Fluorescent Labeling Can Alter Polymer Solution Dynamics

Document Type


Publication Date


Publication Title



There is a widespread assumption that modest chemical modification of a large polymer molecule, by adding a fluorescent label or the like, has no significant effect on polymer solution dynamics. We here report that light tagging of hydroxypropylcellulose (HPC) with fluorescein dye has a significant effect on the dynamic behavior of the chains, as measured using fluorescence photobleaching recovery (FPR) and dynamic light scattering (DLS). We compared unprocessed HPC, HPC processed in preparation for chemical modification, and HPC chemically modified by tagging with a fluorescein moiety. Addition of covalently bound fluorescein to the polymer eliminates the ultraslow (D ≈ 10–10 cm2/s) relaxational mode found with DLS in the unlabeled HPC samples. Our findings explain the perceived discrepancies between DLS and FPR studies of HPC solutions. The discrepancies arise from differences in sample preparation. Comparison of FPR spectra (which measure the single particle diffusion process) and DLS spectra (which measure the relative motions of pairs of particles), each with its own intrinsic time and distance scales, provides insight into the nature of diffusion and the state of dissolution in dilute and nondilute HPC solutions.


The authors acknowledge the support of NSF-DMR 1005707 (P.R.) and The Donors of the Petroleum Research Fund (P.R.); NSF-REU CHE-0648841 and CSU’s Engaged Learning Undergraduate Research Program (R.M.); CSU’s 2005 Faculty Research Development Award and 2006 COTTRELL Science Award CC6821 (K.A.S.); NSF-IMR 0526949 (R.C.).