Poly Alpha-methylstyrene Research Articles

Blending Petroleum Waxes with Suitable Polymeric Additives as a Simple and Promising Way to Improve the Quality of Petroleum Waxes for Numerous Industrial Applications

New compounded high compatible blends of Paraffin wax (PW) and Microcrystalline waxes (MCW) of specific properties were prepared. The additives include ethylene vinyl acetate (EVA) copolymer as a viscosity modifier as well as the tackifing resins,( poly hydrogenated dicyclo pentadiene (HD) and poly alpha methylstyrene (MS)) enhanced the wax performance based on molecular weight (Mw),the number of carbons and the crystallinity. The ingredients were combined together of high compatibility within the wax blends. The MS and HD resins created promising physical, mechanical and technological properties to be used in food packaging, hot melt, labeling and various industrial applications. The blend compatibility , melting behavior (congealing point (CP), softening point (SP) and drop melting point (DMP)), dynamic viscosity, hardness (low penetration value) , the mechanical properties (tensile strength and elongation at break) as well as adhesion property are dependent on the composition of the wax blends.

Microstructure and morphology evolution of high-Z/low-Z gradient coatings on PAMS microspheres

Gradient coatings exhibit excellent implosion performance in double-shell targets for Inertial Confinement Fusion (ICF). Here, we present the controllable preparation of high-Z/low-Z (Z is the atomic number) gradient alloy coatings which can be used for ICF double-shell targets. Tungsten/carbon (W/C), tungsten/silicon (W/Si) and tungsten/aluminum (W/Al) gradient coatings were successfully deposited on silicon substrates and poly-alpha-methyl-styrene (PAMS) spheres by direct-current magnetron sputtering. The morphology, component and surface roughness of gradient coatings were characterized. Although there are significant differences in morphology and surface roughness compared with planar gradient coatings, the spherical gradient coatings still have a dense microstructure and smooth surface. The root-mean-square (RMS) roughness of our gradient coatings experience an improvement compared with the previous films which used in ICF experiments. The gradient coatings deposited by co-sputtering of high-Z and low-Z elements in this work provide competitive candidate materials for ICF double-shell targetsee.

Capsule implosions for continuum x-ray backlighting of opacity samples at the National Ignition Facility.

Direct drive implosions of plastic capsules have been performed at the National Ignition Facility to provide a broad-spectrum (500-2000 eV) X-ray continuum source for X-ray transmission spectroscopy. The source was developed for the high-temperature plasma opacity experimental platform. Initial experiments using 2.0 mm diameter polyalpha-methyl styrene capsules with ∼20 μm thickness have been performed. X-ray yields of up to ∼1 kJ/sr have been measured using the Dante multichannel diode array. The backlighter source size was measured to be ∼100 μm FWHM, with ∼350 ps pulse duration during the peak emission stage. Results are used to simulate transmission spectra for a hypothetical iron opacity sample at 150 eV, enabling the derivation of photometrics requirements for future opacity experiments.

Reactive molecular dynamics simulations on the thermal decomposition of poly alpha-methyl styrene.

Using molecular dynamics simulations with ReaxFF reactive force field, the thermal decomposition mechanism of poly alpha-methyl styrene (PAMS) materials and the effects of heating rate and impurity fluorobenzene on PAMS thermal decompositions are studied. The results show that: 1) Pyrolysis mechanism of PAMS consists of initiation and propagation processes. In the initiation stage, random scissions of C-C backbone produce fragments, and in the propagation stage, depolymerizing reactions generate monomers and other products. 2) Higher decomposition temperature is needed for greater heating rate. 3) The presence of impurity fluorobenzene retards thermal decomposition of PAMS.

Depolymerization dynamics study of poly-alpha-methylstyrene

Polymers are macromolecus composed of repeated monomer subunits, which construct the fabulous world of DNA, protein, cellulose, rubber, plastic, etc. and possess crucial positions in fields like life science, chemistry industry and material preparation with special demands. However, the performance of polymer would decay because of the influence of environment effects and even be depolymerized. While under particular scenarios, such a decomposition process might be valuable. Poly-alpha-methylstyrene (PAMS) is the substrate materials for preparing glow discharge polymer (GDP) shell which coats the fuel target for inertial confinement fusion. The key step for its involvement is to depolymerize into single molecules under high temperature so that it can escape through the space among GDP molecules which has deposited on it, and then leaves only the GDP shell. Besides of this special application, the atomic level understanding of depolymerization processes is also at the key position to modulate other reactions involving polymer materials. Here, through molecular dynamic simulation based on density functional tight-binding methods containing dispersion correction (DFTB-D), we demonstrate the typical dissociation of sequential poly-alpha- methylstyrene (PAMS) tetramer fragments with unsaturation on both ends, on the C- end and on the CH2- end, respectively. DFTB method we used here is an approximation based on the second order expansion of the density functional theory (DFT) total energy with respect to charge density variation relative to a chosen reference density. It promotes the efficiency of DFT method around two to three orders meanwhile remains acceptable precision for electronic structure calculation and large-scale quantum dynamic simulations. The reliability of the method has been admitted in massive researches, especially those on carbon-based molecules and organic systems. Our results show, with the temperature of 500 and 600 K, the dissociation of PAMS fragments is implemented by depolymerization processes, where monomers separate from one of the unsaturated ends one by one, and rising temperature could reasonably accelerate the reaction. Further simulations of a longer hexamer PAMS fragment under 600 K indicates the length effect won’t cause qualitative influence on the depolymerization process. The electronic structures of these three fragments indicate both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are localized at the bond-breaking unsaturated ends, which supports the prediction of dynamic simulations for reaction sits. Furthermore, the DFTB-D electronic structure calculations following the C—C bond breaking steps at different possible sites along the backbone chain also show the preference of the reaction to unsaturated end sites, from the view of potential energy surface. Spin distribution analysis also reflects the energy curves respect to the different depolymerization processes are closely related to the spin-polarized electronic structures of corresponding products. These results give a representative atomic-level prospect about the decomposition process of sequential PAMS under high temperature with detailed interpretation on the reaction sit preference and order, which may be informative for preparation of relative device. Besides, we hope this theoretical study could offer a fundamental reference for understanding the mechanism of decomposition for polymer materials beyond PAMS and spread across the wonderful microscopic world.

Thickness, Doping Accuracy, and Roughness Control in Graded Germanium Doped CHX Microshells for LMJ

In the Commissariat à l’Energie Atomique Laser Megajoule (LMJ) facility, amorphous hydrogenated carbon (a-C:H or CHX) is the nominal ablator used to achieve inertial confinement fusion experiments. These targets are filled with a fusible mixture of deuterium-tritium in order to perform ignition. The a-C:H shell is deposited on a polyalphamethylstyrene (PAMS) mandrel by glow discharge polymerization with trans-2-butene, hydrogen, and helium. Graded germanium doped CHX microshells are supposed to be more stable regarding hydrodynamic instabilities. The shells are composed of four layers, for a total thickness of 180 μm. The germanium gradient is obtained by doping the different a-C:H layers with the addition of tetramethylgermanium in the gas mixture.As the achievement of ignition greatly depends on the physical properties of the shell, the thicknesses, doping concentration, and roughness must be precisely controlled.Quartz microbalances were used to perform an in situ and real-time measurement of the thickness in order to reduce the variations - and so our fabrication tolerances - on each layer thickness. Ex situ control of the thickness of each layer was carried out, with both optical coherent tomography and interferometry (wallmapper).High-quality PAMS and a rolling system have been used to lower the low-mode roughness [root-mean-square (rms) (mode 2) < 70 nm]. High modes were clearly reduced by coating the pan containing the shells with polyvinyl alcohol + CHX instead of polystyrene + CHX resulting in an rms (>mode 10) < 20 nm, which can be <15 nm for the best microshells.The germanium concentration (0.4 and 0.75 at.%) in the a-CH layer is obtained by regulating the tetramethylgermanium flow. Low range mass flow controllers have been used to improve the doping accuracy.

Probing high quality pentacene monolayers by optical methods

We report optical studies of pentacene monolayers grown on poly-alpha-methyl-styrene (PAMS) substrates of high uniformity that reaches into the micron length-scale in the lateral dimension. Raman scattering intensities from a two-monolayer pentacene film exhibit large resonance enhancements when incoming and outgoing photon energies overlap the free exciton measured in optical emission. The incoming and outgoing resonance enhancements are of about the same strength. The free exciton optical emission band is sharp and intense, and it blue-shifts by about 85 meV from that of the pentacene single crystal.

Coating and Mandrel Effects on Fabrication of Glow Discharge Polymer NIF Scale Indirect Drive Capsules

Targets for the National Ignition Facility (NIF) need to be about 200 μm thick and 2 mm in diameter. These dimensions are well beyond those currently fabricated on a routine basis. We have investigated fabrication of near NIF scale targets using the depolymerizable mandrel technique. Poly-alpha-methylstyrene (PAMS) mandrels, about 2 mm in diameter, of varying qualities were coated with as much as 125 μm of glow discharge polymer (GDP). The surface finish of the final shells was examined using a variety of techniques. A clear dependence of the modal spectrum of final GDP shell on the quality of the initial PAMS mandrels was observed. Isolated features were found to be the greatest cause for a shell not meeting the NIF standard.

Enlargement of Glass and Plastic Shells to 2 mm in Diameter by Redropping through a Short Heated Tower

Large glass shells (≥ 1200 μm diameter) made by the traditional very high temperature (1650°C) long drop tower are usually wrinkled. We have found that these shells soften at relatively low temperatures. We have enlarged these shells by filling them with a few atmospheres of helium and dropping them down a very short (few feet long) tower heated to 900 to 1100°C. The helium acts as a blowing agent as the shell goes through the heated zone and causes the shells to grow larger. We have been able to smooth out large wrinkled shells by this process, as well. Glass shells as large as 2 mm in diameter and less than 6 μm out-of-round that do not have any obvious wrinkles have been made. In addition, the same process can be applied to both poly-alpha-methylstyrene (PAMS) and glow discharge polymer (GDP) shells at lower tower temperatures. Roundness of the enlarged shells is very much dependent on the wall thickness uniformity of the initial mandrels.