Competitive Substitution of Charged polymers and Trimer Formation: A Mean-Field Model

We have modeled the invasion of a polyelectrolyte complex made of a polycation chain and a polyanion chain by another polyanion chain using a mean-field model. Depending on various polyion specificities, the invading chain may completely substitute the chain being displaced or form a stable trimer. Our results reveal many intricate details of the substitution reaction, including conformational changes of the chains and competition between the invading chain and the one being displaced. We show that the invading chain must be sufficiently asymmetric compared to the chain being displaced to effect the substitution or form stable conformations. We also explore the effects of salt and solvent specificity on the stability of the trimers. Our results shed light on the dominant driving force of the substitution process and the parameters that affect the stability of the trimers.