Super-resolution study of polymer mobility fluctuations near c∗

John T. King, Changqian Yu, William L. Wilson, Steve Granick

Research output: Contribution to journalArticlepeer-review

Abstract

Nanoscale dynamic heterogeneities in synthetic polymer solutions are detected using super-resolution optical microscopy. To this end, we map concentration fluctuations in polystyrene-toluene solutions with spatial resolution below the diffraction limit, focusing on critical fluctuations near the polymer overlap concentration, c. Two-photon super-resolution microscopy was adapted to be applicable in an organic solvent, and a home-built STED-FCS system with stimulated emission depletion (STED) was used to perform fluorescence correlation spectroscopy (FCS). The polystyrene serving as the tracer probe (670 kg mol-1, radius of gyration RG ap; 35 nm, end-labeled with a bodipy derivative chromophore) was dissolved in toluene at room temperature (good solvent) and mixed with matrix polystyrene (3,840 kg mol-1, RG ap; 97 nm, Mw/Mn = 1.04) whose concentration was varied from dilute to more than 10c. Whereas for dilute solutions the intensity-intensity correlation function follows a single diffusion process, it splits starting at c∗ to imply an additional relaxation process provided that the experimental focal area does not greatly exceed the polymer blob size. We identify the slower mode as self-diffusion and the increasingly rapid mode as correlated segment fluctuations that reflect the cooperative diffusion coefficient, Dcoop. These real-space measurements find quantitative agreement between correlation lengths inferred from dynamic measurements and those from determining the limit below which diffusion coefficients are independent of spot size. This study is considered to illustrate the potential of importing into polymer science the techniques of super-resolution imaging.

Original languageEnglish (US)
Pages (from-to)8802-8809
Number of pages8
JournalACS Nano
Volume8
Issue number9
DOIs
StatePublished - Sep 23 2014

Keywords

  • polymer dynamics
  • semidilute polymer solutions
  • super-resolution spectroscopy

ASJC Scopus subject areas

  • General Materials Science
  • General Engineering
  • General Physics and Astronomy

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