title: Reentrant Variation of Single-Chain Elasticity of Polyelectrolyte Induced by Monovalent Salt.
abstract: The interactions between monovalent counterions and polyelectrolyte are important in chemical and biological systems. The condensation and screening effect of counterions complicate the polyelectrolyte solutions. By means of single-molecule AFM, the single-chain mechanics of a strong polyelectrolyte, poly(sodium styrenesulfonate) (PSSNa), in KCl aqueous solutions over almost whole concentration range have been studied. The M-FJC model has been used to describe the single-chain elasticity of PSSNa in KCl solutions with a parameter of single-chain modulus (K0). Along with the increase of the concentration of KCl from zero to almost the saturation concentration, a reentrant variation of K0of single PSSNa chain can be observed. When [K+] is between 0.01 to 3 M, the charges on the PSSNa backbone are almost completely screened, i.e., the PSSNa chain is virtually neutral in this case. Because K0has a positive correlation with the net charge of the polymer chain, the increased K0at very high KCl concentrations (≥3.5 M) indicates that the chain is charged again. Due to the negative charges on the backbone of PSSNa, only the positively charged counterions (K+) can be adsorbed on the chain. Thus, the PSSNa chain should be positively charged when KCl concentrations ≥3.5 M. That is, the charge inversion occurs in this case, which is induced by a monovalent salt. This finding may lay the foundation for the future applications of drug delivery and gene therapy.
authors.affiliation: Key Laboratory of Advanced Technologies of Materials (Ministry of Education), Southwest Jiaotong University , Chengdu 610031, China.
authors.forename: Miao
authors.initials: M
authors.lastname: Yu
authors.affiliation: Key Laboratory of Advanced Technologies of Materials (Ministry of Education), Southwest Jiaotong University , Chengdu 610031, China.
authors.forename: Lu
authors.initials: L
authors.lastname: Qian
authors.affiliation: Key Laboratory of Advanced Technologies of Materials (Ministry of Education), Southwest Jiaotong University , Chengdu 610031, China.
authors.forename: Shuxun
authors.identifier: 0000-0002-7713-7377
authors.initials: S
authors.lastname: Cui