Self-diffusion and Cooperative Diffusion in Semidilute Polymer Solutions as measured by Fluorescence Correlation Spectroscopy

TL;DR

This study compares fluorescence correlation spectroscopy and dynamic light scattering to measure self and cooperative diffusion in semidilute polymer solutions, revealing a new cooperative diffusion mode linked to transient entanglements.

Contribution

It demonstrates that FCS can detect a new cooperative diffusion mode in semidilute polymers, aligning with DLS measurements and theoretical models.

Findings

FCS reveals a new fast diffusion mode in semidilute entangled polymers.

The second mode in FCS matches the cooperative diffusion coefficient from DLS.

The cooperative mode is due to long-range interactions via transient entanglements.

Abstract

We present a comprehensive investigation of polymer diffusion in the semidilute regime by fluorescence correlation spectroscopy (FCS) and dynamic light scattering (DLS). Using single-labeled polystyrene chains, FCS leads to the self-diffusion coefficient while DLS gives the cooperative diffusion coefficient for exactly the same molecular weights and concentrations. Using FCS we observe a new fast mode in the semidilute entangled concentration regime beyond the slower mode which is due to self-diffusion. Comparison of FCS data with data obtained by DLS on the same polymers shows that the second mode observed in FCS is identical to the cooperative diffusion coefficient measured with DLS. An in-depth analysis and a comparison with current theoretical models demonstrates that the new cooperative mode observed in FCS is due to the effective long-range interaction of the chains through the transient entanglement network.