Ergodicity Breaking Underlies Nonequilibrium Dynamics of Individual Adsorbed Polymers at Solid–Liquid Interfaces

Abstract

Time-dependent aging phenomena in polymer adsorption at solid–liquid interfaces from dilute solutions were discovered over three decades ago. However, how the properties of a single polymer chain evolve over macroscopic timescales remains poorly understood. Here, we conducted a long-term experimental study on polyethylene glycol (PEG) chains adsorbed from ultradilute solutions by complementarily using single-molecule fluorescence tracking, liquid-environment atomic force microscopy, and sum-frequency generation vibrational spectroscopy. We observe distinctly nonequilibrium and aging dynamics in individual adsorbed polymer chains. Immediately after adsorption, the polymer conformations exhibit a coexistence of states with both low and high segment–surface contact, which display significantly different desorption timescales. The observed time-dependent aging phenomenon can be attributed to the probabilistic formation of distinct conformations upon adsorption, rather than from postadsorption rearrangements. This behavior is well rationalized by a nonergodic continuous-time random walk model. This suggests that ergodicity breaking underlies the nonequilibrium polymer dynamics at solid–liquid interfaces under ultradilute conditions.