The conformation and titration curves of weak (or annealed) hydrophobic polyelectrolytes have been examined using Monte Carlo simulations with screened Coulomb potentials in the grand canonical ensemble. The influence of the ionic concentration pH and presence of hydrophobic interactions has been systematically investigated. A large number of conformations such as extended, pearl-necklace, cigar-shape, and collapsed structures resulting from the subtle balance of short-range hydrophobic attractive interactions and long-range electrostatic repulsive interactions between the monomers have been observed. Titration curves were calculated by adjusting the pH-pK(0) values (pK(0) represents the intrinsic dissociation constant of an isolated monomer) and then calculating the ionization degree alpha of the polyelectrolyte. Important transitions related to cascades of conformational changes were observed in the titration curves, mainly at low ionic concentration and with the presence of strong hydrophobic interactions. We demonstrated that the presence of hydrophobic interactions plays an important role in the acid-base properties of a polyelectrolyte in promoting the formation of compact conformations and hence decreasing the polyelectrolyte degree of ionization for a given pH-pK(0) value.
Monte Carlo simulations were used to investigate the adsorption of a polyelectrolyte chain on an oppositely charged micelle. The influence of the concentration of monovalent salt on the isolated polyelectrolyte chain was investigated by considering the chain expansion factor and persistence length. The polyelectrolytemicelle complex was characterized in terms of the amount of adsorbed polymer in trains, loops, and tails. The overcharging of the complex and the conformation of the adsorbed polyelectrolyte chain was also studied. The ionic strength adsorption-desorption limits were estimated at different micelle charge densities and compared to existing data for the experimental system of sulfonated poly(vinyl alcohol) and micelles of dimethyldodecylamineoxide of varying degrees of protonation. The effect of the relative micelle concentration on the adsorption-desorption limit of the system was also investigated.
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