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MECHANICAL AND DIELECTRIC LOSS SPECTRA
OF AMBERS
M. Weller, C. Wert, D. Schlee
To cite this version:
MECHANICAL AND DIELECTRIC LOSS SPECTRA OF AMBERS
M. WELLER, C.A. WERTf AND D. SCHLEEif
Max-Planck-Institut fur Metallforschung, Institut fur Werkstoffwissenschaften, 0-7000 Stuttgart, F.R.G.
'Department of Metallurgy, University of Illinois, Urbana, IL 61801, U.S.A.
"Staatliches Museum fur Naturkunde, Stuttgart, F.R.G.
Rtsumt - L'ambre reprtsente une resine fossiliste avec une structure macromoltcu- -reille
P
celle des autres carbures d'hydrogine fossiles. I1 montre des pics de frottement inttrieur qui ressemblentP
ceux dans les polymires synthttiques e t les autres mattriaux de carbures d'hydrogine macromoltculaire. 11 est un ditlectrique excellent qui posside aussi un spectre de pertes ditlectriques. On a utilist les spectres de frottement inttrieur e t les spectres de pertes ditlectriques afin d'tlucider quelques characteristiques des ambres provenant des ptriodes gtologiques difftrentes.Abstract
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Amber is a fossilized resin with a molecular structure similar to that of o t h e r s s i l hydrocarbons. It displays internal friction peaks similar to those of synthe- tic polymers and other macromolecular hydrocarbon materials. It is an excellent di- electric, and has a dielectric loss spectrum as well. We have utilized internal friction and dielectric loss spectra to elucidate some features of ambers from different geo- logical periods.1 - INTRODUCTION
Ambers are formed from resins modified over geological periods. Some ambers derive from pine resins and others from exudants from deciduous trees. Most study of ambers has focussed on inclusions: insects, plant residue and small animals. Ambers have been shown t o possess characteristic internal friction and dielectric loss spectra similar to that for coal and other macromolecular solids
/ I - ~ / .
This paper reports a comparative study of the loss spectra of ambers of different origins.I1 - EXPERIMENTS
Internal friction measurements near IHZ were carried out in an inverted torsional pendulum.
Samples about 50 x 1.5 x 1.5, mm were cut from natural amber; they were glued into brass pins which fitted into the torsional pendulum / 5 / . Measurements were first made on Baltic amber. Figure Ia shows the internal friction and £2 (recall that £2 is proportional to the real part of the modulus) measured with increasing temperature for clear yellow Baltic amber. The internal friction of milky Baltic amber is shown in Fig. rb. Data for a sample cut from another clear amber is shown in Fig. IC. These curves demonstrate the similarity of the in-
ternal friction spectrum of different samples of Baltic amber. The spectrum contains two in- ternal friction peaks designated Y and 0. The first occurs a t 13oK and the second a t 2ooK. These peaks are well known from measurements on many synthetic polymers. Correlated with the internal friction peaks are steps in the real modulus expected for anelastic relaxation, such as that of Fig. Ia.
The internal friction spectra of ambers from different sources are plotted in Fig. 2a. These are arranged in sequence of increasing geological age: Dominican, Mexican, Baltic and Austrian ambers, with geological periods varying from Miocene to Lower Cretaceous. The solid lines in all curves of Fig. 2 show the internal friction for the first traverse in tempera- ture; dashed curves were obtained after annealing a t 385K for 600s. All spectra show peaks a t the Y and i3 positions and a steep increase above 3ooK, the bottom edge of the a-peak. The internal friction peaks are correlated with appropriate changes in elastic modulus.
C10-566 JOURNAL DE PHYSIQUE
Fig. 1. Internal friction m e a s u r e m e n t s in t h r e e differe'nt s a m p l e s of Baltic amber.
001
001
2a
0 100 ZOO 300
T IK1
Fig. 2. I F s p e c t r a (f a b o u t 1 Hz;
-
f i r s t run, --- second run, a f t e r h e a t i n g t o 38510. Fig. 2a = a m b e r of d i f f e r e n t origin. Dominican a m b e r (about 2 5 million y e a r s old), Mexi- c a n a m b e r (about 2 5 million years), B a l t i c a m b e r (about 40 million years), and Austrian a m b e r (about 1 1 0 million years).Fig. 2b = Dominican c o p a l (probably a b o u t 200 y e a r s only), and resinous pine wood (Pinus silvestris).
Fig. 3. I F and f 2 us terriperature of B a l t i c a m b e r (Eigenvibrations, s a m p l e 5 0 x 5 x 1 mm). Fig. 4 . D i e l e c t r i c loss s p e c t r a of Baltic ( a ) a n d Dominican (b) a m b e r s (f = 1 0 KHz;
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f i r s t run, --- s e c o n d run).curve I. This is compared with a normal specimen of wood cut from a section far removed
from the gall, curve, 2. The difference between curves I and 2 is designated D; this is pre-
sumably the internal friction associated with the resin.
Eigenvibration measurements were also made at about 1.2 KHz (Fig. 3) using a sample from
the same Baltic amber as for Fig.
~ b .
At this frequency the Y-peak is shifted to 2ooK and the B-peak to about 250K. This frequency shift allows the relaxation parameters to be calcu- lated. According to the equation r = r, exp (HILT):The two peaks below 15oK which correlate with stages in the £ 2 (modulus) curve may be due to ferroelectric phase transformations.
Dielectric loss measurements were carried out with an automatic AC bridge in the frequency range 0.1 to 10 kHz. The specimens were circular wafers about 16 mm in diameter and I
C10-568 JOURNAL DE PHYSIQUE
111
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DISCUSSIONComposition of amber. Amber originates from resins which contain a heterogeneous mixture of many organic constituents: terpenes, resin acids, alcohols, esters and aromatic compounds. It is formed during burial for millions of years (sometimes associated with considerable heat and pressure) causing chemical reactions and transformations of an unknown character. Information on individual chemical constituents has been obtained using physical chemical or physical methods such as infrared spectroscopy, gas chromatography or mass spectroscopy 16-101. Baltic amber has the approximate formula C10H1608 / I I / .
The '1-relaxation is attributed t o the twisting or bending of short aliphatic methylene chains. For coal we concluded that these linear chains act as cross links between aromatic clusters 141. The ?'-peak has no dielectric analogue; the relaxing unit is not electrically polar.
The B-relaxation exhibits both mechanical and dielectric loss; it is also correlated with motion of a relatively small atomic unit. This may be an OH unit or other heavier radicals such as COH, COOH or CH20H.
Thea-peak above 3ooK is correlated with the glass transition for many polymers.
Internal friction and dielectric loss spectra can be used to deduce models of the macromole- cular structure of different ambers. Differences in the spectra of the various ambers shown in Figs. 2 and 3 imply that different stages of polymerization exist for various ambers. The height of the "I-peak may be taken as a measure of the amount of linear methylene carbon chains. The increase with age t o Baltic amber may reflect an increasing degree of poly- merization. The subsequent decrease for Austrian amber may be due to the increased formation of a more rigid molecular network as is also reflected in a higher shear modulus for this amber (which not only is very old, but has also suffered from extremely strong natu- ral heat and pressure during the formation of the Alps /12/). The existence of the 8-peak for
all ambers means that electrically polar units of small size are attached t o the main chains of all ambers.
IV
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CONCLUSIONSAmber is a macromolecular solid with viscoelastic properties similar t o that of synthetic polymers. This is revealed by the internal friction and dielectric loss spectra. Ambers of different origin have different heights of the ?'- and 8-peaks. The presence of both peaks makes them similar t o the other fossil hydrocarbons, coal, asphalts and oil shale, rather than to the parent wood, lignin or resins from which the fossilized hydrocarbons are derived.
ACKNOWLEDGEMENTS
The technical assistance of Miss Hamm, Mr. Henke, Miss Lakemeyer and Mr. Rahn of the Max-Planck-lnstitut is gratefully acknowledged.
REFERENCES
/I/
Weller, M. and Wert, C.A., J. de Physique44
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(1984) 891./5/ Weller, M. and Wert, C.A., Stuttgarter Beitrage zur Naturkunde C18 (1984) "Bernstein- Neuigkeiten" (ed. by Staatliches Museum fiir Naturkunde, Stuttgart).
/6/ Serganova, G.K. and Rafikov, S.R., J. of Appl. Chemistry of the U.S.S.R. (New York)
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(1965) 1772./7/ Frondel, J.W., Economic Botany 22 (4) (1968) 371. /8/ Langenheim, J., Science (1963 I 157.
/g/ Schlee, D. and Glockner, W., Bernstein, Stuttgarter Beitrage zur Naturkunde (1978).
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Langenheim, J.H. and Beck, C.W., Science (1965) 52./ I I / Tschirch, A. and Stock, E., Die Harze, 11. Band, 2. Hllfte, 2. Teil, Kap. 111 (Gebr. Born- triiger, Berlin, 1935) 1017.
