Investigating the Dynamic Viscoelasticity of Single Polymer Chains using Atomic Force Microscopy

ABSTRACT In single‐molecule force spectroscopy (SMFS), many studies have focused on the elasticity and conformation of polymer chains, but little attention has been devoted to the dynamic properties of single polymer chains. In this study, we measured the energy dissipation and elastic properties of single polystyrene (PS) chains in toluene, methanol, and N,N‐dimethylformamide using a homemade piezo‐control and data acquisition system externally coupled to a commercial atomic force microscope (AFM), which provided more accurate information regarding the dynamic properties of the PS chains. We quantitatively measured the chain length‐dependent changes in the stiffness and viscosity of a single chain using a phenomenological model consistent with the theory of viscoelasticity for polymer chains in dilute solution. The effective viscosity of a polymer chain can be determined using the Kirkwood model, which is independent of the intrinsic viscosity of the solvent and dependent on the interaction between the polymer and solvent. The results indicated that the viscosity of a single PS chain is dominated by the interaction between the polymer and solvent. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1736–1743 The dynamic viscoelasticity of single polystyrene chains was measured over the frequency region of 7‐9 kHz by applying oscillation to the cantilever. The chain length‐dependent changes were measured using a phenomenological model consistent with the theory of viscoelasticity for polymer chains in dilute solution. The results indicate that the effective viscosity of a polymer chain is independent of the intrinsic viscosity of the solvent and dependent on the interaction between the polymer and solvent.