doi:10.1016/j.jfluchem.2007.01.012
Copyright © 2007 Elsevier B.V. All rights reserved.
Degradation of γ-irradiated linear perfluoroalkanes at high dosage
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Sadulla R. Allayarova, 
, Sergey V. Konovalikhina, Yurii A. Olkhova, Virgil E. Jacksonb, Lowell D. Kispertb, , David A. Dixonb, 
, , Daryush Ilac, and Uwe Lappand,
aInstitute of Problems of Chemical Physics of the Russian Academy of Sciences, Chernogolovka, Moscow 142432, Russia
bDepartment of Chemistry, The University of Alabama, Tuscaloosa, AL 35487-0336, USA
cCenter for Irradiation of Materials, Alabama A&M University, Normal, AL 35762-1447, USA
dInstitute of Polymer Research Dresden, Dresden 01069, Germany
Received 25 September 2006;
revised 23 January 2007;
accepted 24 January 2007.
Available online 2 February 2007.
Graphical abstract
A combined computational and experimental study of the irradiation of perfluoroalkanes and polytetrafluoroethylene shows that individual chains of the perfluoropolymer show less radiation damage than do polyethylene chains. The helical structure of individual perfluroalkanes readily distorts on removal of a fluorine leading to loss of the mechanical stability of bulk polytetrafluoroethylene as compared to polyethylene.
Keywords: Linear short chain perfluoroalkanes; Polytetrafluoroethylene; γ-Irradiation; EPR spectra; Stabilized radicals; Decomposition mechanism; Density functional theory
Fig. 1. The EPR spectra as a function of radiation dose of n-C6F14 (a and a′), n-C8F18 (b and b′), n-C12F26 (c and c′), n-C16F34 (d and d′) and PTFE (e and e′) γ-irradiated at 77 K with low dose [0.0167 MGy (a–c), 0.04 MGy (d), 0.8 MGy (e)] and high dose [6.82 MGy (a′ and b′), 2.8 MGy (c′ and d′), 5.44 MGy (e′)].
Fig. 2. The total concentration of radicals [R] formed vs. radiation dose (MGy) at 77 K of n-C6F14 (1), n-C8F18 (2), n-C12F26 (3), n-C16F34 (4) and PTFE indicated by the symbols (5) and (6). The upper plot is an expansion of the low dose region near the origin from 0 to 0.10 MGy.
Fig. 3. The total concentration of radicals [R] formed vs. radiation dose (MGy) during γ-irradiation at 77 K of PE (1) and n-C7H16 (2). The upper plot is an expansion of the low dose region near the origin from 0 to 0.10 MGy.
Fig. 4. Dependence of the EPR spectral intensity of the –CF2C
F2 and –F2CCFCF2– radicals with irradiation dose at 77 K for n-C6F14 (1), n-C8F18 (2), n-C12F26 (3), n-C16F34 (4) and PTFE (5).
Fig. 5. Dependence of the ratio of the EPR spectral intensity of the –CF2CF2 and –F2CCFCF2– radicals as a function of 3/(n − 2), where n is the number of carbon atoms of irradiated perfluoroalkane molecules at high radiation dose (>2 MGy).
Fig. 6. DFT optimized structures of the perfluro-n-alkane radicals generated by breaking a C–F bond in the parent perfluro-n-alkane.
Fig. 7. Change of the weight molecular mass averaged over four topographical blocks of PTFE 
(1) and the average numerical weight molecular mass of PTFE in the amorphous block 
(2) with irradiation dose at 27 °С. The molecular weight change of PTFE (3) during radiolysis at room temperature from Ref. [4].
Table 1.
Experimental EPR hyperfine parameters of the free radicals formed by radiolysis at 77 K of polytetrafluoroethylene and short-chain linear perfluoroalkanes as reported in Refs. [11] and [12]
a Parallel (
) and perpendicular
components of hyperfine coupling constant with fluorine atom.
b Ir = separation between the highest and lowest EPR lines of –CF
2C
F
2 (45.0 mT) and –F
2CC
FCF
2– radicals (24.0 mT).
c 
= || component and
=
component.
d 
=
,
=
.
e Hyperfine coupling constant with three fluorine atoms.
Table 2.
Calculated DFT EPR hyperfine parameters (mT) of fluroocarbon radicals
a Parallel (
) and perpendicular
components of hyperfine coupling constant with fluorine atom.
b 
= || component and
=
component.
=
,
=
.
c Isotropic hyperfine coupling constant with three fluorine atoms.
Table 3.
The radiation-chemical yields of products for polymer radiolysis
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