Four different variations of doped, planar targets were fabricated using multilayer glow discharge polymerization for the foil thickness campaign at the Extended Performance Facility at the University of Rochester. The planar film targets consisted of from one to four layers of CH, CHGe, and CHSi. The composition of Ge and Si was controlled by the flow of dopant gas (either tetramethyl germane or tetramethyl silane) and measured with X-ray florescence. After laser cutting the 200 x 900 x 80-mu m film targets out of the larger film, the targets were released from the substrate. Coating nonuniformity when using an inductively coupled discharge device can be a challenge. We improved the uniformity by rotating the substrate. Film thickness was measured with a chromatic confocal sensor system. Thickness measurements were fit to a Gaussian function, which smoothed the thickness data set and allowed accurate interpolation of thickness measurements. A challenge for freestanding, planar glow discharge polymer films is intrinsic stress in the coating. Prior to coating the final targets, the coating stress for various deposition parameters was measured. A series of runs with CH, CHGe, and CHSi were coated on thin silicon wafers. The wafers were characterized for bending before and after coating with a stylus profilometer to determine the coating stress using the Stony equation. In general, higher chamber operating pressures resulted in lower stress coatings.

Complex and precise research targets are required for the inertial confinement fusion (ICF) experiments conducted at the National Ignition Facility. During the National Ignition Campaign (NIC) the target development team embarked on and completed a science and technology campaign to provide the capability to produce the required targets at the rate needed by the NIC. An engineering design for precision, manufacturing, and fielding was developed. This required new processes, new tooling, and equipment to metrologize and assemble components. In addition, development of new processing technology was also required.Since the NIC had to respond to new results from ICF experiments, the target development team had to respond as well. This required target designs that allowed for flexibility in accommodating changes in the targets for capsule dimensions and doping levels, hohlraztm dimensions and materials, and various new platforms to investigate new physics. A continuous improvement of processes was also required to meet stringent specifications and fielding requirements.

Mechanical behavior of free-standing polymer films with submicron thicknesses exposed to a radiation environment is poorly understood. Here, we study 110-nm-thin free-standing polyvinyl formal (Formvar) films irradiated at room temperature with 1-5 keV electrons or 3 MeV alpha particles. We measure mechanical properties and the elemental composition by spherical indentation and high-energy ion scattering, respectively. Results show that, with increasing radiation dose, the effective failure strain and film thickness decrease monotonically, while the dose dependence of the Young's modulus is non-monotonic. The failure strain and modulus scale with the average energy deposited in the film, while the film thickness exhibits a more complex behavior. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4746403]

We report the preparation of low density polymeric aerogels using the ring opening metathesis polymerization (ROMP) approach to copolymerize dicyclopentadiene (DCPD) with norbornene-based monomers (NB-R) employing a first generation Grubbs' ruthenium-based catalyst. The ROMP approach offers an attractive synthetic method that enables the fabrication of low-density (0.02-0.05 g cm(-3)), uniform thickness aerogel coatings on non-planar substrates. First, we explore the effect of crosslinking in the polymer backbone on the uniformity of the gel coatings formed under shear by either adding a multi-norbornene based crosslinker (NBn-R) to increase, or linear NB-R comonomers to decrease, the degree of crosslinking, respectively. We observed that adding linear monomers dramatically improved the uniformity of the gel films which we attribute to cross-linking induced changes in the rheological properties at the gel point. Second, the copolymerization of DCPD and NB-R with a different pendant group also causes a significant change in the morphology of the PDCPD-based aerogels by modifying the lengths of the strands in the fibrous polymer network. The effect of NB-R addition on the pore structure of the aerogels is discussed in the context of a molecular and interparticle crosslinking model. Finally, (bis) iodo-norbornene was synthesized to demonstrate the feasibility to fabricate functionalized aerogels by using our copolymerization approach. Our results highlight the potential of the ROMP-based copolymerization approach as a facile and versatile route to functionalized low density polymeric aerogels.

Porosity generally embrittles ceramics. In contrast to such expectations, this report demonstrates that an effective fracture strain of nanoporous silica aerogels increases with increasing porosity. At ultralow relative densities of < 0.5%, nanoporous monoliths start exhibiting super-compressible deformation with effective fracture strains of > 50%. This is attributed to consequences of an increase in the aspect ratio of ligaments with decreasing density.

Coating of cylindrical and spherical surfaces with thin and homogeneous low-density aerogel films requires precise control over viscosity and gel time. If the viscosity is too low, shear forces can damage the growing gel network and prevent the formation of uniform coatings. Using the example of dicyclopentadiene-based polymer gels, we demonstrate that the gelation behaviour can be manipulated by reducing the amount of cross-linking through co-polymerization with a monomer that can only form linear chains. Even small additions of a linear co-polymer (1-10 wt. %) increase the viscosity at the sol-gel transition by several orders of magnitude, and drastically improve the uniformity of gel films formed under the influence of shear. These results are discussed in the context of the classical gel theory.

Ultraviolet (UV)-cured adhesives are used to assemble targets for the National Ignition Campaign. Since cure behavior and adhesive strength are critical to successful, leak-free production of targets, it is desirable to establish a testing procedure to verify the viability of adhesives. To measure reaction conversion, we used Fourier transform infrared spectroscopy, viscometry, and differential scanning calorimetry (DSC) each specially adapted to allow UV exposure within the measuring instrument. We found that photo-DSC was the most sensitive technique of those we investigated for measuring conversion and reaction rate. The effect of adhesive age was measured. We found that as adhesives aged the total heat of reaction dropped.

ABSTRACTThe condensation polymerization of resorcinol and formaldehyde catalized by sodium carbonate produces a sol that aggregates to form a gel. Using viscometry the effect of temperature and catalyst concentration on the sol-gel transition was investigated. At a solids concentration of 3%, gelation occurred in 1500 minutes. The rate of increase in viscosity was a function of both catalyst concentration and temperature. The structure of the gels was studied by freeze-fracture TEM. In the sol phase the RF solutions contain particles of 5 to 20 nm diameter. After gelation the particles form a crosslinked network with a pore structure of 100 nm.

The centering of an ignition target capsule strongly depends on high-quality "tents" with closely matched mechanical properties. The relevant properties are tent stiffness and relaxation behavior. Tent stiffness is matched by choosing tents of equal thickness. Here, we describe recent advances in tent fabrication that have increased the quality and production rate of tents. The most significant improvement comes from the use of a meniscus coater to produce Formvar tents of high uniformity and with good control of tent thickness and good yield. Other improvements include a switch to silicon wafers as deposition substrate and standardized tent holders. The improvements have resulted in a sixfold increase of the production rate while increasing the yield by a factor of 2, despite tighter quality control.

water. It is inevitable that when they are removed from a fabrica<on chamber they will encounter some. They are also placed in water for smoothing and polishing effects. It is crucial to know how the capsules respond physically and chemically to water. The materials division inves<gated this and we found that water is absorbed depending on the concentra<on of the water vapor in the air. We controlled this by ven<ng varying controlled amounts of dry air vs. hydrated air into the chamber and recording the results of the absorbed amounts. We also were wondering whether pyrolyzing (fire furnace trea<ng) the material affected how it would later absorb water. It seemed to make very liEle difference as shown in the graph above. In this experiment we saturated a sample of CH polymer ini<ally with water then back to vacuum, a4er that we expose it to deuterium oxide (heavy water). We can see from the plot that the process is essen<ally reversible and that heavy water adds more rela<ve weight to the polymer sample than water.

Robust ultrathin polymer membranes offer significant technical and economic advantage over conventional carbon capture methods due to their potential for high throughput, high selectivity, and relative ease of implementation. We have been developing a simple, ultrathin, polymer membrane system to capture CO2 from post-combustion industrial exhaust streams. The approach involves nano-engineered membrane fabrication using an LLNL-developed solvent-less vapor deposition followed by in-situ polymerization (SLIP) process. The SLIP process vapor deposits ultrathin polymer films onto high throughput substrates to fabricate composite membranes. Single component gas permeation tests for PMDA-ODA films with thicknesses between 100-1000 nm were conducted. Permeability was found to be in the 30-100 Barrer range while maintaining CO2/N-2 selectivity of similar to 20:1. Membrane performance may be enhanced via improved film quality, reduced thickness, the development of new materials which are compatible with the SLIP process, and a modeling effort to understand the underlying transport phenomena within the membrane material. (C) 2011 Published by Elsevier Ltd.

A novel prototype optical sensor for monitoring cumulative hydrogen gas exposure was fabricated and evaluated. Chemical-to-optical transduction was accomplished by detecting the intensity of 670nm laser light transmitted through a hydrogen getter-doped polymer film mounted at the end of an optical fiber; the transmittance of the composite film increased with uptake of hydrogen by the embedded getter. The composite film consisted of the hydrogen getter 1,4-bis(phenylethynyl)benzene, also known as DEB, with carbon-supported palladium catalyst embedded in silicone elastomer. Because the change in transmittance was irreversible and occurred continuously as the getter captured hydrogen, the sensor behaved like a dosimeter, providing a unique indication of the cumulative gas exposure.

Abstract Graded copper-doped Be shells have been fabricated by sputter coating on spherical mandrels. While such coatings have consistent microstructure and acceptable void content and size, we have found that they suffer from sufficient interconnected porosity leading to relatively rapid gas leakage. In this paper, we present an extensive study of D2 leakage out of Be shells made by sputter coating. The leakage appears to follow molecular flow dynamics as determined by examining the temperature dependence of the flow. Furthermore, the time dependence of the leakage suggests that the flow channels are nanometerish in diameter, propagating through the thickness of the coating, possibly brought about by residual stress in the coatings. We have investigated the D2 leakage time constant as a function of a large number of coating parameters, including the effect of introducing boron-doped layers. Addition of thin 0.25 μm amorphous boron-doped layers near the inside surface has been most effective in producing shells with long time constants (greater than 7 days to immeasurable) with yield of greater than 50%. There is still substantial scatter in the data, even within a given coating batch, suggesting a possible stochastic cracking process driven by residual stress in the coating.

Ablative targets for the National Ignition Campaign (NIC) have been fabricated by sputter coating spherical mandrels made of glow discharge polymer (GDP) with graded copper doped beryllium (Be) layers. The inner mandrel must be completely removed to meet specific ignition design requirements. The process of removing the mandrel requires elevated temperature in the presence of oxygen. However, elevating the temperature in air also oxidizes the Be and can cause blistering on the inner surface of the Be shell. This paper will discuss a refined technique, which removes the GDP mandrel without compromising the integrity of the inner Be surface. The oxygen gradient that develops during the mandrel removal and the impact of its presence will also be discussed.

Sputtered beryllium and copper-doped beryllium coatings as thick as 170μm have been deposited on spherical substrates to produce hollow shells that are required as targets for inertial fusion experiments. Be coatings by magnetron sputtering achieved ∼95±2% bulk density consistently up to 170μm thick. Coatings on the spherical substrates exhibit the typical columnar structure throughout the entire thickness. Transmission electron microscopy indicates the presence of submicron, nearly spherical voids mainly aggregated along the columnar structure and grain boundaries, as well as some smaller intragranular elongated voids. Holes have been drilled in beryllium shells produced in this manner to allow filling with deuterium (the fusion fuel). Gas retention of these shells has been examined using mass spectrometry. It appears that a fraction of the pores in the coatings are interconnected, which leads to leakage of the hollow shells. Boron-doped Be layers near the eutectic phase, at a concentration of ∼11at.%, have been added to the Be shells to significantly improve D2 gas retention of the shells. However, there remains a considerable scatter in the measured leakage.

Abstract Various morphologies have been observed in sputter-deposited Be ablator capsules, including nodular growth, cone growth and twisted grain growth. By devising an agitation method that includes both bouncing and rolling the spherical mandrels during deposition, and by reducing the coating rate, consistent columnar grain structure has now been obtained up to 170 mm. Low mode deformation of the shells is observed on thin CH mandrels, but is suppressed if stiffer mandrels are used. Ablator density measured by weighing and x-ray radiography is 93%–95% of bulk density of Be. Transmission electron microscopy shows 100.200 nm size voids in the film and striations inside the grains. Be shells produced with rolling agitation have met most of the NIF specifications. Some of the few remaining issues will be discussed.