Henri Van Damme

Adsorption of nonionic surfactants at the solid—solution interface and micellization: A comparative fluorescence decay study

Abstract The fluorescence decay of the phenoxy group of two monodisperse and one polydisperse (Triton X-100) polyoxyethylene alkyl phenols has been studied in aqueous solution, and in the adsorbed state on a hydrophilic (hydroxylated) or hydrophobic (methylated) silica surface. In aqueous solution, below the CMC, one single exponential decay is observed with a lifetime of 4.5 nsec. Above the CMC, a second exponential component with a lifetime of 37 nsec appears with the monodisperse compounds, but not with Triton X-100. This long decay is assigned to dimeric species and its amplitude is quantitatively correlated to the fraction of molecules involved in micellar aggregates. On the hydrophilic silica surface, the same long decay appears from the very beginning of the adsorption isotherm and its amplitude remains constant up to the plateau of the isotherm, close to the value observed in the pure liquid surfactant. This is taken as evidence that, from the outset of adsorption, the majority of molecules is involved in molecular aggregates. On the hydrophobic surface, the constant amplitude regime is observed only at high surface coverage. At low surface coverage, the amplitude increases linearly with θ, suggesting that, in this regime, the adsorbed phase can be described as a dilute gas.

Influence of surface heterogeneity on the luminescence decay of probe molecules in heterogeneous systems Ru(bpy)2+3 on clays

The decay of a luminescent probe [Ru(bpy)2+3] adsorbed on solids (clays) containing quenching impurities (Fe3+) has been examined. The time law is a multi-exponential function which stems from (i) the quasi-total translational immobility of the probe on the microsecond scale, and (ii) the heterogeneous nature of the surface, which is influenced by the local concentration of iron in the clay lattice. An elementary model has been proposed based on a randomly decorated 2-dimensional lattice for the probe and a second underlying and randomly decorated 2-dimensional lattice for the quencher ions. Assuming that the quenching probability for an excited probe is linearly related to the number of neighbouring quenchers, a decay function has been derived which, for very low quencher concentrations, reduces to the Infelta–Gratzel–Thomas equation for quenching in micellar solutions. The parameters of the decay function have been correlated to the chemical composition of the clays and to their swelling properties.

Pattern formation in particulate complex fluids: A guided tour

Dispersion of colloidal particles in a liquid leads to the formation of complex fluids which are most often non-Newtonian and viscoelastic. When larger particles are used, plastic pastes may be obtained. Without dispersion medium, the particles just form a powder. Each of these systems exhibit peculiar flow or fracture behaviors which allows for a rich variety of fractal patterns, including viscous fingers, viscoelastic fracturing patterns, rough fracture surfaces, and granular displacement patterns.

Influence of Fillers on Textural and Mechanical Properties of C3S Pastes

How active is a filler and what is the mechanism of its activity? Is the activity related to a change in hydrate composition, hydrate (micro)texture, or hydration kinetics? Those are the questions that we tried to answer in our work by combining 2H NMR surface area determinations, calorimetric measurements and Portlandite determination, on a series of pastes prepared by mixing C3S with limestone, quartz or α-alumina filler. Our results point towards a selective influence of fillers on the kinetics of C3S hydration and of CSH surface area development, as shown by 2H NMR relaxation.

Viscous fingering and viscoelastic fracture in clays

Publisher Summary This chapter describes viscous fingering and viscoelastic fracture in clays. Clay minerals are ubiquitous in nature. They occur in discrete geological deposits, in soils, and in all products of erosion and breakdown of rocks. They are, by definition, the fine-grained fraction of minerals. It turns out that this purely granulometric definition closely corresponds to a particular class of the silicates with a layer lattice structure—the phyllosilicates, of which micas are probably the most widely known. The essential feature of phyllosilicates is their two-dimensional atomic structure, which is often reflected by the platy shape of their microcrystals. The most interesting family of clays, as far as physical properties are concerned, is the family of smectites. Their 2:1 layer charge is large and is compensated by hydrated interlayer cations which, in natural clays, are essentially hydrated sodium, calcium, or magnesium ions. The hydration energy of the interlayer ions allows water to enter the interlayer space. This makes the original interlayer cations easily exchangeable by other metal cations or by any other cationic species. Each 2:1 layer has an extremely high aspect ratio. Its lateral extension is of the order of 500 nm and it is only 1 nm thick.