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The adsorption properties of polyacrylamides and xanthans on mineral surfaces carrying silanol and aluminol groups such as sand and kaolinite are described. The influence of the main parameters such as the nature of adsorption sites, surface charge, chemical structure and conformation of polymer and interactions of mono- and divalent ions with polymer and mineral surface has been investigated and interpreted. Some operating parameters in polymer flooding such as pH and salinity of injected solution, the nature of the polymer and its degree of ionicity were found to be determining factors from the adsorption level. The results give key elements for reducing adsorption by a proper choice of polymer nature and ionicity and of injection conditions. Les propriétés d'adsorption des polyacrylamides et des xanthanes sur des surfaces minérales portant des groupements silanols et aluminols comme le sable et la kaolinite ont été examinées. L'influence de différents paramètres est analysée : nature des sites d'adsorption, charge de surface, structure chimique et conformation du polymère, interactions des ions mono et divalents avec la surface. Il apparaît que le pH et la salinité de la solution injectée, la nature du polymère et, en particulier son degré d'ionicité, qui sont les paramètres opérationnels lors d'une injection de polymère destinée à augmenter le taux de récupération du pétrole, sont déterminants en ce qui concerne les niveaux d'adsorption. On en déduit les principaux moyens pour réduire l'adsorption dans un cas d'application donné.

We have employed Langmuir monolayers of polydimethylsiloxane-polystyrene diblock copolymers as a model system for examining layers of tethered chains under good solvent conditions. The range of surface density accessible with this system coincides with the ranges reported in the literature for chains tethered onto solid substrates from dilute solution in good solvents. We have varied both the surface density (σ) and the molecular weight (M) of the submerged polystyrene block independently, covering over a decade in each variable. Both the form of the segmental concentration profile and the variation of the layer height with σ and M are in good agreement with numerical self-consistent-field (SCF) calculations. On the other hand, we do not observe precise agreement with the scaling predictions for strongly stretched chains, in contrast to some previous reports. Through measurements of the surface pressure (Π), we present the first direct comparison between anchoring energies and differential chain energies in tethered layers. We find these to be of equal magnitude at the desorption transition. However, the chain energies reach values roughly an order of magnitude larger than can be accounted for by the osmotic interaction of the polystyrene segments in the good solvent. In addition, the dependence of Π on σ is more consistent with a model of soft spheres with hard cores than that of a semidilute polymer mesh. The hard core areas seem to be loosely related to Rg. We attribute these observations to a steric effect which limits lateral interpenetration of the submerged blocks. The sharp rise in Π with σ is of great practical importance as it limits the maximum surface coverage in this system, and may also do so for other systems. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have determined by neutron reflectivity the volume fraction profile, [lowercase_phi_synonym](z) of poly(dimethylsiloxane) chains in toluene adsorbed at the free surface of the solution. [lowercase_phi_synonym](z) is found to vary as (a/z)4/3 conforming to scaling laws proposed by de Gennes. The extension of the profile is of the order of the radius of gyration. To arrive at these results, the use of two different isotopic compositions and the simultaneous analysis of results obtained with various polymer chain lengths and concentrations are necessary. The validity of several models has been tested. With a few realistic hypotheses compatible with already existing experimental data, it appears that only the self-similar profile is acceptable for the system studied. [ABSTRACT FROM AUTHOR]

The surfactant film bending elasticity can be described by a spontaneous curvature C0 and two elastic constants K and K associated with the mean curvature and the Gaussian curvature, respectively. These parameters are very important in the determination of the structure of the dispersions stabilized by the surfactant (droplets or sponge-like structures). We have studied ternary mixtures of oil, water, and nonionic surfactants of different chain lengths. Depending on the temperature, the microemulsions are in equilibrium with excess oil (o/w structure), excess water (w/o), or both excess oil and water (bicontinuous). We present neutron scattering data from which we determine the microemulsion structure and, in the case of droplet structures, of the droplet polydispersity. These results, in combination with those from earlier experiments using ellipsometry, are used to estimate K. [ABSTRACT FROM AUTHOR]