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. This reconformation promoted the emergence of the diffusion-limited aggregation process that accompanies the permanent reaction-limited aggregation process. The fractal dimension of the latex particles/polyvinylamine aggregates was determined to be 2.12.

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. For saturated polymer layers, the relaxation process was demonstrated when the exceedingly adsorbed molecules desorbed. Modifications in the adsorption on the successive filters were thus converted into changes in the interfacial area of adsorbed molecules, taking into account the deviation from the plateau adsorption expected for nonrelaxing systems. Adsorption characteristics of nonrelaxed polymer layers were determined from the adsorption values determined before relaxation occurred. Adsorption and relaxation characteristics were determined to depend strongly on molecular weight and degree of hydrolysis of the polyvinylamine molecules. Half-hydrolyzed polymers had adsorption and relaxation characteristics close to those of the fully hydrolyzed polyvinylamine. Accordingly, adsorption isotherms on the cellulose/water interface were carried out to possibly extend the main conclusions of the study.

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. Diffuse layers are characterized by a surface coverage limited to 0.65 mg/g cellulose in salt-free solutions. Addition of NaCl or CaCl(2) to the fiber dispersion and the polymer solution promotes the adsorption rate and increases the amount of adsorption to 1.5 mg/g cellulose. For dense polymer layers, for which the coverage amounts to values close to 10 mg/g cellulose in salt-free systems, addition of electrolyte does not change the kinetic and adsorption characteristics. Insofar as the variation of the molecular areas of the polymer within the diffuse layers as a function of the ionic strength parallels the variation of the molecular characteristics of solute molecules, the formation of diffuse layers is expected to proceed by random deposition of solute molecules which later individually sustain strong reconformation. Adsorption isotherms show a limited influence of the ionic strength. Obviously, the passage from dense layers of high surface coverage to low adsorption values at equilibrium requires extended reconformation of adsorbed macromolecules and desorption of a great part of the molecules already adsorbed.

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. The main observation is the emergence of two types of polymer layers corresponding to diffuse and dense layers. The former were characterized by adsorption layers of density smaller than 0.65 mg/g cellulose that are composed of adsorbed polymers having sustained extended flattening in the adsorbed state. The latter reach densities as high as 10 mg/g cellulose when the fiber surface is fully coated, thus indicating that reconformation is limited or even impeded at short terms. The threshold adsorption corresponds more or less to equilibrated layers, since the final coverage determined at adsorption equilibrium did not exceed 0.6 to 0.7 mg/g cellulose.

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. For polyvinylamine, the histograms are peaked and the height of the peak was determined to depend greatly on the rate of polymer supply to the column that was controlled by monitoring the polymer concentration and/or the rate of elution (mass-transfer-controlled adsorption). Modifications in the adsorption on the successive filters were converted into changes in the interfacial area of adsorbed molecules taking into account model histograms as well as experimental adsorption histograms of non reconforming systems. Macromolecule concentration in the mobile phase and contact time between solute and adsorbed molecules were determined to be the two parameters controlling the extent of polymer desorption. The unusual shape of the histogram thus was attributed to reconformation of the adsorbed polymer, which was stimulated by interfacial exchange between segments belonging to trains of adsorbed macromolecules and chain segments of solute ones.