Chapter 12
An Improved Disc Centrifuge Photosedimentometer and Data System for Particle Size Distribution Analysis Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on March 11, 2018 | https://pubs.acs.org Publication Date: February 12, 1987 | doi: 10.1021/bk-1987-0332.ch012
M. E. Koehler,R.A.Zander,T.Gill, Theodore Provder, andT.F.Niemann The Glidden Company, DwightP.Joyce Research Center, Strongsville,OH44136
An improved disc centrifuge photosedimentometer (DCP) was developed for use in the determination of the particle size and size distribution of latices, pigments and other particulates. Separation is based on Stokes Law for the sedimentation of particles in a centrifugal force field and does not rely on the use of particle size calibrants or standards. The DCP instrument provides accurate stable particle size analyses over a wide range of conditions while at the same time is rugged enough for heavy use in both a research and quality control environment. A stand-alone data collection, analysis and management system was developed both for routine quality control operation and for research use of the instrument.
The d i s c c e n t r i f u g e p h o t o s e d i m e n t o m e t e r ( D C P ) i s a n i n s t r u m e n t used t o determine t h e p a r t i c l e s i z e and s i z e d i s t r i b u t i o n o f l a t i c e s , pigments and o t h e r p a r t i c u l a t e s . S e p a r a t i o n i s based on S t o k e s Law f o r t h e s e d i m e n t a t i o n o f p a r t i c l e s i n a c e n t r i f u g a l f o r c e f i e l d . P a r t i c l e s a r e assumed t o be s p h e r i c a l . I n t h e most common mode o f o p e r a t i o n t h e s e p a r a t i o n t a k e s p l a c e i n a c y l i n d r i c a l c a v i t y o f known d i m e n s i o n s a n d c o n t a i n i n g a known volume o f f l u i d . A d i l u t e s u s p e n s i o n o f t h e p a r t i c l e s o f i n t e r e s t i s i n j e c t e d onto t h e surface o f the f l u i d while t h e d i s c i s s p i n n i n g and t h e p a r t i c l e s sediment i n t h e c e n t r i f u g a l f o r c e f i e l d r a d i a l l y outward p a s t a d e t e c t o r system. The appearance t i m e o f the p a r t i c l e a t t h e d e t e c t o r , t , i n minutes i s g i v e n by
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0097-6156/87/0332-0180$06.00/0 © 1987 American Chemical Society
Provder; Particle Size Distribution ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
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Improved Disc Centrifuge Photosedimentometer
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w h e r e D i s t h e d i a m e t e r o f t h e p a r t i c l e i n m i c r o m e t e r s , R. i s t h e radius at the surface of the f l u i d i n centimeters, R i sthe r a d i u s a t t h e d e t e c t o r i n c e n t i m e t e r s , Ω i s t h e r o t a t i o n a l speed of the d i s c i n r e v o l u t i o n s per minute, η i s the v i s c o s i t y of the f l u i d i n p o i s e , Δρ i s t^he d e n s i t y d i f f e r e n c e b e t w e e n t h e p a r t i c l e s a n d t h e f l u i d i n gm^cm a n d k, a c o l l e c t i o n o f c o n s t a n t t e r m s , i s e q u a l t o 6.299 χ 10 . I t c a n b e s e e n t h e n t h a t t h e m e t h o d r e l i e s o n l y on measureable p h y s i c a l parameters and t h e use o f p a r t i c l e s i z e c a l i b r a n t s or standards i s not required. The g o a l o f t h i s w o r k was t o d e v e l o p a DCP i n s t r u m e n t w h i c h would provide accurate s t a b l e p a r t i c l e s i z e analyses over a wide r a n g e o f c o n d i t i o n s w h i l e a t t h e same t i m e b e i n g r u g g e d e n o u g h f o r heavy use i n both a r e s e a r c h and q u a l i t y c o n t r o l environment. I n a d d i t i o n a r e l a t i v e l y inexpensive stand-alone system f o r data c o l l e c t i o n , a n a l y s i s a n d management was n e e d e d f o r b o t h r o u t i n e q u a l i t y c o n t r o l o p e r a t i o n and f o r r e s e a r c h use o f t h e instrument. This paper d i s c u s s e s t h e t e c h n i c a l d e t a i l s o f t h e instrument and d a t a s y s t e m . Instrument performance, methodology and comparative p a r t i c l e s i z e analyses are discussed elsewhere i n t h i s v o l u m e (1_,2).
Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on March 11, 2018 | https://pubs.acs.org Publication Date: February 12, 1987 | doi: 10.1021/bk-1987-0332.ch012
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Experimental Instrument. The i n s t r u m e n t ( 3 ) i s shown s c h e m a t i c a l l y i n F i g u r e 1. ( A c o m m e r c i a l v e r s i o n o f t h e i n s t r u m e n t d e s c r i b e d i n t h i s p a p e r i s now a v a i l a b l e f r o m B r o o k h a v e n I n s t r u m e n t s C o r p o r a t i o n , R o n k o n k o m a , New Y o r k a s t h e B r o o k h a v e n D C P - 1 0 0 0 P a r t i c l e S i z e A n a l y z e r . ) I t i s based on t h e use o f a v a r i a b l e r a t i o t r a c t i o n d r i v e t r a n s m i s s i o n ( K o p p M o d e l R1.0HS, A n d a n t e x USA I n c . , 1 8 0 0 - T B r i e l l e A v e . , Wanamassa, Ocean T o w n s h i p , N J 07712) c o u p l e d w i t h a one-half-horsepower ac-motor o p e r a t i n g a t e s s e n t i a l l y constant s p e e d . The r o t a t i o n a l s p e e d o f t h e d i s c i s s e l e c t e d m a n u a l l y b y means o f a d i a l a n d i s c o n t i n u o u s l y v a r i a b l e o v e r a r a n g e f r o m a p p r o x i m a t e l y 1,200 t o 1 2 , 0 0 0 r p m . T h e r o t a t i o n a l s p e e d i s c o n t i n u o u s l y m o n i t o r e d b y means o f a d i g i t a l t a c h o m e t e r l o c a t e d o n t h e c o n t r o l m o d u l e . The d i s c c a v i t y i s m a c h i n e d f r o m a s u i t a b l e p l a s t i c m a t e r i a l , t y p i c a l l y polymethylmethacrylate, and i s mounted on a m e t a l h u b . T h e d i s c c a v i t y i s d y n a m i c a l l y b a l a n c e d o v e r t h e o p e r a t i n g speed range t o i n s u r e v i b r a t i o n f r e e o p e r a t i o n . A Vortec c o o l e r ( V o r t e c C o r p o r a t i o n , 1 0 1 2 5 C a r v e r R d . , C i n c i n n a t i , OH 45242) p r o v i d e s c h i l l e d a i r w h i c h c o o l s t h e t r a n s m i s s i o n as i t passes t h r o u g h a heat exchanger i n t h e t r a n s m i s s i o n f l u i d and i s then blown i n t o t h e d e t e c t o r block assembly. This c o o l i n g prevents heat generated i n t h e t r a n s m i s s i o n and by t h e s p i n n i n g d i s c c a v i t y from warming t h e s p i n f l u i d d u r i n g t h e course o f a l o n g a n a l y s i s run. D e t e c t i o n o f t h e p a r t i c l e s i s a c c o m p l i s h e d b y means o f t h e i r a t t e n u a t i o n o f a l i g h t beam p r o v i d e d b y a h a l o g e n l a m p a n d c o l l i m a t e d by two s l i t a s s e m b l i e s . A s i l i c o n p h o t o d i o d e and a n o p e r a t i o n a l a m p l i f i e r c i r c u i t a r e used t o monitor the l i g h t i n t e n s i t y . A d j u s t a b l e g a i n and o f f s e t potentiometers a r e l o c a t e d o n t h e c o n t r o l m o d u l e . The s i g n a l c a n be d i s p l a y e d o n a s t r i p c h a r t r e c o r d e r a n d i s m o n i t o r e d b y means o f a d i g i t a l p a n e l m e t e r .
Provder; Particle Size Distribution ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
Provder; Particle Size Distribution ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on March 11, 2018 | https://pubs.acs.org Publication Date: February 12, 1987 | doi: 10.1021/bk-1987-0332.ch012
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The a n a l y s i s m e t h o d e m p l o y e d i s t h e p a t e n t e d e x t e r n a l g r a d i e n t m e t h o d d e s c r i b e d i n d e t a i l e l s e w h e r e (_1,4) · The o v e r a l l i n s t r u m e n t p e r f o r m a n c e was e v a l u a t e d u s i n g m o n o d i s p e r s e p o l y s t y r e n e l a t e x s t a n d a r d s , c o v e r i n g a r a n g e f r o m 0.176 μπι t o 1.09 μπι, o b t a i n e d f r o m Dow D i a g n o s t i c s , I n d i a n a p o l i s , I n d i a n a . Calibration. The i n s t r u m e n t i s c a l i b r a t e d b y u s i n g a c a t h e t o m e t e r t o measure t h e d i a m e t e r o f t h e f l u i d s u r f a c e w i t h 5 ml and w i t h 15 m l o f w a t e r i n t h e s p i n n i n g d i s c c a v i t y . C a l i b r a t i o n was d o n e w i t h t h e d i s c c a v i t y r o t a t i n g a t 5 0 0 0 rpm. V a r i a t i o n s i n t h e d i a m e t e r o f t h e f l u i d s u r f a c e as a f u n c t i o n o f r o t a t i o n a l speed w e r e f o u n d t o be n e g l i g i b l e . The d e t e c t o r b l o c k was a l i g n e d t o t h e 5 m l - p o s i t i o n o f t h e d i s c c a v i t y by p l a c i n g 5 m l o f w a t e r i n t h e c a v i t y , a n d a d j u s t i n g t h e d e t e c t o r b l o c k p o s i t i o n u n t i l a maximum a t t e n u a t i o n o f t h e l i g h t beam was o b s e r v e d i n d i c a t i n g s c a t t e r i n g b y t h e m e n i s c u s . F o r a s p i n f l u i d v o l u m e o f 15 m l w i t h t h e d e t e c t o r a t t h e 5 m l - p o s i t i o n , t h e measured d i a m e t e r s a t 5 ml and 15 m l y i e l d a n d R^ o f e q u a t i o n ( 1 ) d i r e c t l y . A t a n o t h e r s p i n f l u i d v o l u m e , V, t h e s e m e a s u r e d r a d i i , a t 5 a n d 15 m l , ^ ^ ^ 15 1 * g i l l y c a l c u l a t e t h e r a d i u s , R^, o f t h e f l u i d surface using equation (2). a n
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Literature Cited 1. Holsworth, R. M.; Provder, T . ; Stansbrey, J. J. "A Novel External Gradient Formation Method for Disc Centrifuge Photosedimentometry Particle Size Distribution Analysis" This Volume. 2. Koehler, M. E.; Provder, T. "Comparative Particle Size Analysis" This Volume. 3. Koehler, M. E.; Provder, T.; Zander, R. A. U. S. Patent 4 311 039, 1982. 4. Holsworth, R. M.; Provder, T. U. S. Patent 4 478 073, 1985. RECEIVED October 6, 1986
Provder; Particle Size Distribution ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
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