The influence of surface roughness on the adhesive interactions and phase behavior of suspensions of calcite nanoparticles

We investigate the impact of nanoparticle roughness on the phase behaviour of suspensions in models of calcium carbonate nanoparticles. We use a Derjaguin approach that incorporates roughness effects and interactions between the nanoparticles modelled with a combination of DLVO forces and hydration forces, derived using experimental data and atomistic molecular dynamics simulations, respectively. Roughness effects, such as atomic steps or terraces appearing in mineral surfaces result in very different effective inter-nanoparticle potentials. Using stochastic Langevin Dynamics computer simulations and the effective interparticle interactions we demonstrate that relatively small changes in the roughness of the particles modify significantly the stability of the suspensions. We propose that the sensitivity of the phase behavior to the roughness is connected to the short length scale of the adhesive attraction arising from the ordering of water layers confined between calcite surfaces. Particles with smooth surfaces feature strong adhesive forces, and form gel fractal structures, while small surface roughness, of the order of atomic steps in mineral faces, stabilize the suspension. We believe that our work helps to rationalize the contrasting experimental results that have been obtained recently using nanoparticles or extended surfaces, which provide support for the existence of adhesive or repulsive interactions, respectively. We further use our model to analyze the synergistic effects of roughness, pH and ion concentration on the phase behavior of suspensions, connecting with recent experiments using calcium carbonate nanoparticles

Finite-time adiabatic processes: derivation and speed limit

Obtaining adiabatic processes that connect equilibrium states in a given time represents a challenge for mesoscopic systems. In this paper, we explicitly show how to build these finite-time adiabatic processes for an overdamped Brownian particle in an arbitrary potential, a system that is relevant both at the conceptual and the practical level. This is achieved by jointly engineering the time evolutions of the binding potential and the fluid temperature. Moreover, we prove that the second principle imposes a speed limit for such adiabatic transformations: there appears a minimum time to connect the initial and final states. This minimum time can be explicitly calculated for a general compression/decompression situation.Comment: Main text: 5 pages; 18 pages with appendices and references; major revision with results for a general non-linear potential and study of fluctuations added; Physical Review E in pres

The impact of the interfacial Kapitza resistance on colloidal thermophoresis

Thermal gradients impart a force on colloidal particles pushing the colloids towards cold or hot regions, a phenomenon called thermophoresis. Existing theories describe thermophoresis by considering the local perturbation of the thermal field around the colloid. While these approaches incorporate interfacial surface free energies, they have consistently ignored the impact of the Kapitza resistance associated with the colloid-solvent interface. We propose a theoretical approach to include interfacial Kapitza resistance effects, and we test the new equations using non-equilibrium molecular dynamics simulations. We demonstrate that the Kapitza resistance influences the local thermal field around a colloid, modifying the Soret coefficient. We conclude that interfacial thermal conductance effects must be included to describe thermophoresis.Comment: Main paper/: 6 pages, 4 figures; Supplementary: 6 pages, 6 figure

Role of Mo in catalysts based on noble metals in hydrodeoxygenation reactions

The use of bio-energy as a renewable alternative to fossil fuels is nowadays attracting more and more attention. The bio-fuel from biomass seems to be a potential energy substitute for fossil fuels since it is a renewable resource that could contribute to sustainable development and global environmental preservation and it appears to have significant economic potential1. The problem is its high oxygen content, which gives undesirable properties for combustion. To remove oxygen, catalytic hydrodeoxygenation (HDO) reactions are carried out. Monometallic Mo/Si, Pt/Si as well as bimetallic PtMo/Si catalysts were prepared and evaluated in the hydrodeoxygenation (HDO)reaction of dibenzofurane (DBF) as a model molecule in biomass derived bio-oil.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Application of Image Processing Programs in Color Analysis of Wood Photodegradation

In general, polymer photodegradation is an important aspect of polymer science that is of great interest to chemistry, materials science, biology, and physics students who engage in this field of research. Wood consists of three main polymers, which makes it a good candidate for such photodegradation studies. Aside from structural changes based on chemical analysis, color change assessment can also be employed to check any extent of degradation on wood without the need for sophisticated analytical equipment. This study presents the application of two image processing programs in color analysis of wood photodegradation: ImageJ and Colormath library, which are Java-based and Python-based software, respectively. Images of unexposed and UV-exposed wood samples were taken using a smartphone as an affordable digital camera. RGB channel values from these images were analyzed and quantified by ImageJ software. These values were converted to the corresponding CIEL*a*b* parameters using the Colormath library to calculate the color change, ΔE. For the 3-hour exposed sample, ?E is equal to 4.29. This value indicates appreciable color change, according to the criteria from literature. Regardless of the exposure time, the wood samples become darker as indicated by the negative value in the change in lightness L

Polyparameter linear free energy relationship for wood char–water sorption coefficients of organic sorbates

Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here by permission of John Wiley & Sons for personal use, not for redistribution. The definitive version was published in Environmental Toxicology and Chemistry 34 (2015): 1464-1471, doi:10.1002/etc.2951.Black carbons (BCs), including soots, chars, activated carbons, and engineered nanocarbons, have different surface properties, but we do not know to what extent these affect their sorbent properties. To evaluate this for an environmentally ubiquitous form of BC, biomass char, we probed the surface of a well-studied wood char using 14 sorbates exhibiting diverse functional groups and then fit the data with a polyparameter linear free energy relationship (ppLFER) to assess the importance of the various possible sorbate-char surface interactions. Sorption from water to water-wet char evolved with the sorbate's degree of surface saturation and depended on only a few sorbate parameters: log Kd(L/kg) = [(4.03 ± 0.14) + (-0.15 ± 0.04) log ai)] V + [(-0.28 ± 0.04) log ai)] S + (-5.20 ± 0.21) B where ai is the aqueous saturation of the sorbate i, V is McGowan’s characteristic volume, S reflects polarity, and B represents the electron-donation basicity. As generally observed for activated carbon, the sorbate’s size encouraged sorption from water to the char, while its electron donation/proton acceptance discouraged sorption from water. However, the magnitude and saturation dependence differed significantly from what has been seen for activated carbons, presumably reflecting the unique surface chemistries of these two BC materials and suggesting BC-specific sorption coefficients will yield more accurate assessments of contaminant mobility and bioavailability and evaluation of a site's response to remediation.This material is based upon work supported by the U.S. Army Corps of Engineering, Humphreys Engineer Center Support Activity under Contract No. W912HQ-10-C-0005 awarded as part of the SERDP program.2016-05-1

Parallelizing the Sparse Matrix Transposition: Reducing the Programmer Effort Using Transactional Memory

AbstractThis work discusses the parallelization of an irregular scientific code, the transposition of a sparse matrix, comparing two multithreaded strategies on a multicore platform: a programmer-optimized parallelization and a semi-automatic parallelization using transactional memory (TM) support. Sparse matrix transposition features an irregular memory access pattern that de- pends on the input matrix, and thereby its dependencies cannot be known before its execution. This situation demands from the parallel programmer an important effort to develop an optimized parallel version of the code. The aim of this paper is to show how TM may help to simplify greatly the work of the programmer in parallelizing the code while obtaining a competitive parallel version in terms of performance. To this end, a TM solution intended to exploit concurrency from sequential programs has been developed by adding a fully distributed transaction commit manager to a well-known STM system. This manager is in charge of ordering transaction commits when required in order to preserve data dependencies

Communication: Improving the density functional theoryU description of CeO 2 by including the contribution of the O 2p electrons

Density functional theory (DFT) based approaches within the local-density approximation or generalized gradient approximation frameworks fail to predict the correct electron localization in strongly correlated systems due to the lack of cancellation of the Coulomb self-interaction. This problem might be circumvented either by using hybrid functionals or by introducing a Hubbard-like term to account for the on site interactions. This latter DFTU approach is less expensive and therefore more practical for extensive calculations in solid-state computational simulations. By and large, the U term only affects the metal electrons, in our case the Ce 4f ones. In the present work, we report a systematic analysis of the effect of adding such a U term also to the oxygen 2p electrons. We find that using a set of U f 5 eV and U p 5eV effective terms leads to improved description of the lattice parameters, band gaps, and formation and reduction energies of CeO