Single-Molecule Tracking of Polymer Dynamics at Solid/Liquid Interfaces

Dapeng Wang1, Daniel K. Schwartz2

1State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, P. R. China
2Department of Chemical and Biological Engineering, University of Colorado, Boulder, Colorado 80309, United States 80309

We recently developed a high-throughput single-molecule fluorescence tracking method that allows us to image dynamics of millions of individual molecules at solid/liquid and liquid/liquid interfaces[1-3]. These single-molecule experiments go beyond understanding the average behavior of adsorbates and enable us to probe variability in surface chemistry, molecular conformations, and adsorbate dynamics. Making such measurements, we often find that the behavior is much richer and more interesting than conventional wisdom suggests. In this abstract, we demonstrated that polymer diffusion at solid/liquid interfaces can be described by an analytical theory involving intermittent hopping where diffusion is switched between apparent immobile periods and occasional long flights[1,3]. This type of diffusion could be adequately modeled by continuous time random walk (CTRW) statistics. Moreover, we provided clear evidence that the occasional long flights are a process involving desorption, bulk diffusion, and readsorption at a new surface location. Very recently, we developed a 3D tracking method to in-situ visualize the full process desorption-mediated diffusion of tracer polymers at solid/liquid interfaces with varying surface-polymer electrostatic interactions[4,5]. We realized that the lateral length between consecutive surface encounters is associated with the surface-polymer interaction. The desorption-mediated diffusion at the direction vertical to the interface was well-described by kinetic Monte Carlo simulations of one-dimensional biased Brownian motion where the biased probability (the main undetermined parameter) was conceptually related to the surface-polymer interaction.

[1] D Wang, et al. ACS nano, 9, 1656-1664 (2015).
[2] D Wang, et al. Journal of the American Chemical Society, 137, 12312-12320 (2015).
[3] D Wang, et al. ACS Macro Letters, 5, 509-514 (2016).
[4] D Wang, et al. Applied Physics Letters, 110, 211107 (2017).
[5] D Wang, et al. Physical Review Letters,119, 268001 (2017)