Single molecule demonstration of Debye–Stokes–Einstein breakdown in polystyrene near the glass transition temperature

Abstract

Rotational-translational decoupling, in which translational motion is apparently enhanced over rotational motion in violation of Stokes-Einstein (SE) and Debye-Stokes-Einstein (DSE) predictions, has been observed in materials near their glass transition temperatures (Tg). This has been posited to result from ensemble averaging in the context of dynamic heterogeneity. In this work, ensemble and single molecule experiments are performed in parallel on a fluorescent probe in high molecular weight polystyrene near its Tg. Ensemble results show decoupling onset at approximately 1.15Tg, increasing to over three orders of magnitude at Tg. Single molecule measurements also show a high degree of decoupling, with typical molecules at Tg showing translational diffusion coefficients nearly 400 times higher than expected from SE/DSE predictions. At the single molecule level, higher degree of breakdown is associated with particularly mobile molecules and anisotropic trajectories, providing support for anomalous diffusion as a critical driver of rotational-translational decoupling and SE/DSE breakdown.

Single-Molecule Fluorescence Investigations of Solute Transport Dynamics in Nanostructured Membrane Separation Materials

“…This could be partly because of the presence of microscale defects in the actual materials. Direct comparison between single-molecule and ensemble-averaged dynamics at the same material regions, which have recently demonstrated, 44,87 will reveal the significance of the molecular-level dynamics and also microscale defects on membrane separations. In addition, multiplex SMT 38 may be applicable to investigate single-molecule dynamics for multiple solute species under identical conditions, permitting single-molecule dynamics and membrane separation selectivity to be linked directly.…”

“…SMT is a powerful technique to gain detailed information on solute dynamics that are associated with spatiotemporal heterogeneity in polymer films. − For example, SMT has been used to investigate the heterogeneity of solute dynamics in glassy polymer films. , Recently, Mandel et al showed the key contribution of anomalously diffusing molecules to rotational-translational decoupling observed in polystyrene (PS) films near their glass transition temperature . Ito et al assessed the lateral and surface-normal diffusion of hydrophobic and hydrophilic fluorescent dyes in glassy poly­(2-hydroxyethyl acrylate) films using astigmatic single-molecule imaging .…”

“…39,43 Recently, Mandel et al showed the key contribution of anomalously diffusing molecules to rotationaltranslational decoupling observed in polystyrene (PS) films near their glass transition temperature. 44 Ito et al assessed the lateral and surface-normal diffusion of hydrophobic and hydrophilic fluorescent dyes in glassy poly(2-hydroxyethyl acrylate) films using astigmatic single-molecule imaging. 45 Both types of dyes similarly exhibited preferential distribution around the middle of the films and also faster diffusion in the lateral direction than in the surface-normal direction.…”

Tracking of Protein Adsorption on Poly(l-lactic acid) Film Surfaces: The Role of Molar Mass

“…Protein adsorption has been extensively studied using various sensitive techniques such as quartz crystal microbalance, mass spectrometry, sum frequency generation spectroscopy, Fourier transform infrared spectroscopy, fluorescence correlation spectroscopy, isothermal titration calorimetry, and atomic force microscopy (AFM). ,, These techniques have greatly contributed to our understanding of protein adsorption. – Recently, total internal reflection fluorescence microscopy (TIRFM) has emerged as a powerful tool for studying the dynamics of fluorescent species in different environments at a spatial resolution of approximately 10 nm and a temporal resolution of a few milliseconds. – By combining TIRFM with a highly sensitive camera, this technique can exploit the evanescent field to illuminate fluorescent molecules within 100 nm of the interface. This makes it very suitable for studying the diffusion and adsorption of polymers, peptides, and proteins in ultrathin films, on lipid bilayers, , at interfaces, – during chemical reaction, and for quantifying the spatial/temporal heterogeneity upon protein adsorption. ,– …”

Validity of Single Fluorescent Molecule to Report Local Dynamics of a Polymer Matrix: The Effect of Molecular Architecture

“…The powerfulness of these techniques comes from its high detection sensitivity as well as the good spatial and enough time resolutions. [8][9][10][11][12][13][14] In the experiments, the fluorescent molecules, either doped inside the polymeric liquid or chemically connected onto the polymer chains, help to probe the cooperative motion of the polymer segments by the information of its rotational motion. By monitoring the rotational trajectories of fluorescent probes, single molecule fluorescence microscopy can report the local dynamics around the probes in a quantitative manner, as the rotational motion of individual probe is highly coupled to the local segmental dynamics.…”