Scaling of Polymer Dynamics at an Oil–Water Interface in Regimes Dominated by Viscous Drag and Desorption-Mediated Flights

Abstract

Polymers are found near surfaces and interfaces in a wide range of chemical and biological systems, and the structure and dynamics of adsorbed polymer chains have been the subject of intense interest for decades. While polymer structure is often inferred from dynamic measurements in bulk solution, this approach has proven difficult to implement at interfaces, and the understanding of interfacial polymer conformation remains elusive. Here we used single-molecule tracking to study the interfacial diffusion of isolated poly(ethylene glycol) molecules at oil-water interfaces. Compared to diffusion in dilute aqueous solution, which exhibited the expected dependence of the diffusion coefficient (D) upon molecular weight (M) of D ∼ M(-1/2) for a Gaussian chain, the behavior at the interface was approximately D ∼ M(-2/3), suggesting a significantly more expanded polymer conformation, despite the fact that the oil was a poor solvent for the polymer. Interestingly, this scaling remained virtually unchanged over a wide range of oil viscosity, despite the fact that at low viscosities the magnitude of the diffusion coefficient was consistent with expectations based on viscous drag (i.e., Stokes-Einstein diffusion), and for high viscosity oil, the interfacial mobility was much faster than expected and consistent with the type of intermittent hopping transport observed at the solid-liquid interface. The dependence on molecular weight, in both regimes, was consistent with results from both self-consistent field theory and previous Monte Carlo simulations, suggesting that an adsorbed polymer chain adopted a partially swollen (loop-train-tail) interfacial conformation.

Cross-over in the dynamics of polymer confined between two liquids of different viscosity

“…These results agree with the mean square displacements of the chain central monomer ( figure 3) and show that the presence of a more viscous fluid slows the dynamics of the polymer. The simulation results agree remarkably well also with the experimental ones where the same trends of the non-Gaussian behaviour and the slow polymer dynamics associated with high viscous fluid were also observed [20].…”

“…Recently, we have performed a set of simulations of polymer chains entrapped in a soft two-dimensional slit formed by two immiscible solvents [28]. The results of the simulations show that, in agreement with experiments [20], the polymer chain is adsorbed at the interface even if one of the two solvents is a poor solvent and that the polymer shows an extended conformation. The scaling analysis of various dynamical properties indicated however that the polymer follows the expected Zimm model [29] therefore with HI effects dominating and that the effect of the presence of the interface could be appreciated only in the sub-diffusive regime which, for short polymer chains, almost disappears.…”

“…Explanations for such screening included the possibility that the lateral movements of the lipids dissipate energy reducing the HI and that the polymer enters a reptationlike regime when confined on an inhomogeneous surface [18,19]. More recently, using fluorescent microscopy Wang et al [20] studied the dynamics of poly(ethylene glycol) at an oil/water interface. In that study, the authors decoupled the polymer dynamics from the lipid one and inferred the structure of the chain from its diffusion coefficient.…”

Cadherin Diffusion in Supported Lipid Bilayers Exhibits Calcium-Dependent Dynamic Heterogeneity

“…All experiments were performed at room temperature using an objectivebased Nikon Ti-E total internal reflection fluorescence microscope with a 100Â Apo TIRF oil-immersion objective (34). An iXon EMCDD camera (model No.…”

Generalized recovery algorithm for 3D super-resolution microscopy using rotating point spread functions

“…Single-molecule and super-resolution imaging 1 2 3 4 5 have changed our understanding of biological processes 6 7 , dynamics at interfaces 8 9 10 11 12 , and functions of catalysts at the single molecule level 13 14 15 . Molecular motors are now known to move hand-over-hand 5 16 .…”