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1.
Dagdug L Berezhkovskii AM Makhnovskii YA Zitserman VY Bezrukov SM 《The Journal of chemical physics》2011,134(10):101102
Using Brownian dynamics simulations, we study the effective mobility and diffusion coefficient of a point particle in a tube formed from identical compartments of varying diameter, as functions of the driving force applied along the tube axis. Our primary focus is on how the driving force dependences of these transport coefficients are modified by the changes in the compartment shape. In addition to monotonically increasing or decreasing behavior of the effective mobility in periodic entropy potentials reported earlier, we now show that the effective mobility can even be nonmonotonic in the driving force. 相似文献
2.
We study two-dimensional diffusion in a channel formed by periodic overlapping circles. Periodic variation of the channel width leads to the slowdown of diffusion along the channel axis. There are several approximate approaches, which allow one to analyze the slowdown. We use these approaches to derive five expressions for the effective diffusion coefficient of a point Brownian particle in the channel. To check the accuracy of the expressions we compare their predictions with the effective diffusion coefficient obtained from Brownian dynamics simulations. 相似文献
3.
The interaction between polyelectrolyte complexes formed by a linear polyelectrolyte and a dendrimer or a spherical particle with the opposite charge has been investigated via computer simulation. The influence of the compositions of the complexes on the effective force of the interaction between them has been studied. It has been shown that the effective attraction between the complexes appears at short distances in the vicinity of the isoelectric point. This attraction is correlative in nature and stronger for the complexes of the linear polyelectrolyte with spherical particles than for the complexes with dendrimers. 相似文献
4.
Experimental study on geochemical characteristic of methane hydrate formed in porous media
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The natural occurrence of methane hydrates in marine sediments has been intensively studied over the past decades, and geochemical charac-teristic of hydrate is one of the most attractive research fields. In this paper, we discussed the geochemical anomaly during hydrate formation in porous media. By doing so, we also investigated the temperature influence on hydrate formation under isobaric condition. It turns out that sub-cooling is an important factor to dominate hydrate formation. Larger subcooling provides more powerful driving force for hydrate formation. During the geochemical anomaly research, six kinds of ions and the total dissolved salt (TDS) were measured before and after the experiment in different porous media. The result is that all kinds of ionic concentration increased after hydrate formation which can be defined as salting out effect mainly affected by gas consumption. But the variation ratio of different ions is not equal. Ca2+ seems to be the most significantly influenced one, and its variation ratio is up to 80%. Finally, we theoretically made a model to calculate the TDS variation, the result is in good accordance with measured one, especially when gas consumption is large. 相似文献
5.
Nagashima K Suzuki T Nagamoto M Shimizu T 《The journal of physical chemistry. B》2008,112(32):9876-9882
Directional growth of tetrahydrofuran (THF) clathrate hydrates was studied in a mixture of glass beads and a stoichiometric THF-water solution. Results showed that disseminated pore space type hydrates formed in a mixture containing 50-microm beads. However, a pure hydrate layer formed pushing the beads in a mixture containing 2-microm beads (frost heaving of hydrates). As the growth proceeded, new layers were formed repeatedly, leading to the eventual formation of a periodic layered pattern. It was found that as the growth rate increased, both the thickness of a hydrate layer and the interval between the neighboring layers decreased according to power laws. The effects of the applied temperature gradient and the weight ratio of the solution and glass beads were also systematically studied. Further, the possibility of applying our model experiments to the formation of natural methane hydrates was discussed. 相似文献
6.
Yung Park 《Journal of mathematical chemistry》2001,29(1):35-40
The theory of fractal sets is used to describe convective diffusion of a passive impurity in a partly-saturated porous medium. 相似文献
7.
The deposition of colloidal particles onto the collector surfaces of porous media is investigated using the Brownian dynamics simulation method. The pore structure in a filter bed was characterized by the constricted tube model. The effects of various shapes of the total interaction energy curves of DLVO theory and the effects of different particle diameters on the collection efficiencies of particles are examined. The simulation results show that the particle collection efficiency is strongly dependent on the geometry of the tube and on the shape of the total interaction energy curve. In a comparison with the available experimental measurements of the filter coefficient, it is found that the present model can give a smaller discrepancy than that of the convective diffusion model in the unfavorable deposition region. 相似文献
8.
A sonochemical approach to hierarchical porous titania spheres with enhanced photocatalytic activity 总被引:1,自引:0,他引:1
A novel sonochemical approach has been developed to prepare hierarchical porous titania spheres in the presence of a triblock copolymer; it was found that textural meso- and macro-porosity could enhance the photocatalytic activity of mesoporous TiO2. 相似文献
9.
《Journal of membrane science》1997,133(2):195-205
A copolyamic acid was synthesized from 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) as the dianhydride and 4,4′-oxydianiline (4,4′-ODA) and 2,4-diaminotoluene (2,4-DAT) as the diamine and was coated on the outer surface of a porous alumina support tube. The film was imidized and then carbonized by varying reaction period, temperature and atmosphere. Permeances of the BPDA-ODA/DAT carbon membrane were much lower than those of BPDA-ODA carbon membranes. However, the performance of the BPDA-ODA/DAT copolyimide-based membrane was greatly improved by treating in air at temperatures up to 500°C for 1 h, followed by carbonizing in nitrogen at temperatures up to 700°C. Permeance to CO2 for the BPDA-ODA/DAT carbon membrane prepared under optimum conditions was 3 × 10−8 mol m−2 s−1 Pa−1, and the separation coefficient of CO2 to CH4 was 60 at a permeation temperature of 35°C. These were comparable to the results of carbon membranes prepared from BPDA-ODA polyimide. The micropore structure of the BPDA-ODA/DAT carbon membrane was thus successfully controlled by an optimized combination of oxidation and carbonization after imidization. 相似文献
10.
Shear rheology and porous media flow of wormlike micelle solutions formed by mixtures of surfactants of opposite charge 总被引:1,自引:0,他引:1
The rheology of solutions of wormlike micelles formed by oppositely charged surfactant mixtures (cationic cetyl trimethylammonium p-toluene sulfonate, CTAT, and anionic sodium dodecyl sulfate, SDS), in the dilute and semi-dilute regimes, were studied under simple shear and porous media flows. Aqueous mixtures of CTAT and SDS formed homogeneous solutions for SDS/CTAT molar ratios below 0.12. Solutions of mixtures exhibited a strong synergistic effect in shear viscosity, especially in the semi-dilute regime with respect to wormlike micelles, reaching a four order of magnitude increase in the zero-shear rate viscosity for solutions with 20 mM CTAT. Oscillatory shear results demonstrated that the microstructure of CTAT wormlike micelles is sensitive to SDS addition. The cross-over relaxation times of wormlike micelles of 20 mM CTAT solutions increased by three orders of magnitude with the addition of up to 2 mM of SDS, and the solutions became increasingly elastic. The shear thickening process observed in shear rheology became more pronounced in porous media flow due to the formation of stronger cooperative structures induced by the extensional component of the flow. 相似文献
11.
In this work, the electronic and structural characterization of polyaniline (PANI) formed in cavities of zeolites Y (ZY) and Mordenite (MOR) and montmorillonite (MMT) clay having Cu(II) as oxidant agent are presented. The formation of PANI and its structure is analyzed by Resonance Raman, UV-Vis-NIR, FT-IR and N K XANES techniques. In all cases the structure of PANI formed is different from the “free” polymer. The presence of azo bonds linked to phenazine-like rings are observed only for PANI-MMT composites, independent of the kind of oxidant agent employed in the synthesis. The presence of Cu(II) ions leads to the formation of Phenosafranine-like rings. The presence of these phenazine-like rings in the structure of confined PANI chains can also contribute to the enhancement of the thermal stability observed for all composites. 相似文献
12.
Swiatkowska-Warkocka Z Kawaguchi K Shimizu Y Pyatenko A Wang H Koshizaki N 《Langmuir : the ACS journal of surfaces and colloids》2012,28(11):4903-4907
We report the synthesis of Au-based submicrometer-sized spherical particles with uniform morphology/size and integrated porosity-magnetic property in a single particles. The particles are synthesized by a two-step process: (a) selective pulsed laser heating of colloidal nanoparticles to form particles with Au-rich core and Fe-rich shell and (b) acid treatment which leads to formation of porous architecture on particle surface. The simple, fast, inexpensive technique that is proposed demonstrates very promising perspectives for synthesis of composite particles. 相似文献
13.
Shengbo Wang Changlong Chen Mohannad J. Kadum Jeffrey H. Harwell 《Journal of Dispersion Science and Technology》2018,39(5):734-743
Several new foaming agent formulations (surfactants and polymers) in the presence of multi-walled carbon nanotube (MWCNT) were developed in 3% salinity (NaCl, 2.4?wt%, CaCl2, 0.6?wt%). The dispersion stability of the MWCNT and the viscosity of the solutions were examined as a prerequisite for reservoir applications. Foam was generated in situ and one-dimensional flow-through tests were performed by co-injecting air and foaming solution either in the presence of MWCNT or at particle-free condition. The pressure drop (Δp) across the sand-pack and the nanoparticles breakthrough were closely monitored. The fluid injection rate, gas fraction, and the effect of MWCNT on foams in porous media were investigated.Our results reveal that foams stabilized by the selected nanoparticles are capable of generating stronger foams leading to higher apparent Δp. The Δp profile varies with gas fraction, which largely affects the foam texture and quality. Also, the viscosity of foaming agent solutions influences Δp values. Adding MWCNT to the foaming agent solutions appears beneficial to the flooding as surfactants adsorption onto nanoparticle surfaces, which facilitates surfactants partitioning to the G/L interface.Addition of nanoparticles in the developed foam formulations leads to the formation of high-quality stronger foams in porous media, which could potentially improve the sweep efficiency and increase the oil recovery. 相似文献
14.
Recent years have seen significant progress in the NMR study of porous media from natural and industrial sources and of cultural significance such as paintings. This paper provides a brief outline of the recent technical development of NMR in this area. These advances are relevant for broad NMR applications in material characterization. 相似文献
15.
16.
Shi JY Wang CA Li ZJ Wang Q Zhang Y Wang W 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(22):6206-6213
We report a new method for the synthesis of hollow-structured phenylene-bridged periodic mesoporous organosilica (PMO) spheres with a uniform particle size of 100-200 nm using α-Fe(2)O(3) as a hard template. Based on this method, the hollow-structured phenylene PMO could be easily functionalized with MacMillan catalyst (H-PhPMO-Mac) by a co-condensation process and a "click chemistry" post-modification. The synthesized H-PhPMO-Mac catalyst has been found to exhibit high catalytic activity (98% yield, 81% enantiomeric excess (ee) for endo and 81% ee for exo) in asymmetric Diels-Alder reactions with water as solvent. The catalyst could be reused for at least seven runs without a significant loss of catalytic activity. Our results have also indicated that hollow-structured PMO spheres exhibit higher catalytic efficiency than solid (non-hollow) PMO spheres, and that catalysts prepared by the co-condensation process and "click chemistry" post-modification exhibit higher catalytic efficiency than those prepared by a grafting method. 相似文献
17.
A synthetic approach for synthesizing spherical aminopropyl-functionalized ethane-bridged periodic mesoporous organosilicas (APEPMOs) is reported. The mesoporous material was prepared by a one-step co-condensation of 1,2-bis(triethoxysilyl)ethane (BTSE) and 3-aminopropyltriethoxysilane (APTES) using cetyltrimethylammonium chlorine (C(18)TACl) as a template with the aid of a co-solvent (methanol) in basic medium. The APEPMOs were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), powder X-ray diffraction (XRD), nitrogen sorption measurement, Fourier transform infrared spectroscopy (FT-IR) and elemental analysis. It was shown that this material exhibited spherical morphology, ordered cubic mesostructure and good mechanical strength. The APEPMOs were tested as a potential stationary phase for liquid chromatography (LC) because the column exhibited reduced back pressure. Moreover, they exhibited good chemical stability in basic mobile phase, which can be ascribed to the ethane groups in the mesoporous framework. 相似文献
18.
Katsanos NA Bakaoukas N Koliadima A Karaiskakis G Jannussis A 《The journal of physical chemistry. B》2005,109(22):11240-11246
The new inverse gas chromatography methodology of reversed-flow gas chromatography has been applied to measure diffusion and adsorption in porous solids. The theoretical analysis leads to equations describing the experimental data with very few approximations. From these, the total overall rate constant of transference (k = k(R) + k(2)), its probable error, the diffusion coefficient (D(1)) into porous solids (alpha-alumina and gamma-alumina), and its probable error are calculated by means of a simple PC program. The methodology was applied to pentane, hexane, and heptane diffusing into porous alpha- and gamma-alumina at various temperatures. A comparison of the results is made with those obtained by the Knudsen formula and with those of other researchers. 相似文献
19.
The methods developed in a previous paper (Phys. Rev. E.: Stat. Phys., Plasmas, Fluids, Relat. Interdiscip. Top. 2003, 68, 046127) are used to calculate the permeability of argon in alpha-quartz, a system containing large energy barriers. The permeability is reported at three different temperatures and follows Arrhenius behavior. The permeabilities obtained from a hopping model combined with transition state theory closely follow our predicted values but are systematically lower. Lattice flexibility cannot be neglected in this system, and the energy-transfer between alpha-quartz and the argon atom through lattice vibrations occurs on a fast enough time scale such that it plays a role in the guest diffusive motion. 相似文献
20.
Lainez A del Burgo P Junquera E Aicart E 《Langmuir : the ACS journal of surfaces and colloids》2004,20(14):5745-5752
Speed of sound, density, conductivity, and fluorescence spectroscopy experiments were run to analyze the mixed aggregation process of a nonionic-cationic surfactant system in aqueous media at 298.15 K. The mixed system comprises a nonionic surfactant, n-octyl-beta-D-glucopyranoside (OBG), and a cationic surfactant, tetradecyltrimethylammonium bromide (C14TAB), with 8 and 14 carbon atoms on the hydrophobic tails, respectively. From these data, the total and partial critical micellar concentrations, the total and partial aggregation numbers, apparent molar volumes and isentropic compressibilities, hydration numbers, and the corresponding changes in the latest properties due to the mixed aggregation process were determined. Pure and mixed micelles were analyzed from a geometrical point of view by determining the packing parameter of the aggregates. Furthermore, the experimental characterization of both the monomeric and micellar phases was completed with a theoretical study of the mixed micellization phenomena studied herein, by means of some of the most relevant theoretical models. 相似文献