Polyelectrolytes at Charged Particles:  Particle Number Density, Molecular Weight, and Charge Ratio Effects

Abstract

The effect of molecular weight, particle number density, and charge ratio on the colloidal behavior of positively charged polystyrene particles (PSA) in the presence of the natural polyanion carboxymethyl cellulose (CMC) was investigated by zeta potential and light scattering measurements. For low ionic strength, a phase diagram with three distinct regimes was proposed. Flocculation is favored for R values close to 1, where R is the ratio of the total negative charge (N tn ) to the total positive charge (N tp ). Colloidal stabilization is achieved in the R range of 2.5-200 and with polyelectrolytes chain length smaller than the critical chain length (L crit ), which is the contour length corresponding to the particle mean perimeter. For R values larger than 200, isolated particles and/or doublets are present in the dispersion and with polyelectrolytes chain length smaller than L crit , whereas doublets and/or aggregates are observed when the polyelectrolytes chain length is larger than L crit . The effect of the particle number density on the colloidal stabilization was weak. The adsorption behavior of CMC onto PSA particles was not comparable to that of CMC onto PSA films.

Small‐Angle X‐Ray Scattering on Solutions of Carboxymethylcellulose and Bovine Serum Albumin

“…In the case of very low polymer concentrations, bridging flocculation may occur as the polymer chain forms bridges by adsorbing on more than one particle 32. Surface charge neutralization generally leads to aggregation,33 although for proteins this is not so trivial because of the surface chemical heterogeneity. The number of positive charges on the BSA surface can be estimated from earlier studies17,18 as +23 surface charges per molecule (see Experimental Part).…”

Effect of Polyelectrolyte Structural Features on Flocculation Behavior: Cationic Polysaccharides vs. Synthetic Polycations

“…Nevertheless, the effect of molecular weight becomes less important as soon as polyelectrolytes have medium or high charge density and perform mainly through the charge neutralization or “charge patch” mechanisms7–9 when aggregation occurs as a result of attraction between oppositely charged regions on partially covered particles. In this case a match in spacing between polyelectrolyte functional groups and oppositely charged surface sites,8,10 as well as chain stiffness8,11 should also be considered as parameters significantly affecting the adsorption and flocculation behavior.…”

Colloid Stability of Lipid/Polyelectrolyte Decorated Latex

“…Particles in the presence of oppositely charged polyelectrolytes can either flocculate or become stabilized as singlets or doublets depending on the polyelectrolyte molecular weight and concentration, particle number density, molar ratio for charges on particles and macromolecules, pH, and ionic strength. [48][49][50][51] We have recently studied colloid stability of charged polymeric particles in the presence of oppositely charged polyelectrolytes so that experimental conditions for improved colloid stability, namely, occurrence of a vast majority of singlets and/or doublets in dispersion, could be established. 50,51 In the present work the effect of adsorbing cationic lipids from BF on colloid stability of CMC-covered particles was evaluated.…”

“…[48][49][50][51] We have recently studied colloid stability of charged polymeric particles in the presence of oppositely charged polyelectrolytes so that experimental conditions for improved colloid stability, namely, occurrence of a vast majority of singlets and/or doublets in dispersion, could be established. 50,51 In the present work the effect of adsorbing cationic lipids from BF on colloid stability of CMC-covered particles was evaluated. The production of colloidally stable particle singlets covered by a composite polyelectrolyte/lipid layer required relatively large concentrations of the cationic lipid, which massively adsorbed onto the polyelectrolyte layer and produced a compressed cationic film on particles with zeta potentials well below the one usually determined for DODAB cationic bilayers.…”