Electrolyte and Poly electrolyte Induced Aggregation of Colloids. Mechanism of Colloid Destabilization

Spherical latex particles were used as a colloid model to investigate the aggregation process resulting from the action of electrolytes and polyelectrolytes. The colloid size distribution was directly determined using a particle counter technique. Bell shaped curves were expected for diffusion limited aggregation (DLA) when particle sticking succeeded each interparticle collision. The colloid size frequency was described by a continuously decreasing curve when reaction limited aggregation (RLA) was expected. The last mode implied that the collision efficiency for sticking might depend on the aggregate size. Starting with the cluster size distribution, we calculated the different moments of the size distribution. When electrostatic forces modulated the interparticle interactions, in the presence of a excess of electrolyte or at a polymer concentration inducing fast aggregation, the reduced size distribution exhibited a typical maximum and the aggregation kinetic was described by a simple scaling law. As a result, a time invariant size polydispersity characterized the long time behavior. Apart from these ideal coagulation conditions, the flocculation proceeded at a slower rate and the dynamic scaling laws required two scaling exponents, w and z. The cluster size polydispersity factor increased with aggregation period as a result of variable collision efficiency. When flexible polymer acted as an interparticle bridging agent, the amount of polymer adsorbed on a colloid surface also modulated the rate of aggregation but the aggregation mode itself was only determined by the poly- mer/colloid interaction. Fast aggregation wets found to induce maximal cluster size polydispersity. In all these situations, colloid aggregation modes were analyzed using the results of computer simulation of the cluster-cluster aggregation and the experimental results were presented via a scaling approach. Validity of scaling relations was verified for electrolyte and polyelectrolyte induced aggregation and the different processes corresponded to diffusion and reaction limited aggregatio

Irreversible Adsorption from Dilute Polymer Solutions

We study irreversible polymer adsorption from dilute solutions theoretically. Universal features of the resultant non-equilibrium layers are predicted. Two cases are considered, distinguished by the value of the local monomer-surface sticking rate Q: chemisorption (very small Q) and physisorption (large Q). Early stages of layer formation entail single chain adsorption. While single chain physisorption times tau_ads are typically microsecs, for chemisorbing chains of N units we find experimentally accessible times tau_ads = Q^{-1} N^{3/5}, ranging from secs to hrs. We establish 3 chemisorption universality classes, determined by a critical contact exponent: zipping, accelerated zipping and homogeneous collapse. For dilute solutions, the mechanism is accelerated zipping: zipping propagates outwards from the first attachment, accelerated by occasional formation of large loops which nucleate further zipping. This leads to a transient distribution omega(s) \sim s^{-7/5} of loop lengths s up to a size s_max \approx (Q t)^{5/3} after time t. By tau_ads the entire chain is adsorbed. The outcome of the single chain adsorption episode is a monolayer of fully collapsed chains. Having only a few vacant sites to adsorb onto, late arriving chains form a diffuse outer layer. In a simple picture we find for both chemisorption and physisorption a final loop distribution Omega(s) \sim s^{-11/5} and density profile c(z) \sim z^{-4/3} whose forms are the same as for equilibrium layers. In contrast to equilibrium layers, however, the statistical properties of a given chain depend on its adsorption time; the outer layer contains many classes of chain, each characterized by different fraction of adsorbed monomers f. Consistent with strong physisorption experiments, we find the f values follow a distribution P(f) \sim f^{-4/5}.Comment: 18 pages, submitted to Eur. Phys. J. E, expanded discussion sectio

Electrolyte and Poly electrolyte Induced Aggregation of Colloids. Mechanism of Colloid Destabilization

Spherical latex particles were used as a colloid model to investigate the aggregation process resulting from the action of electrolytes and polyelectrolytes. The colloid size distribution was directly determined using a particle counter technique. Bell shaped curves were expected for diffusion limited aggregation (DLA) when particle sticking succeeded each interparticle collision. The colloid size frequency was described by a continuously decreasing curve when reaction limited aggregation (RLA) was expected. The last mode implied that the collision efficiency for sticking might depend on the aggregate size. Starting with the cluster size distribution, we calculated the different moments of the size distribution. When electrostatic forces modulated the interparticle interactions, in the presence of a excess of electrolyte or at a polymer concentration inducing fast aggregation, the reduced size distribution exhibited a typical maximum and the aggregation kinetic was described by a simple scaling law. As a result, a time invariant size polydispersity characterized the long time behavior. Apart from these ideal coagulation conditions, the flocculation proceeded at a slower rate and the dynamic scaling laws required two scaling exponents, w and z. The cluster size polydispersity factor increased with aggregation period as a result of variable collision efficiency. When flexible polymer acted as an interparticle bridging agent, the amount of polymer adsorbed on a colloid surface also modulated the rate of aggregation but the aggregation mode itself was only determined by the poly- mer/colloid interaction. Fast aggregation wets found to induce maximal cluster size polydispersity. In all these situations, colloid aggregation modes were analyzed using the results of computer simulation of the cluster-cluster aggregation and the experimental results were presented via a scaling approach. Validity of scaling relations was verified for electrolyte and polyelectrolyte induced aggregation and the different processes corresponded to diffusion and reaction limited aggregatio

Shrinkage Characteristics of Experimental Polymer Containing Composites under Controlled Light Curing Modes

The adsorption of polymethylmethacrylate polymer of different molecular weight at the aerosil/ethyleneglycol- or 1,3 butanediol-dimethacrylate interfaces was determined to provide microstructured networks. Their structural characteristics were determined to be controlled by the amount of polymer initially supplied to the system. The sediment (the settled phase) characteristics, determined as a function of the polymer concentration and the rate of the polymerization shrinkage determined for composite resins, obtained by extrusion of the sediment after centrifugation, were found to be correlated. The specific role of the adsorbed polymer was found to be differently perturbed with the supplementary supply of dimethacrylate based monomer additives. Particularly, the bisphenol A dimethacrylate that generated crystals within the sediment was found to impede the shrinkage along the crystal lateral faces and strongly limit the shrinkage along its basal faces. Addition of ethyleneglycol- or polyethylene-glycoldimethacrylate monomers was determined to modify the sedimentation characteristics of the aerosil suspension and the shrinkage properties of the composites. Finally, the effects of stepwise light curing methods with prolonged lighting-off periods were investigated and found to modify the development and the final values of the composite shrinkage

Effet des structures fractales sur la vitesse de rétraction des résines composites

REIMS-BU Santé (514542104) / SudocSTRASBOURG-Medecine (674822101) / SudocLILLE2-UFR Odontologie (593502202) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

Colloid aggregation in the presence of polymers. Effects of mobility and reactivity of clusters on the flocculation kinetics

International audienc

Adsorption—desorption processes in charged polymer/colloid systems; structural relaxation of adsorbed macromolecules

International audienc