4
1. S. Geller, Accts. Chem. Res. 11, 87 (1978). 2. B. B. Owens and G. R. Argue, J. Phys. Chem. 72, 2106 (1968); Science 157, 308 (1967). 3. S. Geller, P. M. Skarstad, and S. A, Wflber, J. Electrochem. Soc. 122, 332 (1975). 4. B. B. Owens and G. R. Argue, J. Electrochem. Soc. 117, 898 (1970). 5. B. B. Owens, Adv. Electrochem. Eng. 8, 61 (1971). 6. B. B. Owens, "Thermodynamic properties of solid electrolytes," in Fast Ion Transport in Solid State Batteries and Devices, W. van Gool, Ed. (American Elsevier, New York, 1973); D. O. Raleigh, J. Appl. Phys. 41, 1876 (1970). 7. B. B. Owens, J. Electrochem. Soc. 122, 1536 (1970). 8. B. B. Owens, J. H. Christie, and G. T. Tiedeman, J. Electrochem. Soc. 118, 1144 (1971). 9. M. M. Thackeray and J. Coetzer, Electrochim. Acta, 24, 495 (1979) and references therein. 10. S. Geller and B, B. Owens, J. Phys. Chem. Solids, 33, 1241 (1972). 11. S. Geller, Science 176, 1016 (1972). 12. J. B. Goodenough, Mat. Res. Bull. U, 203 (1976). 13. J. B. Wagner, in Electrode Processes in Solid State Ionics, M. Kleitz and J. Dupoy, Eds. (D. Reidel, Boston, 1975), pp. 185-222. 14. T. Hibma, Phys. Rev. B 15, 5797 (1977}. 15. C. E. Weir, E. R. Lippincott, A. Van Valkenburg, and E. N. Bunting, J. Res. Nat. Bur. Stand., Sect. A 63, 55 (1959). 16. J. R. Ferraro, S. S. Mitra, and C. Postmus, Inorg. Nucl. Chem. Lett. 2, 269 (1966). 17. J. R. Ferraro and L. J. Basile, Appl. Spectrosc. 28, 505 (1974). 18. C. Postmus, J. R. Ferraro, and S. S. Mitra, Inorg. Nucl. Chem. Lett, 4, 155 (1968). 19. J. R. Ferraro, in Spectroscopy in Inorganic Chemistry, C. N. R. Rao and J. R. Ferraro, Eds. (Academic Press, New York, 1971), pp. 57-77. 20. J. R. Ferraro and L. J. Baste, Appl. Spectrosc. 34, 217 (1980). 21. P. LaBonville Walling and J. R. Ferraro, Rev. Sci. Instrum. 49, 1557 (1978}. 22. S. Block and G. J. Piermarini, Phys. Today 44, 29 (September 1976). 23. L J. Van der Pauw, Phflips Ras. Rep. 13, 1 (1978); 20, 220 (1978). 24. S. Geller, in Superionic Conductors, G. D. Mahan and W. L. Roth, Eds. (Plenum Press, New York, 1976), p. 177. 25. C. Tubandt and E. Lorenz, Z. Phys. Chem. 87,513 (1914). 26. B. B. Owens, in Advances in Electrochemistry and Electrochemical Engi- neering, C. W. Tobias, Ed. (Wiley, New York, 1971), Vol. 8, pp. 1-62. 27. R. S. Bradley, D. C. Munro, and S. I. All, High. Temp.-High Press. 1, 103 (1969). 28. F. P. Bundy, J. S. Kasper, and M. J. Moore, High Temp.-High Press. 3, 303 (1971). 29, H. G. Drickamer, in Solids Under Pressure, W. Paul and D. M. Warschauer, Eds. (McGraw-Hill Co., New York, 1963), pp. 357-384; H. G. Drickamer and C. W. Frank, Electronic Transitions and the High Pressure Chemistry and Physics of Solids (Chapman and Hall, London, 1973), pp. 103-108. 30. T. E. Slykhouse and H. G. Drickamer, J. Phys. Chem. Solids 7, 207 (1958}. 31. A. S. Balchan and H. G. Drickamer, J. Phys. Chem. Solids 19, 261 {1961). 32. D. Greig, D. F. Shriver, and J. R. Ferraro, J. Chem. Phys, 66, 5249 (1977). 33. R. C. Hanson, T. A. Fjeldly, and H. D. Hocheimer, Status Solidi B 70, 567, (1975). 34. D. Greig, G. C. Joy, and D. F. Shriver, Inorg. Chem. 8, 914 (1969). 35. G. L. Bottger and A. L. Geddes, J. Chem. Phys. 46, 3000 (1967). 36. B. M. Riggleman and H. G. Drickamer, J. Chem. Phys. 38, 2721 (1963}. 37. T. Takahasi, K. Kuwabara, and O. Yamanato, J. Electrochem. Soc. Solid State Sci. 116, 357 (1969). 38. A. Van Valkenburg, J. Res. Natl. Bur. Stand. 68A, 97 (1964). 39. R. N. Schock and S. Katz, J. Chem. Phys. 48, 2094 (1968). Relaxation Spectrum of Polytetrafluoroethylene Obtained from Electron Paramagnetic Resonance and Nuclear Magnetic Resonance Spectra* SHIGETAKA SHIMADA, TAKESHI TANIGAWA, and HISATSUGU KASHIWABARA Nagoya Institute of Technology, Showa.ku, Nagoya 466, Japan Distribution of the correlation time in solid polymers was taken into consideration in the analysis of the magnetic resonance data. Motional narrowing of the line width of the EPR spectrum of fluoroalkyl radicals in polytetrafluoroethylene and that of broad line NMR spectrum (fluorine resonance) were observed on the same samples at the temperatures ranging from 260 to 320K. Since EPR and NMR measurements are measurements with different characteristic times of observation, representa- tive correlation times corresponding to respective measure- ments were found to agree with the relaxation theory proposed by Miyake [J. Polym. Sci. 28:476 (1958)] in which distributions of correlation time were taken into consideration. Based on these values, the real activation energy of the molecular motion associated with the motional narrowings of EPR and NMR studies were found to be 310 KJ/mol. On the other hand, the activation energy which gives the same relaxation spectrum as obtained from EPR and NMR data was found to be 318 KJ/mol. This reflects that the analysis in the present paper is a proper analysis. The present paper presents an example in which the Received 29 August 1979; revision received February 1980. * Presented at the 21st Annual Rocky Mountain Conference on Ana- lytical Chemistry, 30 July 1979. See Vol. 34, No. 3, May/June 1980 for other papers. Volume 34, Number 5, 1980 consideration of the distribution of the correlation time was successfully applied. Index Headings: EPR; NMR; Relaxation spectrum; Polymers. INTRODUCTION Application of nuclear magnetic resonance method to the study of the molecular motions in solid polymers is rather popular. Usually, the correlation times in the temperature region, in which the line width is narrowing, are estimated by use of the Bloembergen, Purcel, and Pound (BPP) 1 equation and the related activation ener- gies are calculated also. However, the activation energy estimated from the temperature dependence of the cor- relation times obtained in this way is smaller than that obtained from the other methods of studying molecular motion like dielectric or dynamic mechanical methods. Miyake discussed this problem 2 taking a broad distribu- tion of relaxation times (correlation times) into consid- eration and he proposed a useful equation for estimating a relaxation spectrum from the NMR data. On the other hand, application of electron paramagnetic resonance APPLIED SPECTROSCOPY 575

Relaxation Spectrum of Polytetrafluoroethylene Obtained from Electron Paramagnetic Resonance and Nuclear Magnetic Resonance Spectra

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Page 1: Relaxation Spectrum of Polytetrafluoroethylene Obtained from Electron Paramagnetic Resonance and Nuclear Magnetic Resonance Spectra

1. S. Geller, Accts. Chem. Res. 11, 87 (1978). 2. B. B. Owens and G. R. Argue, J. Phys. Chem. 72, 2106 (1968); Science 157,

308 (1967). 3. S. Geller, P. M. Skarstad, and S. A, Wflber, J. Electrochem. Soc. 122, 332

(1975). 4. B. B. Owens and G. R. Argue, J. Electrochem. Soc. 117, 898 (1970). 5. B. B. Owens, Adv. Electrochem. Eng. 8, 61 (1971). 6. B. B. Owens, "Thermodynamic properties of solid electrolytes," in Fast Ion

Transport in Solid State Batteries and Devices, W. van Gool, Ed. (American Elsevier, New York, 1973); D. O. Raleigh, J. Appl. Phys. 41, 1876 (1970).

7. B. B. Owens, J. Electrochem. Soc. 122, 1536 (1970). 8. B. B. Owens, J. H. Christie, and G. T. Tiedeman, J. Electrochem. Soc. 118,

1144 (1971). 9. M. M. Thackeray and J. Coetzer, Electrochim. Acta, 24, 495 (1979) and

references therein. 10. S. Geller and B, B. Owens, J. Phys. Chem. Solids, 33, 1241 (1972). 11. S. Geller, Science 176, 1016 (1972). 12. J. B. Goodenough, Mat. Res. Bull. U, 203 (1976). 13. J. B. Wagner, in Electrode Processes in Solid State Ionics, M. Kleitz and J.

Dupoy, Eds. (D. Reidel, Boston, 1975), pp. 185-222. 14. T. Hibma, Phys. Rev. B 15, 5797 (1977}. 15. C. E. Weir, E. R. Lippincott, A. Van Valkenburg, and E. N. Bunting, J. Res.

Nat. Bur. Stand., Sect. A 63, 55 (1959). 16. J. R. Ferraro, S. S. Mitra, and C. Postmus, Inorg. Nucl. Chem. Lett. 2, 269

(1966). 17. J. R. Ferraro and L. J. Basile, Appl. Spectrosc. 28, 505 (1974). 18. C. Postmus, J. R. Ferraro, and S. S. Mitra, Inorg. Nucl. Chem. Lett, 4, 155

(1968). 19. J. R. Ferraro, in Spectroscopy in Inorganic Chemistry, C. N. R. Rao and J.

R. Ferraro, Eds. (Academic Press, New York, 1971), pp. 57-77. 20. J. R. Ferraro and L. J. Baste, Appl. Spectrosc. 34, 217 (1980). 21. P. LaBonville Walling and J. R. Ferraro, Rev. Sci. Instrum. 49, 1557 (1978}. 22. S. Block and G. J. Piermarini, Phys. Today 44, 29 (September 1976). 23. L J. Van der Pauw, Phflips Ras. Rep. 13, 1 (1978); 20, 220 (1978). 24. S. Geller, in Superionic Conductors, G. D. Mahan and W. L. Roth, Eds.

(Plenum Press, New York, 1976), p. 177. 25. C. Tubandt and E. Lorenz, Z. Phys. Chem. 87,513 (1914). 26. B. B. Owens, in Advances in Electrochemistry and Electrochemical Engi-

neering, C. W. Tobias, Ed. (Wiley, New York, 1971), Vol. 8, pp. 1-62. 27. R. S. Bradley, D. C. Munro, and S. I. All, High. Temp.-High Press. 1, 103

(1969). 28. F. P. Bundy, J. S. Kasper, and M. J. Moore, High Temp.-High Press. 3, 303

(1971). 29, H. G. Drickamer, in Solids Under Pressure, W. Paul and D. M. Warschauer,

Eds. (McGraw-Hill Co., New York, 1963), pp. 357-384; H. G. Drickamer and C. W. Frank, Electronic Transitions and the High Pressure Chemistry and Physics of Solids (Chapman and Hall, London, 1973), pp. 103-108.

30. T. E. Slykhouse and H. G. Drickamer, J. Phys. Chem. Solids 7, 207 (1958}. 31. A. S. Balchan and H. G. Drickamer, J. Phys. Chem. Solids 19, 261 {1961). 32. D. Greig, D. F. Shriver, and J. R. Ferraro, J. Chem. Phys, 66, 5249 (1977). 33. R. C. Hanson, T. A. Fjeldly, and H. D. Hocheimer, Status Solidi B 70, 567,

(1975). 34. D. Greig, G. C. Joy, and D. F. Shriver, Inorg. Chem. 8, 914 (1969). 35. G. L. Bottger and A. L. Geddes, J. Chem. Phys. 46, 3000 (1967). 36. B. M. Riggleman and H. G. Drickamer, J. Chem. Phys. 38, 2721 (1963}. 37. T. Takahasi, K. Kuwabara, and O. Yamanato, J. Electrochem. Soc. Solid

State Sci. 116, 357 (1969). 38. A. Van Valkenburg, J. Res. Natl. Bur. Stand. 68A, 97 (1964). 39. R. N. Schock and S. Katz, J. Chem. Phys. 48, 2094 (1968).

Relaxation Spectrum of Polytetrafluoroethylene Obtained from Electron Paramagnetic Resonance and Nuclear Magnetic Resonance Spectra*

SHIGETAKA SHIMADA, TAKESHI TANIGAWA, and H I S A T S U G U K A S H I W A B A R A Nagoya Institute of Technology, Showa.ku, Nagoya 466, Japan

Distr ibut ion o f the corre lat ion t ime in sol id p o l y m e r s w a s taken into cons iderat ion in the ana lys i s o f the m a g n e t i c r e s o n a n c e data. Mot ional n a r r o w i n g o f the l ine w id th o f the EPR spec trum of f luoroa lky l radicals in po ly te t ra f luoroe thy lene and that o f broad l ine NMR spectrum (f luorine re sonance ) w e r e o b s e r v e d on the same samples at the t empera tures r a n g i n g from 260 to 320K. Since EPR and NMR m e a s u r e m e n t s are m e a s u r e m e n t s w i t h di f ferent character i s t i c t imes o f observat ion , representa - t ive corre lat ion t imes correspond ing to respec t ive measure - m e n t s w e r e found to agree w i th the re laxat ion t h e o r y proposed by Miyake [J. Po lym. Sci. 2 8 : 4 7 6 (1958)] in w h i c h d i s tr ibut ions o f corre lat ion t ime w e r e taken into cons iderat ion . B a s e d on these values , the real ac t ivat ion e n e r g y o f the molecu lar mot ion assoc ia ted w i th the mot iona l n a r r o w i n g s o f EPR and NMR studies w e r e found to be 310 K J / m o l . On the o ther hand, the ac t ivat ion e n e r g y w h i c h g ives the same re laxat ion spec trum as obta ined from EPR and NMR data w a s found to be 318 K J / m o l . This ref lects that the ana lys i s in the presen t paper is a proper analys i s . The present paper present s an example in w h i c h the

Received 29 August 1979; revision received February 1980. * Presented at the 21st Annual Rocky Mountain Conference on Ana-

lytical Chemistry, 30 July 1979. See Vol. 34, No. 3, M a y / J u n e 1980 for other papers.

Volume 34, Number 5, 1980

cons iderat ion of the d is tr ibut ion o f the corre lat ion t ime w a s success fu l ly appl ied. Index Headings: EPR; NMR; R e l a x a t i o n spectrum; Po lymers .

INTRODUCTION

Application of nuclear magnetic resonance method to the study of the molecular motions in solid polymers is rather popular. Usually, the correlation times in the temperature region, in which the line width is narrowing, are estimated by use of the Bloembergen, Purcel, and Pound (BPP) 1 equation and the related activation ener- gies are calculated also. However, the activation energy estimated from the temperature dependence of the cor- relation times obtained in this way is smaller than that obtained from the other methods of studying molecular motion like dielectric or dynamic mechanical methods. Miyake discussed this problem 2 taking a broad distribu- tion of relaxation times (correlation times) into consid- eration and he proposed a useful equation for estimating a relaxation spectrum from the NMR data. On the other hand, application of electron paramagnetic resonance

APPLIED SPECTROSCOPY 575

Page 2: Relaxation Spectrum of Polytetrafluoroethylene Obtained from Electron Paramagnetic Resonance and Nuclear Magnetic Resonance Spectra

(EPR) to the study of molecular motion in polymers has also been made for the past 15 years. As in the case of NMR, the temperature dependence of the EPR line width could be useful for estimation of the correlation times and corresponding activation energies. Faster rates measured in the case of EPR applications are typically associated with smaller activation energies.

The present paper proposes a simple method for ap- plication of Miyake's equation to the case of EPR and NMR studies of polymers in which the correlation time is distributed in a broad range. It must be noted that the application of Miyake's equation was previously made by Kakudate. 3 for semicrystalline polymers and the feature of the present paper is the application to the case in which both EPR and NMR methods are used.

An example of a similar application of Miyake's theory was reported for the study of local molecular motion in the polyethylene molecule in the urea-polyethylene in- clusion complex. 4 The case of polytetrafluoroethylene will be presented in this paper.

I. ANALYSIS OF MAGNETIC RESONANCE DATA FOR THE CASE OF A DISTRIBUTION OF RELAXATION TIMES IN THE POLYMER

A. Miyake's Equation. In the temperature region where motional narrowing of the line width of the mag- netic resonance spectrum occurs the correlation time associated with the corresponding molecular motion, ~-~, can be obtained by the famous BPP equation) In the case of two-step narrowing of the line width, an equation modified by Gutowsky and Meyer ~ as shown in Eq. (1) can be applied.

(AJ) - <~J)F (1)

2 ((A 2) n (AOO2)F) tan_l(a%/T2) 77

where (A~2)n and (AW2)F are the second moments of rigid and free states, respectively, and T2 is spin-spin relaxation time. a is a constant approximately equal to unity.

According to Miyake's paper, the distribution of the correlation time, I(T~), satisfies the following relation,

(~ 0 )2 ) - - (AL02) F = 2 ((AO02)R

or (2)

- (AcO2)F) tan-l(o~rc/T2)I(rc)d log % oo

When I(Tc) is a symmetric function, it can be expressed by the following equation,

I ( a / ~ / ~ . a ( T ) ) = [2(AJ)/((hw2)a

- <5002)F)] {1 + ddl°glog ~/~ja(T) .It -~ (3)

Where a(T) is a shift factor at any particular tempera- ture, T, and ~'c at that temperature can be expressed by the following relation

~'~(T) = a(T)rc(Tr) (4)

Where Tr is a reference temperature and Eq. (4) indicates

576 Volume 34, Number 5, 1980

a temperature-time-superposition principle, which was established for the relaxation phenomena in polymer physicsf Since an Arrhenius type relation can generally be adopted for the temperature dependence of Zc, the shift factor a(T) can be expressed by Eq. (5).

a ( T ) = e x p { ( E / R ) ( - T - ~ ) } (5)

B. Distribution Function of Correlation Time, I(~c). If the activation energy E is determined, I(~'c) can be obtained from Eq. (3) using a(T) estimated by Eq. (5). This means that the relaxation spectrum associated with a certain mode of molecular motion can be obtained both from NMR data and EPR data assuming a proper value of the activation energy, when the motional nar- rowings are observed both for NMR and EPR observa- tions in similar temperature regions. Of course, the tem- perature region for the latter shall reasonably be higher than that for the former because the characteristic time of EPR measurement is usually shorter than that of NMR measurement. As mentioned above, I(z,.) obtained from Eq. (3) is dependent on the values of E since a(T) in Eq. (3) is dependent on E as shown in Eq. (5). There- fore, we can estimate various I(0-c) for various values of E. If I(~c) obtained from NMR data and separately from EPR data are in good agreement for the same value of E, that value of E must be the actual activation energy of the associated molecular motion. If this is the case, it can be said that both NMR and EPR measurements observe the same mode of molecular motion.

C. Representative Correlation Time. As Miyake pointed out, the activation energy estimated from an Arrhenius plot of the correlation times estimated by simple application of Eq. (1) is not the real activation energy when the correlation times are distributed widely. However, if different kinds of measurements with differ- ent characteristic times are made and if a representative value of the correlation time in each of the measurements is obtained, the actual activation energy can be obtained easily as in the case of a dynamic mechanical study. The representative value must be the correlation time for which the distribution function has the maximum value. At the present stage, making EPR and NMR measure- ments is a performance of different kinds of measure- ments with different characteristic times (order of 10 7 s -1 in the case of EPR and 10 4 s-' for NMR). By chance, in the application of BPP theory modified by Miyake 2, the following equation can be satisfied with proper (AJ) , , and Tin.

(A¢J)m- (A~)F = ((A~J)R

fl 1 - (AJ)~) I(rc)dlog rc = ~ ((AJ)R - (A¢o2)F) (6)

n

In Eq. (6), ~m can be interpreted as a correlation time corresponding to the maximum value of the distribution of correlation time at the temperature, at which the value of the second moment is (hJ)m. This is valid if the distribution I(~) is symmetric about rm. Time scales of observations in EPR and NMR methods are reasonably reflected by the temperature corresponding to 0-,,'s. When two 0"m'S are estimated and two temperatures correspond-

Page 3: Relaxation Spectrum of Polytetrafluoroethylene Obtained from Electron Paramagnetic Resonance and Nuclear Magnetic Resonance Spectra

ing to respective ~'m'S are found, an Arrhenius plot of these ~-,,'s must give a "real activation energy" of the considered motion. The activation energy E correspond- ing to the same relaxation spectra determined by EPR and NMR data should be the same as the activation energy determined by Arrhenius plot of r,,'s mentioned above when the same molecular motion is observed by both EPR and NMR methods, rm obtained in this way is a representative correlation time specifying the molecu- lar motion considered. In other words, ~'m corresponds to the relaxation time obtained in usual dynamic mechani- cal or dielectric studies, rm's obtained in EPR and NMR studies are, therefore, the correlation times obtained in the measurements with different time scales of observa- tion.

II. EXPERIMENTAL

A sample of polytetrafluoroethylene, Aflon G 80 (Prod- uct of Asahi Glass Company), was -/-irradiated up to 40 Mrad with a dose rate of 0.15 Mrad/h at room tempera- ture. After the irradiation, the sample was heat treated at 550 K for 40 min in order to observe only the stable free radicals which remain after the heat treatment. Fluorinated alkyl radicals in irradiated polytetrafluoro- ethylene (PTFE) were observed with an X-band spec- trometer (JEOL ME 3X) at various temperatures, and the line widths of the spectra were measured at each of the temperatures. EPR observations were made with 100 KHz modulation and microwave power of 0.1 mW. Broad line NMR (BL-NMR) spectra (fluorine resonance) were observed at temperatures ranging from 260 to 320 K and second moments of the spectra were estimated at each of the temperatures. A JEOL JNM-BE-1 (40 MHz) NMR spectrometer was used and the spectra were recorded with 35 Hz modulation frequency.

III. RESULTS AND DISCUSSIONS

The temperature dependence of the line width of the double quintet EPR spectrum coming from fluoroalkyl radicals, ~CF2CF2CFCF2CF2~, is shown by open circles in Fig. 1. Second moments of BL-NMR spectrum were determined at various temperatures, and they are also plotted by black circles in the same figure. Estimations of the correlation times by use of Eq. (1) in this case were made for various temperatures. Fig. 2 shows the temper- ature dependence of the correlation time estimated. Open circles in Fig. 2 indicate the correlation times estimated

~"lOO I - ? 0

oESR

X~k "NMR I 0 0 ~

g o E 9 , o

50 g

8.0:5

260 270 2 0 290 300 3 0 320 Temperoture (K)

FIG. 1. Line widths of L E P R spectra of fluoroalkyl radicals in P T F E (©) and second moments of BL-NMR of irradiated P T F E (e) at various temperatures.

from the line widths of EPR spectra and black circles are those for NMR data. Both plots show, by chance, the same slope corresponding to an activation energy of 142 KJ/mol. As mentioned previously (Section IC), the slopes of the solid lines in Fig. 2 do not correspond to real activation energies. However, the dotted line in Fig. 2 connects the ~',n'S defined in Eq. (6) and this line shows a slope corresponding to 310 KJ/mol. If both EPR and NMR measurements correspond to the observations of the same molecular motion, the actual activation energy should be 310 KJ/mol based on the discussion in Section I. Since the measurement of EPR corresponds to the measurement with the frequency of 107 s -] and the mea- surement by NMR corresponds to 104 s -~, the difference between narrowing temperatures in EPR and NMR is reflected by the dotted line, and its slope indicates the actual activation energy of the molecular motion under consideration. Numerical values obtained are as follow- ing: • m in EPR is 0.4 x 10 -~ s, temperature corresponding to ~-m in EPR is 297 K, rm in NMR is 0.7 × 10 -4 s, and the temperature corresponding to rm in NMR is 280 K.

8,0

7.0

6.0

o ~ 5.0

4.0

\ \

\ \

I I 3.3 3.4

oESR "NMR

\ \

\ \

\

315 316 I / T ( X I0 -~)

FIG. 2. Arrhenius plots of correlation t imes est imated from E P R line width (©) and BL-NMR line width (Q) of PTFE. Dot ted line shows Arrhenius plots of representat ive correlation times, z,,'s obtained from E P R and BL-NMR studies (see Fig. 3 also).

-0.I

o

-0.5

o

E=142

°:: o o

o

1 I I -8 -6 -4

log T'

E:356 C

0 E=251

eo*

-0.5 ° ° .o'. • o •

o

-8 - -4 log 'Z"

E=41S

~o -0.5 "8 o

• • ° cn * o • o o

: 2

- - 6 - 4

Iog '~ Iog 'T

FIG. 3. C ompar i sonso f t he r e l axa t i onspec t r aa t r e f e r ence t empe ra tu r e (T, = 290 K) obtained from E P R data (©) and N M R data (O) based on Eq. (3). Values indicated for the respective figures are activation energies (KJ mol 4) assumed for the respective cases.

A P P L I E D S P E C T R O S C O P Y 5 7 7

Page 4: Relaxation Spectrum of Polytetrafluoroethylene Obtained from Electron Paramagnetic Resonance and Nuclear Magnetic Resonance Spectra

O.C o ESR

• NMR

-0.5

o

-LC

-8 .0 -7.0 -6.0 -5 tog (~)

FIG. 4. Relaxation spectrum of PTFE at reference temperature (Tr = 290 K) when activation energy is assumed to be 318 KJ/mol: (©) plots based on EPR data; (O) plots based on NMR data.

As mentioned previously, the relaxation spectrum at a reference temperature (in this case Tr ffi 290 K) can be obtained by use of Eq. (3). Fig. 3 shows a comparison of the relaxation spectra obtained from EPR and NMR data, in which the value of the activation energy is a parameter. As shown clearly in Fig. 3, the coincidence between the relaxation spectra obtained from EPR and NMR data is not good when the activation energies indicated at each of spectra are assumed. However, when the activation energy is assumed to be 318 KJ/mol, the coincidence is very good as shown in Fig. 4. From Fig. 2, an activation energy of 310 KJ/mol was obtained. If the EPR and NMR measurements corresponding to the ob- servation of the same molecular motion, relaxation spec- tra obtained from both data must be the same. This means also that the value of 318 KJ/mol, which results in the same relaxation spectra for EPR and NMR, must be the actual activation energy of the molecular motion

under the consideration. Thus, it can be said that com- parison of the relaxation spectra in the above-mentioned way gave the value of the activation energy. On the other hand, as mentioned previously, the activation energy was found to be 310 KJ/mol for the molecular motion asso- ciated with motional narrowings of line widths of EPR and NMR spectra. Since two values of activation ener- gies, 310 and 318 KJ/mol, are in good agreement within an experimental error, it can safely be said that activation energies obtained from Fig. 2 and discussions concerning Figs. 3 and 4 must be the same.

According to the discussions mentioned above and several values obtained in this study, it is quite reasona- ble to say that the EPR and NMR measurements are monitoring the same molecular motion in polytetrafluo- roethylene. More than 15 years ago, Tamura 7 made a similar study and he concluded that narrowings of the line widths of EPR and NMR correspond to the molec- ular motion associated with the peak of tan 8 near room temperature in the dynamic mechanical study of the same materials. In the present paper, Tamura's study was confmned with much more consistent discussions in which the distribution of correlation time in solid poly- mer was taken into consideration successfully.

ACKNOWLEDGMENT

The present study was partly supported by the Scientific Research Expendi- ture of Ministry of Education, Grant 455343.

1. N. Bloembergen, E. M. Purcel, and P. V. Pound, Phys. Rev. 73, 679 (1948). 2. A. Miyake, J. Polym. Sci. 28, 476 (1958). 3. T. Kakudate, Ph.D. Thesis, Hokkaido University (1977). 4. S. Shimada, T. Tanigawa, and H. Kashiwabara, Polymer, in press. 5. H. S. Gutowsky, and L. H. Meyer, J. Chem. Phys. 21, 2122 (1953). 6. For example, J. D. Ferry, Viscoelastic Properties of Polymers (Wiley, New

York, 1961) or N. Saito, K. Okano, S. Iwayanagi, and T. Hideshima, Solid State Physics, F. Seitz and D. Turnbull, Eds. (Academic Press, New York, 1963), vol. 14, p. 343.

7. N. Tamura, J. Chem. Phys. 47,479 (1962).

Atmospheric Pressure Active Nitrogen (APAN)--A New Source for Analytical Spectroscopy

A. P. D'SILVA, G. W. RICE, and V. A. FASSEL Ames Laboratory* and Department of Chemistry, Iowa State University, Ames, Iowa 50011

An a tmosphe r i c p r e s su re "ac t ive n i t rogen" (APAN) a f te rg low w a s generated in pure f lowing n i t rogen (<10 p p m 02) exc i t ed in an e lec t rodeless ozonizer d ischarge . The af terglow, which con- ta ins severa l metas tab le spec ies , has been obse rved to be an eff ic ient source for the exci ta t ion of a tomic emission, th r o u g h energy t rans fe r . The appl ica t ion of the APAN af te rg low for the

Received 1 November 1979; revision received 7 April 1980. * Operated for the U.S. Department of Energy by Iowa State University

under contract No, W-7405-Eng-82. This research was supported by the Division of Chemical Sciences, Budget Code KC-03-02-03, Office of Energy Research.

578 Volume 34, Number 5, 1980

detec t ion and determinat ion of u l tratrace levels of Hg and the volati le hydr ide fo rming e lements , As, Bi, Ge, Pb, Sb, Se, Sn, and Te is documented .

Index Headings: A tmosphe r i c pres sure act ive n i t rogen (APAN); Elec trode less ozonizer d ischarge; Hydr ide fo rming e lements .

INTRODUCTION

Laboratory investigations on the nature of auroral phenomena have led to observations that low pressure

APPLIED SPECTROSCOPY