Electrokinetic phenomena, such as electroosmosis (fluid-flow induced by applied electric fields) and streaming potential (the complementary process) are known to exist in brine-saturated porous media, but are very difficult to measure. With modern instrumentation and an ac method, we can now determine these transport coefficients accurately, and use them to characterize the permeability k1, the effective throat radius Re, and the electric potential at the slip-plane, or ζ-potential. Our study shows that permeability can be determined by two different means: by combining the dc values of the streaming potential, electroosmotic pressure and conductivity; or from the frequency response of ac electroosmosis alone. The high sensitivity of the method allows us to measure k over the 0.1–10,000 millidarcy range with less than lOkPa applied pressure. This article reviews some of the basics of electrokinetics and describes our methods. We also discuss effects of brine salinity and possible effects due to the fractal nature of the pore surface.

Experiments show that the coexistence region of a vapor-liquid system or binary liquid mixture is dramatically narrowed when the fluid is confined in a dilute porous medium such as a silica aerogel. We propose a simple model of the gel as a periodic array of cylindrical strands, and study the phase behavior of an Ising system confined in this geometry. Our results suggest that the coexistence region should widen out at lower temperatures, and that the narrowness observed near the critical point may be a fluctuation-induced effect.

We have studied the dynamics of contact lines formed by water-alkane interfaces in capillaries with random surface disorder. We find that the contact-line velocity V scales with the applied capillary pressure P as V∼ (P – Pt)ζ over two decades in V. This is consistent with a critical depinning transition. We obtain this result by using a sensitive ac differential-pressure measurement technique to measure dP/dV. We find that dP/dV αV−0 8 (5) implying that 1/ζ = 0. 20 (5).

We report a study of the dynamics of capillary rise of water in a column of glass beads. The water column height h is measured as a function of time t. Analyzing the late-time data in terms of critical pinning, dh/dt α (P − Pa)β, we find an anomalously large exponent β. A similar measurement for contact line pinning in capillary tubes indicates β < 1. We discuss these findings in light of recent theories for domain wall pinning in the random-field Ising model and suggest a new equation of motion which corresponds to the Wolf-Villain model with quenched noise.

The fractal structure of SiO2 - ZrO2 mixed aerogel prepared for catalytic purpose is investigated using morphological statistical methods, small angle X-ray scattering and N2 adsorption-desorption measurements. These three methods provide a description of the aerogel structure over several decades.

The surface fractal dimension (Ds) of pyrolytic carbon blacks (CBp) was determined using small angle X-ray scattering (SAXS). The CBp were produced by vacuum pyrolysis of used tires at different temperatures and pressures. For the CBp a dependence of the pyrolysis conditions on the fractal dimension was observed. The fractal dimension decreases, suggesting a smother surface, with increasing pyrolysis pressure and to a lesser intent with increasing pyrolysis temperature. Earlier SIMS and ESCA investigations have indicated that an evident correlation exists between the surface morphology and the surface chemistry of the CBp. According to these investigations, the smoothing of the CBp surface is due to the formation of carbonaceous deposits from adsorbed hydrocarbons on the CBp.

The changes in the radial distribution function (RDF) and vibrational density of states (DOS) of porous silicon (p-Si) with change of porosity are studied within a modified diffusion limited aggregation model and molecular dynamics simulations. By decomposing the first peak of the radial distribution function of p-Si on to partial RDFs, for atoms having different coordinations, and partial RDFs, for bonds connecting atoms with different coordinations, we show that appearance of the structure in the first peak of the RDF in p-Si is stipulated by bonds between undercoordinated surface atoms. The vibrational DOS projected on surface atoms are also shown to be different from that corresponding to crystalline phonons. It is characterised by the relative increase of the intensity of vibrations in the acoustic region and by appearance of surface-like vibrations split from the optical band.

A fine pore characterization method is investigated for a disordered solid including inaccessible pores. Here inaccessible pores denote ones into which N2 molecule cannot access at 77 K. Activated carbons prepared differently are examined. The basic idea of the method is as follows: (1) Pores are classified into effective micropores (further devided into smaller and larger micropores distinguished from DR (Dubinin-Radushkevich) analysis and inaccessible pores. (2) Volume fraction is determined for each type of pore considering densities. (3) Debye-Bueche plot derived from SAXS analysis is used to estimate the average transversal length of solid part and pore, respectively, convinedwith their volume fractions obtained from (1) and (2). (4) In case of a porous systemwith a symmetrical shape of pores, relative number and size of inaccessible pore to effective micropore are calculated.

Sedimentary rocks have complicated permeability patterns arising from the geological processes that formed them. Here we address the longstanding question of how such patterns are generated. We also analize data on two sandstone samples from different geological environments, and find that the permeability fluctuations display long-range power-law correlations characterized by an exponent H. For both samples, we find H ≈ 0.82 – 0.90. These permeability fluctuations significantly affect the flow of fluids through the rocks.

We present a simple model to explain anomalous relaxation in random porous media. The model, based on the properties of random walks on a disordered structure, is able to describe essential features of the relaxation process in terms of a one body picture, in which the many body effects are approximated by geometrical restrictions on the particles diffusion. Disorder is considered as a random variable (quenched and annealed) taken from a power-law distribution |μ|ξμ−1. Quantities relevant to relaxation phenomena, such as the characteristic function and the particle density are calculated. Different regimes are observed as a function of the disorder parameter μ. For μ > 1 the relaxation is of exponential or Debye type, and turns into a stretched exponential as μ decreases. We compare numerical predictions (based on Monte Carlo simulations) with experimental data from porous rocks obtained by Nuclear Magnetic Resonance, and numerical data from other disordered systems.

Colloidal particles in mixed solvents can show reversible aggregation in the one-phase regime of the mixture near the mixture's phase separation temperature [1–5]. This aggregation condition has been shown to be related to the affinity of the colloidal surfaces for one of the solvent components. In particular, for a 2,6 lutidine plus water (LW) mixture with colloidally dispersed polystyrene latex spheres (PLS) in a temperature range near the critical temperature, Tc, in the mixture's two-phase region, the particles will partition into one of the solvent phases, with the meniscus between the liquid phases clear to the eye and showing no sign of population by colloidal particles. Which phase of the solvent attracts the particles depends on the surface charge density of the particles, with high surface charge density particles preferring the water-rich phase and low charge density particles preferring the lutidine rich phase. As temperature is advanced deeper into the two-phase region (all effects discussed here are equilibrium effects), there is a temperature, Tw, at which particles appear on the meniscus (most particles remain in the preferred phase, whose population depletion is too small to measure). Tw changes with the surface charge density of the particles [4], but not with radius or with number density of the particles in the sample. The aggregation observed in the one-phase region [5] is then restricted to the side of the solvent's coexistence curve poor in the component which is rich in the partitioning-favored phase.

Dissipative particle dynamics is essentially a coarse-grained molecular dynamic simulation technique that captures the essential physics with considerably less computer effort. We have given a sound theoretical foundation to the technique with respect to the equilibrium and hydrodynamic properties. In this paper we further explore the connection of the model parameters of DPD with the underlying microscopic dynamics for the case of a simple model of a solid. This provides some insight into the difficulties of interpretation of DPD simulations.

A solution of 30 % by mass, 7 nm diameter, colloidal silica spheres has been studied during gelation using small angle neutron scattering (SANS). A peak in the static structure factor appears early at a wavevector q ≈ 0.1 nm−1, and then grows in height and shifts to lower wavevectors as gelation proceeds. This is consistent with a cluster growth model in which this low-q peak in the structure factor indicates the presence of correlations between growing clusters. The peak continues to grow after the solution has visibly gelled indicating that the gel coarsens even after a stiff solid-like network has formed. The clear presence of cluster correlations at length scales only one order of magnitude larger than the particle size means that the usual fractal slope analyses are invalid in this system. We interpret the results by comparing the measured time evolution of the structure factor with computer simulations of Lennard-Jones particles quenched far below the critical line.

Light sensitive colloidal particles of copper hydrous oxides were prepared at interfaces of exopolymeric materials. Dislike copper oxide or hydroxide nanoclusters were obtained which might be useful as p-type semiconductors. The colloidal Cu2O xH2O and Cu(OH)2 particles reveal fractal dimensions of D = 2.15 ±0.05 for Cu(OH)2 and D= 1.75 ±0.07 for Cu2O xH20.

Velocity and attenuation measurements of compressional waves at 3 and 5 MHz are presented for suspensions made of 1μm size particles of kaolinite or glass beads in water or light oil. At a critical concentration of 40%, the attenuation shows a sharp peak in attenuation as well as a sudden change in velocity. This behavior is observed in all suspensions and is independent of frequency or particle geometry. The observed behavior is consistent, with the excess attenuation induced by the fluid-shearing between particles. This behavior is the first experimental evidence for the existance of the freezing point, predicted by computer simulations.

It has been well established by theory and simulations that the reaction rates of diffusion-limited reactions can be affected by the spatial dimension in which they occur. The types of reactions A + B → C, A + A → A, and A + C→, C have been shown, theoretically and/or by simulation, to exhibit non-classical reaction kinetics in low and fractal dimensions. We present here experimental results from several 1D and fractal systems.

An A+B → C type reaction was experimentally investigated in a long, thin capillary tube in which the reactants, A and B, are initially segregated. This initial segregation of reactants means that the net diffusion is along the length of the capillary only, making the system effectively 1D and allowing some of the properties of the resulting reaction front to be studied. The reaction rate of excitonic fusion, A + A →A, as well as trapping, A + C→ C, reactions were observed via phosphorescence(P) and delayed fluorescence(F) of naphthalene within the channels of Vycor glass, in isotopically mixed naphthalene crystals and in the isolated chains of dilute polymer blends. In these experiments, the non-classical kinetics are measured in terms of the heterogeneity exponent, h, from the equation: Rate ∼ F =; kt-hpn,, which gives the time dependence of the rate coefficient. Classically h =; 0, while h =; 1/2 in 1D, as well as in the fractal dimensions discussed here, for A + A → A as well as A + C →C type reactions.

The presence of a reaction front is a characteristic feature of a variety of physical, chemical and biological processes. The reaction exhibits a front, provided that the diffusing reactants are separated in space. We study the reaction front dynamics of both A+B→C bimolecular and A+2B→C termolecular reactions with initially separated components in a capillary. We measure and compare with theory and simulations the dynamic quantities that characterize the kinetic behavior of the system: the global reaction rate R(t), the location of the reaction center xf(t), the front's width w(t), and the local production rate R(xft). The non-classical nature of this dynamical system is confirmed.

We performed dynamic and static light scattering measurements in nematic LC (5CB) confined in silica porous glasses with average pore sizes of 1000 A˚ (volume fraction of pores 40%) and 100 A˚ (27%). The experiments show significant changes in physical properties of confined LC. Nematic-isotropic phase transition temperature TNI is depressed by 0.6°C in 1000 A˚ pores compared to that bulk value and this phase transition was not detected at all in 100 A˚ pores. We found that even about 20°C below bulk melting temperature the relaxational processes in confined LC were not frozen. Slow relaxation process which does not exist in the bulk LC and wide spectrum of relaxation times (10−8 –)s appear in both 100 A˚ and 1000 A˚. In 100 A˚ pores slow relaxation exists even at T corresponding to the bulk isotropic phase. Our data can not be described using the standard form of dynamical scaling variable (t/r) but they obey activated dynamical scaling with the scaling variable x = lnt/lnr.

We have used Brillouin light scattering (BLS) to measure the glass transition temperature of thin, freely-standing poly(styrene) (PS) films. The freely-standing films were prepared by spincoating solutions of PS in toluene onto glass substrates, annealing the supported films in vacuum, and then using a water surface transfer technique to place the films across a 3 mm diameter orifice. Ellipsometry measurements of similar floated films transferred to Si(001) wafers allow the determination of the film thicknesses. Atomic force microscopy measurements revealed that the films have an rms roughness of less than 10 A˚. With the freely-standing films placed in an optical furnace, we performed BLS measurements of the films using a high-contrast, multipassed, tandem Fabry-Perot interferometer. We obtained a reliable, reproducible measure of the glass transition temperature, Tg, from the large changes in the frequencies of the thermally-excited, viscoelastic, film-guided waves within the PS films as the films were heated above Tg. BLS results for bulk PS and a 1800 A˚ thick, freely-standing PS film are presented. We find the same glass transition temperature for the 1800 A˚ thick film as the bulk PS sample. This Tg value is the same as that obtained using differential scanning calorimetry (DSC).

We study the A + B→B trapping reaction under steady state conditions for the case in which both A particles and traps(B) are mobile. Using Monte Carlo simulations, we follow the kinetic rate law in one dimension. Anomalies arise due to self-organization of the A particles, which results in a slower steady state reaction rate than is predicted classically. We find a partial order of reaction with respect to trap density of X = 2, and an overall order for the reaction of Z = 3.2. These results are in agreement with other works which predict an exponential rather than an algebraic decay law with respect to the A particle density.