Glassy dynamics of polymethylphenylsiloxane (PMPS) is studied by broadband dielectric spectroscopy in one-dimensional (1D) and two-dimensional (2D) nanometric confinement; the former is realized in thin polymer layers having thicknesses down to 5 nm, and the latter in unidirectional (thickness 50 μm) nanopores with diameters varying between 4 and 8 nm. Based on the dielectric measurements carried out in a broad spectral range at widely varying temperatures, glassy dynamics is analyzed in detail in 1D and in 2D confinements with the following results: (i) the segmental dynamics (dynamic glass transition) of PMPS in 1D confinement down to thicknesses of 5 nm is identical to the bulk in the mean relaxation rate and the width of the relaxation time distribution function; (ii) additionally a well separated surface induced relaxation is observed, being assigned to adsorption and desorption processes of polymer segments with the solid interface; (iii) in 2D confinement with native inner pore walls, the segmental dynamics shows a confinement effect, i.e., the smaller the pores are, the faster the segmental dynamics; on silanization, this dependence on the pore diameter vanishes, but the mean relaxation rate is still faster than in 1D confinement; (iv) in a 2D confinement, a pronounced surface induced relaxation process is found, the strength of which increases with the decreasing pore diameter; it can be fully removed by silanization of the inner pore walls; (v) the surface induced relaxation depends on its spectral position only negligibly on the pore diameter; (vi) comparing 1D and 2D confinements, the segmental dynamics in the latter is by about two orders of magnitude faster. All these findings can be comprehended by considering the density of the polymer; in 1D it is assumed to be the same as in the bulk, hence the dynamic glass transition is not altered; in 2D it is reduced due to a frustration of packaging resulting in a higher free volume, as proven by ortho-positronium annihilation lifetime spectroscopy.
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28 May 2017
Research Article|
February 02 2017
Glassy dynamics of polymethylphenylsiloxane in one- and two-dimensional nanometric confinement—A comparison
Mohamed Elsayed;
Mohamed Elsayed
2Department of Physics,
Martin Luther University Halle
, 06099 Halle, Germany
3Department of Physics, Faculty of Science,
Minia University
, 61519 Minia, Egypt
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Reinhard Krause–Rehberg;
Reinhard Krause–Rehberg
2Department of Physics,
Martin Luther University Halle
, 06099 Halle, Germany
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Friedrich Kremer
Friedrich Kremer
1Institute of Experimental Physics I,
University of Leipzig
, 04103 Leipzig, Germany
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a)
Electronic mail: [email protected]
J. Chem. Phys. 146, 203302 (2017)
Article history
Received:
November 03 2016
Accepted:
December 14 2016
Citation
Wycliffe K. Kipnusu, Mohamed Elsayed, Reinhard Krause–Rehberg, Friedrich Kremer; Glassy dynamics of polymethylphenylsiloxane in one- and two-dimensional nanometric confinement—A comparison. J. Chem. Phys. 28 May 2017; 146 (20): 203302. https://doi.org/10.1063/1.4974767
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