Dynamical heterogeneity in nanoconfined poly(styrene) chains

Abstract

Fluids in nanoscopic confinements possess a variety of unusual properties, and in particular, remarkable dynamical heterogeneities which vary on length scales as short as a fraction of a nanometer. While the surface forces apparatus provides an experimental probe of macroscopic properties of fluids in contact with atomically smooth solid surfaces, few experimental probes are available which test the microscopic origins of these heterogeneities. In this article we describe our recent efforts to apply nuclear magnetic resonance spectroscopy to nanoscopically confined poly͑styrene͒ ͑PS͒ created by intercalation into a surface-modified fluorohectorite. A comparison between surface-sensitive cross polarization experiments with spin-echo experiments which probe the entire organic layer suggests that PS in the center of the nanopores is more mobile than the bulk at comparable temperatures, while chain segments which interact with the surface are dynamically inhibited.

Molecular Motion in Surfactant Layers Inside Polymer Composites with Synthetical Magadiite

“…Compared with other solid-state NMR techniques ( 1 H, 13 C), which were applied to polymers in PLS nanocomposites before, [15][16][17][18][19][20][21][22] 2 H NMR gives a more detailed picture of molecular motion. [10] To test for heterogeneity of the surfactant layer in OLS, we apply 31 P NMR on phosphonium surfactants.…”

Estimation of the Binding Energy in Random Poly(Butylene terephtalate-co-thiodiethylene terephtalate) Copolyesters/Clay Nanocomposites via Molecular Simulation

“…It is critical to have many, independent, well-equilibrated initial configurations of the system to be simulated: as the polymer is held together by covalent bonds, the relaxation of the chain is determined by the slowest moving segments along the polymer. Even though mobile segments are expected to exist in large numbers [31], they will be bonded to portions of the polymer that remain "frozen" for timescales vastly longer than what is accessible by MD. Therefore, the only realistic way to explore a large portion of the configurational space is to start with many independent initial system conformations.…”

Structure–Property Relationships of Nanocomposites

“…It was concluded that cooperative relaxations of the intercalated polymer (i.e., totally confined) are weak and that confinement effectively prohibits bulklike crystallization. DSC and NMR studies of intercalated polystyrene (PS) also confirmed the absence of glassy relaxation [Krishnamoorti et al, 1996;Zax et al, 2000].…”