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The Spin Probe Dynamics and the Free Volume in a Series of Amorphous Polymer Glass‐Formers
Author(s) -
Švajdlenková H.,
Iskrová M.,
Šauša O.,
Dlubek G.,
Krištiak J.,
Bartoš J.
Publication year - 2011
Publication title -
macromolecular symposia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.257
H-Index - 76
eISSN - 1521-3900
pISSN - 1022-1360
DOI - 10.1002/masy.201000103
Subject(s) - glass transition , amorphous solid , materials science , polymer , relaxation (psychology) , delocalized electron , fragility , spin probe , polymer chemistry , molecular dynamics , electron paramagnetic resonance , chemical physics , nuclear magnetic resonance , crystallography , chemistry , physics , computational chemistry , composite material , organic chemistry , psychology , social psychology
We report the results of a combined study of the local structure and the reorientation dynamics in a series of five amorphous polymers of different fragility: cis‐trans‐1,4‐poly(butadiene) ( c‐t‐1,4‐PBD ), cis‐1,4‐poly(isoprene) (cis‐1,4‐PIP) , poly(isobutylene) (PIB) , poly(vinyl methylether)(PVME) and poly (propylene glycol) (PPG) by using two different probe methods. The reorientation dynamics of the molecular spin probe 2,2,6,6‐tetramethyl‐1‐piperidinyloxy ( TEMPO ) from electron spin resonance (ESR) is related to the annihilation behaviour of the atomic ortho‐positronium (o‐Ps) one as obtained by positron annihilation lifetime spectroscopy (PALS). It was found that a slow to fast transition in the spin probe rotation mobility at the operationally defined spectral temperature parameter, T 50G , is connected with the mean o‐Ps lifetime, τ 3 (T 50G ) = (2.04 ± 0.26) ns. Consequently, using the free‐volume concept of the o‐Ps annihilation in terms of a quantum‐mechanical model of o‐Ps lifetime this transition can be connected with the occurrence of the mean free volume hole, V h (T 50G ) = (102 ± 17) Å 3 , nearly independent of the chemical composition and the basic structural relaxation parameters of the amorphous polymers investigated. Finally, the free volume hole distribution aspect of the slow to fast transition indicates the presence of a sufficient free volume fluctuation at T 50G for both typical fragile PVME and strong PIB polymer and emphasizes the essential role of free volume in the spin probe dynamics.