gamma-Al2O3 is one of the most extensively utilized metal oxides in heterogeneous catalysis. Conventional forms of this oxide typically exhibit a surface area and pore volume less than 250 m2/g and 0.5 cm3/g, respectively. Previous efforts to prepare mesostructured forms of alumina resulted only in structurally unstable derivatives with amorphous framework walls. The present work reports mesostructured aluminas with walls made of gamma-Al2O3, denoted MSU-gamma. These materials are structurally stable and provide surface areas and pore volumes up to 370 m2/g and 1.5 cm3/g, respectively. The key to obtaining these structures is the formation of a mesostructured surfactant/boehmite precursor, denoted MSU-S/B, assembled through the hydrolysis of an aluminum cation, oligomer, or molecule in the presence of a nonionic surfactant. Mesostructured, gamma-aluminas offer the possibility of improving the catalytic efficiency of many heterogeneous catalytic processes, such as petroleum refining, petrochemical processing, and automobile exhaust control.

Linear low-density polyethylene (LLDPE) blown films fabricated under two different processing conditions, namely a non-stalk bubble configuration and a stalk bubble configuration, were investigated. Morphological characterization was performed using small-angle X-ray scattering, transmission electron microscopy, infrared dichroism, and differential scanning calorimetry. The findings on crystal orientation characteristics of the films suggest that modification on the widely accepted row orientation model of Keller and Machin may be needed. In comparison to the conventional non-stalk bubble geometry for LLDPE film blowing, the stalk bubble configuration can produce a more randomly orientated lamellar texture, resulting in less anisotropy in mechanical properties and a higher dart impact resistance. A good correlation between mechanical properties and morphological features was found.

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Carbon blacks (CE) demonstrate varied structural features on length scales from angstroms to micrometers. Widely used as fillers in polymers, carbon blacks improve the mechanical and electrical properties of the host material. In general, CB is a low-dimensional mass-fractal aggregate of carbonaceous primary particles. Here we investigate the effect of processing on the interpenetration of aggregates in CB/polymer composites by small-angle X-ray scattering (SAXS). We performed SAXS measurements on a series of N330/EPR and N330/HDPE composites containing different amounts of a commercially available N330 carbon black. N330/HDPE composites were prepared by two different methods. The first method is Brabender dispersion of depelletized N330 in molten polymer; the second method is high-shear mixing of depelletized N330 in HDPE dissolved in a good solvent and subsequent addition of this mixture to a poor solvent for polyethylene. SAXS experiments were performed at the University of New Mexico/Sandia National Laboratories SAXS Laboratory. Data were collected on the Bonse-Hart camera with a a-range of 0.003 < q < 1 nm(-1). This wide q-range probes the structure of both the primary carbon black particles and aggregates of these particles. Depelletized N330 displays two power law regimes from which we deduce a surface-fractal dimension D-s = 2.3 for the primary particles and a mass fractal dimension D-m = 1.8 for the aggregate. For pelletized N330, the mass fractal domain vanishes as a result of aggregate interpenetration and, therefore,loss of correlation between primary particles. For N330/HDPE composites prepared by the Brabender method, the SAXS curve is similar to that obtained for the depelletized samples, indicative of little to no interpenetration of the aggregates. For N330/HDPE composites prepared by the solvent method and N330/EPR composites the SAXS curve is similar to that obtained for pelletized N330, indicative of extensive interpenetration of the aggregates.

The scaling function S(q/­) is constrained by the physics of the highand low-frequency limits. As q=­ ! `, S must approach i­/q in order for j to assume its superconducting form, equation (1). At low frequencies, S approaches a real constant S1(0) which characterizes the d.c. conductivity of the normal state. By comparing the measured complex conductivity to equation (2), we can extract both the phase stiffness and correlation time at each temperature. To analyse the experimental data in terms of equation (2), we note that the phase angle of the complex conductivity, J [ tan 2 1…j2=j1†, equals the phase angle of S(q/­). Therefore J depends only on the single parameter ­, and is independent of Tu. With the appropriate choice of ­(T), all the measured values of J should collapse to a single curve when plotted as a function of the normalized frequency q/­. Knowing ­(T), Tu is obtained from a collapse of the normalized conductivity magnitude, (~­=kBT0v†jj…q†j=jQ, to jS…q=­†j. Figure 3 shows the collapse of the data to the phase angle and magnitude of S. As anticipated, S approaches a real constant in the limit q=­ ! 0, and approaches i­/q as q=­ ! `. When analysed further, the data reveal a con®rmation of thermal generation of vortices in the normal state. In the KTB picture we expect that the d.c. conductivity will equal kBT/nfD© 2 0, which is the ` ̄ux̄ow' conductivity of nf free vortices with quantized ̄ux ©0, and diffusivity D (ref. 16). Together with equation (2), this implies that ­ is a linear function of nf, that is, ­ ˆ ­0nf avc=£, where avc is the area of a vortex core, £ [ T=Tu is the reduced temperature, and ­0 [ p 2S1…0†D=avc. Moreover, we expect that nf will be a thermally activated function, except for T very close to TKTB. The activation energy is simply CkBT 0 u, where C is a non-universal constant of order unity. It follows that the ̄uctuation frequency depends exponentially on the reciprocal of the reduced temperature, ­ ˆ …­0=£†exp…2 2C=£†. The inset to Fig. 3 is a plot of log(£­) versus 1/£ which shows that the exponential relation is observed over nearly four orders of magnitude. This is direct evidence that vanishing of phase coherence in our samples re ̄ects the dynamics of thermally generated vortices. From the slope and intercept of a straight-line ®t we obtain C ˆ 2:23 and ­0 ˆ 1:14 3 10 14 s 2 . In Fig. 4 we present the behaviour of the bare stiffness and phasecorrelation time obtained from our measurement and modelling of j(q). The main panel contrasts Tu with the dynamical stiffness Tu(q) measured at 150 and 400 GHz. The inset shows t as a function of temperature together with hatching that highlights the region where t , ~=kBT. The parameters displayed in Fig. 4 suggest that while phase correlations indeed persist above Tc, they vanish well below T . The loss of coherence is driven by the decrease of Tu with increasing temperature, which renders the system increasingly defenceless to the proliferation of free vortices. This decrease of Tu is consistent with a phenomenological description of a d-wave superconductor derived from a Mott insulator. In this picture, the phase stiffness of an underdoped copper oxide superconductor is undermined below T by the thermal generation of normal electrons very near the points in momentum space where the superconducting gap vanishes. The pairing which remains in other regions of momentum space appears to contribute little to the overall phase stiffness. Near 95 K, t falls to its minimum detectable value of ~/kBT, which is the electron mean free time. Beyond this point, superconductivity becomes indistinguishable from the ballistic dynamics of normal electrons and the recovery of the incoherent normal state is complete. M

Particles possessing nanometre-scale pores of well-defined size and connectivity are of interest for catalysis, chromatography and controlled release of drugs, and as fillers with low dielectric constant, pigments and hosts for optically active compounds 1 , 2 . Silica containing ordered mesopores (of nanometre-scale width) can be prepared by templating of surfactant 3 , 4 and block copolymer 5 liquid-crystalline mesophases, and interfacial phenomena have been used to control the macroscopic form of these materials, providing mesoporous particles 1 , 6 , fibres 7 , 8 and films 9 , 10 . A variety of spherical or nearly spherical particles has been reported 1 , 6 , 7 , 11 , 12 , 13 , but the degree of ordering and the range of the porous mesostructures have been limited. Here we report a rapid, aerosol-based 14 , 15 , 16 process for synthesizing solid, well-ordered spherical particles with stable pore mesostructures of hexagonal and cubic topology, as well as layered (vesicular) structures. Our method relies on evaporation-induced interfacial self-assembly 17 confined to spherical aerosol droplets. This simple, generalizable process can be modified for the formation of ordered mesostructured thin films.

By combining the molecular silica precursor tetramethoxysilane (TMOS) with an alkaline, micellar, water: methanol solution, we form surfactant-templated silica gel (STSG) monoliths. The wet monoliths can be exchanged with ethanol and then supercritically extracted with carbon dioxide to produce surfactant-templated silica aerogels (STSAs). STSAs represent a new class of aerogels that are composed of aggregated submicron porous particles that have tunable intraparticle nanoporosity. STSAs catalyzed with NH4OH experience no measurable shrinkage upon extraction and have bulk densities less than ~0.15 g/cc. The STSAs can then be calcined to remove the remainder of the surfactant. The calcination process leads to minimal shrinkage (<8%), high surface area (~700 m2/g), uncracked monoliths with hierarchical inter- and intraparticle porosities, and bulk densities less than 0.08 g/cc. We use XRD, SAXS, SEM. 29Si NMR. and N2 Sorption to characterize the structure and porosity of these novel aerogels.

Small-angle x-ray scattering has been used to investigate the structure of some carbon blacks, some silicas, and an alumina-silica catalyst carrier on length scales from about 5 to 10,000 Å. Equations developed for structural studies of fractal and non-fractal aggregates of primary particles have been employed to analyze the scattering data. From the intensity data, the average diameters of the primary particles could be calculated or estimated. Despite the very different origins of the samples and the fact that the average diameters of the particles varied from about 30 to over 1000 Å, the scattered intensities from the samples had many common features. The data showed that the primary particles had a uniform density and were bounded by smooth or fractal surfaces. On length scales greater than the diameters of the primary particles but not more than a few times larger than the average diameters of the aggregates, some of the aggregates were mass fractals, and others were surface fractals.

Neutron small angle scatteiing is an efficient method to investigate mesoscopic structures in condensed matter physics, material science and biology, for dimensions between 1 and 103 nm, or Q-values between 10-2 and 10-5 A-I.The most common instrument is the slit hole camera [IJ with very long distances between entrance slit, sample and detector, e.g. up to 80 m for the well-known D 11 at the ILL in Grenoble.For very high resolution, the Bonse Hart camera covers a Q-range between l 0-4 and 10-5 A-I using a pair of parallel ideal silicon crystals as collimator [21.By multi-slit crystals the analyser can be multiplexed.Recently, we succeeded to build a prototype of a focusing camera [3] with a 4 m long copper-covered glass minor of very high quality; the entrance slit is imaged in the detector plane.For the first time, Q-values down to a few 10-4 A-I were reached, with a very low parasitic background.This instrument is well suited for pulsed sources because the detector is ojj'tl1e ptimary bean1, and the length is relatively small.