Heterogeneous Diffusion in Thin Polymer Films As Observed by High-Temperature Single-Molecule Fluorescence Microscopy

Abstract

Single-molecule fluorescence microscopy was used to investigate the dynamics of perylene diimide (PDI) molecules in thin supported polystyrene (PS) films at temperatures up to 135 °C. Such high temperatures, so far unreached in single-molecule spectroscopy studies, were achieved using a custom-built setup which allows for restricting the heated mass to a minimum. This enables temperature-dependent single-molecule fluorescence studies of structural dynamics in the temperature range most relevant to the processing and to applications of thermoplastic materials. In order to ensure that polymer chains were relaxed, a molecular weight of 3000 g/mol, clearly below the entanglement length of PS, was chosen. We found significant heterogeneities in the motion of single PDI probe molecules near T(g). An analysis of the track radius of the recorded single-probe molecule tracks allowed for a distinction between mobile and immobile molecules. Up to the glass transition temperature in bulk, T(g,bulk), probe molecules were immobile; at temperatures higher than T(g,bulk) + 40 K, all probe molecules were mobile. In the range between 0 and 40 K above T(g,bulk) the fraction of mobile probe molecules strongly depends on film thickness. In 30-nm thin films mobility is observed at lower temperatures than in thick films. The fractions of mobile probe molecules were compared and rationalized using Monte Carlo random walk simulations. Results of these simulations indicate that the observed heterogeneities can be explained by a model which assumes a T(g) profile and an increased probability of probe molecules remaining at the surface, both effects caused by a density profile with decreasing polymer density at the polymer-air interface.

Structural characteristics of a cooperatively rearranging region during the glass transition of a polymer system

“…42 By using the single-molecule uorescence microscopy, Wöll's group found that the temperature dependence of fraction of mobile molecules in polystyrene lms exhibited similar trends with that of PSM. 42 By using the single-molecule uorescence microscopy, Wöll's group found that the temperature dependence of fraction of mobile molecules in polystyrene lms exhibited similar trends with that of PSM.…”

Long-term live cell microscopy studies of lipid droplet fusion dynamics in adipocytes

“…For temperature-dependent lifetime measurements, an indium tin oxide (ITO) coverslip was used instead. The temperature of the ITO coverslip was then resistively heated to temperatures of up to 160°C ( 40 ). FLIM measurements in live cells were done on the microscope with the Petri dishes either being held at room temperature or at 37°C using a commercial heating stage (Tokai Hit, Japan).…”

Single-Molecule Imaging Reveals Topology Dependent Mutual Relaxation of Polymer Chains

“…Singlemolecule imaging studies have been revealing the spatiotemporal heterogeneity of polymer dynamics by visualizing the motion of individual polymer chains [32][33][34][35][36] or small fluorophores embedded in polymer matrices. [37][38][39][40][41][42][43][44] Using single-molecule localization and tracking (SMLT) technique, we previously reported the multimode diffusion of a cyclic and dicyclic polymers under the entangled conditions by incorporating a fluorophore into the chains. 17,45,46 These studies have suggested a direct connection between the conformational state of the chains and the diffusive motion.…”