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

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• 作者：Dapeng Wang ; Renfeng Hu ; Joshua N. Mabry ; Bing Miao ; David T. Wu ; Kaloian Koynov ; Daniel K. Schwartz
• 刊名：Journal of the American Chemical Society
• 出版年：2015
• 出版时间：September 30, 2015
• 年：2015
• 卷：137
• 期：38
• 页码：12312-12320
• 全文大小：457K
• ISSN：1520-5126

文摘

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鈥搘ater interfaces. Compared to diffusion in dilute aqueous solution, which exhibited the expected dependence of the diffusion coefficient (D) upon molecular weight (M) of D 鈭?M^鈥?/2 for a Gaussian chain, the behavior at the interface was approximately D 鈭?M^鈥?/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鈥揈instein 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鈥搇iquid 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鈥搕rain鈥搕ail) interfacial conformation.