Advanced Photon Source

A U.S. Department of Energy, Office of Science,
Office of Basic Energy Sciences national synchrotron x-ray research facility

Publications from year 2008

Temperature responsive hydroxypropyl cellulose for encapsulation. This work focuses on the use of temperature responsive gels (TRGs) (polymeric hydrogels with a large temperature-dependent change in volume) for flavor retention at cooking temperatures. Specifically, we have studied a gel with a lower critical solution temperature (LCST) that swells at low temperatures and collapses at high temperatures. In the collapsed state, the polymer acts as a transport barrier, keeping the volatile flavors inside. We have successfully synthesized a cellulose gel that exhibits this volume change and have encapsulated an oil phase inside the gel. The flavor-loaded encapsulated oil exhibited an increased release time when compared to similar gelatin capsules. (c) 2007 Elsevier B.V. All rights reserved.
K.A. Heitfeld, T. Guo, G. Yang and D.W. Schaefer. Cited: Materials Science & Engineering C-Biomimetic and Supramolecular Systems, 2008, 28 (3), Apr 1, p 374-379.

Phase Behavior of Binary Blends of High Molecular Weight Diblock Copolymers with a Low Molecular Weight Triblock. Binary blends of four different high molecular weight poly(styrene-b-isoprene) (SI) diblock copolymers with a lower molecular weight poly(styrene-b-isoprene-b-styrene) (SIS) triblock copolymer were prepared, and their morphology was characterized by transmission electron microscopy and ultra-small-angle X-ray scattering. All the neat block copolymers have nearly symmetric composition and exhibit the lamellar morphology. The SI diblock copolymers had number-average molecular weights, M n, in the range 4.4 ◊ 105 1.3 ◊ 106 g/mol and volume fractions of poly(styrene), ¶PS, in the range 0.43 0.49, and the SIS triblock had a molecular weight of M n ~ 6.2 ◊ 104 g/mol with ¶PS = 0.41. The high molecular weight diblock copolymers are very strongly segregating, with interaction parameter values, «N, in the range 470 1410. A morphological phase diagram in the parameter space of molecular weight ratio (R = Mndiblock/1/2Mntriblock) and blend composition was constructed, with R values in the range between 14 and 43, which are higher than previously reported. The phase diagram revealed a large miscibility gap for the blends, with macrophase separation into two distinct types of microphase-separated domains for weight fractions of SI, wSI < 0.9, implying virtually no solubility of the much higher molecular weight diblocks in the lower molecular weight triblock. For certain blend compositions, above R ~ 30, morphological transitions from the lamellar to cylindrical and bicontinuous structures were also observed.
R.A. Mickiewicz, E. Ntoukas, A. Avgeropoulos and E.L. Thomas. Cited: Macromolecules, 41(15), 5785-5792, 2008.

In situ ultra-small-angle X-ray scattering study of the solution-mediated formation and growth of nanocrystalline ceria. A.J. Allen, V.A. Hackley, P.R. Jemian, J. Ilavsky, J.M. Raitano and S.-W. Chan. Cited: Journal Of Applied Crystallography, 2008, 41 (5), p 918-929.

Three-dimensional coherent x-ray diffraction imaging of a ceramic nanofoam: Determination of structural deformation mechanisms. Ultralow density polymers, metals, and ceramic nanofoams are valued for their high strength-to-weight ratio, high surface area, and insulating properties ascribed to their structural geometry. We obtain the labrynthine internal structure of a tantalum oxide nanofoam by x-ray diffractive imaging. Finite-element analysis from the structure reveals mechanical properties consistent with bulk samples and with a diffusion-limited cluster aggregation model, while excess mass on the nodes discounts the dangling fragments hypothesis of percolation theory.
A. Barty, S. Marchesini, H.N. Chapman, C. Cui, M.R. Howells, D.A. Shapiro, A.M. Minor, J.C.H. Spence, U. Weierstall, J. Ilavsky, A. Noy, S.P. Hau-Riege, A.B. Artyukhin, T. Baumann, T. Willey, J. Stolken, T. Van Buuren and J.H. Kinney. Cited: Physical Review Letters, 2008, 101 (5), Aug 1

Small angle X-ray scattering analysis of the effect of cold compaction of Al/MoO3 thermite composites. Nanothermites composed of aluminum and molybdenum trioxide (MoO3) have a high energy density and are attractive energetic materials. To enhance the surface contact between the spherical Al nanoparticles and the sheet-like MoO3 particles, the mixture can be cold-pressed into a pelleted composite. However, it was found that the burn rate of the pellets decreased as the density of the pellets increased, contrary to expectation. Ultra-small angle X-ray scattering (USAXS) data and scanning electron microscopy (SEM) were used to elucidate the internal structure of the Al nanoparticles, and nanoparticle aggregate in the composite. Results from both SEM imaging and USAXS analysis indicate that as the density of the pellet increased, a fraction of the Al nanoparticles are compressed into sintered aggregates. The sintered Al nanoparticles lost contrast after forming the larger aggregates and no longer scattered X-rays as individual particles. The sintered aggregates hinder the burn rate, since the Al nanoparticles that make them up can no longer diffuse freely as individual particles during combustion. Results suggest a qualitative relationship for the probability that nanoparticles will sinter, based on the particle sizes and the initial structure of their respective agglomerates, as characterized by the mass fractal dimension.
J.A. Hammons, W. Wang, J. Ilavsky, M.L. Pantoya, B.L. Weeks and M.W. Vaughn. Cited: Physical Chemistry Chemical Physics, 2008, 10 (1), p 193-199.

High-Surface-Area Biocarbons for Reversible On-Board Storage of Natural Gas and Hydrogen, Peter Pfeifer, Jacob W. Burress, Mikael B. Wood, Cintia M. Lapilli, Sarah A. Barker, Jeffrey S. Pobst, Raina J. Cepel, Carlos Wexler, Parag S. Shah, Michel J. Gordon, Galen J. Suppes, Philip S. Buckley, Darren J. Radke, Jan Ilavsky, Anne C. Dillon, Philip A. Parilla, Michael Benham, and Michael W. Roth, , Invited paper in: Life Cycle Analysis for New Energy Conversion and Storage Systems, eds. V.M Fthenakis, A.C. Dillon, and N. Savage, Mater. Res. Soc. Symp. Proc. 1041, 1041-R02-02 (2008).

Protection of organic carbon in soil microaggregates via restructuring of aggregate porosity and filling of pores with accumulating organic matter. We examined relationships between the pore structure of microaggregates and the protection of organic matter (OM) within that structure. By using ultra-small angle X-ray scattering (USAXS) before and after combustion of microaggregates at 350†∞C, we took advantage of differences in X-ray scattering contrast among soil minerals, OM, and air to evaluate the distribution of the total- and OM-filled porosity within microaggregates (53-250†[mu]m in diameter). Systematic changes in microaggregate structure were observed for long-term field manipulations of land use (a chronosequence of tallgrass prairie restorations) and agricultural management (conventional tillage versus no-till at two levels of nitrogen fertilization). Our results imply that OM preservation arose from the evolution of the architectural system of microaggregates during their formation and stabilization. Soils and treatments with increasing OM in microaggregates were associated with encapsulation of colloidal OM by minerals, thereby creating protected OM-filled pores at the submicron scale within the microaggregate structure. For example, in the prairie chronosequence, microaggregates from the cultivated soil had the lowest concentration of OM, but 75% of the OM that had survived cultivation was in OM-filled pores. Following restoration, the concentration of OM in microaggregates increased rapidly, but the proportion of OM in OM-filled pores declined initially and then increased over time until 90% of the OM was in OM-filled pores. OM totally encapsulated within the pore structure can create spatial and kinetic constraints on microbial access to and degradation of OM. Encapsulation of OM increases the capacity for its protection relative to sorption on mineral surfaces, and comparison of its extent among treatments suggests important feedback loops. The use of USAXS, which has not previously been applied to the study of soil aggregate structures and the distribution of OM within those structures, provided new information on the mechanisms of OM protection in soil microaggregates, and insights relevant to strategies for enhancing carbon-sequestration in soil through changes in agricultural management practices and land use.
J.F. McCarthy, J. Ilavsky, J.D. Jastrow, L.M. Mayer, E. Perfect and J. Zhuang. Cited: Geochimica et Cosmochimica Acta, 2008, 72 (19), p 4725-4744.

Quantitative Measurement of Nanoparticle Halo Formation around Colloidal Microspheres in Binary Mixtures. A new colloidal stabilization mechanism, known as nanoparticle haloing (Tohver, V.; Smay, J. E.; Braem, A.; Braun, P. V.; Lewis, J. A. Proc. Natl. Acad. Sci. U.S.A. 2001, 98, (16), 8950 8954), has been predicted theoretically and inferred experimentally in microsphere nanoparticle mixtures that possess high charge and size asymmetry. The term halo implies the existence of a nonzero separation distance between the highly charged nanoparticles and the negligibly charged microspheres that they surround. By means of ultrasmall-angle X-ray scattering, we have quantified the microsphere nanoparticle separation distance as well as the number of nanoparticles and their lateral separation distance within the self-organized halos that form in these binary mixtures.
F. Zhang, G.G. Long, P.R. Jemian, J. Ilavsky, V.T. Milam and J.A. Lewis. Cited: Langmuir, 2008, 24 (13), p 6504-6508.

Quantitative characterization of the contrast mechanisms of ultra-small-angle X-ray scattering imaging. F. Zhang, G.G. Long, L.E. Levine, J. Ilavsky and P.R. Jemian. Cited: Journal Of Applied Crystallography, 2008, 41 (2), p 416-427.

Highly dispersed nanosilica-epoxy resins with enhanced mechanical properties Epoxy–nanocomposite resins filled with 12-nm spherical silica particles were investigated for their thermal and mechanical properties as a function of silica loading. The nanoparticles were easily dispersed with minimal aggregation for loadings up to 25 wt% as determined using transmission electron microscopy (TEM) and ultra-small-angle X-ray scattering (USAXS). A proportional decrease in cure temperatures and glass transition temperature (for loadings of 10 wt% and above) was observed with increased silica loading. The morphology determined by USAXS is consistent with a zone around the silica particles from which neighboring particles are excluded. The ‘‘exclusion zone’’ extends to 10 the particle diameter. For samples with loadings less than 10 wt%, increases of 25% in tensile modulus and 30% in fracture toughness were obtained. More highly loaded samples continued to increase in modulus, but decreased in strength and fracture toughness. Overall, the addition of nanosilica is shown as a promising method for property enhancement of aerospace epoxy composite resins. C. Chen, R.S. Justice, D.W. Schaefer and J.W. Baur. Cited: Polymer, 2008, 49 (17), 2008, p 3805-3815.

Silica Fillers for Elastomer Reinforcement. D.J. Kohls, D.W. Schaefer, R. Kosso and E. Feinblum. Current Topics in Elastomers Research, 2008

Nanofibre Reinforcement of Soft Materials. D.W. Schaefer, J. Zhao, H. Dowty, M. Alexander and E.B. Orler. Soft Matter, 2008, 4 (10), p 2071 - 2079.

Well-Ordered Polymer Melts with 5 nm Lamellar Domains from Blends of a Disordered Block Copolymer and a Selectively Associating Homopolymer of Low or High Molar Mass. The use of short chain block copolymer melts as nanostructured templates with sub-10 nm domains is often limited by their low segregation strength (chi N). Since increasing molar mass to strengthen segregation also increases the interdomain spacing of block copolymer melts, it is more desirable to increase the Hory-Huggins segment-segment interaction parameter, chi, to produce strong segregation. We have recently shown that poly(oxyethylene-oxypropylene-oxyethylene) block copolymer melts can undergo disorder-to-order transition when blended with a selectively associating homopolymer that can hydrogen bond with one of the blocks. Here, we study the effect of the molar mass of poly(acrylic acid) in the range 1-13 times that of the copolymer on the segregation of a 6.5 kg/mol poly(oxyethylene-oxypropylene-oxyethylene) copolymer melt. The neat copolymer is disordered, and the addition of poly(acrylic acid) resulted in a well-ordered lamellar morphology with an interdomain spacing of 10 +/- 1.0 nm. Using small-angle and ultrasmall-angle X-ray scattering, we found that the blends remain well ordered at 80 degrees C over the entire range of homopolymer chain lengths. A small increase in the interdomain spacing of the lamellae and an order-order transition from lamellae-to-cylindrical morphology was observed in all blends as a function of increasing homopolymer concentration. The trends observed in experiments were validated by self-consistent field theoretical simulations.
V.R. Tirumala, V. Daga, A.W. Bosse, A. Romang, J. Ilavsky, E.K. Lin and J.J. Watkins. Cited: Macromolecules, 2008, 41 (21), Nov 11, p 7978-7985.

Comparison of New and Legacy TATBs. D.M. Hoffman, T.M. Willey, A.R. Mitchell and S.C. Depiero. Cited: Journal of Energetic Materials, 2008, 26 (3), p 139-162.