For many species the study of photophysical behaviour by fluorescence spectroscopy has been confined to low concentration as a result of the influence of the inner filter effect. In this paper we report how the total internal reflection technique of evanescent wavefluorescence spectroscopy (EWIFS) allows both the collection of distortion free steady-state fluorescence emission spectra and quantitative analysis of such species, in ‘bulk’ solution environment, to significantly higher concentration than can be achieved with a conventional ( right-angle ) geometry. A study of two species, the laser dye rhodamine 101 and anovel meso-substituted zinc prophyrin is presented.

We present results of simultaneous efforts to develop: 1.) Bragg-Fresnel Optics(BFO) to be used in X-ray microdiffraction methods, in particular as applied to structural studies of complex fluids and biomaterials under confinement and flow conditions; and 2.) Methodologies for confining complex fluids and biomaterials for in-situ structural studies. Using microelectronics process technology, we have fabricated linear and circular Bragg-Fresnel Lenses (BFL) in Si and III-V compound semiconductor substrates such as InP, GaAs and GaAs heterostructures with outermost zone width to 0.25 μm. X-ray characterization of linear BFLs were performed on a wiggler beamline at Stanford Synchrotron Radiation Laboratory (SSRL) at x-ray energies of 8 keV and 16 keV. A ∼5 μm focal spot size was obtained with a 50 μm incident beam, which was determined by the partial coherence of the source. On the confinement techniques, we have developed the X-ray Surface Force Apparatus (XSFA) which allows in-situ x-ray diffraction measurements to be made on fluid thin films confined between two atomically smooth surfaces. A new approach is being pursued to study the effects of confinement and flow on complex fluids and biological materials using microchannels fabricated on glass substrates.

Surface tension gradients created by a nonuniform temperature distribution in athin liquid film can force vertical spreading beyond the equilibrium meniscus [1]. Experiments designed to probe the flow behavior of super-meniscus films have shown that the leading edge can either spread uniformly with complete surface coverage or become corrugated and breakupinto long slender rivulets. We show that within linear stability analysis, both the conditions for unstable flow and the most unstable wavelength compare favorably with recent experiments reported in the literature.

Field-cycling 1H and 2H NMR relaxometry and field-gradient 1H NMR diffusometry were applied to polar and nonpolar liquids filled into porous glasses and fineparticle agglomerates (SiO2, ZnO, TiO2, globular proteins). The orders of magnitude of the length scales of the pore spaces ranged from 100 to several 102 nm. Pronounced differences of the spin-lattice relaxation dispersion for “weak” (nonpolar) and “strong” (polar) adsorption were found. In the latter case, the correlation times of the adsorbate orientation are up to eight orders of magnitude longer than in bulk. Trans-lational diffusion in liquid surface layers was directly studied with the aid of field-gradient NMR diffusometry in systems where the free liquid was frozen. The spin-lattice relaxation dispersion can be explained on the basis of reorientations mediated by translational displacements (RMTD) of adsorbate molecules on the surfaces. Thisprocess appears to be enhanced by a Levy walk mechanism so that the propagator adopts the form of a Cauchy distribution. The evaluated surface correlation functions are characterized by surface correlation lengths in the same order as the pore diameters, that is, up to three orders ofmagnitude larger than the length scale of dipolar interaction.

We present new experimental data on the properties of monodispersed glass spheresas a function of sphere diameter and gas flow in a gas fluidized bed. The data obtained by a novel non-intrusive probe of the average particle kinetic energy, or granular temperature, at thewall is used to explore and understand the well known empirical distinction between fluidized particles which exhibit a single phase state at initial fluidization (Geldart A powders) and fluidized particles that exhibit gas bubbles at initial fluidization (Geldart B powders). Specifically we show that the experimental “jump” we observe in the granular temperature atthe Geldart / transition is sufficient to account for the initial stability of the Geldart A phase on the basis of the one dimensional, first order, two wave, stability theory first introduced by Jackson in the early sixties. We present new data on the diameter dependent properties of the glass spheres during bed collapse and bed expansion, which demonstrate the distinctionbetween Geldart A and B behavior for these monodispersed glass spheres. Finally we present a simple Langevin model to account for the dependence of the granular temperature on sphere diameter and gas flow, and discuss the implications of these new experimental data for the fundamental physics of the Geldart A phase.

In this work we simulate the diffusion of gases in a microporous solid models using a newly developed dual control volume grand canonical molecular dynamics technique. This allows spatial variation of chemical potential and hence an accurate simulation of steady-state pressure driven diffusion. The molecular sieving nature of microporous zeolites are discussed and compared with that for amorphous silica from sol-gel methods. Massively parallel supercomputers allow a quick and insightful study of these microporous structures.

Due to their high electrical conductivity, their large specific surface area and their high porosity sol-gel derived nanoporous carbons are promising materials for electrodes, e.g. in water desalination systems or fuel cells. In order to optimize their properties with respect to these applications information is needed about transient and steady state transport through the interconnected pores.

Dynamic gas expansion and time resolved permeation measurements allow to determine the relevantquantities, i.e. the permeability, the ratio of gas phase to surface diffusion and the volume of dead end pores along with the tortuosity.

Experimental data on nanoporous carbons of different density are presented. All samples investigated were prepared via pyrolysis of resorcinol formaldehyde aerogels. The measurements were performed with different gases below 0.1 MPa.

We report a study of the dynamics of capillary rise of water in glass tubes and glass bead packs. The water column height h is measured as a function of time t byvideo imaging. Analyzing the late time data in terms of critical pinning, dh/dt ∞ (P – Pc)β, we find an anomalously large exponent β for interfaces in bead packs and β ≈ 1 for contact lines in capillary tubes. Repetitive rise and fall experiments in capillary tubes suggests that thinning of the wetting film plays an important role in the dynamics. We discuss these findings in light of recent theories and experiments.

We observe by Small Angle Neutron Scattering (SANS) the structure of polystyrene chains in semi-dilute solutions confined in model porous medium, Vycor. The size of the free polymer chains in solution is always larger than the pore diameter, 70 Å. The use of a suitable mixture of hydrogenated and deuterated solvents and polymers enables us to directly measure the form factor of one single chain among the others. The penetration of the chain in the porous media is almost complete for the concentration (Φ = 20%) and the range of molecular weights (35000 <M< 800000) used. The measured radius of gyration of confined chains is always smaller than the radius of gyration of free chains in the equivalent bulk solution.

We have carried out x-ray radiography and computed tomography (CT) to study two-phase flow in 3-D porous media. Air-brine displacement was imaged for drainage and imbibition experiments in a vertical column of glass beads. By correlating water saturation Sw with resistance R, we find that there is a threshold saturation S* ≈ 0.2, above which R(SW) ∼ Sw−2, in agreement with the empirical Archie relation. This holds true for both drainage and imbibition with littlehysteresis, provided that Sw remains above S*. Should Sw drop below S* during drainage, R(Sw) rises above the Archie prediction, exhibiting strong hysteresis upon reimbibition. This behavior suggests a transition in the connectivity of the water phase near S*, possibly due to percolation effects.

Using a scanning probe microscope, the influence of adhesion on measured film height of mixed-chain-length fatty acid Langmuir-Blodgett monolayers was investigated. A 1:1 mixture of CH3[CH2]22COOH and CH3[CH2]14COOH, was deposited in which the long chain-length acid, C24, was segregated from the short chain-length acid, C16. Two experiments were performed, contact scanning and force curve mapping. From both experiments, the film height difference measured between the C16 and C24 regions was larger than expected. Adhesion of the tip was 20% larger over the C16 acid regions. Using a compressional modulus derived from film pressure vs. area isotherms of the pure components, the adhesion difference and apparent filmheight difference over the two regions can be understood.