0.5% and 5.0% cerium-doped LaBr/sub 3/ and found that the higher level of Ce-doping yielded superior results with little to no degradation in light output or energy resolution. The time resolution for a single 5.0% Ce-doped LaBr/sub 3/ crystal (4 mm /spl times/ 4 mm /spl times/ 30 mm) coupled directly to a PMT was measured to be 275 ps full-width at half-maximum (FWHM). With an array of 100 crystals coupled to a light guide and seven PMT cluster an average time resolution of 290 ps FWHM was obtained by summing the signals from the PMT cluster. Ultimately, two 5.0% Ce-doped LaBr/sub 3/ Anger-logic detectors placed in coincidence yielded a time resolution of 313 ps FWHM.

The effect of the surface charge of nucleation agents on the crystallization behavior of poly(vinylidene fluoride) (PVDF) has been investigated. Ion-dipole interaction between the positive surface of nucleation agents and the partially negative CF(2) dipoles of PVDF is established as a main factor for further lowering the free energy barrier for nucleation, and thus increasing significantly the crystallization kinetics. This is in contrast to the behavior observed for nucleation agents possessing either negative surface or neutral charges. Positive nucleation agents led to a remarkable increase in the crystallization temperature of PVDF (lower supercooling) as compared with that of neat PVDF. The dispersion of each type of nucleation agent is also important. The melting temperatures of nucleation agents need to be higher than the melting temperature of PVDF. The melting point and degree of crystallinity of PVDF can also be raised by using specific nucleation agents. The detailed crystallization kinetics and conformational changes of the PVDF chain have been investigated. With the addition of positive nucleation agents, the γ and β chain conformations, instead of the α phase, dominate.

A simple one-step approach to electrospin Type I collagen in the presence of the chemical crosslinking agents 1-ethyl-3-(3-dimethyl-aminopropyl)-1-carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) has been developed to generate water-insoluble collagen nanofiber scaffolds without the need for post-crosslinking. SEM images indicate that fibrous surface morphology of collagen scaffolds was well retained after the in situ crosslinking process and following water treatment. The resultant collagen demonstrated a similar uniaxial tensile behavior of native tissue in mechanical testing.

An in-line rheometer and data acquisition system are used to monitor the melt pressure, melt temperature, and environmental temperatures while producing parts via fused filament fabrication (FFF). Melt pressures are observed to increase when printing parts with small layer heights, which is attributed to the confined space created between the nozzle and the previous layer (i.e., an exit pressure). These exit pressures (referred to as contact pressure) and the resulting interlayer contact areas are analyzed for 2863 layers created at 21 different processing conditions. The measured contact pressure was found to directly influence the shape of the layers and the resulting interlayer contact. An intimate contact model based on contact pressure is combined with a wetting model to accurately predict the interlayer contact of FFF parts. This pressure-driven intimate contact model for FFF shows strong agreement with the observed interlayer contact. No theoretical model has previously existed for predicting interlayer contact, so this research provides a critical component for developing a comprehensive part strength model. Both the measurements and proposed model are sufficiently simple and accurate for real-time analysis of FFF quality, so the described in-line sensors provide valuable quality insights and are recommended for future researchers, printer manufacturers, and end-users.

Abstract The original flash sintering experiment was carried out by applying an electric field, and switching to current control at the onset of the flash, signaled by a rise in conductivity. Here, we consider experiments where the experiment is controlled from the very start, by injecting current, which is increased at a constant rate. The current rates are varied from 50 mA/min to 5000 mA/min. The experiment is continued until, in all cases, the current density reaches 100 mA/mm 2 . The total duration of the experiment ranged from approximately 7 seconds to 700 seconds. The following comparisons to the earlier voltage‐to‐current experiments are noted: (a) in both instances, the onset of the flash is signaled by an unusual rise in conductivity; however, since the power supply remains in the current control mode, the increase in conductivity is manifested by a drop in the voltage generated across the specimen; (b) the blackbody radiation model is modified to include the energy absorbed in specific heat, in order to determine the time‐dependent change in temperature as the current is increased—this correction is particularly significant at the very high current rates; (c) sintering occurs continuously, reaching full density, in all instances, when the current density reaches ~100 mA/mm 2 ; and (d) these early experiments suggest that the current‐rate experiments yield fine‐grained microstructure across the entire gauge section of the dog‐bone specimen, presumably because the highly transient conditions of voltage‐to‐current flash experiments are sidestepped. The experiments were carried out on 3 mol% yttria‐stabilized zirconia.

A uniform dispersion of reactants is necessary to achieve a complete reaction involving multicomponents. In this study, we have examined the role of plasticizer in the reaction of two seemingly unlikely reactants: a highly crystalline hexamethylenetetramine (HMTA) and a strongly hydrogen bonded phenol formaldehyde resin. By combining information from NMR, infrared spectroscopy and differential scanning calorimetry, we were able to determine the role of specific intermolecular interactions necessary for the plasticizer to dissolve the highly crystalline HMTA and to plasticize the phenol formaldehyde resin in this crosslinking reaction. The presence of the plasticizer increased the segmental mobility, disrupted the hydrogen bonded matrix, and freed the hydroxyl units, which further increased the solubility of the HMTA. Both the endothermic and exothermic transitions are accounted for in the calorimetric data obtained. For the first time, it is possible to obtain the effective molar ratio of each component needed to complete the crosslinking reaction efficiently. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 1519–1526

A laboratory study has been carried out to develop mechanical models for the dynamic modulus, fatigue life, and rutting performance of asphalt concrete as a function of air void content. The experimental program includes an axial compression complex modulus test, indirect tensile (IDT) fatigue test, and triaxial repeated load permanent deformation (TRLPD) test on the two most commonly used asphalt–aggregate mixtures in North Carolina. The dynamic moduli are determined using axial compression tests with and without confining pressure, and the results are compared to evaluate the effect of confining pressure on the dynamic modulus. The relationship between the dynamic moduli that are determined from the uniaxial compression test and the air void content is developed. The growth of the tensile strain and axial permanent strain is measured from the IDT fatigue test and TRLPD test, respectively, and is used to determine the fatigue life and rutting behavior of the mixtures. The fatigue and rutting models adopted in the new NCHRP 1-37A Mechanistic-Empirical Pavement Design Guide have been refined to represent the IDT and TRLPD test results more accurately and to incorporate the air void content as an input parameter.

ABSTRACT A uniform dispersion of reactants is necessary to achieve a complete reaction involving multiple components. Using a combination of infrared spectroscopy, thermal analysis, and low field NMR, we have elucidated the role of a new class of nonreactive plasticizers on the crosslinking reaction between hexamethylenetetramine (HMTA) and phenol formaldehyde resin. These two seemingly dissimilar reactants are responsible for the exceptionally high mechanical strength in a number of organic–inorganic composites. The efficiency of the curing reaction is characterized by the changing functionality of HMTA. Infrared active vibrations are used to characterize the changing molecular structures as a function of temperature. The T 1 spin‐lattice relaxation time is used for the characterization of segmental dynamics of the chains in the formation of the crosslinked product. The segmental mobility depends on the amount of crosslinking and the stiffness of the chain. This study shows that this new class of nonreactive plasticizer can induce highly crosslinked structures without any of the environmental impact of the current technology. An efficient crosslinking reaction in phenolic resin can be achieved by using methyl benzoate as a nonreacting plasticizer. Low field NMR, in conjunction with infrared spectroscopy (mid and near) and DSC, clarified the crosslinking reaction mechanism and the ensuing structure. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55 , 206–213

Abstract Fundamental understanding of the fixed abrasive slicing of photovoltaic silicon wafers is crucial for producing low‐cost wafers with superior surface quality and mechanical strength. With the goal of understanding the diamond wire sawing process, this paper investigates the scribing of mono‐ and multi‐crystalline silicon by the abrasive grits on an actual diamond wire. Specifically, the effects of grit shape and silicon crystal structure on the resulting surface morphology, subsurface damage, and the critical depth of cut at which ductile‐to‐brittle transition occurs are investigated. Results show that surface cracking depends on the grit shape. Scribing across the grain and twin boundaries in multi‐crystalline silicon impacts the resulting surface morphology, with grit shape producing a greater effect than crystallographic orientation in the grain interior relative to the grain boundary. Subsurface damage depends on the grit shape and crystal structure. Differences in the critical depth of cut for ductile‐to‐brittle transition in scribing of mono‐crystalline silicon are explained via analysis of the stress state produced by idealized grit shapes.

Multicomponent gas transport is investigated with unprecedented precision by AC impedance analysis of porous YSZ anodesupported solid oxide fuel cells. A fuel gas mixture of H 2 -H 2 O-N 2 is fed to the anode, and impedance data are measured across the range of hydrogen partial pressure (10-100%) for open circuit conditions at three temperatures (800 C, 850 C and 900 C) and for 300 mA applied current at 800 C. For the first time, analytical formulae for the diffusion resistance (R b ) of three standard models of multicomponent gas transport (Fick, Stefan-Maxwell, and Dusty Gas) are derived and tested against the impedance data. The tortuosity is the only fitting parameter since all the diffusion coefficients are known. Only the Dusty Gas Model leads to a remarkable data collapse for over twenty experimental conditions, using a constant tortuosity consistent with permeability measurements and the Bruggeman relation. These results establish the accuracy of the Dusty Gas Model for multicomponent gas diffusion in porous media and confirm the efficacy of electrochemical impedance analysis to precisely determine transport mechanisms.

Gallium oxide (Ga₂O₃) is an emerging ultra-wide bandgap semiconductor that has unique properties ideal for high-power, high-temperature, optoelectronic, and sensing applications and has piqued interest over the last decade. It has the potential to be technologically and economically superior to commercially available wide bandgap semiconductor materials, such as silicon carbide and gallium nitride, because its wider bandgap enables increased breakdown voltages and lower on-state resistances, and its ability to be grown from melt enable cost-competitive economics. In this study, we present a techno-economic analysis that projects the cost of 6" β-Ga₂O₃ wafers fabricated from crystals grown via edge-defined film-fed growth (EFG). At a manufacturing volume of 5000 wafers per month, we predict a unit cost of $320 for a 6" EFG grown β-Ga₂O₃ epi-wafer. We determine that, when calculated using 2021 iridium crucible costs, EFG has a 2x cost advantage compared to previously reported epi-wafers grown via the Czochralski (CZ) method. We further identify key cost parameters for 6" β-Ga₂O₃ epi-wafers and present cost-sensitivity analysis of their impact on the final cost.

The main thrust for this work is the investigation and design of a positron emission tomography (PET) scanner based on new Lanthanum Halide scintillators. In three-dimensional (3-D) PET the major limitations are scanner dead-time and ability to reject randoms and scatter. Therefore, to reach the full potential of 3-D PET requires a scintillator with good timing resolution and good energy resolution. The new Lanthanum Halide scintillators have very fast decay and very high light output which leads to timing resolution and energy resolution that are both superlative. For application to PET, the authors have constructed pixels with dimensions 4 /spl times/ 4 /spl times/ 30 mm/sup 3/ and have measured energy resolution of 4.6% (fwhm) at 662 keV and a timing resolution (fwhm) of 350 ps, in coincidence with a plastic scintillator. Using a detector based on LaBr/sub 3/, a 3-D PET scanner with 90 cm diameter and 25 cm axial extent is predicted to achieve a sensitivity of 1400 kc/s//spl mu/Ci/cc and a peak NEC count-rate of 120 kc/s using the NEMA NU2-2001 standard. Further, the excellent timing resolution opens the possibility of measuring time-of-flight with sufficient accuracy to reduce the noise propagation during image reconstruction, thus leading to a significant gain in signal-to-noise. Assuming a system timing resolution of 500 ps, one can expect the effective NEC to increase by a factor of 3 for a thin patient (20 cm diameter) and a factor 6 for a very heavy patient (40 cm diameter). Thus, even with lower stoping power than other PET scanners, the combination of excellent energy resolution and timing resolution of LaBr/sub 3/ can potentially lead to a very significant improvement in PET performance.

Crystalline nucleation is investigated during the dynamical heat treatment of a ZrO 2 –MgO–Al 2 O 3 –SiO 2 glass by high‐temperature Zr K‐edge X‐ray absorption near‐edge spectroscopy. In the parent glass, the Zr coordination number is higher than in most glasses, explaining the structural instability of Zr during thermal treatment. The Zr local structure is modified at 30°C above the nucleation onset. Crystalline nucleation is characterized by the formation of peculiar nano‐ZrO 2 particles, which are stable until completion of the thermal treatment. These nano‐ZrO 2 particles are stable during the elaboration of glass–ceramics, without any Zr 4+ remaining in the glassy matrix of the final material.

Sintering in air of a pure yttria powder was investigated on green samples shaped by slip casting. The “relative density/grain size” trajectory has been drawn and hypotheses concerning the mechanisms controlling grain growth and densification were formulated. Samples were fully densified by an additional hot isostatic pressing step on pre‐sintered samples. After optimal polishing, optical properties were measured in the UV, visible, and infrared ranges.

Discontinuation of contact lens wear as a result of ocular dryness and discomfort is extremely common; as many as 26% of contact lens wearers discontinue use within the first year. While patients are generally satisfied with conventional hydrogel lenses, improving on-eye comfort continues to remain a goal. Surface modification with a biomimetic, ocular friendly hydrophilic layer of a wetting agent is hypothesized to improve the interfacial interactions of the contact lens with the ocular surface. In this work, the synthesis and characterization of poly(2-hydroxyethyl methacrylate) surfaces grafted with a hydrophilic layer of hyaluronic acid are described. The immobilization reaction involved the covalent attachment of thiolated hyaluronic acid (20 kDa) on acrylated poly(2-hydroxyethyl methacrylate) via nucleophile-initiated Michael addition thiol-ene "click" chemistry. The surface chemistry of the modified surfaces was analyzed by Fourier transform infrared spectroscopy-attenuated total reflectance and X-ray photoelectron spectroscopy. The appearance of N (1s) and S (2p) peaks on the low resolution X-ray photoelectron spectroscopy spectra confirmed successful immobilization of hyaluronic acid. Grafting hyaluronic acid to the poly(2-hydroxyethyl methacrylate) surfaces decreased the contact angle, the dehydration rate, and the amount of nonspecific sorption of lysozyme and albumin in comparison to pristine hydrogel materials, suggesting the development of more wettable surfaces with improved water-retentive and antifouling properties, while maintaining optical transparency (>92%). In vitro testing also showed excellent viability of human corneal epithelial cells with the hyaluronic acid-grafted poly(2-hydroxyethyl methacrylate) surfaces. Hence, surface modification with hyaluronic acid via thiol-ene "click" chemistry could be useful in improving contact lens surface properties, potentially alleviating symptoms of contact lens related dryness and discomfort during wear.

We have demonstrated that Li can be substantially incorporated into the matrix of NaI under an optimized crystal growth process. The incorporation of Li introduces efficient neutron detection into an already successful commercial gammaray scintillator. Exceptional gamma-neutron pulse shape discrimination (PSD) has been demonstrated in Li co-doped NaI:Tl crystals with up to 8% Li concentration. Neutron-gamma PSD figure of merits are typically above 2 and can be high as 4.3 depending on the Li concentration. Gamma-ray performance of a single crystal Li co-doped NaI:Tl is on par with standard NaI:Tl. Simulations show that a Ø 50 mm × 50 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> Li doped at 2% NaI:Tl detector has comparable neutron detection efficiency as a <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> Li-enriched Cs <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> LiYCl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> :Ce of the same size. Hightemperature measurements have confirmed good gamma-neutron PSD to at least 160 °C. Creation of large volume (>1000 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ), low cost, and dual-gamma spectroscopy/neutron sensitive detectors is possible with this technology.

A high-energy electron in condensed matter deposits energy by creation of electron-hole pairs whose density generally increases as the electron slows, reaching the order of ${10}^{20}$ eh/${\mathrm{cm}}^{3}$ near the end of its track. The subsequent interactions of the electrons and holes include nonlinear rate terms and transport as first hot and then thermalized carriers in the nanometer-scale radial dimension of the track. Charge separation and strong radial electric fields occur in a material such as CsI with contrasting diffusion rates of self-trapped holes and hot electrons. Eventual radiative recombination has a nonlinear relation to the primary electron energy because of these interactions. This so-called intrinsic nonproportionality of electron response limits the achievable energy resolution of a given scintillation radiation detector material. We use a system of coupled transport and rate equations to describe a pure host (three equations) and one dopant (four more equations per dopant). Applying it first to the experimentally well-characterized system of CsI and CsI:Tl in this work, we use results of picosecond absorption spectroscopy, interband $Z$-scan measurements of nonlinear rate constants, and other experiments and calculations to determine most of the more than 20 rate and transport coefficients required for modeling. The model is solved in a track environment approximated as cylindrical and is compared to the proportionality curve and total light yield of undoped CsI at temperatures of 295 and 100 K, as well as thallium dopant in CsI:Tl at 295 K. With this degree of validation, the space and time distributions of carriers and excitons, both untrapped and trapped, are examined within the model to gain an understanding of the main competitions controlling the nonproportionality of response.