Based on computer-generated templates, percolation objects were fabricated. Random-site, semi-continuous swiss cheese, and semi-continuous inverse swiss-cheese percolation models above the percolation threshold were considered. The water-filled pore space was investigated by nuclear magnetic resonance (NMR) imaging and in the presence of a pressure gradient, by NMR velocity mapping. The percolation backbones were determined using velocity maps. The fractal dimension of the backbones turned out to be smaller by about 17 % than that of the complete cluster. As a further relation of interest, the volume-averaged velocity was calculated as a function of the probe volume radius. In a certain scaling window, the resulting dependence can be represented by a power law. The experimental results favorably compare to computer simulations with the finite-element method (FEM) or the finite-volume method (FVM). Thermal convection in percolation clusters of different porosities was studied using the NMR velocity mapping technique. The velocity distribution is related to the convection roll size distribution. The maximum velocity as a function of the porosity clearly visualizes a closed-loop percolation transition if the Rayleigh number conditions are appropriate. Percolation theory suggests a relationship between the anomalous diffusion exponent and the fractal dimension of the cluster, i.e. between a dynamic and a structural parameter. Interdiffusion between two compartments initially filled with H2O and D2O, respectively, was examined by proton imaging. The results confirm the theoretical expectation. Finally, advection driven dispersive transport was investigated in the large Péclet number limit. The superdiffusive transport anomaly was demonstrated and discussed in terms of the non-local advection-diffusion and the fractional diffusion theories.

Porous silicon formed in p+ single crystal silicon is an interesting material for the study of the behavior of a fluid confined in mesoporous media, because it is a simple system of non interconnected straight pores, all perpendicular to the substrate and it can be well characterized by different methods. Moreover, the pores may be closed at one end when the porous layer is supported by the substrate or opened at both ends when the layer is removed from the substrate. Surprising results have been obtained. A hysteresis loop of type H2 (IUPAC classification), which is generally obtained for highly interconnected porous material, is also observed. Furthermore, a hysteresis of same type is also observed in pores closed at one end which is in contradiction with the Cohan model. The steep desorption process does not account for the large pore size distribution extracted from transmission electronic microscopy study. It is believed that, during the desorption process, the presence of an adsorbed layer on the external surface of the pores and/or the coupling between the pores via the silicon walls must be taken into account.

Clays present remarkable electrokinetic features since they exist from very dilute colloidal state to nanoporous materials, according to the ration water/clay. The case of low volume fraction Vwater/Vtot which corresponds to compact systems is examined. The ionic distributions havebeen evaluated from Poisson-Boltzmann like models and compared to discrete solvent simulations. Electroosmosis and conductance ha v ebeen calculated, in the framework of the Mean Spherical Approximation (MSA) introduced in the Fuoss-Onsager transport theory.

We present a new experimental system to study the kinetics of the reaction front in A + B→C reaction-diffusion systems with initially-separated reactants. The set-up is composed of a CCD camera monitoring the kinetics of the front formed in the reaction-diffusion system Cu2++ tetra→1:1 complex (in aqueous, gel-free solution) inside a 150 micron gap between two flat microscope slides. This is basically a two-dimensional system. The results are consistent with the theoretical predictions for the anomalous time dependence of the front's width, height,and location.

Chemical reactions at the interface between two liquids and a solid can lead to very complex situations. For example, after the reaction the substrate may become less wettable allowing the formation of running droplets. We propose a model where droplets of reactive fluids of a given radius, are injected into a porous system. In their advance, the droplets react chemically with the solid surface, making it less wettable. The velocity of the droplet after the reaction is calculated for different reaction kinetics including adsorption and solute solubility, for situations where gravity effects are negligible. In all cases, a transition from a Brownian motion regime to a ballistic displacement is observed.

We study propagation dynamics of a particle phase in a single-file pore connected to a reservoir of particles (bulk liquid phase). We show that the total mass M(t) of particles entering the pore up to time t grows as (Mt) = 2m(J,ρF) √D0t, where D0 is the “bare” di usion coeffcient and the prefactor m(J,ρF) is a non-trivial function of the reservoir density ρF and the amplitude J of attractive particle-particle interactions. Behavior of the dynamic density pro les is also discussed.

We present a calculation using a relaxation method for the study of the orientational ordering of a nematic liquid crystal near the surfaces confining the system. We comment on the advantage of using this method as compared with molecular dynamics simulation. The system is simulated by a lattice model with a superposition of isotropic and anisotropic intermolecular interaction of the Maier-Saupe and induced dipole-induced dipole type force for the bulk nematic phase. For the nematic confining surface we consider a Rapini-Papoular interaction. We present simulations for negative dielectric anisotropy.

Dielectric spectroscopy was applied to investigate the dynamic properties of liquid crystal octylcyanobiphenyl (8CB) confined in 2000 Å cylindrical pores of Anopore membranes with homeotropic and axial (planar) boundary conditions on the pore walls. Homeotropic boundary conditions allow the investigation of the librational mode in 8CB by dielectric spectroscopy. We found that the dynamics of the librational mode is totally different from the behavior observed in investigations of relaxation due to reorientation of molecules around their short axis. The interpretation of the temperature dependence of relaxation times and of the dielectric strength of the librational mode needs the involvement of the temperature dependence of orientational order parameter. For samples with axial boundary conditions, layers of LCs with different thickness were obtained on the pore walls as a result of controlled impregnation of porous matrices with 8CB from solutions of different liquid crystal concentration. The process due to rotation of molecules around their short axis with single relaxation time observed for bulk 8CB is replaced by a process with a distribution of relaxation times in thin layers. This relaxation process broadens with decreasing layer thickness.

Molecular dynamics simulations of ethylene polymerization have been performed using a chemically realistic, reactive potential. These simulations have been performed in the bulk liquid and in the interior of both (10,10) and (7,7) nanotubes as a means of investigating the effects of nanoscale confinement on the polymerization reaction. The structure of the resulting polymer was found to be similar in the bulk and in the (10,10) tube at the elevated temperatures investigated, while only very small oligomers were formed in the (7,7) tube. The reaction rate was substantially reduced in the nanotubes, when compared to the bulk, primarily as a result of spatial interference due to reaction products. These simulations have implications for the possible use of nanotubes as synthetic reaction vessels, as well as for the general understanding of association reactions in confined spaces.

An experimental demonstration is shown for non-classical reaction kinetics in a homogeneous system with an elementary reaction, A+B→C. Sensitivity to the initial distribution of reactants is observed, along with a new reaction-kinetics regime which is a direct consequence of speckles in the laser beam. The long-time regime gives the first experimental demonstration of the asymptotic self-segregation (“Zeldovich”) effect, in spite of the non-random, speckled initial distribution of reactant B. Monte-Carlo simulation results are consistent with the experiments, and spatial analysis of these results correlates the excess of long-wavelength components in the initial reactant distribution with an anomalous slowing of the reaction progress.

Adhesive and tribological properties of the tip of an AFM on viscoelastic samples are studied. The kinetics of the indentation process is shown to be governed by bulk rather than by contact edge dissipations. It is shown that the transition from static to dynamic friction regimes takes place at a critical strain. During the static friction regime, the contact size remains nearly constant. Owing to this property, viscoelastic moduli is measured in this regime. Obtained results, characteristic of a micrometric domain are in a very good agreement with the same properties measured on centimetric samples using dynamical mechanical analysis. Finally, a stick-slip friction regime is observed in a range of velocities.

We present an interpretation of the self diffusion propagator for a molecular fluid confined in a porous medium. Breaking with conventional routes of interpretation, we focus in reciprocal space on the time dependence of the propagator at a fixed wave vector q. New theoretical results are reported, as well as NMR measurements on a water-saturated packing of glass beads and on a stack of plastic platelets with rough surfaces. It is shown that at least three time regimes may be distinguished, characteristic of new ways in which the propagator is affected by the geometry of the system: a short-time exponential regime of almost unrestricted diffusion, a pseudo-exponential regime probing the transport process across the material at the length scale λ=2π/q, and an algebraic regime at long times with exponent -d/2, where d is the dimensionality of connected parts of the pore space.

A model is presented for the shear (or frictional) forces Fs between two surfaces a distance D apart as they slide past each other while bearing mutually compressed polymer brushes, on the assumption that sliding takes place at the brush-brush interface. The predictions of the model for the rapid increase in Fs at increasing compressions are in reasonable agreement with experiments on polystyrene brushes immersed in toluene over two decades in Fs. At higher compressions (smaller D) the experimental shear forces increase only slowly, and diverge from the calculated ones which continue to increase rapidly; at the same time the form of the shear force response at these higher compressions reverts from a viscous-like one to a stick-slip behaviour. These observations strongly indicate that at sufficiently high compressions the plane of slip crosses over from the brush-brush interface to the polymer-solid surface.

The sol-gel process opens new possibilities in the field of biotechnologies. Sol-gel glasses are formed at room temperature via the polymerization of molecular precursors. Enzymes can be added to the solution of precursors and trapped within the growing silica network. Small substrate molecules can diffuse through the pores allowing reactions to be performed in-situ, within the silica gels. Enzyme are encased by the hydrated silica in a cage tailored to their size, they retain their biocatalytic activity and may even be stabilized within the sol-gel matrix.

Whole cell bacteria have also been immobilized within sol-gel glasses. They behave as a "bag of enzymes" and their membrane protects enzymes against denaturation and leaching. The cellular organization of bacteria cells is preserved upon encapsulation. Experiments performed with Escherichia coli induced to β-galactosidase show that they still exhibit noticeable enzymatic activity. Some degradation of the cell walls may even occur increasing the “measured” activity. However silica gels made from aqueous precursors seem to prevent bacteria from natural degradation upon ageing.

Antibody-antigen recognition has been shown to be feasible within sol-gel matrices. Trapped antibodies bind specifically the corresponding haptens and can be used for the detection of traces of chemicals. Even whole cell protozoa have been encapsulated without any alteration of their cellular organization. For medical applications, trapped parasitic protozoa have been used as antigens for blood tests with human sera. Antigen-antibody interactions were followed by the so-called Enzyme Linked ImmunoSorbent Assays (ELISA).

The tribological properties of two smooth surfaces in the presence of a thin confined film are investigated with a generic model for the interaction between two surfaces and with computer sim- ulations. It is shown that at large normal contact pressures, an ultra thin film automatically leads to static friction between two flat surfaces - even if the surfaces are incommensurate. Commen- surability is nevertheless the key quantity to understand the tribological behavior of the contact. Qualitative differences between commensurate and incommensurate contacts remain even in the presence of a thin film. The differences mainly concern the thermal diffusion of the contact and the transition between smooth sliding and stick-slip.

The dynamic movements of tracer particles have been used to characterize their local environment in dilute networks of microtubules, and within living cells. In the former case, 300 nm diameter beads are fixed to individual microtubules, so that the movements of the bead reveal undulatory modes of the polymer. The mean square displacement shows a scaling of t3/4 in keeping with mode analysis arguments. Inside a cell, beads show a more complicated behavior that reflects internal dynamics of the cytoskeleton and associated motors.

When placed near the cell edge, 3 micron diameter beads coated by proteins that mediate membrane adhesion are engulfed underneath the membrane and drawn toward the center by a contracting flow of actin. On reaching the region surrounding the nucleus, the beads continue to move but lose directionality, so that they wander within a restricted space. Measurement of the mean square displacement now shows a scaling of t1 up to times of ~1 sec. At longer times the scaling varies between t and t1/2 in the various runs. The data do not fit a crossover between ballistic (t2)and diffusive (t1) behavior. The movement is clearly driven by non-thermal interactions, as it cannot be stopped by an optical trap. Treatment of the cell to depolymerize microtubules restores ordinary diffusion, while actin depolymerization has no effect, indicating that microtubule-based motor proteins are responsible for the motion. Immunofluorescence microscopy shows that the mesh size of the microtubules is smaller than the bead diameter.

We propose that the observations are related, and that the non-trivial scaling in the polymer system leads to time-dependent friction in a network, which in turn leads to a generalized Einstein relation operative in the intracellular environment. This results, in the driven system, in sub-ballistic motion at short times and sub-diffusive motion at longer times.

The magnetic field dependence of 1H spin lattice relaxation rates in noncrystalline macromolecular solids including engineering polymers, proteins, and biological tissues is described by a power law, 1/T1 = Aω0-b, where ω0 is the Larmor frequency, A and b are constants. We show that the magnetic field dependence of the proton 1/T1 may be quantitatively related to structural fluctuations along the backbone that modulate proton-proton dipolar couplings. The parameters A and b are related to the dipolar coupling strength, the energy for the highest vibrational frequency in the polymer backbone, and the fractal dimensionality of the proton spatial distribution.

Molecular dynamics simulations have been used to study the pyrolysis of eicosane (C2042 both in the gas phase and when confined to the interior of a (7,7) carbon nanotube. A reactive bond-order potential was used to model the thermal decomposition of covalent bonds. The unimolecular dissociation is first-order in both cases. The decomposition kinetics demonstrate Arrhenius temperature dependence, with similar activation barriers in both geometries. The decomposition rate is slower by approximately 30% in the confined system. This rate decrease is observed to be a result of recombination reactions due to collisions with the nanotube wall.

Transportcoe[ ]cients in charged media exhibit strong variations, according to the conditions of displacement of the particles. Electrical transport, characterized by the simultaneous displacement of positive and negative charges in opposite directions obeys Ohm's law, but its variation with concentration (non-ideality), depends on several types of interactions, whose time of establishment varies from picosecond to nanosecond. Several diffusion processes can occur: mutual diffusion, where ions move simultaneously in the same direction, keeping local elec- troneutrality, and self diffusion where individual ionic particles move separately. The variation of diffusion coefficients with concentration dependson non-ideality factors analogous to those occuring in conductance, and their experimental evidence is facilitated b y the availability of experimental tec hniquesowing different characteristic times of observation. This phenomenon is particularly noticeable for self-diffsuion coefficients, where the dynamical processes can be observed from the picosecond range (neutron quasi-elastic scattering), to millisecond (NMR) and to hour scale (radiactive tracers). The results are especially enhanced for porous charged media like ion exchanging membranes (nafions).

Those results are be explained here theoretically in the framework of contin uous solv en t model theories (brownian dynamics) and experimentally in the study of self-diffusion in nafion membranes.

Disordered mesoporous materials with pore sizes ranging from 2 nm to some 10 nm develop large specific surface areas. These matrices can be easily filled with polar fluids And the interfacial region between the solid matrix and the pore network strongly influences the molecular dynamics of the entrapped fluid. A promising way to probe such a coupling on a large time-scale is to look at the dispersion of the nuclear spin-lattice relaxation rate of the polar liquid using field cycling NMR relaxometry technique. We have performed such an experiment on a fully hydrated porous Vycor glass, free of electron paramagnetic impurities. The proton nuclear magnetic relaxation rate (1/T1) exhibits a logarithmic dependence on Larmor frequency over the range from 0.01 to 30 MHz. A cross-over is observed below 0.1 MHz. In order to understand the relationship between geometric disorder, interfacial confinement, and nuclear magnetic relaxationdispersion (NMRD), we first compute an off-lattice reconstruction of the Vycor glass This model agrees with available experimental data (specific surface, porosity, chord length distributions, small angle scattering and tortuosity). A Brownian dynamics simulation is performed to analyze long time molecular self-diffusion and NMRD data. These later are well reproduced and appear to be connected with the translation diffusion of water near the SiO2 interface. The logarithmic character of the NMRD is specifically related to the interfacial geometry of the Vycor glass. Several other multiconnected interfacial structures such as periodic minimal surfaces do not exhibit such an evolution. Therefore, NMRD appears to be selectively sensitive to the interfacial geometry of mesoscopic disordered materials (MDM).