Conformation and dynamics of discrete poly(ethylene glycol) chains in nano-scale-thickness solution next to a gold substrate

Abstract

The functions and applications of flexible molecules rely heavily on their properties, such as conformation and dynamics. Despite numerous studies on the properties of flexible molecules in various conditions, the properties of discrete molecules in a dilute solution of nano-scale thickness sandwiched between a solid substrate and a bulk solution have not been sufficiently studied. In this study, based on the quartz crystal microbalance with dissipation monitoring, we demonstrate a facile way to investigate the conformation and dynamics of discrete polymer chains in nano-scale thickness solution by estimating the specific values of exclude volume exponent v and pre-factor k in the modified Mark-Houwink equation, respectively. Using poly(ethylene glycol) (PEG) as an example, the results suggest that the properties of a PEG with a molecular weight of 2 k are not significantly affected by the solid substrate. Moreover, for PEGs with molecular weights of 6 k and 20 k, the changes in conformation and dynamics are minimal and significant, respectively, in comparison with those in bulk solution. The proposed method can be further extended to probe the conformation, dynamics, and related phenomena of linear neutral polymers, and polyelectrolytes (including biopolymers) with a high salt condition.