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THE INFLUENCE OF STEARIC ACID
MONOLAYERS ON THE INTERNAL FRICTION OF
COPPER
W. Chomka, E. Denga, T. Lewis, B. Zaba
To cite this version:
Colloque C10, suppl6ment a u n012, Tome 46, d6cembre 1985 page
THE INFLUENCE OF STEARIC ACID MONOLAYERS ON THE INTERNAL FRICTION OF COPPER
W. CHOMKA, E. DENGA, T . J. LEWIS+AND B. ZABA'
T e c h n i c a l U n i v e r s i t y o f ~ d a r i s k , Department o f T e c h n i c a l P h y s i c s and Applied Mathematics, ~ d a i s k , Poland
+ U n i v e r s i t y C o l l e g e o f North Wales, School o f E l e c t r o n i c E n g i n e e r i n g S c i e n c e . Bangor, G r e a t B r i t a i n
A b s t r a c t
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The i n t e r n a l f r i c t i o n Q"/T/, o f Cu samples covered by monolayers o f s t e a r i c a c i d h a s been measured. The l a y y r s weregrown by Langmuir-Blodgett technique. The o b t a i n e d Q' /T/ s p e c t r a e x h i b i t t h e c h a r a c t e r i s t i c maximum a t about 210 X which i n c r e a s e s w i t h t h e i n c r e a s i n g number o f d e p o s i t e d l a y e r s . A d d i t i o n a l l y Q-1
h a s been measured f o r Cu l u b r i c a t e d w i t h l i q u i d s t e a r i c a c i d . Such p r e p a r e d l a y e r c a u s e s t h e Q-1 maxima a t a b o u t 340 K.
I
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INTRODUCTIONThe i n f l u e n c e o f t h i n s u r f a c e l a y e r s on t h e i n t e r n a l f r i c t i o n , Q"/T/, o f m e t a l l i c samples h a s been r e p o r t e d i n some p r e v i o u s i n v e s t i g a t i o n s
/1,2/. The damping p r o p e r t i e s of such composite sample a r e suggested t o be connected n o t o n l y with t h e i n t r i n s i c p r o p e r t i e s o f a l a y e r b u t a l s o w i t h t h e mutual i n t e r a c t i o n s between t h e s u r f a c e l a y e r and sub- s t r a t / 3 / . F u r t h e r i n v e s t i g a t i o n s a r e performed t o e x p l a i n t h e appear- ance o f new maxima i n Q' /T/ spectrum.
I1
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EXPERIMENTAL METHODSThe t e m p e r a t u r e dependence o f i n t e r n a l f r i c t i o n of c o a t e d Cu samples h a s been measured u s i n g t h e low-frequency t o r s i o n pendulum method. Cu samples had a form o f w i r e s about 60 mm i n l e n g h t and 1 mm i n diameter. The s u r f a c e l a y e r s o f s t e a r i c a c i d have been grown by Langmuir-Blodqett t e c h n i q u e . A d d i t i o n a l sample h a s been l u b r i c a t e d w i t h l i q u i d s t e a r i c a c i d and such o b t a i n e d l a y e r was r e l a t i v e l y t h i c k /5
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1 0 p m / .The l o g a r thmic decrement o f f r e e v i b r a t i o n damping
6
h a s been d e t e r - mined /Q-' =6 / n
,
d u r i n gheat in^
t h e sample from 740-
150 R up t o 400 K w i t h t h e c o n s t a n t r a t e o f 1 K/min. Simultaneously t h e i b r a t i o n3
frequency p r o p o r t i o n a l t o t h e s h e a r modulus of t h e sample / f & G / h a s been recorded.I11
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RESULTS AI'ID DISCUSSIONPrimary measurements were performed w i t h c l e a n and p r e h e a t e d Cu samples t o o b t a i n t h e i n t e r n a l f r i c t i o n nbackgroundtl. Although t h e v a l u e of i n t e r n a l f r i c t i o n depends on h e a t i n g tempera u r e and time, i n t e s t e d temperature range t h e r e were no maxima o f
Q-I.
The samples on which t h e Langmuir-Blodgett l a y rs o f s t e a r i c a c i d were d e p o s i t e d showed t h e marked maxima i n t h e i r Q-?/T/ s p e c t r a . The r e s u l t s a r e p r e s e n t e d onC10-818 JOURNAL DE PHYSIQUE
P i g 1 , f o r 2, 4 and 8 L-B l a y e r s of s t e a r i c a c i d . The maximum o f i n t e r - n a l f r i c t i o n a p p e a r s a t a b o u t 210 K and can be e a s i l y observed even
f o r 2 L-B l a y e r s . For t h e sample w i t h 8 l a y e r s , t h e a d d i t i o n a l maximum a p p e a r s a t 180 K.
F i g 1. Q"/T/
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s p e c t r a f o r Cu sample covered with: ---*-. 2 ,---
4 r 8 L-
B l a y e r s o f s t e a r i c a c i d .S i m i l a r r e s u l t s /210 K maximum/ have been o b t a i n e d a l s o f o r t h e samples w i t h 6, 10 and 14 l a y e r s .
It can be presumed t h a t t h e r e i s a r e l a t i o n between t h e h e i g h t of t h e main i n t e r n a l f r i c t i o n maximum and number o f d e p o s i t e d l a y e r s . The maximum i n c r e a s e s w i t h t h e i n c r e a s i n q number o f . l a y e r s . I n each case
t h e maximum i s accom a n i e d by t h e i n c r e a s e of v i b r a t i o n frequency. The
4
t y p i c a l changes of f /!F/ dependence a r e p r e s e n t e d on F i g 2, f o r t h e samples w i t h 8 L-B l a y e r s ,It i s a l s o worth w h i l e n o t i c i n g t h a t t h e l a y e r s can i n f l u e n c e t h e i n t e r n a l f r i c t i o n spectrum even a f t e r h e a t i n g d u r i n g t h e f i r s t run up t o 370 K / F i g 2/. The second run shows b o t h maxima, though t h e i r h e i e h t d e c r e a s e s and t h e y a r e d i f f u s e d and s h i f t e d t o lower t e m p e r a t u r e s , comparing w i t h -che f i r s t run.
It must be emphasized t h a t p r e v i o u s measurements performed w i t h samples j u s t l u b r i c a t e d w i t h s a t u r a t e d hydrocarbons /I
/
i n d i c a t e d t h e i n t e r n a l f r i c t i o n maximum r i g h t a t t h e m e l t i n g temperature o f a given hydrocarbon. In t h e c a s e o f E B l a y e r s o f s t e a r i c a c i d no maximum h a s been observed a t 340 K, which i s t h e m e l t i n g p o i n t o f s t e a r i c a c i d / i n t h e b u l k / ,The a d d i t i o n a l measurement h a s been done w i t h t h e Cu sample l u b r i c a t e d w i t h m e l t e d s t e a r i c a c i d . During l u b r i c a t i n g t h e copper sample h a s been m a i n t a i n e d a t t h e t e m p e r a t u r e o f about 350 K and l a t e r
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slowly cooled down t o RT. The Q-I/T/ spectrum o f such prepared sample i s p r e s e n t e d i n F i g 3 . Two, weakly s e p a r a t e d maxima can be observed a t about 340 K.2
P i g 2. Q-'/T/ and f
/I/
s p e c t r a f o r Cu covered w i t h 8 L-B l a g e r s ;-
f i r s t run,-
-
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second run2
F i g 3. Q"/T/ and f /T/ s p e c t r a f o r Cu l u b r i c a t e d w i t h l i q u i d s t e a r i c a c i d .
I V
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CONCLUSIONSC10-820 JOURNAL DE PHYSIQUE
o f phase t r a n s i t i o n . I f t h e maximum observed f o r t h e samples with L-B
l a y e r s was a l s o regarded as connected w i t h t h e phase t r a n s i t i o n it
should t o be s u g g e s t e d t h a t i n t h i n L-B f i l m s o f s t e a r i c a c i d t h e phase t r a n s i t i o n o c c u r s i n much lower t e m p e r a t u r e s t h a n f o r t h i c k l a y e r s . Some l i t e r a t u r e d a t a /4,5/ confirm t h a t m e l t i n g p o i n t i n t h i n l a g e r s i s lower t h a n f o r t h i c k ones.
I t a l s o s h o u l d be p o i n t e d o u t t h a t t h e i n t e r n a l f r i c t i o n method a l l o w s t o p e r c e i v e t h e mechanical l o s s mechanism i n a sample w i t h even o n l y two L-B l a y e r s .
The second maximum observed f o r l u b r i c a t e d - s a m p l e i n h i g h e r tempera- t u r e may be p r o b a b l y connected w i t h t h e i n t e r a c t i o n s between l a y e r
molecules and s u b s t r a t
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i t s i n t e r p r e t a t i o n r e q u i r e s more f u r t h e r inves- t i g a t i o n s .REFERENCES
/I/ Chomka,W, and Denga, E.,J. de Phys., C9, 44, (1983) C9-505.
/ 2 / Augustyniak,B. and Fantozzi,G., J. de Phys., C9,
44,
(1983) C9-493. /3/ Chomka,W. and Denga,E., Proceedings o f t h e RENIOM-84, S i l e s i a n Uni-v e r s i t y , Katowice 1984, i n p r e s s .
/4/ Adamson,A.W., P h y s i c a l Chemistry o f S u r f a c e s , / P o l i s h ed.
