Grain boundary morphologies in poly(styrene-6-butadiene) lamellar diblock copolymers were characterized using transmission electron microscopy (TEM). Two types of twist grain boundaries were observed in which microphase separation of the two blocks was maintained in the grain boundary region by intermaterial dividing surfaces that approximate classically known minimal surfaces. The geometry of these interfaces was demonstrated by comparing experimental TEM images with ray tracing computer simulations of the model surfaces as the projection direction was systematically varied in both the experimental and simulated images. The two morphologies observed were found to have intermaterial dividing surfaces that approximate either Scherk's first (doubly periodic) surface or a section of the right helicoid. The helicoid section boundary was observed at low twist angles, less than or equal to about 15°. The Scherk surface family of boundary morphologies, which consists of a doubly periodic array of saddle surfaces, was found over the entire twist range from 0 to 90°. As the twist angle approaches 0°the Scherk surface grain boundary morphology is transformed into a single screw dislocation that has an intermaterial dividing surface with the geometry of a single helicoid. Direct TEM imaging of the detailed core structure of this screw dislocation is presented. These images demonstrate that in the lamellar diblock copolymer the screw dislocation core is nonsingular. This nonsingular core structure represents a radical classical studies of dislocations in atomic crystals.

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This work is a summary of experiments, numerical simulations, and analytic modeling that demonstrate improved radiation confinement when changing from a hohlraum made from gold to one made from a mixture of high Z materials ("cocktail").First, the results from several previous planar sample experiments are described that demonstrated the potential of cocktail wall materials. Then a series of more recent experiments are described in which the radiation temperatures of hohlraums made from uranium-based cocktails were directly measured and compared with a gold reference hohlraum. Once cocktail hohlraums with minimal oxygen contamination were made, an increase in radiation of up to ~7 eV was measured, which agrees well with modeling.When applied to an indirectly-driven fusion capsule absorbing ~160 kJ of x-ray energy, 2 this data suggests that a hohlraum made from a suitably chosen uranium-based cocktail would have about 17% less wall losses and require about 10% less laser energy than a gold hohlraum of the same size. 3Increasing the hohlraum coupling efficiency (ratio of capsule absorbed energy to laser energy) for indirectly-driven inertial confinement fusion experiments at the National Ignition Facility (NIF) is desired because it would allow one to drive an ignition capsule with reduced laser energy. The radiation temperature a hohlraum achieves is the result of a balance between sources and sinks ( Fig. 1). This radiation energy balance is described by the following equation [1].Here, E cap is the x-ray energy absorbed by the fusion capsule in the center of the hohlraum, (E Laser -E Scatter ) is the laser energy delivered inside the hohlraum with backscatter losses accounted for, η CE is the fraction of that energy that is converted to xrays, E wall is the x-ray energy lost into the hohlraum wall, and E LEH is the x-ray energy that escapes out the laser entrance holes (LEHs). In this work, we show that we can reduce E wall by replacing a standard gold hohlraum with one made from a combination of high Z materials. For a fixed E cap , which is set by the ignition capsule design, reducing the wall losses allows one to reduce the amount of laser energy required for ignition, which increases the lifetime of NIF laser optics and thus has a large impact on facility operating costs. Alternatively, at fixed laser energy, reducing wall losses allows one to drive a capsule with more absorbed energy, thus increasing margin for ignition.The x-ray losses into the hohlraum wall are well modeled as a radiation ablation front diffusing into a cold wall, the so-called Marshak wave [2]. The starting point for that theory is the one-dimensional diffusion equation that describes the conservation of energy for a radiating fluid. In words, that equation states that the time derivative of the energy density is equal to the gradient of the diffusive energy flux. If we neglect the 4 radiation component of the energy density and the material component of the diffusive energy flux, we get ! " "t #ewhere ρ is the density, e is t...

We report here on the two-dimensional patterns formed by supramolecular materials deposited from solution on oxidized silicon substrates. The supramolecular materials studied are composed of mushroom-shaped nanostructures measuring 2−5 nm in cross-section and approximately 7−8 nm in height. Two different materials were studied, one containing nanostructures with a hydrophilic phenolic base surface and the other containing a hydrophobic one with trifluoromethyl groups. The substrates were exposed to solutions of these materials for a set induction time at a series of concentrations using a motorized dipping apparatus. Samples were characterized by contact-angle measurements and tapping-mode atomic force microscopy. We observed distinct patterns as a function of concentration in phenolic supramolecular materials that interact favorably with the oxidized silicon surface. At low concentrations (0.01 wt %), the nanostructures form islands with uniform size of approximately 0.02 μm, which have the height of a single nanostructure (7.2 nm). As concentration increases, a string-like morphology with uniform width is observed first, followed by a percolating texture. At yet higher concentrations, the film transforms to a honeycomb morphology, but its height still remains equal to that of a single nanostructure. When interactions between the nanostructure and the surface are not favorable (i.e., between trifluoromethyl end groups and oxidized silicon), uniform height patterns are not observed. The distinct geometries are possibly the result of strong material−substrate interactions balanced by a repulsive force that could have electrostatic origin. The extremely uniform thickness of the two-dimensional patterns may originate in the hydrophobic and hydrophilic nature of opposite poles of the nanostructures, thus suppressing vertical growth of the film.