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Positron annihilation and free volume related issues in polymeric systems : a Sketch of Günter Dlubek's contributions Ashraf Alam Physics, University of.

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Presentation on theme: "Positron annihilation and free volume related issues in polymeric systems : a Sketch of Günter Dlubek's contributions Ashraf Alam Physics, University of."— Presentation transcript:

1 Positron annihilation and free volume related issues in polymeric systems : a Sketch of Günter Dlubek's contributions Ashraf Alam Physics, University of Bristol

2 But, also a personal tribute to a teacher A tribute on behalf of the positron community

3 Bristol 1989

4 Bristol 1999 Bristol 2004

5 PSPA 2004 PSPA 2007

6 PSPA 2010 – last conference attended

7 Positron lifetime studies of free volume hole size distribution in glassy polycarbonate and polystyrene, phys. stat. sol. (a) 157, 351 (1996) Gűnter’s start with polymer: understanding of the size / size distribution of the free volume holes what is feasible to measure/analyse and more importantly what is not realistic (e.g Bimodal distribution? – more than one polymer phases? ) Positron lifetime studies of free volume hole size distribution in amorphous and in semi-crystalline polymers, J. Rad. & Nucl. Chem. 211, 69 (1996) Earliest papers on polymers

8 Important contribution themes: hole volume vs ‘states / compostions’ of polymers: deformed co-polymers, cross linking, branching partially crystalline Microscopic hole volume vs. macrosocopic volume (specific volume: density, PVT measurements) Number density of holes and related issues Chemical environments of the local free volume

9 Most important contribution, in my view is in the understanding the practical implications of free volumes in : Diffusion related issues mediated by free volumes Ionic conductivity in electrolyte polymers Polymer dynamics PVT, Simha-Somcynski eq. of state, free volume etc. Cohen-Turnbull & structural relaxation: Free Volume Fluctuations & Dynamic Heterogeneity In the following, a selection of examples

10 Effect of Cross-Linking on the Free-Volume Properties of Polymer Networks: Macromolecules, 31, No. 14, 1998 Macromolecules 1998, 31,

11 Probe for the Chemical Environment of Free Volume Holes in Polymers Based on simple S-parameter like approach (faster estimation) Macromolecules, 33, No. 1, 2000

12 Probe for the Chemical Environment of Free Volume Holes in Polymers Based on simple S-parameter like approach (faster estimation) Macromolecules, 33, 187, 2000 Polymer 47, 3486, 2006

13 Diffusion & free volume: ionic conductivity in a polymer electrolyte J. Chem. Phys., 115, 7260, 2001 J. Chem. Phys., 118, 9420, 2003

14 Diffusion & free volume: ionic conductivity in a polymer electrolyte J. Chem. Phys., 115, 7260, 2001 Extended Cohen-Turnbull free volume theory + Nernst-Einstein eq: J. Chem. Phys., 118, 9420, 2003

15 PVT, Simha-Somcynski equation of state, free volume etc. Polymer, 46, 869, 2005 Polymer, 46, 859, 2005

16 Mean hole volume vs Tg /groups of polymers Miscellaneous Pressure densification e-Polymers, no 108, (2007d). Compilation from a number of Dlubek Authored papers

17 Free volume & polymer dynamics Free volume & structural relaxation: Macromol. Chem. Phys. 207, 721, 2006

18 Free Volume Fluctuations & Dynamic Heterogeneity Polymer dynamics!  Movements of molecular segments (relaxations) :  High T ‘a-relaxation above cross-over T  Below a ‘cross-over’ T  A fast  -process : Arrhenius T-dependence; thermally activated and segment mobility independent of surrounding  A slower a-process: non-Arrhenius T dependence  physical origin of the non-Arrhenius behavior  locally heterogeneous dynamics

19  mobility governed by cooperative movement of several molecular segments in a localised volume – the cooperatively rearranging region (CRR) CRR Composed of ‘an island’ of high mobility (Glarum-Levy defect) surrounded buy a shell of lower mobility. The smallest sub system related to relaxation Glarum-Levy defect free volume hole? Free Volume Fluctuations & Dynamic Heterogeneity

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