This study deals with the fine-tuning of the interactions between silica nanoparticles and a LCST polymer in order to build permanent rigid linear aggregates. LCST polymers become hydrophobic and collapse above a critical temperature. The collapse of the polymer chains at the surface of the silica particles generates an attractive potential that can overcome the repulsive electrostatic forces between the silica particles under certain circumstances. The combined use of the thermoresponsiveness of poly(ethylene oxide) and of the chemical condensation properties of silica enables us to build permanent rigid aggregates displaying rodlike shapes just by increasing the temperature. These aggregates have been characterized using two complementary techniques: transmission electron microscopy and small angle neutron scattering. For low curing time, it appears that small linear aggregates are obtained when the electrostatic surface potential (pH = 8.5) is high and the initial ionic strength is low (I approximately = 10(-3) M). For higher heating time these objects aggregate further leading to some branching and ultimately to 3D gels which phase separate.

In this article we shall describe our quest and ultimate success in furthering our understanding of the action of superplasticizers on the rheology of cement and concrete. By specifically producing superplasticizers with varied architectures, we have been able to show the important structural features of the macromolecules that lead to a successful superplasticizer or water reducing agent. Both polycarboxylate and lignosulfonate polymers have been investigated. Using both non-reactive model MgO powders, three different types of cement blends, the adsorption behaviour and the effect on the rheological properties of these two important superplasticizer families have been used to further develop a conceptual model for superplasticizer — cement behaviour. This paper will deal mainly with the conceptual model, the materials and methods used to asses the polymer adsorption behaviour and rheological properties of the systems studied. We shall briefly describe the adsorption of the polymers onto the different surfaces and their influence on surface charge and rheology and the influence of the various ionic species found in cement pore solutions that may influence polymer-cement affinity. The key factors are shown to be the effective adsorbed polymer thickness and the induced surface charge which can be influenced by the polymer architecture, the pore solution composition and the initial particle surface charge.

Responsive copolymers have been prepared by grafting onto a poly(acrylamide-co-sodium acrylate) backbone [PAM-co-PANa] poly(N-isopropylacrylamide) stickers [PNIPA] characterized by a lower critical solution temperature (LCST) in water. From adsorption isotherms and DSC studies performed on PNIPA/silica mixtures, it was shown that PNIPA chains irreversibly interact with silica particles and that at low coverage they partially lose their responsiveness with temperature. When PNIPA is grafted onto a PAM-co-PANa backbone, which has no specific attraction to silica surfaces (only electrostatic repulsions), their binding process remains very similar to the one analyzed with PNIPA chains alone. Above critical copolymer and silica concentrations (Cp congruent with 1 g/L and CSi congruent with 30 g/L), hybrid networks can be formed following the rules of percolation theory. The viscoelastic properties of these networks are controlled by the concentration of inorganic cross links and the fraction of PNIPA grafts participating in bridges between particles, the others being involved in inelastic loops or pendant chains. For all of the mixtures investigated, an optimum weight ratio of RSi/PNIPA = 10-15 was found for the viscoelastic properties, in agreement with the saturation of silica beads by the copolymer. Because of the responsive behavior of PNIPA in aqueous solutions, graft copolymers are able to self-assemble with temperature, giving rise to a sol/gel transition upon heating. In the presence of added silica, hybrid aggregates (silica/PNIPA) coexist at high temperature with organic ones (PNIPA/PNIPA) with synergistic or antagonistic effects on the elastic properties depending on the proportion of PNIPA grafts per silica particle.

Abiomimetic motility assay is used to analyze the mechanism of force production by site-directed polymerization of actin. Polystyrene microspheres, functionalized in a controlled fashion by the N-WASP protein, the ubiquitous activator of Arp2/3 complex, undergo actin-based propulsion in a medium that consists of five pure proteins. We have analyzed the dependence of velocity on N-WASP surface density, on the concentration of capping protein, and on external force. Movement was not slowed down by increasing the diameter of the beads (0.2 to 3 microm) nor by increasing the viscosity of the medium by 10(5)-fold. This important result shows that forces due to actin polymerization are balanced by internal forces due to transient attachment of filament ends at the surface. These forces are greater than the viscous drag. Using Alexa488-labeled Arp2/3, we show that Arp2/3 is incorporated in the actin tail like G-actin by barbed end branching of filaments at the bead surface, not by side branching, and that filaments are more densely branched upon increasing gelsolin concentration. These data support models in which the rates of filament branching and capping control velocity, and autocatalytic branching of filament ends, rather than filament nucleation, occurs at the particle surface.

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.

Nous avons préparé des polymères hydrosolubles par réaction topochimique de l'iminodiacétate de sodium sur le polymethylolacrylamide. Leurs propriétés complexantes vis-à-vis de quelques cations métalliques ont été étudiées par potentiométrie et spectroscopie, et comparées à celles de l'acide iminodiacétique et d'une molécule modèle plus précise des séquences sequestrantes du polymère. Les résultats montrent que les chélates 1-1 du polymère et du modèle sont plus stables que ceux de l'acide iminodiacétique. Nous avons expliqué cette différence par la participation de la fonction amide à la coordination au cation des deux premiers ligands.

Dans le but d’étudier les chélations saccharidiques persistant en solution, nous avons examiné les liaisons hydrogène intra- moléculaires dans quelques molécules modèles (cyclohexane-diols-1.2, hydroxyméthyl-2 tétrahydropyranne et alcools de le série cyclohexyloxy-2 tétrahydropyranne), en solution dans des mélanges DMSO/CCl4 concentrés en CCl4. L’étude infrarouge des absorptions ν(O — H), met en évidence la persistance de cycles de chélation à 5 chaînons, qui peut être observée jusqu’à 25 % en volume de DMSO. La plupart des mono- et des disaccharides sont solubles dans des mélanges DMSO/ CCl4 contenant de 75 % à 90 % en volume de CCl4. L’étude analogue de 8 monosaccharides, du β-D-maltose et du β-D-cellobiose, a montré également une persistance de chélations à 5 chaînons. Ces chélations saccharidiques à 5 chaînons peuvent être classées, suivant leurs configurations cis ou trans.

Journal of Polymer Science: Polymer SymposiaVolume 52, Issue 1 p. 261-269 Article Liaisons Hydrogene Intramoleculaires Dans Les Chaines De Cellulose Françoise Lafuma, Françoise Lafuma Laboratoire de Physico-Chimie Macromoléculaire de l'Université Pierre et Marie Curie (Paris VI), Ecole Supérieure de Physique et de Chimie, 10 rue Vauquelin, 75231, Paris, Cédex 05Search for more papers by this authorClaude Quivoron, Claude Quivoron Laboratoire de Physico-Chimie Macromoléculaire de l'Université Pierre et Marie Curie (Paris VI), Ecole Supérieure de Physique et de Chimie, 10 rue Vauquelin, 75231, Paris, Cédex 05Search for more papers by this author Françoise Lafuma, Françoise Lafuma Laboratoire de Physico-Chimie Macromoléculaire de l'Université Pierre et Marie Curie (Paris VI), Ecole Supérieure de Physique et de Chimie, 10 rue Vauquelin, 75231, Paris, Cédex 05Search for more papers by this authorClaude Quivoron, Claude Quivoron Laboratoire de Physico-Chimie Macromoléculaire de l'Université Pierre et Marie Curie (Paris VI), Ecole Supérieure de Physique et de Chimie, 10 rue Vauquelin, 75231, Paris, Cédex 05Search for more papers by this author First published: 1975 https://doi.org/10.1002/polc.5070520122Citations: 2AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume52, Issue11975Pages 261-269 RelatedInformation