Molecular weight dependence of chain conformation of strong polyelectrolytes

Guofeng Xu; Jingfa Yang; Jiang Zhao

doi:10.1063/1.5035458

Molecular weight dependence of chain conformation of strong polyelectrolytes

J Chem Phys. 2018 Oct 28;149(16):163329. doi: 10.1063/1.5035458.

Authors

Guofeng Xu¹, Jingfa Yang¹, Jiang Zhao¹

Affiliation

¹ Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China and The University of Chinese Academy of Sciences, Beijing 100049, China.

PMID: 30384707
DOI: 10.1063/1.5035458

Abstract

Using sodium polystyrene sulfonate (NaPSS) and quarternized poly 4-vinylpyridine (QP4VP) as model systems, the chain conformation of polyelectrolytes under finite salt concentrations is investigated at a single molecular level. By fluorescence correlation spectroscopy (FCS), the hydrodynamic radius (R _h) of the samples with the molecular weight ranging more than one order of magnitude was measured. The variations of R _h as a function of molecular weight reveal the molecular weight dependence: under moderate salt concentrations (such as 10^-4 and 0.1M), the shorter chains of both NaPSS and QP4VP take the rod-like conformation, while the longer chains take the coiled conformation (random coil or swelled random coil conformation, respectively). At high enough salt levels, both the charged chains take the coiled conformations. Photon counting histogram (PCH) measurements of the local pH value at the vicinity of the NaPSS chain expose the higher extent of counterion adsorption for longer chains as well as higher salt concentrations, telling that the charge regularization process is the major governing factor.