Study Viscoelasticity of Ultrathin Poly(oligo(ethylene glycol) methacrylate) Brushes by a Quartz Crystal Microbalance with Dissipation

Abstract

Ultrathin polymer brushes play important roles in natural and artificial systems. To better understand and utilize their unique behaviors, characterization is a fundamental, but not trivial, task. In this paper, we demonstrated that the quartz crystal microbalance with dissipation (QCM-D) could be applied to study ultrathin poly(oligo(ethylene glycol) methacrylate) brushes. First, we identified four linear relations between dissipation/frequency changes and thickness changes, which were measured by QCM-D and ellipsometry, respectively. Next, we derived a set of equations starting from the Voigt model to further extract viscoelasticity of poly(OEGMA) brushes (<or=30 nm) under high-frequency vibration in contact with water. The viscosity was approximately 10(-3) N s m(-2) and the elasticity was approximately 10(5) N m(-2). Both were frequency dependent. Also discussed were other quantities such as the density (both the dry and wet film) and the working range of linear relations. These equations and quantitative information are important in advancing our understanding of ultrathin polymer brushes, which consequently promote our ability in designing functional surface coatings (i.e., in biosensor applications) and studying related interfacial phenomena.

Quartz crystal microbalance study of the kinetics of surface initiated polymerization

“…Finally, the now polymer coated QCM chip was measured for its absolute frequency, resulting in Δf iii . Note that the frequency change (Δf ) was named to be consistent with previous reports [48,54] . In this report, however, only the Δf iii and Δf vi were applied to study the kinetics of SIP.…”

“…We will come back to this point later). For OEGMA475, the lower the initial initiator density is, the higher k 4 value becomes; (iii) k 4 was solvent dependent (i.e., viscoelasticity dependent [48] ). For OEGMA526, extra amount of methanol decreased the k 4 value.…”

“…Experimental details for OEGMA300 and 475 could be found in early publications [48,54] . Briefly, AGET-SIP was applied to grow poly(OEGMA) brushes.…”

“…The experimental design was evolved from previous reports [48,54] . Briefly, an initiator functionalized QCM chip was first measured for its absolute resonating frequency in air (Scheme 1), which was automatically set to be the (0, 0) point.…”

“…We recently applied quartz crystal microbalance (QCM) to determine the area averaged mass and viscoelasticity of the surface tethered polymer films (dry) [48] . If the number of growing sites (i.e., the initiator efficiency, IE) is accurately determined, M n is easily calculated, for the area averaged mass increases which is shown in QCM study.…”