Hollow spheres with uniform coatings on the inner surface have applications in optical devices, time- or site-controlled drug release, heat storage devices, and target fabrication for inertial confinement fusion experiments. The fabrication of uniform coatings, which is often critical for the application performance, requires precise understanding and control over the coating process and its parameters. Here, we report on in situ real-time radiography experiments that provide critical spatiotemporal information about the distribution of fluids inside hollow spheres during uniaxial rotation. Image analysis and computer fluid dynamics simulations were used to explore the effect of liquid viscosity and rotational velocity on the film uniformity. The data were then used to demonstrate the fabrication of uniform sol-gel chemistry derived porous polymer films inside 2 mm inner diameter diamond shells.

We report on the grain size dependent morphological, physical and chemical properties of thick microwave-plasma assisted chemical vapor deposited (MPCVD) diamond films that are used as target materials for high energy density physics experiments at the Lawrence Livermore National Laboratory. Control over the grain size, ranging from several μm to a few nm, was achieved by adjusting the CH4 content of the CH4/H2 feed gas. The effect of grain size on surface roughness, morphology, texture, density, hydrogen and graphitic carbon content was systematically studied by a variety of techniques. For depositions performed at 35 to 45 mbar and 3000 W microwave power (power density ~ 10 W cm− 3), an abrupt transition from micro-crystalline diamond to nanocrystalline diamond was observed at 3% CH4. This transition is accompanied by a dramatic decrease in surface roughness, a six percent drop in density and an increasing content in hydrogen and graphitic carbon impurities. Guided by these results, layered nano-microhybrid diamond samples were prepared by periodically changing the growth conditions from nano- to microcrystalline.

The fabrication of uniform sol–gel coatings with embedded functional nanomaterials inside cylinders requires detailed understanding of the gelation behavior. For sol–gel systems the viscosity is a function of gelation time that affects sol–gel coatings on the inside of a slowly, horizontally rotating cylinder. Therefore the angular velocity has to be adjusted to this time dependence. The higher the viscosity the more liquid is dragged along with the moving cylinder wall while the balance of gravity and drag limits the layer thickness. In addition, inertial forces and surface tension can create instabilities within the coated layer. Here, we show that it is important to suppress these instabilities by transitioning the viscous sol directly to a velocity that allows for the formation of an almost uniform layer. In this regime, which is the so-called rimming state, the recirculation of the gel precursor solution is strongly reduced which allows to fabricate coatings with shear sensitive sol–gel chemistries. Here, we tested this approach with 4 different aerogel systems, with low-density CH-based-, TiO2-, SiO2- and Fe2O3-aerogels, that represent a wide variety of different sol–gel behaviors. We show that the required rotational velocities for these aerogel systems can be predicted with a simple analytical approximation, and we performed computational fluid dynamics simulations to predict local shear and thickness uniformity.

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.

Taking full advantage of the unique laboratory environment created by the National Ignition Facility (NIF) will require the availability of foam-lined indirect-drive inertial confinement fusion targets. Here, we report on a new approach that enables fabrication of target structures that consist of a thin-walled (<30 mu m) ultra-low-density (<30 mg cm(-3)) hydrocarbon foam film inside a thick-walled, similar to 2 mm diameter ablator shell. In contrast to previous work on direct-drive targets that started with the fabrication of foam shells, we use a prefabricated ablator as a mold to cast the foam liner within the shell. This work summarizes crucial components of this new approach, including the aerogel chemistry, filling of the ablator shell with the aerogel precursor solution with nanolitre precision, creating uniform polymer gel coatings inside the ablator capsule, supercritical drying and doping.

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.

This Diplomarbeit deals with the characterization of 9 differently grown diamond samples. Several techniques were used to determine the quality of these specimens for inertial confinement fusion targets. The quality of chemical vapor deposition diamond is usually considered in terms of the proportion of sp3-bonded carbon to sp2-bonded carbon in the sample. For fusion targets smoothness, Hydrogen content and density of the diamonds are further important characteristics. These characteristics are analyzed in this thesis. The research for thesis was done at Lawrence Livermore National Laboratory in collaboration with the Fraunhofer Institut für angewandte Festkörperphysik Freiburg, Germany. Additionally the Lehrstuhl fuer Nukleartechnik at Technical University of Germany supported the work.