Author
T. P. Rieker
Other affiliations: National Science Foundation, University of Colorado Boulder
Bio: T. P. Rieker is an academic researcher from University of New Mexico. The author has contributed to research in topics: Small-angle X-ray scattering & Small-angle scattering. The author has an hindex of 23, co-authored 33 publications receiving 3070 citations. Previous affiliations of T. P. Rieker include National Science Foundation & University of Colorado Boulder.
Papers
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TL;DR: In this article, the authors report a rapid, aerosol process that results in solid, completely ordered spherical particles with stable hexagonal, cubic, or vesicular mesostructures, which relies on evaporation-induced interfacial self-assembly confined to a spherical aerosol droplet.
Abstract: Nanostructured particles exhibiting well-defined pore sizes and pore connectivities (1-, 2-, or 3-dimensional) are of interest for catalysis, chromatography, controlled release, low dielectric constant fillers, and custom-designed pigments and optical hosts During the last several years considerable progress has been made on controlling the macroscopic forms of mesoporous silicas prepared by surfactant and block copolymer liquid crystalline templating procedures Typically interfacial phenomena are used to control the macroscopic form (particles, fibers, or films), while self-assembly of amphiphilic surfactants or polymers is used to control the mesostructure To date, although a variety of spherical or nearly-spherical particles have been prepared, their extent of order is limited as is the range of attainable mesostructures They report a rapid, aerosol process that results in solid, completely ordered spherical particles with stable hexagonal, cubic, or vesicular mesostructures The process relies on evaporation-induced interfacial self-assembly (EISA) confined to a spherical aerosol droplet The process is simple and generalizable to a variety of materials combinations Additionally, it can be modified to provide the first aerosol route to the formation of ordered mesostructured films
937 citations
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TL;DR: Mise en evidence de the structure par des etudes de diffusion de rayons X haute resolution d'echantillons minces smectiques C prepares entre deux lames solides par refroidissement a partir de the phase smectique A.
Abstract: Mise en evidence de la structure par des etudes de diffusion de rayons X haute resolution d'echantillons minces smectiques C prepares entre deux lames solides par refroidissement a partir de la phase smectique A
446 citations
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TL;DR: In this paper, three different water-alcohol cosolvent systems were used to assemble mesoporous molecular sieve silicas with wormhole framework structures (previously denoted HMS silicas) from an electrically neutral amine surfactant (S{degree}) and a silicon alkoxide precursor (I{degree).
Abstract: Three different water-alcohol cosolvent systems were used to assemble mesoporous molecular sieve silicas with wormhole framework structures (previously denoted HMS silicas) from an electrically neutral amine surfactant (S{degree}) and a silicon alkoxide precursor (I{degree}). The fundamental particle size and associated textural (interparticle) porosity of the disordered structures were correlated with the solubility of the surfactant in the water-alcohol cosolvents used for the S{degree}I{degree} assembly process. Polar cosolvents containing relatively low volume fractions of C{sub n}H{sub 2n+1}OH alcohols (n = 1--3) gave heterogeneous surfactant emulsions that assembled intergrown aggregates of small primary particles with high textural pore volumes (designated HMS-HTx). Conversely, three-dimensional, monolithic particles with little or no textural porosity (designated HMS-LTx) were formed from homogeneous surfactant solutions in lower polarity cosolvents. Aluminum substituted AL-HMS-HTx analogues with high textural porosity and improved framework accessibility also were shown to be much more efficient catalysts than AL-HMS-LTx or monolithic forms of hexagonal AL-MCM-41 for the sterically demanding condensed phase alkylation of 2,4-di-tert-butylphenol with cinnamyl alcohol. Transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) studies verified the textural differences between wormhole HMS and electrostatically assembled hexagonal MCM-41 and SBA-3 molecular sieves. Power law fits to the scattering data indicated a surface fractal (D{submore » s} = 2.76) for HMS-HTx, consistent with rough surfaces. A second power law at lower-q indicated the formation of a mass fractal (D{sub m} = 1.83) consistent with branching of small fundamental particles. Hexagonal MCM-41 and SBA-3 silicas, on the other hand, exhibited scattering properties consistent with moderately rough surfaces (D{sub s} = 2.35 and 2.22, respectively) and large particle diameters ({much{underscore}gt}1 {micro} m). HMS-LTx silicas showed little or no mass fractal character (D{sub m} = 2.87), and no surface fractal scattering.« less
334 citations
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TL;DR: In this paper, the authors show that stabilization of the director field occurs at the chevron interface, so that SC cells behave as two nearly independent cells optically and electrically in series.
Abstract: The recent discovery of ``chevron'' structured smectic-C (SC) layers in surface-stabilized ferroelectric liquid-crystal (SSFLC) cells [T. P. Rieker, N. A. Clark, G. S. Smith, D. S. Parmar, E. B. Sirota, and C. R. Safinya, Phys. Rev. Lett. 59, 2568 (1987)] enables the understanding of many commonly observed features of SSFLC director and layer structure. We present the full three-dimensional layer structure of zigzag walls, the predominant SSFLC defect, which we find to mediate change in chevron direction. We show that stabilization of the director field in SC chevron cells occurs at the chevron interface, so that SC chevron cells behave as two nearly independent cells optically and electrically in series.
156 citations
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TL;DR: In this paper, high-resolution calorimetric studies have been made of the liquid crystal phase transitions for several dispersions of 70-Angstrom-diam silica spheres (aerosil) in octylcyanobiphenyl (8CB) as a function of silica density.
Abstract: High-resolution calorimetric studies have been made of the liquid crystal phase transitions for several dispersions of 70-{Angstrom}-diam silica spheres (aerosil) in octylcyanobiphenyl (8CB) as a function of silica density {rho}{sub S}. The excess specific heat peaks associated with the nematic-isotropic (N-I) and the nematic{endash}smectic-{ital A} (N-SmA) transitions both exhibit shifts to lower temperatures, decreases in the specific heat maximum values, and decreases in the transition enthalpies as {rho}{sub S} is increased. Two distinct regimes of {rho}{sub S}-dependent behaviors are observed with a crossover between them at {rho}{sub S}{congruent}0.1thinspgthinspcm{sup {minus}3}. For lower silica densities, sharp second-order C{sub p} peaks are observed at the N-SmA transitions, characterized by effective critical exponents that decrease monotonically with {rho}{sub S} from the pure 8CB value toward the three-dimensional {ital XY} value, and two closely spaced but distinct first-order C{sub p} features are observed at the N-I transition. For higher silica densities, both the N-SmA and the N-I transitions exhibit a single rounded C{sub p} peak, shifting in temperature and decreasing in total enthalpy in a manner similar to that observed in 8CB+aerogel systems. Small angle x-ray scattering data are qualitatively aerogel-like and yield temperature-independent mass-fractal dimensionalities for aerosil aggregates that differ for samples with silicamore » densities above and below the crossover density. {copyright} {ital 1998} {ital The American Physical Society}« less
153 citations
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2,090 citations
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TL;DR: In this paper, a review of the preparation of ordered mesoporous catalysts is presented, and the essential properties of the resulting materials are described in the first part of this review.
1,994 citations
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1,814 citations
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TL;DR: In this article, a review of state-of-the-art synthetic routes for the preparation of magnetic nanoparticles useful for biomedical applications is presented, with a special emphasis on showing the benefits of using nanoparticles.
Abstract: This review is focused on describing state-of-the-art synthetic routes for the preparation of magnetic nanoparticles useful for biomedical applications. In addition to this topic, we have also described in some detail some of the possible applications of magnetic nanoparticles in the field of biomedicine with special emphasis on showing the benefits of using nanoparticles. Finally, we have addressed some relevant findings on the importance of having well-defined synthetic routes to produce materials not only with similar physical features but also with similar crystallochemical characteristics.
1,753 citations
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TL;DR: In this paper, a review of state-of-the-art synthetic routes for the preparation of magnetic nanoparticles useful for biomedical applications is presented, with a special emphasis on showing the benefits of using nanoparticles.
Abstract: This review is focused on describing state-of-the-art synthetic routes for the preparation of magnetic nanoparticles useful for biomedical applications. In addition to this topic, we have also described in some detail some of the possible applications of magnetic nanoparticles in the field of biomedicine with special emphasis on showing the benefits of using nanoparticles. Finally, we have addressed some relevant findings on the importance of having well-defined synthetic routes to produce materials not only with similar physical features but also with similar crystallochemical characteristics.
1,623 citations