The dynamic and equilibrium water vapor sorption properties of Sylgard-184, a commercially available poly(dimethylsiloxane) elastomer (PDMS), were determined via gravimetric analysis from 30 to 70 °C. Described here is methodology for quantitatively assessing how diffuses ad/absorbs into polymeric materials that are traditionally considered hydrophobic. PDMS frequently chosen their moisture barrier properties; our results, however, demonstrate able penetrate the material over range...

HMX-based explosives LX-10 and PBX-9501 were heated through the β-δ phase transition. Ultra-small angle x-ray scattering (USAXS) molecular diffraction simultaneously recorded as HMX was heated. Mesoscale voids structure dramatically change promptly with transition, rather than other thermal effects. Also, induced damage, observed in USAXS, occurs more readily at elevated temperatures; such, dose reduced to mitigate this effect. Optical microscopy performed during a similar heating cycle...

In this study, we investigate the curing reaction kinetics and degree of cross-linking LL50, a polydimethylsiloxane (PDMS)-based polymer, using isothermal heat flow calorimetry (HFC). developed by Lawrence Livermore National Laboratory, is two-part addition-curing liquid silicone rubber for direct-ink-writing additive manufacturing. The process, driven platinum-catalyzed hydrosilylation reaction, was monitored under conditions at various temperatures. We kinetic model to predict rate extent...

The effect of pressure on the global thermal decomposition rate energetic material HMX was studied. precompressed in a diamond anvil cell (DAC) and heated at various rates. parent species population monitored as function time temperature using Fourier transform infrared (FTIR) spectroscopy. Global rates were determined by fitting fraction reacted to extended-Prout-Tompkins nucleation-growth model Friedman isoconversional method. results these experiments analysis indicate that accelerates...

Here we report nano- through microsecond time-resolved IR experiments of iron-catalyzed alkene isomerization in room-temperature solution. We have monitored the photochemistry a model system, Fe(CO)4(η2-1-hexene), neat 1-hexene UV photolysis starting material leads to dissociation single CO form Fe(CO)3(η2-1-hexene), singlet spin state. This CO-loss complex shows dramatic selectivity an allyl hydride, HFe(CO)3(η3-C6H11), via internal C−H bond-cleavage reaction 5−25 ns. find no evidence for...

Recently, transition-metal−boryl compounds have been reported that selectively functionalize primary C−H bonds in alkanes high yield. We investigated this process with one of the well-defined systems reacts under photochemical conditions using both density functional theory calculations and pico- through microsecond time-resolved IR spectroscopy. UV irradiation Cp*W(CO)3(Bpin) (Cp* = C5(CH3)5; pin 1,2-O2C2-(CH3)4) neat pentane solution primarily results dissociation a single CO ligand...

The process of iron- and ruthenium-assisted alkene isomerization is investigated with ultrafast time-resolved infrared spectroscopy under ambient conditions. M(CO)4(η2-1,4-PD) (M = Ru, Fe; PD pentadiene) was irradiated a 100 femtosecond pulse 266 nm light in solution cyclohexane, single carbonyl photodissociated. When M experimental results indicate that both Ru(CO)3(η4-1,4-PD) HRu(CO)3(η3-allyl) form within few picoseconds, their populations do not change significantly out to 800 ps. Fe,...

Abstract Water‐vapor‐uptake experiments were performed on a silica‐filled poly(dimethylsiloxane) (PDMS) network and modeled by using two different approaches. The data was established methods the model parameters used to predict moisture uptake in sample. predictions are reasonably good, but not outstanding; many of shortcomings modeling discussed. A high‐fidelity approach is derived improve diffusion. Our captures physics kinetics diffusion adsorption/desorption, simultaneously. It predicts...

Abstract Moisture uptake and outgassing can be detrimental to a system by altering the chemical mechanical properties of materials within over time. In this work, we conducted isotherm experiments investigate dynamic moisture sorption desorption in markedly different materials, i.e., polymeric material, Sylgard-184 ceramic aluminosilicate Zircar RS-1200, at temperatures (30 °C–70 °C) varying water activity (0.0–0.90). showed linear behavior with no-hysteresis entire temperature range...

The time scale and/or products of photoinduced decomposition 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) were investigated at ambient pressure and compared with formed 8 GPa. Ultrafast time-resolved infrared steady-state Fourier transform IR (FTIR) spectroscopies used to probe TATB its after photoexcitation a 5 ns pulse 532 nm light. At pressure, transient spectra indicate that the molecule has significantly decomposed within 60 ns; also formation CO2, an observed product, is complete 30−40...

The photochemistry of the trimetal cluster Ru3(CO)12 was investigated on ultrafast time scale using UV−vis pump, infrared probe spectroscopy in order to study transient intermediates formed upon photoexcitation. dynamics these can only be unambiguously identified by monitoring small but distinct absorptions bridging carbonyls. nature and role carbonyl both coordinating noncoordinating solvents is discussed. In an inert solvent such as cyclohexane, photoexcitation with 400 nm light produces...

The ultrafast solvation and rearrangement dynamics following the photolysis of M(CO)6 (M = Cr, Mo, W) in terminal alkyne solutions have been investigated. Upon photoinitiated loss a ligand from parent metal hexacarbonyl, coordination to an solvent molecule is followed by complex that bound site π-bonded fashion. This occurs on time scale anticorrelated with metal−ligand binding energy. A dissociative ruled out for this process favor associative or interchange mechanism. Previous theoretical...

Moisture sorption and diffusion exacerbate hygrothermal aging can significantly alter the chemical mechanical properties of polymeric-based components over time. In this study, we employ a multi-pronged multi-scale approach to model understand moisture processes in polyimide polymers. A reactive transport with triple-mode (i.e., Henry's, Langmuir, pooling), experiments, first principles atomistic computations were combined synergistically explore representative systems Kapton H HN We find...

A high-fidelity model of kinetic and equilibrium sorption diffusion is developed exercised. The gas-diffusion coupled with a triple-sorption mechanism: Henry's law absorption, Langmuir adsorption, pooling or clustering molecules at higher partial pressures. Sorption experiments are conducted span range relative humidities (0-95 %) temperatures (30-60 °C). Kinetic properties effective diffusivity determined by minimizing the absolute difference between measured modeled uptakes. Uncertainty...

Ground-state structures with side-on nitrosyl (η2-NO) and isonitrosyl (ON) ligands have been observed in a variety of transition-metal complexes. In contrast, excited-state bent-NO proposed for years but never directly observed. Here, we use picosecond time-resolved infrared spectroscopy density functional theory (DFT) modeling to study the photochemistry Co(CO)3(NO), model transition-metal−NO compound. Surprisingly, no evidence ON η2-NO structural isomers, two DFT ground- potentials...

Two key phenomena─immobilization and concentration-dependent mixing free energies─simultaneously alter the sorption thermodynamics diffusion of vapors in materials. This interrelation is leveraged to fit a unified model simultaneously capturing both dynamics equilibrium isotherms. transport incorporates quasi-equilibrated immobilization reactions considers Fick's law rigorously terms chemical potential gradients rather than concentration gradients. Five material case studies are discussed...

The ligand rearrangement reaction of Cr(CO)6 is studied in a series alcohol solutions using ultrafast infrared spectroscopy and Brownian dynamics simulations. Excitation with 266 nm light gives Cr(CO)5 which quickly solvated by from the bath. In solutions, solvation an alkyl or hydroxyl site can occur; all bound complexes eventually rearrange to complexes. This has been described both intermolecular (stochastic) intramolecular (chainwalk) mechanism. Experiments alone do not allow for...

We provide measurements of the chemical reaction propagation rate (RPR) as a function pressure using diamond anvil cell (DAC) and strand burner technologies. Materials investigated include HMX RDX crystalline powders, LX‐04 (85% 15% Viton A), Composition B (63% RDX, 36% TNT, 1% wax). The anomalous correspondence between crystal structure, including in some instances isostructural phase transitions, on dependent RPRs are correlated to confocal micro‐Raman spectroscopic results. contrast DAC...

Abstract Hysteretic sorption and desorption of water is observed from 0 to 95% relative humidity 298–333 K on a glassy polyurethane foam. It postulated that sorption-induced swelling the increases concentration accessible hydrogen-bonding adsorption sites for water. The accessibility kinetically controlled due restricted thermal motions chains in polymer, causing difference site concentrations during desorption. This discrepancy leads hysteresis sorbed A coupled chemo-mechanical model...

Femtosecond visible pump−IR probe studies of Cp2W2(CO)6 in P(OMe)3 and CH2Cl2 have allowed direct observation a 19-electron intermediate disproportionation into CpW(CO)3- CpW(CO)3P(OMe)3+ on the ultrafast time scale. A new mechanism involving in-cage electron transfer between 17-electron radical has been proposed.

The initial steps of β-hydrogen elimination from the complex CpW(CO)3(CH2CH3) were studied using ultrafast infrared and step-scan FTIR spectroscopy combined with density functional theory calculations. reaction was initiated by a pulse UV light at 266 nm followed on femto- to microsecond timescale, allowing for identification kinetic characterization transients. In process β-H elimination, primary photoproduct found be an α-H stabilized dynamics elusive species cis-CpW(CO)3(H)(CH2CH2)...

Moisture sorption and transport can pose severe consequences related to the performance lifetime of materials in many applications. This work explores modeling characterization diffusive moisture coupled with kinetic Langmuir adsorption a multi-material system. A finite volume method was applied an implicit Euler time-stepping scheme solve unsteady diffusion-sorption equations. level set framework smoothed Heaviside function used implicitly treat concentration flux conditions at material...

We employ in-situ flash x-ray imaging, together with a detailed multiphase convective burn model, to demonstrate how explosives' binder characteristics influence the burning processes in thermal explosions. Our study focuses on HMX-based explosives LX-10 and PBX 9501. While HMX (cyclotetramethylene-tetranitramine) crystallite size distributions for these two are nearly identical before heating, our experiments simulations indicate that after variations result due differences composition....