ISSN:0021-2148    

DOI:10.1002/ijch.199100007

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractThis paper addresses two topics concerning fluid flow in restricted geometries. The first topic is on the relationship between the dynamic permeability κ(ω), where ω denotes frequency, and the microstructure of a porous medium. It is shown that when κ is normalized by its static value κ0, and the frequency ω by a characteristic ω0particular to the sample, the resulting dimensionless function, withand\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm \tilde \omega = }\omega {\rm /}\omega _{\rm 0} $\end{document}, is dominated by the geometry of the throat regions in a porous medium. If the pore cross‐sectional areaSvaries slowly near the throats, i.e.,dS/dz≅ 0 where z is the distance normal to the cross section, then\documentclass{article}\pagestyle{empty}\begin{document}$ \tilde \kappa ({\rm \tilde \omega)} $\end{document}is an approximate universal function independent of other features of the microstructure. Both theoretical and experimental evidences are presented for such scaling behavior. When scaling holds, the dynamic permeability κ(ω) is found to contain only two pieces of geometric information, and the knowledge of either the low‐frequency or the high‐frequency asymptotic constants of κ(ω) would enable one to deduce the other missing parameters. In particular, since the high‐frequency asymptotic constants of κ(ω) can be related to the electrical formation factor and a weighted volume‐to‐surface ratio, the static permeability value κ0may be directly deduced from the knowledge of these parameters. Whereas the first topic concerns single‐phase flow, the second topic of this paper involves the displacement of a fluid by another immiscible fluid in a capillary tube. Here the basic physics lies in the dynamics of the moving contact line, defined as the intersection of the moving fluid‐fluid interface with the tube wall. Through first‐principle hydrodynamic calculations and comparison with experiments, the macroscopic behavior of fluid displacement is linked to the microscopic parameters governing the region around the contact line. It is shown that there are two frictional forces associated with the motion of the contact line. One is the viscous stress, which is primarily responsible for the deformation of the fluid‐fluid interface as the velocity of the moving interface increases. The other frictional force, found experimentally to vary as the square root of velocity, is explained on the basis of capillary‐wave excitation at the fluid‐fluid interface due to contact line motion over wall roughness. Excellent agreement be

ISSN:0021-2148    

DOI:10.1002/ijch.199100008

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractIn the present paper, we review the evidence that intergranular contacts in sedimentary rocks are normally much smaller than the grain size. We show that an analysis by Ghosh and Fuchs of the frequency‐dependent dielectric constant of a brine‐filled whitestone and a sandstone implies a ratio of contact radius to grain size in the 10−3to 10−2range. We argue that sintering is prevented in situ by strong repulsive forces arising from charging and hydration of the grain surfaces in contact with the brine within the pore space. We show, in fact, that considering only these repulsive forces consolidation is prevented, thereby reducing the question of the origin of small contacts to the question of the nature of the consolidation process in the presence of strong repulsions. We outline briefly a mechanism of consolidation, but defer detailed study of consolidation for futu

ISSN:0021-2148    

DOI:10.1002/ijch.199100009

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractDepending on the size of the pores and on the temperature and pressure of the fluid, flow in microporous materials can be through gas diffusion, surface diffusion, and viscous liquid flow driven by capillary forces or by hydraulic pressure. We have studied these flow regimes with toluene in untreated Vycor glass with a pore radius of 31 Å and Vycor glass with a pore radius of 21 Å whose pores were derivatized with C18H38. The observed increase in viscosity with decreasing pore size is ascribed to the attractive interaction of the monolayer adsorbed on the pore walls. The surface diffusion coefficient at 22°C is 5 × 10−5cm2s−1for both the derivatized and underivatized Vycor, with an activation energy of 3 kcal in the temperature range 2

ISSN:0021-2148    

DOI:10.1002/ijch.199100010

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractNuclear magnetic relaxation in a porous medium is simulated by a random walk on the open sites of a percolation lattice. This model is used to study relaxation in the case that diffusion to the pore surface is slow compared to relaxation at the surface. The computed decay curves can be fit by sums of exponentials. For slow diffusion the principal relaxation time is independent of the surface relaxation rate. It is inversely proportional to the diffusion coefficient and directly proportional to the mean square displacement of the walkers. It appears that a measurement of nuclear magnetic relaxation in the slow diffusion range will yield only an average pore size. This pore size is given by the root mean square displacement to the surface for a random walker starting with equal probability from any point in the pore space.

ISSN:0021-2148    

DOI:10.1002/ijch.199100011

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractThe interface between two partly miscible polymers is characterized by a finite interfacial region of widthwcomparable to the polymer size. The composition variation and in particular the time development of this restricted zone have recently been studied experimentally using a new depth‐profiling approach based on nuclear reaction analysis. The results showwto vary quantitatively in a way consistent with mean‐field models, while its time development appears to follow a power laww∝tα, with the mean value of the exponent α = 0.34 ± 0.06 being significantly lower than its free interdiffusion valu

ISSN:0021-2148    

DOI:10.1002/ijch.199100012

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractEnergy transfer experiments were carried out on a material composed of poly(methyl methacrylate) (PMMA, 98.5 monomer mol%) and polyisobutylene (PIB, 1.5 monomer mol%), with PMMA labeled with phenanthrene, the donor, and PIB labeled with pyrene, the acceptor. In this material, prepared by nonaqueous dispersion polymerization, all of the PIB is present as a graft copolymer with PMMA. Here we demonstrate that the extent of energy transfer increases enormously when the particles are dispersed in aliphatic hydrocarbon liquids. These swell the PIB phase leading to formation of a diffuse interface where substantial mixing of the PMMA and PIB components occurs. The amount of energy transfer, and hence the amount of swelling, varies significantly among the various solvents.

ISSN:0021-2148    

DOI:10.1002/ijch.199100013

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractWhen a polymer is subject to a geometrical constraint, such as being confined to a pore, there may be a loss in configurational entropy. If a linear polymer is in dilute solution in a good solvent, then it can be modelled as a self‐avoiding walk on a lattice and, in this case, it is possible to make rigorous statements about this entropy loss. We shall discuss some of these results for self‐avoiding walks in a half‐space, a slab, a prism, etc. We then examine the dependence of this entropy loss on the architecture of the polymer and ask if ring or star or comb polymers all lose the same amount of entropy when confined in the same way. It turns out that this depends on the nature of the confinement. We also look at the case where a polymer interacts with a surface and investigate how the adsorption behavior depends on the architecture of the polymer. The behavior is strikingly different in two and in three dimen

ISSN:0021-2148    

DOI:10.1002/ijch.199100014

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractIn this paper we present a detailed experimental study of molecular adsorption on interfaces of silica gels from binary solutions of alcohol/toluene. The adsorption measurements are corroborated with infrared spectra of the surface hydroxyl groups and with NMR results. The adsorption isotherms are analyzed within the framework of the Everett approach and possible scaling relations between alcohol monolayer capacities and adsorbate cross sections are discussed. We conclude that reliable morphological information on the interfaces cannot be obtained from these adsorption experiments.

ISSN:0021-2148    

DOI:10.1002/ijch.199100015

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractReactions in restricted spaces rarely get stirred vigorously by convection and are thus controlled by diffusion. Furthermore, the compactness of the Brownian motion leads to both anomalous diffusion and anomalous reaction kinetics. Elementary binary reactions of the type A + A → Products, A + B → Products, and A + C → C + Products are discussed theoretically for both batch and steady‐state conditions. The anomalous reaction orders and time exponents (for the rate coefficients) are discussed for various situations. Global and local rate laws are related to particle distribution functions. Only Poissonian distributions guarantee the classical rate laws. Reactant self‐organization leads to interesting new phenomena. These are demonstrated by theory, simulations, and experiments. The correlation length of reactant production affects the self‐ordering length scale. These effects are demonstrated experimentally, including the stability of reactant segregation observed in chemical reactions in one‐dimensional spaces, e.g., capillaries and microcapillaries. The gap between the reactant A (cation) and B (anion) actually increases in time and extends over millimeters. Excellent agreement is found among theory, simulation, and experiment for the various scal

ISSN:0021-2148    

DOI:10.1002/ijch.199100016

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY