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See detailThe number of structures compatible with any correlation function
Gommes, Cédric ULg

Conference (2013, July)

A two-point correlation function provides a crucial yet an incomplete characterization of a microstructure because distinctly different microstructures may have the same correlation function. We address ... [more ▼]

A two-point correlation function provides a crucial yet an incomplete characterization of a microstructure because distinctly different microstructures may have the same correlation function. We address here the microstructural degeneracy question: What is the number of microstructures compatible with a specified correlation function? We compute this degeneracy in the framework of reconstruction methods, which enables us to map the problem to the determination of ground-state degeneracies. Since the configuration space of a reconstruction problem is a hypercube on which a Hamming distance is defined, we can calculate analytically the energy profile of any reconstruction problem, corresponding to the average energy of all microstructures at a given Hamming distance from a ground state. The steepness of the energy profile is a measure of the roughness of the energy landscape associated with the reconstruction problem, which can be used as a proxy for the ground-state degeneracy. The relationship between this roughness metric and the ground-state degeneracy is calibrated using a Monte Carlo algorithm for determining the ground-state degeneracy of a variety of microstructures (e.g., realizations of hard disks and Poisson point processes at various densities), as well as with microstructures with a known degeneracy (e.g., single disks of various sizes and a particular crystalline microstructure). We show that our results can be expressed in terms of the information content of the two-point correlation functions. From this perspective, the a priori condition for a reconstruction to be accurate is that the information content, expressed in bits, should be comparable to the number of pixels in the unknown microstructure. We provide a formula to calculate the information content of any two-point correlation function, which makes our results directly applicable by other researchers in the field. [less ▲]

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See detailThree-dimensional reconstruction of liquid phases in disordered mesopores using in situ small-angle scattering
Gommes, Cédric ULg

in Journal of Applied Crystallography (2013), 46

Small-angle scattering of X-rays (SAXS) or neutrons is one of the few experimental methods currently available for the in situ analysis of phenomena in mesoporous materials at the mesoscopic scale. In the ... [more ▼]

Small-angle scattering of X-rays (SAXS) or neutrons is one of the few experimental methods currently available for the in situ analysis of phenomena in mesoporous materials at the mesoscopic scale. In the case of disordered mesoporous materials, however, the main difficulty of the method lies in the data analysis. A stochastic model is presented, which enables one to reconstruct the three-dimensional nanostructure of liquids confined in disordered mesopores starting from small-angle scattering data. This so-called plurigaussian model is a multi-phase generalization of clipped Gaussian random field models. Its potential is illustrated through the synchrotron SAXS analysis of a gel permeated with a critical nitrobenzene/hexane solution that is progressively cooled below its consolute temperature. The reconstruction brings to light a wetting transition whereby the nanostructure of the pore-filling liquids passes from wetting layers that uniformly cover the solid phase of the gel to plugs that locally occlude the pores. Using the plurigaussian model, the dewetting phenomenon is analyzed quantitatively at the nanometre scale in terms of changing specific interface areas, contact angle and specific length of the triple line. [less ▲]

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See detailTHREE-DIMENSIONAL RECONSTRUCTION OF LIQUID PHASES CONFINED IN DISORDERED POROUS MEDIA: AN IN SITU SYNCHROTRON SAS ANALYSIS
Gommes, Cédric ULg; Hermida Merino, Daniel

Conference (2012, December)

We use Synchrotron Small-Angle X-ray Scattering to investigate temperature-induced morphological changes in binary hexane/nitrobenzene solutions confined in the pores of disordered mesoporous solids. The ... [more ▼]

We use Synchrotron Small-Angle X-ray Scattering to investigate temperature-induced morphological changes in binary hexane/nitrobenzene solutions confined in the pores of disordered mesoporous solids. The scattering data is analyzed with a plurigaussian model, which enables us to reconstruct the 3D morphology of the phases with a nanometer resolution. The reconstructions bring to light wetting transitions whereby the morphology of the nitrobenzene passes from a nanometer-thin layer that uniformly covers the solid surface to plugs that locally occlude the pore space. Our analysis enables us to quantitatively analyze the SAS data in terms of changing interface areas and wetting angles. The present contribution offers unprecedented insight into nanometer-scale wetting transitions. It also presents a novel SAS data analysis methodology that is applicable to a host of experimental situations involving disordered mesoporous materials. [less ▲]

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See detailThe number of structures compatible with any given correlation function
Gommes, Cédric ULg

Scientific conference (2012)

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See detailMicrostructural degeneracy associated with a two-point correlation function and its information content
Gommes, Cédric ULg; Jiao, Yang; Torquato, Salvatore

in Physical Review. E : Statistical, Nonlinear, and Soft Matter Physics (2012), 85

A two-point correlation function provides a crucial yet an incomplete characterization of a microstructure because distinctly differentmicrostructures may have the same correlation function. In an earlier ... [more ▼]

A two-point correlation function provides a crucial yet an incomplete characterization of a microstructure because distinctly differentmicrostructures may have the same correlation function. In an earlier Letter [Gommes, Jiao, and Torquato, Phys. Rev. Lett. 108, 080601 (2012)], we addressed the microstructural degeneracy question: What is the number of microstructures compatible with a specified correlation function? We computed this degeneracy, i.e., configurational entropy, in the framework of reconstruction methods, which enabled us to map the problem to the determination of ground-state degeneracies. Here, we provide a more comprehensive presentation of the methodology and analyses, as well as additional results. Since the configuration space of a reconstruction problem is a hypercube on which a Hamming distance is defined, we can calculate analytically the energy profile of any reconstruction problem, corresponding to the average energy of allmicrostructures at a given Hamming distance from a ground state. The steepness of the energy profile is a measure of the roughness of the energy landscape associated with the reconstruction problem, which can be used as a proxy for the ground-state degeneracy. The relationship between this roughness metric and the ground-state degeneracy is calibrated using a Monte Carlo algorithm for determining the ground-state degeneracy of a variety of microstructures, including realizations of hard disks and Poisson point processes at various densities as well as thosewith known degeneracies (e.g., single disks of various sizes and a particular crystalline microstructure). We show that our results can be expressed in terms of the information content of the two-point correlation functions. From this perspective, the a priori condition for a reconstruction to be accurate is that the information content, expressed in bits, should be comparable to the number of pixels in the unknown microstructure. We provide a formula to calculate the information content of any two-point correlation function, which makes our results broadly applicable to any field in which correlation functions are employed. [less ▲]

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See detailMolecular and Morphological Aspects of Annealing-Induced Stabilization of Starch Crystallites
Gomand, Sara; Lamberts, Lieve; Gommes, Cédric ULg et al

in Biomacromolecules (2012), 13

A unique series of potato (mutant) starches with highly different amylopectin/amylose (AP/AM) ratios was annealed in excess water at stepwise increasing temperatures to increase the starch melting (or ... [more ▼]

A unique series of potato (mutant) starches with highly different amylopectin/amylose (AP/AM) ratios was annealed in excess water at stepwise increasing temperatures to increase the starch melting (or gelatinization) temperatures in aqueous suspensions. Small-angle X-ray scattering (SAXS) experiments revealed that the lamellar starch crystals gain stability upon annealing via thickening for high-AM starch, whereas the crystal surface energy decreases for AM-free starch. In starches with intermediate AP/AM ratio, both mechanisms occur, but the surface energy reduction mechanism prevails. Crystal thickening seems to be associated with the cocrystallization of AM with AP, leading to very disordered nanomorphologies for which a new SAXS data interpretation scheme needed to be developed. Annealing affects neither the crystal internal structure nor the spherulitic morphology on a micrometer length scale. [less ▲]

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See detailMesoporosity of Zeolite Y – 3D Quantitative Study by Image Analysis of Electron Tomograms
Zecevic, Jovana; Gommes, Cédric ULg; friedrich, Heiner et al

in Angewandte Chemie (International ed. in English) (2012), 51

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See detailDensity of states for a specified correlation function and the energy landscape
Gommes, Cédric ULg; Jiao, Yang; Torquato, Salvatore

in Physical Review Letters (2012)

The degeneracy of two-phase disordered microstructures consistent with a specified correlation function is analyzed by mapping it to a ground-state degeneracy. We determine for the first time the ... [more ▼]

The degeneracy of two-phase disordered microstructures consistent with a specified correlation function is analyzed by mapping it to a ground-state degeneracy. We determine for the first time the associated density of states via a Monte Carlo algorithm. Our results are described in terms of the roughness of the energy landscape, defined on a hypercubic configuration space. The use of a Hamming distance in this space enables us to define a roughness metric, which is calculated from the correlation function alone and related quantitatively to the structural degeneracy. This relation is validated for a wide variety of disordered systems. [less ▲]

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See detailBridging the gap between cellulose chemistry and heterogeneous catalysis
Van de Vyver, S; Geboers, J; Peng, Li et al

in WIT Transactions on Ecology and the Environment (2011), 154

Although cellulosic biomass offers a promising alternative as an abundant renewable resource in the production of biofuels and platform chemicals, so far only a few studies have reported its aqueous-phase ... [more ▼]

Although cellulosic biomass offers a promising alternative as an abundant renewable resource in the production of biofuels and platform chemicals, so far only a few studies have reported its aqueous-phase conversion into glucose or sugar alcohols using solid chemocatalysts. The principal reason is that these polymeric biomolecules with semi-crystalline structure cannot penetrate the pores of conventional heterogeneous chemocatalysts. New advances in the conversion of cellulose thus require the design of efficient multifunctional catalytic systems with sterically accessible acid and metal sites. [less ▲]

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See detailIn situ SAXS under shear unveils the gelation of aqueous starch suspensions and the impact of added amylose-lipid complexes
Putseys, Joke; Gommes, Cédric ULg; Van Puyvelde, P. et al

in Carbohydrate Polymers (2011), 84

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See detailKrypton adsorption as a suitable tool for surface characterization of multi-walled CNTs
Zilli, Dario; Bonelli, P.; Gommes, Cédric ULg et al

in Carbon (2011), 49

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See detailSynthesis and characterization of highly loaded Pt/carbon xerogel catalysts prepared by Strong Electrostatic Adsorption method
Job, Nathalie ULg; Maillard, F.; Chatenet, M. et al

Conference (2010, July 11)

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See detailRelationship between BET specific surface area, DR- and t-plot pore volume
Scherdel, C.; Reichenauer, G.; Wiener, M. et al

Poster (2010, May 23)

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