Polymer induced crystal organization of composite resins.

Objectives: The elaboration of efficient dental resins requires a high degree of internal cohesion and a strong organization of the filler/matrix systems, and a good compatibility between the organic and inorganic constituents of the composite. Combining fractal aerosils and polymer constitutes an original way to realize promising dental composites. Determination of the combined roles of fractal fillers and polymers in the synthesis of composite resins, and the polymer dose in the crystal arrangement of the composite constituents, both being a requisite for the optimization of the filler/matrix compatibility.

Anisotropic crystal growth in aerosil/polymethylmethacrylate systems dispersed in dimethacrylate monomers.

Complex organized crystals were shown to grow within the settled phase composed of aggregated aerosil/polymethylmethacrylate or aerosil/poly(cetyl vinyl ether-maleic anhydride) resulting from the supply of the corresponding homopolymer or the alternated copolymer to the aerosil initially dispersed in a mixture of dimethacrylate monomers. The basic suspending phase was realized by mixing 1,3-butanediol dimethacrylate and bisphenol A dimethacrylate. The crystal nucleation and growth were both extremely slow processes that developed over months.

Interfacial characteristics of heterogeneous layers of linear polyvinylamine and branched polyethyleneimine or polyethyleneimine grafted with C12-C22 alkyl chains.

We investigated the characteristics of heterogeneous layers composed of linear hydrolyzed polyvinylamine and branched polyethyleneimine adsorbed at silica/water interfaces. The studies also included heterogeneous layers where branched polyethyleneimine was replaced by polyethyleneimine modified by grafting with C12-C22 alkyl chains. Surface area exclusion chromatography was used to determine the interfacial relaxation and surface affinity of the polymer molecules within homogeneous layers.

Relaxation phenomena of polyethyleneimine molecules within saturated homogeneous and heterogeneous layers adsorbed at a silica/water interface.

Surface area exclusion chromatography was used to investigate the adsorption characteristics of the highly branched polyethyleneimine (PEI) molecule and of a related molecule resulting from the grafting of PEI with C12 to C22 alkyl chains. The interfacial relaxation and surface affinity of the two polymers was determined in homogeneous and heterogeneous layers. The presence of hydrophobic moieties within the branched morphology of the grafted PEI molecule was found to modify the adsorption histogram as compared to bare PEI and to lead to greater interfacial stability.

Destabilization of polystyrene latex particles induced by adsorption of polyvinylamine: mass, size and structure characteristics of the growing aggregates.

The obviously visible aggregation of suspended colloidal particles resulting from the addition of polyvinylamine to the aqueous dispersion of polystyrene latex particles bearing surface sulfate groups set in with a delay of 24 h. The aggregation mechanisms and the fractal dimension of the aggregates were derived from the variations with time of the weight and number averaged masses of the aggregates as well as of the weight averaged harmonic mean diameter of the size distribution. Since the establishment of starved layers was determined to be relatively fast and to leave the liquid phase free of polymer, the delay for the obvious destabilization was attributed to the reconformation of adsorbed macromolecules that was expected to be extremely slow.

Relaxation phenomena of hydrolyzed polyvinylamine molecules adsorbed at the silica/water interface III. Interfacial exchange and transfer processes.

Surface area exclusion chromatography (SAEC) was employed to determine the stability characteristics of saturated homogeneous layers when interfacial exchange or transfer of molecules was promoted. In these experiments, the first polymer layer was established by elution of a column composed of stacked glass-fiber filters with one polymer. Then, after displacement of the void by water, the second polymer was subsequently injected under the same elution conditions.

Relaxation phenomena of hydrolyzed polyvinylamine molecules adsorbed at the silica/water interface II. Saturated heterogeneous polymer layers.

Surface area exclusion chromatography (SAEC) was employed to determine the individual relaxation of polymer molecules within a saturated heterogeneous layer composed of two polymers of different molecular characteristics. The investigations focused on three systems differing in molecular weight and/or hydrolysis grade. The molecular relaxation process was determined to be different within the heterogeneous layer when compared with the behavior of the same polymer in the homogeneous layer.

Relaxation phenomena of hydrolyzed polyvinylamine molecules adsorbed at the silica/water interface I. Saturated homogeneous polymer layers.

Surface area exclusion chromatography was used to investigate the adsorption and reconformation characteristics of hydrolyzed polyvinylamine molecules at silica/water interfaces employing radiolabeled polymers. The polymer solution was injected at the inlet of the column, whereas the polymer was successively adsorbed on the stacked glass-fiber filters constituting the stationary phase of the column. The filters and effluent samples collected at the outlet were individually analyzed for radioactivity content, which provided the adsorption histogram and the relative affinity of the various polymers.

Reconformation of polyvinylamine adsorbed on glass fibers.

Surface area exclusion chromatography was used to investigate the reconformation of fully hydrolyzed polyvinylamine. The polymer is adsorbed on stacked glass fiber filters constituting the stationary phase while the polymer solution is injected at the inlet of the chromatography column. From numerical simulation and experimental chromatograms of nonreconforming polyelectrolytes, the amount of polymer adsorbed per filter represented as a function of the filter position along the column (the histogram) was determined to be continuously decreasing and not to depend on the rate of elution.

Kinetics of adsorption of polyvinylamine on cellulose fibers. II. Adsorption from electrolyte solutions.

Adsorption from electrolyte solutions of fully hydrolyzed polyvinylamine on cellulose fibers was investigated by supplying the polymer to the fibers at controlled rate. This was implemented by employing a reactor only open to the fluid in which the fiber dispersion were confined and homogenized. The adsorbed layers may be defined as diffuse or dense layers.

Kinetics of adsorption of polyvinylamine on cellulose fibers. I. Adsorption from salt-free solutions.

Adsorption of fully hydrolyzed polyvinylamine on cellulose fibers in the short term was investigated by supplying the polymer to the fibers, first instantaneously by pouring the polymer solution into a jar containing the fiber dispersion (jar experiments) and second, at controlled rates (the reactor experiments). In the latter case, the rate of supply of polymer to the fiber dispersion confined in the reactor was monitored by setting the concentration of the solution being injected at a controlled rate. The concentration of the polymer solution exerts a paramount influence on the kinetics of adsorption and on the amount of polymer adsorbed at (or near) fiber surface saturation, while the rate of polymer supply only plays a minor role.