Formation of Complexes between Nanoparticles and Weak Polyampholyte Chains. Monte Carlo Simulations

The electrostatic driven complex formation between a weak polyampholyte chain and one pos. charged nanoparticle is investigated using Monte Carlo simulations. The influence of parameters such as the polyampholyte contour length, no. and size of blocks, nanoparticle surface charge d., and soln. properties, such as the pH and ionic concn., on the PA titrn. curves is investigated. It is shown that the presence of one pos. charged nanoparticle significantly modifies the acid/base properties of the weak polyampholyte by, on the one hand, promoting the formation of neg. charged monomers and, on the other hand, limiting the no. of pos. charged monomers. The electrostatic interactions of this system can be modified by pH, ionic concn., and nanoparticle surface charge. The competition between attractive and repulsive, intramol. and intermol. electrostatic interactions leads to a wide range of possible PA conformations at the nanoparticle surface, which have a direct impact on the nanoparticle stabilized or destabilized solns. Extended conformations, electrostatic rosettes, and dense multiplayer structures are obsd. Nonetheless, the intramol. interactions between the pos. and neg. charged PA monomers, in particular at the isoelec. point, are found to play important and subtle roles for both the isolated and adsorbed chain conformations. It is also found that nanoparticle charge inversion is an important ingredient for the formation of multilayer structures at the nanoparticle surface.