Structure of an Adsorbed Polyelectrolyte Monolayer on Oppositely Charged Colloidal Particles

Abstract

An adsorbed layer of a cationic polyelectrolyte, poly(diallyldimethyl-ammonium) chloride (PDADMAC) on negatively charged colloidal latex particles was investigated by small-angle neutron scattering (SANS) and dynamic light scattering (DLS). SANS gives a layer thickness of 8 +/- 1 A and a polymer volume fraction of 0.31 +/- 0.05 within the film. DLS gives a somewhat larger thickness of 18 +/- 2 A, and the discrepancy is likely due to the inhomogeneous nature of the layer and the existence of polymer tails or loops protruding into solution. These results show that a highly charged polyelectrolyte adsorbs on an oppositely charged colloidal particle in a flat configuration due to the attractive forces acting between the polyelectrolyte and the substrate.

Polyelectrolyte Multilayers Containing Triblock Copolymers of Different Charge Ratio

“…68 Figure 7 shows that X w decreases from values close to 1 for low number of layers until a quasiplateau value (N ∼ 10); this qualitative behavior is independent of the system studied in the present work, which suggests that the polymer chains adsorb rather inhomogeneously in the first layers forming isolated adsorbed pancake. [69][70][71] These results are in accordance with the model previously reported by us for multilayers of (PDADMAC þ PSS) n 34 and with the structural results obtained by AFM of multilayers by Kujawa et al 72 The very high content found for the first adsorbed layer is also in qualitative agreement with the results of Vaccaro et al 69 Figure 8 shows X w for multilayers with 20 layers for all the multilayers studied in this work. It is observed that the water content depends on the copolymers and on the concentration of copolymer.…”

Stability of negatively charged latex particles in the presence of a strong cationic polyelectrolyte at elevated ionic strengths

“…From the adsorbed amount and the layer thickness at the ASP, one can estimate the average volume fraction of the polyelectrolyte within the film to be between 10% and 20%. Comparable volume fractions were found for PDADMAC in a very similar system by small angle neutron scattering [19]. While one might be tempted to suspect a strongly swollen film, we rather believe that the adsorbed film is laterally heterogeneous and probably consists of compact patches of the adsorbed polyelectrolyte and partially void surface.…”

“…As a consequence, any polyelectrolyte that is further added remains dissolved in solution, while below the ASP the adsorption of the polyelectrolyte is quantitative. The resulting polyelectrolyte layers are thin and laterally heterogeneous [11,14,19,20]. However, their structure remains a subject of research, and will also be discussed here.…”

“…One is thus tempted to conclude that the same situation applies even in the presence of an adsorbed polyelectrolyte layer, and that such colloidal suspensions can be destabilized with salt irrespective of the polymer dose. However, the adsorbed polyelectrolyte layer is known to have a thickness of few nanometers in the saturated state [11,14,19,20]. One could expect that such layers induce repulsive steric forces, which might provide an additional mechanism for stabilization similar to neutral polymers [11,14,36,37].…”

Probing effects of polymer adsorption in colloidal particle suspensions by light scattering as relevant for the aquatic environment: An overview

“…Small-angle neutron scattering experiments have been successfully used to study this property (Mears et al, 1998;Hone et al, 2002;Oberdisse, 2007;Vaccaro et al, 2009). This technique has the advantage that simultaneous measurements of the adsorbed amount and of the layer thickness are possible.…”