Françoise Lafuma

Flocculation and adsorption properties of cationic polyelectrolytes toward Na-montmorillonite dilute suspensions

Abstract Adsorption and flocculation properties were examined for the system Na-morillonite copolymers of acrylamide with a cationic monomer. Adsorption isotherms underlined the high affinity of the highly charged polymers for the clay surface and showed the crucial role of the interfacial conformation of the polyelectrolyte according to its cationicity. Performances of these copolymers when used as flocculants were followed as a function of their ionicity and molecular weight. The results are consistent with a balance between two flocculation mechanisms: charge neutralization which prevails for highly charged polymers and interparticular bridging which occurs at low cationicity when the optimal flocculation concentration (ofc) is strongly molecular weight dependent.

Determination of microstructure of hydrophobically modified water-soluble polymers by 13C n.m.r.

Abstract Determination of the microstructure of N- octylacrylamide sodium acrylate copolymers has been performed by 13C n.m.r. The 13C n.m.r. spectra were obtained in a CD 3 OD D 2 O mixture in order to minimize the hydrophobic aggregation. These hydrophobically modified water-soluble polymers exhibit a random distribution of the hydrophobic groups along the polymer chain.

Studies of rheological behavior of colloidal silica suspensions with interaction potential

Abstract Rheological measurements of both electrostatically and sterically stabilized silica suspensions are analyzed on the basis of the hard sphere approximation. For electrostatically stabilized suspensions, non-Newtonian viscosity is related to an effective pairwise interaction potential. It is shown that the shear rate dependence of viscosity can be predicted. For sterically stabilized suspensions, a structural model is used in order to obtain, in particular, low shear viscosity. From its dependence on particle volume fraction, the adsorbed polymer layer thickness can be deduced. In addition, the variations of shear modulus as a function of particle volume fraction are scaled with a power law.

13C and 23Na n.m.r. studies of the interactions between cations and kryptofix (2,2) bound to soluble or gel polyacrylamide

Abstract Interactions between univalent cations (Li + , Na + , K + , Ag + ) and bivalent cations (Ba 2+ , Ca 2+ ) with kryptofix (2,2) substituted polyacrylamide have been investigated using 13 C n.m.r. The tendency to form complexes involves the dimensions of both the hydrated ion and the cavity size macrocycle and for Ag + the nature of the interaction site. The sensitivity of the 23 Na n.m.r. method for detecting complex formation in solution from macromolecular species has been applied to the determination of the conditional formation constants of Na + and Ba 2+ complexes.

Polyamides containing dibenzo-18-crown-6 moieties in the backbone: nuclear magnetic resonance studies of their K+ and Cs+ complexes in dimethylsulphoxide

Abstract Complexation of potassium and caesium salts by polyamides containing dibenzo-18-crown-6 in the chain was investigated by 13 C and 133 Cs n.m.r. in dimethylsulphoxide. A study of the chemical shift as a function of crown/cation mole ratio shows that the mechanism of complexation of caesium by the macrocycle involves two equilibria with formation of a 1 1 complex and a sandwich complex, Cs + being bound to two macrocyclic moieties: the formation constant thus depends on the polymer structure.

Synthese de polyacrylamides porteurs de groupements iminodiacetate et etude de leur pouvoir de complexation vis-a-vis de quelques cations metalliques

Resume Nous avons prepare des polymeres hydrosolubles par reaction topochimique de liminodiacetate de sodium sur le polymethylolacrylamide. Leurs proprietes complexantes vis-a-vis de quelques cations metalliques ont ete etudiees par potentiometrie et spectroscopie, et comparees a celles de lacide iminodiacetique et dune molecule modele plus precise des sequences sequestrantes du polymere. Les resultats montrent que les chelates 1-1 du polymere et du modele sont plus stables que ceux de lacide iminodiacetique. Nous avons explique cette difference par la participation de la fonction amide a la coordination au cation des deux premiers ligands.

Recycle gel permeation chromatographic separation of some acetal alcohol diastereoisomers representing partial polyglucosidic sequences

Abstract This paper deals with the separation of some acetal alcohol diastereoisomers by recycling gel permeation chromatography; after several trials, this technique appears to be best suited to semi-preparative work. Acetal alcohols have two, three or four asymmetric carbon atoms and are mixtures of two or four diastereoisomers. They participate in hydrogen bonding with the chromatographic solvent (diisopropyl ether), which leads to different average hydrodynamic volumes and, accordingly, different elution volumes for each diastereoisomer. Semi-preparative separations have been performed by recycling 1 to 2 g of solute; we have also shown that separations could be achieved with crude products when preliminary purification was impossible. In these instances, impurities must be collected as they are resolved at the beginning of recycling.

Compatibilization of copolymers in solution through interchain hydrogen bonding

Abstract Low concentrations of polar units interacting through hydrogen bonds were introduced in polystyrene and polyvinylacetate chains by free radical copolymerization. Phase diagrams of copolymer mixtures in tetrahydrofuran were investigated. The influences on cloud-point isotherms of polar comonomer nature and concentration, and of copolymer molecular weight were studied. Viscometry appears to be reliable for evaluating the interactions betwen the different copolymers synthesized.