title: Diffusion of ionic fluorescent probes atop polyelectrolyte brushes.
abstract: The lateral diffusion of ionic fluorescent molecules atop polyelectrolyte brushes was adopted to probe the distribution of counterions of the polyelectrolyte brushes. With a combination of single molecule fluorescence techniques, fluorescence correlation spectroscopy and single molecule fluorescence imaging, the lateral diffusion of the ionic probes (sulforhodamine B, rhodamine 6G) at the top of the model polyelectrolyte brushes with the opposite charges, poly([2-(methylacryloyloxyl)ethyl] trimethylammonium chloride) (PMETAC) and polystyrene sulfonate (PSS), was studied with different external salt concentrations. A huge decrease of the diffusion rate of the probes was observed at salt concentrations 2-3 orders of magnitude lower than that for any detectable change of brushes thickness could be observed. The results reflect the early collapse of the top portion of the polyelectrolyte brushes and also the penetration of the probes into the brushes due to the increase of osmotic pressure by the salt level in the solution. The diffusion of the fluorescent counterion can serve as a very sensitive probe of the structure atop the polyelectrolyte brushes.
authors.affiliation: Beijing Laboratory of Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Cunfu
authors.initials: C
authors.lastname: Zhang
authors.forename: Xiao
authors.initials: X
authors.lastname: Chu
authors.forename: Zhongli
authors.initials: Z
authors.lastname: Zheng
authors.forename: Pengxiang
authors.initials: P
authors.lastname: Jia
authors.forename: Jiang
authors.initials: J
authors.lastname: Zhao