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31. Revisiting Polymer Surface Diffusion in the ExtremeCase of Strong Adsorption.

Author

Yu, Changqian and Granick, Steve

Subjects
*POLYMERIC sorbents, *SURFACE diffusion, *ADSORPTION (Chemistry), *FLUORESCENCE microscopy, *DIFFUSION coefficients, *POLYSTYRENE, *SURFACE roughness
Abstract

Revisitingpolymer surface adsorption with a level of quantificationnot possible at the time of earlier seminal contributions to thisfield, we employ fluorescence microscopy to quantify the in-planediffusion of end-labeled polystyrene adsorbed onto quartz and micafrom cyclohexane solution, mostly at 25 °C. Care is taken toprohibit a surface-hopping mechanism, and the experimental techniquesare adapted to measurements that persist for up to a few days. Themain conclusion is that we fail to observe a single Fickian diffusioncoefficient: instead, diffusion displays a broad multicomponent spectrum,indicating that the heterogeneity of surface diffusion fails to averageout even over these long times and over distances (∼600 nm, the diameter of a diffraction-limited spot) greatly exceedingthe size of the polymer molecules. This holds generally when we varythe molecular weight, the surface roughness, and the temperature.It quantifies the long-believed scenario that strongly adsorbed polymerlayers (monomer–surface interaction of more than 1kBT) intrinsically present diverse surfaceconformations that present heterogeneous environments to one anotheras they diffuse. Bearing in mind that in spite of adsorption fromdilute solution the interfacial polymer concentration is high, ramificationsof these findings are relevant to the interfacial mobility of polymerglasses, melts, and nanocomposites. [ABSTRACT FROM AUTHOR]

Published
2014
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46. Single-Particle Colloid Tracking in Four Dimensions

Author

M. Anthony, Stephen, Hong, Liang, Kim, Minsu, and Granick, Steve

Abstract

Coating a close-packed fluorescent colloid monolayer with a nanometer-thick metal film followed by sonication in liquid produces modulated optical nanoprobes. The metal coating modulates the fluorescence as these structures rotate in suspension, enabling the use of these particles as probes to monitor both rotational and center-of-mass (translational) dynamics in complex environments. Here, we demonstrate methods to simultaneously measure two translational and two rotational degrees of freedom, with excellent agreement to theory. The capability to determine two angles of rotation opens several new avenues of future research.

Published
2006
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