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 2002

Relation of the fractal structure of organic pigments to their performance. Different pigments embedded in polymer matrices were examined by small angle scattering of x- rays over 3 wave number decades. The scattering intensities show differences both in the mass fractal dimension (varying between 1.4 and 2.67) and the size of the particles. The differences are pronounced between dry pigment powders and the same powders in a polymer matrix as well as between the pigments themselves. Further, a correlation of pigment geometrical configuration and pigment performance, as perceived by the human eye, shows how pigments with a maximum color brightness per pigment mass can be created. (C) 2002 American Institute of Physics.

G. Skillas, N. Agashe, D.J. Kohls, J. Ilavsky, P. Jemian, L. Clapp, R.J. Schwartz and G. Beaucage. Cited: Journal of Applied Physics, 2002, 91 (9), May 1, p 6120-6124.

The effect of interphase coupling on the structure and mechanical properties of silica-siloxane composites. Silica-reinforced siloxane composites are synthesized with heat labile azo groups at the polymer-filler interface. The azo group serves as a "smart interface" in that it is responsive to heat. This system is used to assess the influence of interfacial chemical bonds on mechanical properties. By thermally severing the azo linkage, we can determine the influence of interfacial bonding on properties independent of other morphological factors. The virgin filler powders, azo-modified powders, silica-filled composites and azo-modified-silica-filled composites are characterized using small-angle x-ray scattering, IR spectroscopy, and scanning electron microscopy. Mechanical properties are correlated with the presence or absence of interface coupling, filler loading and thermal exposure. The data show that, at loadings above 5 wt%, elongation is enhanced in the azo-linked composites compared to the composites with bare fillers; modulus is enhanced at low silica loadings (<5wt%) but is reduced at high loadings. On thermal clipping of the coupling agent, we find a slight enhancement of the ultimate elongation, but only at loadings above 5 wt%. We conclude that although interfacial bonding has a positive effect on reinforcement, the influence of physical interactions at the interface overrides that of chemical bonds.

D.W. Schaefer, B.T.N. Vu and J.E. Mark. Cited: Rubber Chemistry and Technology, 2002, 75 (5), Nov-Dec, p 795-810.

Challenges and opportunities in complex materials: silica-reinforced elastomers. Small-angle light and X-ray scattering are used to study the morphology of reinforcing fillers in organic rubbers. The data, which extend over six orders of magnitude in length scale, reveal a complex morphology of the powders consisting of primary particles, aggregates and agglomerates. The fragility of the agglomerates is assessed by observation of partial agglomerate disruption after exposure to intense ultrasound. Upon incorporation into rubber by mechanical mixing, the agglomerates break down all the way to the aggregates. The results are used to outline opportunities to exploit the growth processes underlying the complex structure to optimize the morphology for composite applications. Soft agglomerates that easily break down to aggregates, for example, aid in dispersion of reinforcing fillers in rubbers. The high surface area of the primaries, on the other hand, can be used to adjust the interaction between the rubber and the filler in order to control dynamic mechanical response of the filled rubber. (C) 2002 Elsevier Science B.V. All rights reserved.

D.W. Schaefer, C. Suryawanshi, P. Pakdel, J. Ilavsky and P.R. Jemian. Cited: Physica a-Statistical Mechanics and Its Applications, 2002, 314 (1-4), Nov 1, p 686-695.

Structure optimization in colloidal reinforcing fillers: Precipitated silica. In an attempt to elucidate the role of filler morphology in elastomer reinforcement, we use x-ray, light and neutron scattering to determine the structure of precipitated silica powders. We find the signatures of at least three levels of structure: primary particles, aggregates and agglomerates. By observing the evolution of the scattering profile during solution synthesis, we are able to identify when these structures appear. We also investigate the effect of ionic strength on morphology and find evidence for the interpenetration of aggregates on drying of powders prepared at low ionic strength. Using a reinforcement model by Witten , Rubinstein and Colby, we conclude that the ideal filler will consist of soft agglomerates made up of hard aggregates. Based on the dependence of morphology on synthetic protocol, we present strategies for design of efficient reinforcing fillers.

D.W. Schaefer and C.Y. Chen. Cited: Rubber Chemistry and Technology, 2002, 75 (5), Nov-Dec, p 773-793.

Non-cavitation tensile creep in Lu-doped silicon nitride. The tensile creep behavior of a Lu-doped silicon nitride was studied in the temperature range 1400 1550 degreesC with test periods of up to 10200 h. Strain rates were 3-4 orders of magnitude less than those for Yb-doped grades of silicon nitride under the same conditions, suggesting a potential for prolonged operation of this material at temperatures up to 1470 degreesC. The stress exponent, n, and the activation energy, Q, for creep are 5.3 +/- 2.0 and (757 +/- 117) kJ/mol, respectively. Precise density and ultra-small-angle X-ray scattering measurements revealed that, in contrast to other grades of silicon nitride, cavitation could not be detected in the material studied. Redistribution of the secondary phases via solution-precipitation combined with grain boundary sliding is discussed as a possible creep mechanism. A discussion of the effect of Lu on viscosity indicates that replacement of Y by Lu may explain the improvement of creep behavior. (C) 2002 Published by Elsevier Science Ltd.

F. Lofaj, S.M. Wiederhorn, G.G. Long, B.J. Hockey, P.R. Jemian, L. Browder, J. Andreason and U. Taffner. Cited: Journal of the European Ceramic Society, 2002, 22 (14-15), p 2479-2487.

Effective pinhole-collimated ultrasmall-angle x-ray scattering instrument for measuring anisotropic microstructures. Small-angle scattering is widely used for measuring materials microstructure in the 1-100 nm size range. Ultrasmall-angle x-ray scattering (USAXS), typically achieved through crystal collimation, extends this size range to include features over 1 mum in size. This article reports on USAXS on the UNICAT beam line 33-ID at the Advanced Photon Source. The instrument makes use of a six-reflection crystal pair as a collimator and another six-reflection crystal pair as an analyzer. First principle absolute calibration and a broad scattering vector range make this a very effective instrument, limited only by the fact that the measurement of anisotropic microstructures is excluded due to slit smearing from the crystal collimation. This limitation has recently been removed by adding a horizontally reflecting crystal before and another after the sample. This creates a USAXS instrument with collimation in two orthogonal directions. We call this configuration effective pinhole USAXS. Now, anisotropic materials are probed using 9-17 keV photons in the same physically-relevant (from 50 nm to over 1 mum) microstructural size range as that available for materials which scatter isotropically. (C) 2002 American Institute of Physics.

J. Ilavsky, A.J. Allen, G.G. Long and P.R. Jemian. Cited: Review of Scientific Instruments, 2002, 73 (3), Mar, p 1660-1662.

Using nanotechnology to improve the performance of acrylic bone cements. A. Bellare, W. Fitz, A.H. Gomoll, M.B. Turell, R.D. Scott and T.S. Thornhill. Cited: The Orthopaedic Journal at Harvard Medical School , 2002, 4 p 93-96.