Positron annihilation and free volume related issues in polymeric systems :

a Sketch of Günter Dlubek's contributions

Ashraf AlamPhysics, University of Bristol

But, also a personal tribute to a teacher

A tribute on behalf of the positron community

Bristol 1989

Bristol 1999

Bristol 2004

PSPA 2004

PSPA 2007

PSPA 2010 – last conference attended

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

Important contribution themes:

• hole volume vs ‘states / compostions’ of polymers: deformedco-polymers, cross linking, branchingpartially 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

• 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

Effect of Cross-Linking on the Free-Volume Properties of Polymer Networks:

Macromolecules, 31, No. 14, 1998

Macromolecules 1998, 31, 4574-4580

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

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

Diffusion & free volume: ionic conductivity in a polymer electrolyte

J. Chem. Phys., 115, 7260, 2001 J. Chem. Phys., 118, 9420, 2003

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

PVT, Simha-Somcynski equation of state, free volume etc.

Polymer, 46, 869, 2005 Polymer, 46, 859, 2005

Mean hole volume vs Tg /groups of polymers

Miscellaneous

Pressure densification

e-Polymers, no 108, 1 - 20 (2007d).

Compilation from a number of DlubekAuthored papers

Free volume & polymer dynamics

Free volume & structural relaxation:

Macromol. Chem. Phys. 207, 721, 2006

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

mobility governed by cooperative movement ofseveral 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

Free Volume Fluctuations & Dynamic HeterogeneityFree Volume Fluctuations & Dynamic Heterogeneity