Scaling of polymer dynamics at an oil-water interface in regimes dominated by viscous drag and desorption-mediated flights.
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.
Department of Chemical and Biological Engineering, University of Colorado , Boulder, Colorado 80309, United States.
Dapeng
D
Wang
Department of Chemistry and Geochemistry, Colorado School of Mines , Golden, Colorado 80401, United States.
Renfeng
R
Hu
Department of Chemical and Biological Engineering, University of Colorado , Boulder, Colorado 80309, United States.
Joshua N
JN
Mabry
College of Materials Science and Optoelectronic Technology, University of Chinese Academy of Sciences , Beijing 100049, China.
Bing
B
Miao
Department of Chemistry and Geochemistry, Colorado School of Mines , Golden, Colorado 80401, United States.
David T
DT
Wu
Max Planck Institute for Polymer Research , Ackermannweg 10, 55128 Mainz, Germany.
Kaloian
K
Koynov
Department of Chemical and Biological Engineering, University of Colorado , Boulder, Colorado 80309, United States.
Daniel K
DK
Schwartz
D004058:Diffusion; D056004:Molecular Dynamics Simulation; D008970:Molecular Weight; D009010:Monte Carlo Method; D009821:Oils / Q000737:chemistry*; D011092:Polyethylene Glycols / Q000737:chemistry*; D014783:Viscosity; D014867:Water / Q000737:chemistry*
D009821:Oils; D014867:Water; D011092:Polyethylene Glycols