title: Single chain contraction and re-expansion of polystyrene sulfonate: a study on its re-entrant condensation at single molecular level.
abstract: Single chain conformation of a polyelectrolyte (polystyrene sulfonate, PSS(-)Na(+)) during its re-entrant condensation was studied by fluorescence correlation spectroscopy (FCS) with single molecule sensitivity. The contraction and re-expansion of PSS(-)Na(+) chain were observed with the addition of counterions of different valencies. The formation of aggregation and precipitation of PSS(-)Na(+) and its redissolution were observed in accordance with the chain contraction and re-expansion process for the PSS(-)Na(+) chain upon the addition of trivalent La(3+) ion. Chain contraction and re-expansion of the PSS(-)Na(+) chain were also observed with the addition of monovalent Cs(+) and divalent Ca(2+) ions, under which condition, the re-entrant condensation was not observed. The results demonstrate that the high sensitivity of FCS can really study single PSS(-)Na(+) chain under extremely dilute situation.
authors.affiliation: Beijing National Laboratory of Molecular Science, Joint Laboratory of Polymer Science and Materials, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Pengxiang
authors.initials: P
authors.lastname: Jia
authors.forename: Jiang
authors.initials: J
authors.lastname: Zhao