Polymers under Ionizing Radiations: the Specificity of Swift Heavy Ions

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Stable defects
Polymers under ionizing radiations Macromolecular defects

Gas emission
Interactions with the electrons of the polymer

Cross-linking Vs Chain scissions
Chain scissions in presence of Cross-linking preponderant in polymers with : -CH Why study SHI effects on polymers?

Fig. 1 :
Fig. 1: Energy deposition structure of accelerated ion beams: increase in the density of events, along the track, with increasing LET.

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Centre de Recherche sur les Ions, les Matériaux et la Photonique nom Deep repository = different phases Filling Emission of hazardous gases Inflammability, corrosion… Post-closure Macromolecular defects Polymer leaching Radionuclides complexation Safe management = What is the fate of polymers in conditions of long time periods and high doses?Well-chosen conditions  Effects of a particles simulated by SHI Medium Activity Long Life waste Intended to Deep Repository Ion track = core + penumbra Track: Heterogeneous Track core: more or less homogeneous Gervais&Bouffard NIMB 88 (1994) Velocity effect Radial distribution of dose Radius  when E  Dr 0.5  when E Ion beam characteristics :  Energy deposited along the path in a reduced space  High LET SHI : Energy deposition pattern SHI = 2 Parameters (LET + Dr 0.5 ) Energy deposited through interactions between :  the ions and target electrons  the secondary electrons and the target electrons Centre de Recherche sur les Ions, les Matériaux et la Photonique nom Swift Heavy Ions = High ionization/excitation densities How does high ionization/excitation densities modify the polymers ageing?Aim Objectives Influence of dose and LET under inert and oxidative environments on: Gas emission Creation of new chemical groups (carbonyl groups, trans-vinylenes, vinyls, vinylidenes) Specific defects Centre de Recherche sur les Ions, les Matériaux et la Photonique nom date réunion METHODOLOGY Ion beams of various energies Ion beams of specific characteristics Simulation of a radiolysis Basic science Centre de Recherche sur les Ions, les Matériaux et la Photonique nom Gervais & Bouffard, Nucl.Instrum.Methods Phys.Res., Sect.B 88 (1994), 355Ion beams to simulate α irradiations ?Equivalent LET Equivalent Dr 0.5 How to simulate a radiolysis by SHI irradiation?Electronic interactions Centre de Recherche sur les Ions, les Matériaux et la Photonique nom Gervais & Bouffard, Nucl.Instrum.Methods Phys.Res., Sect.B 88 (1994)Ion beams to simulate α irradiations ?Equivalent LET Equivalent Dr 0.5 How to simulate a radiolysis by SHI irradiation?Equivalent LET and Dr 0.5 Higher ranges for SHI Homogeneous LET Homogeneous irradiation under large thicknesses SHI irradiation Vs a radiolysis Centre de Recherche sur les Ions, les Matériaux et la Photonique nom Irradiation procedures On-line analyses (specific devices) Macromolecular defects Infrared spectroscopy Gas emission or O 2 consumption Mass spectroscopy (RGA mode) Off-line analyses : Two-step protocol Pre-ageing Up to high doses Determination of gas yields Reduced dose Ultra high-resolution gas mass spectrometry Irradiation of thin films Centre de Recherche sur les Ions, les Matériaux et la Photonique nom Energy deposited per unit mass Unit: Gy (Gray, 1Gy = 1J/kg) On-line analyses or two-step protocol G(X) = f(polymer ageing level) Centre de Recherche sur les Ions, les Matériaux et la Photonique nom date réunion RESULTS & APPLICATIONS Centre de Recherche sur les Ions, les Matériaux et la Photonique nom Specificity of SHI on defects creation Two groups of defects created under SHI Defects common to other ionizing radiations Influence on the relative radiation chemical yields Defects Specific to SHI G(defects) when LET Specificity of SHI : Gas emission Primary effect = C-H scission  H 2 emission common in organic molecules LET influence on G(H 2 ) depends on the polymer structure -(CH 2 -CH 2 ) Specificity of SHI : Gas emission LET Effect on H 2 emission Almost inexistent on saturated polyolefines (PE, PP) Existent in presence of unsaturated bonds or more generally in of energy sinks PS: existence of a LET Threshold Below the threshold G(H 2 ) PS < G(H 2 ) PE Above the threshold G(H 2 ) PS ≈ G(H 2 ) PE Benzene ring destruction  with  LET = Protection efficiency lost LET influence on G(H 2 ) depends on the polymer structure Centre de Recherche sur les Ions, les Matériaux et la Photonique nom of SHI : Gas emission V. Picq, J.M. Ramillon, E. Balanzat, NIMB 146 (1998) 496-503 V. Picq & E. Balanzat, NIMB 151(1999) 76-83 Ngono-Ravache et al., Polym.Deg.Stab.111 (2015), 89 Specificity of SHI : Macromolecular defects Evolution of Vinyl groups R-CH 2 -CH=CH 2 Under Inert environment Unsaturated Bonds : LET influence function of the defect type Vinyl groups Concentration with  LET High ionization densities mandatory Groups other than Vinyl At low doses : no LET effect At high doses : Concentration at saturation  with  LET Centre de Recherche sur les Ions, les Matériaux et la Photonique nom date réunion Specificity of SHI : Defects specific to SHI Specific defects Triple bonds ( Alkyne, Cyanates…) Cumulated double bonds ( Allene, Isocyanates…) RC≡CH RCH=C=CHR Energy deposition time scale crucial "simultaneity of ionization events" Existence of a LET Threshold f(defects, polymer structure)  in presence of unsaturated bonds LET< LET Threshold Creation after a dose threshold Under Inert environment nom Application of SHI in the nuclear industry context : influence of SHI under O 2 Gas emission Macromolecular defects G(H 2 ) and G(oxidized groups) = f( dose) Various LET Under O Centre de Recherche sur les Ions, les Matériaux et la Photonique nom Ketones accumulate more rapidly Ratio ketone/acids  with  D Same oxidized defects as under gamma rays but with lower yields G(-O 2 ) 11 MeV/A 13C ≈ 0.2 *G(-O 2 ) 1MeV b Almost no LET effect on carbonyl containing functions Creation of unsaturated bonds under SHI G (acids) + G(Esters)  with D Almost no LET effect on any of the carbonyl containing functions EPDMn g rays (D< 500 kGy)* G(ketone)/G(acids) ≈3 Ion beam ( D<1500 kGy) G(ketone)/G(acids) = 4-5 * Rivaton et al NIMB 227 (2005) et al., Polym.Deg.Stab.111 (2015), 89 Centre de Recherche sur les Ions, les Matériaux et la Photonique nom Almost no LET effect on any of the carbonyl containing functions EPDMn g rays (D< 500 kGy)* G(ketone)/G(acids) ≈3 Ion beam ( D<1500 kGy) G(ketone)/G(acids) = 4Almost no LET effect on any of the carbonyl containing functions EPDMn g rays (D< 500 kGy)* G(ketone)/G(acids) ≈3 Ion beam ( D<1500 kGy) G(ketone)/G(acids) = 4-5 Ratio BMR/HP ↗ when LET↗ HP trend for vinylidenes and alkynes Unsaturated bonds created under SHI but not under gamma Specificity of SHI : oxidation nom Conclusion date réunion Basic research : modifying the heterogeneity of energy deposition gives insight on defects creation mechanisms.LET Effect on C=C Under vacuum  on vinyl and defects specific to SHI Under oxidative environment  On all defects Creation time scale < oxidation time scale LET effect on gas H 2 : Tremendous in presence of sinks after a threshold Hydrocarbon gases : tremendous Centre de Recherche sur les Ions, les Matériaux et la Photonique nom Conclusion date réunion Technological issues : Simulation of a particles with SHI Evolution of gas emission and carbonyls with the dose H 2 emission Oxidized defects Almost no effect on carbonyls but important dose effect in  acids and esters with  dose potential increase in hydrosoluble molecules Presence of C=C : great acceleration of oxidation at high doses Simulation of high dose deposition over long time periods

G(gas) (10 -7 mol.J -1 ) Polymer structure effect Under
vacuum and in presence of gamma rays and electron beams: gas emission is function of the polymer chemical structure

Linear Energy Transfer (g-rays and electrons vs SHI) What happens under Swift Heavy Ions? Centre de Recherche sur les Ions, les Matériaux et la Photonique nom
Two fields of interestBasic science : Study of mechanisms underlying polymer radiation-induced ageing by Tuning the heterogeneous energy deposition pattern Kinetics Time scale of defects formation ….