Molecular Optical Laser Examiner (MOLE) - American Chemical Society

20 Molecular Optical Laser Examiner (MOLE)

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Application to Problems Encountered by Electron Microscopists in the Analysis of Polymers MARK E . ANDERSEN Walter C. McCrone Associates, Inc., Chicago, IL 60616

Individual polymer fibers, layers in laminates, inclusions, and contaminants have been studied with the Raman microprobe, MOLE. The layers of a 14-μm thick five -layer laminated film were identified and molecular maps were obtained. The central polyester layer was deter mined to be of low crystallinity. Polarized Raman spectra were recorded from a 16-μm nylon 6/6fiber. The calcium stearate reaction product of a pharmaceutical solution with a rubber stopper coating was identified using the energy dispersive x-ray analysis system of a scanning electron microscope (SEM) and the Raman spectrum. A 40-μm inclusion of polystyrene in a high-impact polysty rene copolymer was identified. The cause of a plating defect in a circuit board connector was traced to polysty rene packing material.

JL

H E M O L E C U L A R O P T I C A L L A S E R E X A M I N E R (MOLE) is a R a m a n

micro-

p r o b e that w a s d e v e l o p e d i n F r a n c e (J, 2) a n d is n o w available c o m mercially. Contemporaneous w i t h this development, a similar instru m e n t w a s d e s i g n e d a n d b u i l t at t h e U . S . N a t i o n a l B u r e a u o f S t a n d a r d s (3). B o t h o f t h e i n s t r u m e n t s y i e l d m o l e c u l a r i n f o r m a t i o n , n o n d e s t r u c tively, from both organic a n d inorganic samples or regions of samples as s m a l l as 1 μ π ι i n d i a m e t e r . T h e M O L E i s d e s i g n e d a r o u n d a r e s e a r c h q u a l i t y o p t i c a l m i c r o s c o p e a l l o w i n g t h e a n a l y s t to u t i l i z e m i c r o s c o p i c a l techniques to orient a n d characterize the particular sample b e i n g a n a l y z e d (4). T h e M O L E h a s t h e a d d i t i o n a l c a p a b i l i t y t o f o r m i m a g e s of a sample a n d define t h e locations o f various molecular species. B o t h the h i g h spatial resolution a n d the m o l e c u l a r m a p p i n g capability (analogous to x-ray e l e m e n t a l maps) are o f interest to e l e c t r o n m i c r o s copists. M a c r o - R a m a n spectroscopy has p r o v e d to b e a u s e f u l t e c h n i q u e 0065-2393/83/0203-0383$06.00/0 © 1983 A m e r i c a n C h e m i c a l Society

Craver; Polymer Characterization Advances in Chemistry; American Chemical Society: Washington, DC, 1983.

384

POLYMER CHARACTERIZATION

i n r e l a t i n g t h e p h y s i c a l p r o p e r t i e s o f p o l y m e r s to t h e i r m o l e c u l a r s t r u c t u r e s (5—12). T h e m e c h a n i c a l p r o p e r t i e s o f p o l y m e r s , o f t e n s t u d i e d b y e l e c t r o n m i c r o s c o p y , a r e a l s o r e l a t e d to t h e i r m o l e c u l a r properties. W i t h the R a m a n m i c r o p r o b e , m u c h s m a l l e r s a m p l e sizes can n o w be studied, a n d the interaction of electron microscopy w i t h R a m a n spectroscopy c a n o n l y b e e x p e c t e d to g r o w . Industrial production of p o l y m e r products usually involves m i x i n g solvents, fillers, pigments, antioxidants, a n d other compounds w i t h the polymer. P r o d u c t failures m a y arise from inadequate m i x i n g or dissolution of these additives, i m p r o p e r temperature control d u r i n g p r o d u c t f o r m a t i o n , or i n t r o d u c t i o n or i m p r o p e r r e m o v a l of c o n taminants a n d by-products. T r a c k i n g d o w n the source of a failure is o f t e n a d i f f i c u l t a n a l y t i c a l p r o b l e m , f r e q u e n t l y r e q u i r i n g t h e a p p l i c a t i o n of a variety of analytical tools i n c l u d i n g R a m a n m i c r o p r o b e and electron microscopy. T h e p u r p o s e o f t h i s c h a p t e r is to s h o w t h e u n i q u e c a p a b i l i t i e s o f t h e M O L E as a p p l i e d t o p o l y m e r a n a l y s i s , e s p e c i a l l y i n c o n j u n c tion with electron microscopy.

Experimental T h e 514.5-nm l i n e of a Spectra Physics M o d e l 164 argon i o n laser served as the i l l u m i n a t i o n source. P l a s m a l i n e s were r e m o v e d w i t h a 10-Â H B W interference filter. A m i c a halfwave plate was incorporated i n the l i g h t path to control the polarization orientation of the laser i l l u m i n a t i o n source. B o t h 50 x (0.85 N.A.) and 100 x (0.90 Ν .A.) L e i t z objectives have b e e n u s e d to focus the laser b e a m a n d to collect the scattered radiation. A scheme of a portion of the l i g h t path is s h o w n i n F i g u r e 1. A n axis is designated to define the p o l a r i z a t i o n directions. A field diaphragm or p i n hole i n a sample image plane serves as a spatial filter, w h i l e an aperture diaphragm i n an image o f the back focal plane of the objective can be u s e d to l i m i t the s o l i d c o l l e c t i o n angle, or n u m e r i c a l aperture of the objective. F o r polarization studies an analyzer a n d polarization scrambler are inserted i n the l i g h t path. T h e light passing through the monochromator is detected w i t h a T y p e R 374 H a m a m a t s u p h o t o m u l t i p l i e r c o o l e d to - 3 0 °C w i t h a Products for Research thermoelectric h o u s i n g ( M o d e l T E - 1 7 5 R F ) . Measurements were made w i t h a M o d e l 1140A q u a n t u m photometer from P r i n c e t o n A p p l i e d Research. N o n c o n d u c t i v e s a m p l e s for e l e c t r o n m i c r o s c o p y w e r e m o u n t e d o n a l u m i n u m stubs w i t h d o u b l e - s i d e d tape. T h e s e samples were s h a d o w e d w i t h carbon a n d gold. T h e m e t a l l i c sample was adhered to a stub u s i n g silver paint. M i c r o g r a p h s were recorded w i t h a C a m b r i d g e M a r k I I A scanning electron microscope ( S E M ) .

Laminated

Polymer Study

A p o l y m e r i c film was cross-sectioned w i t h a razor blade a n d e x a m i n e d b y S E M ( F i g u r e 2). T h e 14-μ,πι t h i c k f i l m w a s c o m p o s e d of five l a m i n a t e d layers. T h e other h a l f of the cross-section was ex-


οι path. in the light incorporated showing optical components microscope of MOLE Figure 1. Schematic Craver; Polymer Characterization Advances in Chemistry; American Chemical Society: Washington, DC, 1983.

386


Figure 2. SEM micrograph

of 14-μχη thick, five-layer

polymer

laminate.

a m i n e d b y M O L E . A p i n h o l e l i m i t e d the spectral collection area of t h e s a m p l e t o a p p r o x i m a t e l y a 5-μιτι d i a m e t e r . T h e m o s t i n t e n s e l y i l l u m i n a t e d region of the sample (approximately l-/xm diameter) gives r i s e to t h e m a j o r i t y o f t h e c o l l e c t e d R a m a n s c a t t e r r a d i a t i o n . T h e o u t e r l a y e r s w e r e a b o u t 3 μ,πι t h i c k a n d w e r e i d e n t i c a l i n c o m p o s i t i o n ( F i g u r e 3). T h i s m a t e r i a l w a s i d e n t i f i e d as p r e d o m i n a n t l y p o l y p r o p y l e n e . T h e c e n t r a l l a y e r w a s less t h a n 2 μιη t h i c k a n d w a s i d e n t i f i e d as a p o l y e s t e r s i m i l a r t o p o l y e t h y l e n e t e r e p h t h a l a t e ( F i g u r e 4). T h e l a s t t w o l a y e r s w e r e i d e n t i c a l a n d w e r e i d e n t i f i e d as p o l y e t h y l e n e o r a s i m i l a r m a t e r i a l ( F i g u r e 5). S o m e s p e c t r a l l e a k a g e f r o m t h e s u r r o u n d i n g layers occurred a n d a n unambiguous result c o u l d not be obtained. A m o l e c u l a r m a p of the sample was p r o d u c e d w i t h the radiation


Craver; Polymer Characterization Advances in Chemistry; American Chemical Society: Washington, DC, 1983. -1

-1

1

Figure 3. Raman spectra of isotactic polypropylene (top) and the outer layers of a five-layer polymer laminate (bottom). Conditions for polypropylene: laser, 514.5 nm, 5 mW at sample; beam diameter, 1 μm; spectral slitwidth, 4 cm ; time constant, 1 s; scan rate, 42 cm' Imin; full scale, 3000 counts; and Leitz 100 x (0.90 N.A.) objective. Conditions for polymer laminate: laser, 514.5 nm, 10 mW at sample; beam diameter, 1 μχη; spectral slitwidth, 5 cm ; time constant, 1 s; scan rate, 42 cm^lmin; full scale, 1000 counts, and Leitz 100 x (0.90 Ν A.) objective.

§g

M

g

Ο

20.

ANDERSEN

Figure

Molecular

Optical

10. Photomicrograph

Laser

395

Examiner

of a 40-μm polystyrene.

inclusion

in

high-impact

other m i n e r a l s . T h e stoppers are f o r m e d i n m o l d s often c o a t e d w i t h a w a x y m a t e r i a l t h a t s e r v e s as a m o l d r e l e a s e a g e n t . O n e c o m m o n e x a m p l e o f s u c h a c o n t a m i n a t i o n p r o b l e m is s h o w n i n F i g u r e 12, w h i c h is a m i c r o g r a p h o f a s t o p p e r surface c o v e r e d w i t h crystals that have a p p a r e n t l y g r o w n f r o m s o l u t i o n . E n e r g y d i s p e r sive x-ray analysis of these crystals a n d of particles s u s p e n d e d i n the solution i n d i c a t e d that the crystals contained a small amount of cal c i u m but were mostly organic. M O L E analysis of these particles i d e n t i f i e d t h e m as c a l c i u m s t é a r a t e ( F i g u r e 13). T h e c r y s t a l s p r o b a b l y formed b y a reaction b e t w e e n c a l c i u m ions i n the solution a n d r e s i d u a l stearic a c i d m o l d release agent o n the stopper surface. A t o o t h from a d e f e c t i v e c i r c u i t b o a r d c o n n e c t o r i s s h o w n i n F i g u r e 14 w h e r e g o l d p l a t i n g h a s i n c o m p l e t e l y c o v e r e d t h e t o o t h ( F i g u r e 15). T h i s d e f e c t r e g i o n h a d a t h i n t r a n s p a r e n t l a y e r o f m a t e r i a l a d h e r i n g to i t , i d e n t i f i e d b y M O L E as p o l y s t y r e n e . T h e c o n n e c t o r s , w h i c h h a d b e e n s h i p p e d i n b o x e s w i t h p o l y s t y r e n e " n o o d l e s " u s e d as a p a c k i n g material, were degreased before gold plating. Apparently residual particles of polystyrene r e m a i n e d on the connectors d u r i n g the degreasing operation a n d partially dissolved forming a thin layer o n the m e t a l surface w h i c h h i n d e r e d the g o l d plating.


396

POLYMER

CHARACTERIZATION

CO

e

1700

1600

1700

1600

Wave Number Figure 11. Raman spectrum of high-impact polystyrene (A) and in clusion in high-impact polystyrene (B). Conditions: laser, 514.5 nm, 10 mW at sample; beam diameter, 1 μm; spectral slit width, 4 cm' ; time constant, 3 s; scan rate, 17 cm' /min; full scale, 3000 counts; and Leitz 100 x (0.90 N.A.) objective. 1

1


20.

ANDERSEN

Figure

Molecular

Optical

Laser

397

Examiner

12. SEM micrograph of crystals (2-20 of rubber stopper.

μπι in size) on

surface

Conclusion W i t h its h i g h spatial r e s o l u t i o n a n d m o l e c u l a r m a p p i n g c a p a b i l i t i e s , M O L E is a u n i q u e t o o l for a n a l y z i n g p o l y m e r s a n d p r o b l e m s created i n their p r o d u c t i o n a n d use. A s w i t h a l l analytical tools, it c a n b e s t b e u t i l i z e d i n c o n j u n c t i o n w i t h o t h e r i n s t r u m e n t s s u c h as the electron microscope.

Acknowledgments T h e a u t h o r t h a n k s P a u l D h a m e l i n c o u r t for h i s assistance i n d e signing the polarization experiments; and F r a n Adar, L e r o y P i k e , W a l t e r K r a m e r , a n d R o b e r t M u g g l i for p r o v i d i n g h e l p f u l d i s c u s s i o n s . S p e c i a l t h a n k s a r e e x t e n d e d to F r a n E i n b i n d e r a n d J i m G e r a k a r i s for t h e i r p a t i e n c e a n d h e l p i n p r e p a r i n g this m a n u s c r i p t .


398


WAVE NUMBERS

Figure 13. Raman spectra of calcium stéarate (top) and a crystal removed from the stopper (bottom). Conditions for calcium stéarate: laser, 514.5 nm, 20 mW at sample; beam diameter, 1 pm; spectral slitwidth, 3 cm' ; time constant, 1 s; scan rate, 42 cm' /min; full scale, 1000 counts; and Leitz 100 x (0.90 N.A.) objective. Conditions for crystal from stopper: laser, 514.5 nm, 10 mW at sample; beam diameter, 1 pm; spectral slitwidth, 5 cm' ; time constant, 1 s; scan rate, 42 cm'^min; full scale, 1000 counts; and Leitz 100 x (0.90 N.A.) objective. 1

1

1


ANDERSEN

Molecular

Optical

Laser

399

Examiner

ν»

ο ο

•te

A ^ ^ Ο Ο

s s ο


Ο -te Ο $

400

Figure


15. Elemental

map showing gold plating nector tooth.

distribution

on con-

Literature Cited 1. Delhaye, M.; Dhamelincourt, P. J. Raman Spectrosc., 1975, 3, 33. 2. Dhamelincourt, P., Ph.D. Thesis, Lille Univ., Lille, France, 1979. 3. Rosasco, G. J.; Etz, E . S.; Cassatt, W. A. Appl. Spectrosc., 1975, 29, 396. 4. Andersen, M. E.; Muggli, R. Z. Anal. Chem., 1981, 53, 1771. 5. Tadokoro, H. "Structure of Crystalline Polymers"; Wiley: New York, 1979. 6. Melveger, A. J. J. Polym. Sci., 1972,10,317. 7. Sloane, H. J.; Bramston-Cook, R. Appl. Spectrosc., 1973, 27, 217. 8. Ogilvie, G. D.; Addyman, L. Actual. Chim. 1980, 1980, 51. 9. Bailey, R. T.; Hyde, A. J.; Kim, J. J.; McLeish, J. Spectrochim. Acta, 1977, 33A, 1053. 10. Jasse, B.; Koenig, J.L.J.Polym. Sci., 1980, 18, 731. 11. Kobayashi, M.; Tadokoro, H. J. Chem. Phys., 1980, 73, 3635. 12. Koenig, J. L.; Boerio, F. J. J. Chem. Phys., 1970, 52, 4170. 13. Kiefer, W.; Topp, J. A. Appl. Spectrosc., 1974, 28, 26. 14. Porto, S. P. S. J. Opt. Soc. Am., 1966, 56, 1585. 15. Damen, T. C.; Porto, S. P. S.; Tell, B. Phys. Rev., 1966, 142, 570. 16. Rosasco, G. J. In "Advances in Infrared and Raman Spectroscopy"; Clark, R. J. H.; Hester, R. E., Eds.; Heyden: London, 1980, Chap. 4. RECEIVED for review October 14, 1981. ACCEPTED January 18, 1982.


Molecular Optical Laser Examiner (MOLE) - American Chemical Society

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