Polyelectrolyte Adsorption on an Oppositely Charged Spherical Particle. Chain Rigidity Effects

Abstract

We used Monte Carlo simulations to study the formation of complexes between a flexible, semiflexible, and rigid polyelectrolyte and an oppositely charged spherical particle. Polyelectrolyte adsorption on a small particle, whose surface curvature effect is expected to limit the amount of adsorbed monomers, was considered. We focused on the effects of the intrinsic polyelectrolyte rigidity and ionic concentration of the solution and investigated the adsorption/desorption limit and conformation of the adsorbed polyelectrolyte. Polyelectrolyte adsorption is controlled by several competing effects such as the electrostatic confinement energy of the chain due to the electrostatic repulsions between the charged monomers, polyelectrolyte intrinsic flexibility, and electrostatic attractive interaction between the polyelectrolyte monomers and the particle. On one hand, rigidity and electrostatic repulsions force the polyelectrolyte to adopt extended conformations and limit the number of monomers that may be attached to the particle. On the other hand, electrostatic attractive interactions between the particle and the polyelectrolyte monomers force the chain to undergo a structural transition and collapse at the particle surface. In particular, by increasing the intrinsic rigidity, we observed a transition from a disordered and strongly bound complex to a situation where the polymer touches the particle over a finite length, while passing by the formation of a solenoid conformation. We found that the critical ionic concentration at which adsorption/desorption is observed is rapidly decreasing with the polyelectrolyte intrinsic rigidity, and the amount of adsorbed monomers has a maximum value for semiflexible chains. Adsorption is thus promoted by decreasing the chain stiffness or decreasing the salt concentration for a given chain length.

Rodlike Complexes of a Polyelectrolyte (Hyaluronan) and a Protein (Lysozyme) Observed by SANS

“…These main trends have been checked experimentally by Kayitmazer et al who compare the binding of chitosan and PDADMAC, two polyelectrolytes with equal charge density but different persistence lengths, to oppositely charges micelles, dendrimers and proteins 32 . However the authors point out that the relevant parameter for binding is not necessarily the intrinsic persistence length of the chain L p , but the flexibility of the chain on the colloid length scale 6 6 In parallel, computer simulations also studied the role of electrostatic interactions in mixtures of charged strings with charged spheres and their interplay with parameters such as chain stiffness, at first in simulations involving only one protein and one polyelectrolyte chain 30,31 , and more recently on systems dealing with several proteins in the presence of an oppositely charged polyelectrolyte 33, 34 . In ref [34], the heterogeneous charge density of proteins in the presence of weak polyelectrolyte has also been taken into account, whereby different chain lengths and ionic strengths were employed:…”

Influence of Chain Stiffness on the Interaction of Polyelectrolytes with Oppositely Charged Micelles and Proteins

“…14 As noted, the simulations of Stoll and Chodanowski show a desorption-adsorption transition when I exceeds some value that depends on the other variables mentioned above. 22 However, other simulations disclose no transitions with changing I but instead a change in the number of polymer residues residing in the vicinity of the colloid surface. [19][20][21][22]31 What we observe experimentally is a transition from noninteracting to complexed states at fixed ionic strength, upon increase in the surface charge density of a cationic-nonionic mixed micelle in the presence of HA or AMPS 20 /AAm 80 .…”

Role of Polyelectrolyte Persistence Length in the Binding of Oppositely Charged Micelles, Dendrimers, and Protein to Chitosan and Poly(dimethyldiallyammonium chloride)

“…workers 26,33 have indicated that desorption of an oppositely charged spherical particle from a polyelectrolyte chain occurs at a critical salt concentration, which varies inversely with L p . In brief, all these studies have pointed out that flexible, i.e., low L p , polyelectrolyte chains bind more strongly to oppositely charged colloids than stiffer chains do.…”