Chapter 16
Comparative Particle Size Analysis
Downloaded by FUDAN UNIV on November 22, 2016 | http://pubs.acs.org Publication Date: February 12, 1987 | doi: 10.1021/bk-1987-0332.ch016
M.E.Koehler and Theodore Provder The Glidden Company, DwightP.Joyce Research Center, Strongsville,OH44136 A series of monodisperse PMMA latexes was synthesized and characterized with respect to refractive index, percent solids, and solution density. The particle size of each latex was analyzed by Disc Centrifuge Photosedimentometry (DCP), Sedimentation Field Flow Fractionation (SFFF), Hydrodynamic Chromatography (HDC), Quasielastic Light Scattering (QELS), Transmission Electron Microscopy (TEM), and turbidity. A comparison of the apparent particle size averages of the latexes as measured by each method showed that for small, more monodisperse latexes the various methods agree more closely than for larger diameter samples having higher polydispersities. The relative ordering of the apparent sizes by method is consistent. The light scattering methods gave higher apparent particle sizes, TEM the lowest number, while DCP and SFFF were in relatively good agreement in the center of the range. This is explained in terms of the assumptions made and the physical parameters measured by each method.
A v a r i e t y o f d i f f e r e n t i n s t r u m e n t a l methods a r e a v a i l a b l e f o r t h e measurement o f t h e s i z e a n d s i z e d i s t r i b u t i o n o f p a r t i c u l a t e s . T h e s e i n s t r u m e n t s u t i l i z e d i f f e r e n t p h y s i c a l p h e n o m e n a a s a means of a s s e s s i n g t h e p a r t i c l e s i z e . S e d i m e n t a t i o n methods measure a 'hydrodynamic r a d i u s and r e q u i r e a knowledge o f the d e n s i t y o f the p a r t i c l e as w e l l as the d e n s i t y and v i s c o s i t y o f t h e s u s p e n d i n g f l u i d . Dynamic L i g h t s c a t t e r i n g methods measure t h e d i f f u s i o n c o e f f i c i e n t a n d t e n d t o w e i g h t t h e measurement t o l a r g e r p a r t i c l e s a n d a g g l o m e r a t e s . H y d r o d y n a m i c C h r o m a t o g r a p h y (HDC) i s a c h r o m a t o g r a p h i c method w h i c h s e p a r a t e s p a r t i c l e s o n t h e b a s i s o f t h e i r diameter by t h e i r d i f f e r e n t i a l r e t e n t i o n i n the f l o w streams through the i n t e r s t i t i a l channels o f a packed column. T r a n s m i s s i o n E l e c t r o n M i c r o s c o p y (TEM) a l l o w s t h e m e a s u r e m e n t o f t h e p a r t i c l e 1
0097-6156/87/0332-0231$06.00/0 © 1987 American Chemical Society
Provder; Particle Size Distribution ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
Downloaded by FUDAN UNIV on November 22, 2016 | http://pubs.acs.org Publication Date: February 12, 1987 | doi: 10.1021/bk-1987-0332.ch016
232
PARTICLE SIZE DISTRIBUTION
s i z e o f h a r d p a r t i c l e s . H o w e v e r , TEM i s s u s c e p t i b l e t o d i s t o r t i o n o f s o f t p a r t i c l e s , s h r i n k a g e o f p a r t i c l e s i n t h e e l e c t r o n beam, and c a n n o t r e a d i l y a s c e r t a i n i f a g g l o m e r a t i o n h a s o c c u r e d . T h e t u r b i d i t y method measures t h e a p p a r e n t a b s o r b a n c e o f a d i l u t e suspension o f p a r t i c l e s and t h e apparent diameter o f t h e scattering p a r t i c l e s i scalculated using c l a s s i c a l light scattering theory ( 1 ) . The p a r t i c l e s m o s t f r e q u e n t l y u s e d a s s i z e s t a n d a r d s a r e commercially obtained polystyrene latex microspheres. For s e d i m e n t a t i o n methods where knowledge o f t h e d e n s i t y d i f f e r e n c e between t h e p a r t i c l e and t h e suspending f l u i d (water) i s needed, t h e u s e o f p o l y s t y r e n e a s a s t a n d a r d m a t e r i a l c a n be a s e r i o u s problem due t o t h e s m a l l magnitude o f t h i s d e n s i t y d i f f e r e n c e . F o r Sedimentation F i e l d Flow F r a c t i o n a t i o n (SFFF), t h e apparent d i a m e t e r i s p r o p o r t i o n a l t o t h e cube r o o t o f t h e i n v e r s e o f t h e density d i f f e r e n c e ( 2 ) . F o r Disc Centrifuge Photosedimentometry (DCP) t h e a p p a r e n t d i a m e t e r i s p r o p o r t i o n a l t o t h e s q u a r e r o o t o f t h e i n v e r s e o f t h e d e n s i t y d i f f e r e n c e , Δρ (3)· T h i s i s i l l u s t r a t e d i n F i g u r e 1 w h i c h shows t h e r e l a t i v e e r r o r i n a p p a r e n t p a r t i c l e s i z e a s a f u n c t i o n o f t h e e r r o r i n t h e assumed d e n s i t y o f p o l y s t y r e n e l a t e x i n w a t e r f o r DCP a n d f o r S F F F . F o r e x a m p l e , f r o m F i g u r e 1 i t c a n b e s e e n t h a t a ^57 nm d i a m e t e r l a t e x p a r t i c l e w i t h a n o m i n a l d e n s i t y o f 1.057 g/cm h a v i n g a n e r r o r o f - 2 0 % i n (-0.01 g/cm ) w o u l d r e s u l t i n a n e r r o r o f + 1 2 . 4 % i n t h e DCP p a r t i c l e s i z e d i a m e t e r (+44 nm). The c o r r e s p o n d i n g e r r o r i n SFFF p a r t i c l e s i z e d i a m e t r i s +7.9% (+28 nm). I n o r d e r t o make a b e t t e r e v a l u a t i o n o f t h e r e l a t i v e a n d a b s o l u t e p e r f o r m a n c e o f v a r i o u s i n s t r u m e n t s , i t was n e c e s s a r y t o o b t a i n w e l l c h a r a c t e r i z e d , monodisperse latexes having a density greater than that o f polystyrene. Polymethylmethacrylate^(PMMA) l a t e x w i t h a p o l y m e r d e n s i t y o f a p p r o x i m a t e l y 1.21 gm/cm was selected f o r t h i s purpose. A s e r i e s o f m o n o d i s p e r s e PMMA l a t e x e s was s y n t h e s i z e d a n d characterized with respect t o r e f r a c t i v e index, percent s o l i d s , and s o l u t i o n d e n s i t y . T h e p a r t i c l e s i z e o f e a c h l a t e x was a n a l y z e d by s e v e r a l d i f f e r e n t i n s t r u m e n t a l m e t h o d s . T h e m e t h o d s u s e d i n c l u d e DCP, S F F F , HDC, Q u a s i e l a s t i c L i g h t S c a t t e r i n g ( Q E L S ) , TEM, and t u r b i d i t y . Experimental
Methods
Synthesis. A s e r i e s o f l a t e x e s was p r e p a r e d b y s e m i c o n t i n u o u s emulsion polymerization o f methyl methacrylate. A d i a l k y l ester o f sodium s u l f o s u c c i n i c a c i d s u r f a c t a n t y i e l d e d t h e narrow p a r t i c l e s i z e d i s t r i b u t i o n r e q u i r e d . A n ammonium persulfate/sodium m e t a b i s u l f a t e / f e r r o u s s u l f a t e i n i t i a t o r s y s t e m was u s e d . T h e i n i t i a t o r was f e d o v e r t h e p o l y m e r i z a t i o n t i m e , a l l o w i n g b e t t e r control of thepolymerization rate. For thesmaller size latexes ( 2 0 0 t o 4 5 0 n m ) , a s e e d l a t e x was p r e p a r e d i n s i t u b y p o l y m e r i z i n g 10% o f t h e monomer i n t h e p r e s e n c e o f t h e ammonium p e r s u l f a t e . P a r t i c l e s i z e was a d j u s t e d b y v a r y i n g t h e l e v e l o f s u r f a c t a n t d u r i n g t h e h e e l r e a c t i o n . As t h e exotherm o f t h i s r e a c t i o n s u b s i d e d , t h e monomer a n d t h e s o d i u m m e t a b i s u l f a t e / f e r r o u s s u l f a t e f e e d s were s t a r t e d a n d c o n t i n u e d o v e r a p p r o x i m a t e l y one h o u r . The
Provder; Particle Size Distribution ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
16.
KOEHLER AND PROVDER
Comparative Particle Size Analysis
Downloaded by FUDAN UNIV on November 22, 2016 | http://pubs.acs.org Publication Date: February 12, 1987 | doi: 10.1021/bk-1987-0332.ch016
maximum p a r t i c l e s i z e a c h i e v a b l e by t h i s m e t h o d was 440 nm. To a c h i e v e l a r g e r p a r t i c l e s i z e s a l a t e x o f s m a l l e r s i z e was u s e d a s t h e s e e d . Ammonium p e r s u l f a t e was t h e n a d d e d a t p o l y m e r i z a t i o n t e m p e r a t u r e , 80°C, a n d t h e a d d i t i o n a l l e v e l o f monomer r e q u i r e d t o a c h i e v e t h e d e s i r e d p a r t i c l e s i z e was f e d o v e r 1.5 h o u r s . Analysis. The p e r c e n t s o l i d s o f e a c h o f t h e l a t e x e s was m e a s u r e d u s i n g a D u P o n t M o d e l 950 T h e r m o g r a v i m e t r i c A n a l y z e r . S o l u t i o n d e n s i t i e s w e r e d e t e r m i n e d u s i n g a P a r r M e t t l e r M o d e l DMA-60 p r e c i s i o n d e n s i t o m e t e r . The p a r t i c l e d e n s i t y was c a l c u l a t e d f r o m t h e s o l u t i o n d e n s i t y and t h e p e r c e n t s o l i d s . The DCP u s e d was a v a r i a b l e s p e e d u n i t d e v e l o p e d i n o u r own l a b o r a t o r y ( 3 - 6 ) . ( A c o m m e r c i a l v e r s i o n o f t h i s i n s t r u m e n t i s mow a v a i l a b l e a s t h e B r o o k h a v e n DCP-1000 P a r t i c l e S i z e A n a l y z e r 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 . S F F F measurements were performed u s i n g a p r o t o t y p e i n s t r u m e n t provided by D u P o n t (_7). ( A c o m m e r c i a l v e r s i o n o f t h i s i n s t r u m e n t i s now a v a i l a b l e as t h e DuPont S F F F - 1 0 0 0 P a r t i c l e S i z e A n a l y z e r . ) HDC m e a s u r e m e n t s w e r e made b y M i c r o m e r i t i c s o n t h e i r M o d e l HDC-5600 F l o w s i z e r i n s t r u m e n t . QELS m e a s u r e m e n t s w e r e made o n a n instrument c o n s t r u c t e d by P r o f e s s o r A l e x J a m i e s o n a t C a s e W e s t e r n R e s e r v e U n i v e r s i t y ( 8 ) . TEM m e a s u r e m e n t s w e r e made b y t h e P i g m e n t s D i v i s i o n o f SCM C o r p o r a t i o n , A d r i a n J o y c e P l a n t , B a l t i m o r e , M a r y l a n d . T u r b i d i t y m e a s u r e m e n t s w e r e made u s i n g a B a u s c h a n d Lomb Model Spectronic-20 spectrometer. Results A c o m p a r i s o n o f t h e a p p a r e n t p a r t i c l e s i z e a v e r a g e s o f t h e PMMA l a t e x e s a s m e a s u r e d by e a c h m e t h o d i s s h o w n i n F i g u r e 2 ( n u m b e r a v e r a g e s , DN) and F i g u r e 3 ( w e i g h t a v e r a g e s , DW). T h e s e d a t a , along w i t h the p a r t i c l e d e n s i t y , the r e f r a c t i v e index, the percent s o l i d s , a n d t h e p o l y d i s p e r s i t y , (DN/DW), c a l c u l a t e d a s t h e r a t i o o f t h e w e i g h t a v e r a g e p a r t i c l e s i z e t o t h e number a v e r a g e p a r t i c l e s i z e , a l s o a r e s h o w n i n T a b l e 1. D i s c u s s i o n and
Conclusions
B a s e d o n t h e TEM d a t a , i t a p p e a r s t h a t t h e s m a l l l a t e x e s a r e more m o n o d i s p e r s e , a n d i t c a n be s e e n t h a t t h e v a r i o u s m e t h o d a g r e e more c l o s e l y f o r t h o s e s a m p l e s . I n a l l c a s e s h o w e v e r , t h e r e l a t i v e o r d e r i n g o f t h e a p p a r e n t s i z e s by method i s c o n s i s t e n t . T h a t i s , the l i g h t s c a t t e r i n g methods g i v e h i g h e r a p p a r e n t p a r t i c l e s i z e s , TEM g i v e s t h e l o w e r n u m b e r , a n d t h e DCP a n d S F F F a r e i n r e l a t i v e l y good agreement i n t h e c e n t e r o f the r a n g e . F i g u r e s 4 a n d 5 show p l o t s o f t h e a p p a r e n t number and w e i g h t a v e r a g e s d e t e r m i n e d by SFFF p l o t t e d a g a i n s t t h e c o r r e s p o n d i n g data f r o m DCP m e a s u r e m e n t s . F o r p e r f e c t a g r e e m e n t , t h e d a t a w o u l d l i e a l o n g a l i n e w i t h s l o p e o f one w i t h a n i n t e r c e p t o f z e r o . The d e v i a t i o n of these p l o t s from l i n e a r i t y at l a r g e r p a r t i c l e s i z e s i s p r o b a b l y due t o a s t e r i c e f f e c t w h i c h o c c u r s i n S F F F when t h e p a r t i c l e d i a m e t e r becomes a s i g n i f i c a n t f r a c t i o n o f t h e c h a n n e l t h i c k n e s s (2)· The p a r t i c l e s i z e l i m i t a b o v e w h i c h t h e S F F F c h a n n e l used i n t h i s work i s e x p e c t e d t o e x h i b i t t h i s e f f e c t i s
Provder; Particle Size Distribution ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
233
Downloaded by FUDAN UNIV on November 22, 2016 | http://pubs.acs.org Publication Date: February 12, 1987 | doi: 10.1021/bk-1987-0332.ch016
234
PARTICLE SIZE DISTRIBUTION
F i g u r e 1. R e l a t i v e E r r o r i n P a r t i c l e D i a m e t e r v s . R e l a t i v e E r r o r i n D e n s i t y Difference^ - P o l y s t y r e n e L a t e x i n Water: d 3 5 7 nm, ρ - 1.057 g/cm . s
Ο ο
• Ο Δ -+ x ο
HDC DN Τ URΒ I D I Τ Υ QELS S F F F DN DCP DN TEM DN
8
• 0
• Ο Δ -+ x Φ
Μ DC DW TURB I D I Τ Y QELS S F F F DW DCP DW TEM DW
• ο
Δ
ε^
•
UJ ο ω ίο
< Ξ
g
ο ο 00
ο ο
•
Δ X +
é ¥
Ο
Δ
Χ +
ce UJ Η UJ
< Ξ
" s l * w I
Χ
ε m
I
I
ο ο 00
ο
1
SAMPLE
+
ê
ο
ο
X
ο
68B 68A 73B 93A 8A 8C
° •
$
Δ Φ
ο
s* m
x ο '
'
i
l
68B 68A73B 93A 8A 8C
NUMBER
SAMPLE
NUMBER
Figure 2 ( l e f t ) . A p p a r e n t Number A v e r a g e , T u r b i d i t y , P a r t i c l e S i z e s o f PMMA L a t e x e s .
Figure 3 (right). Apparent Weight P a r t i c l e S i z e s o f PMMA L a t e x e s
Average,
Turbidity,
QELS
QELS
0
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.
39 73 72 39 88 3 1.02 1.02 2
4 4 8 4 6 9 1.05
5 7 4 6 1 1 1.06
9 3A 73B
8A
8C
DCP DW DW/DN
6 5 8 6 8 6 1.04
5 5 0 5 6 6 1.03
44 14 83 45 31 2 1.02 1.03 3
2 3 3 2 4 7 1.06
1 8 2 1 9 2 1.05
DN
Average R e f r a c t i v e
Index
β
1.48
D e n t i t y - 1.215
2 3 9 2 4 1 1.01
68A
Average P a r t i c l e
160 162 1.01
TEM DW DW/DN
68B
SAMPLE ID DN
1
SFFF DW DW/DN
6 0 0 6 0 5 1.01
5 2 1 5 2 9 1.02
44 16 03 45 20 1 1.01 1.03 3
2 6 1 2 6 7 1.02
2 0 5 2 2 2 1.08
DN
HDC DW DW/DN
8 9 3 9 0 1 1.01
6 6 4 6 6 8 1.01
52 42 04 52 43 2 1.00 1.00 4
3 2 2 3 4 2 1.06
2 5 5 2 5 7 1.01
DN
DIAMETERS I N NANOMETERS
1.211 1.211 1.218 1.217
22 26 .. 52 90 26.26
4 61 4 683 8 4 578 746 746
4 55 4 597 9 3 667 817 817
Ut
Κ)
».
Î
jIy
1.218 22.59
413
357
1.221 1.221
I
1.213 1.213 23.05
3 30055
2 27755
9.88 9.88
§
1.221
24.56
223
S |
237
SOLUTION DENSITY(g/cc)
QELS
% SOLIDS
Ο
> Ζ
3
g r
TURBIDITY
P A R T I C L E S I Z E AVERAGES FOR PMMA L A T E X E S
TABLE
Downloaded by FUDAN UNIV on November 22, 2016 | http://pubs.acs.org Publication Date: February 12, 1987 | doi: 10.1021/bk-1987-0332.ch016
Downloaded by FUDAN UNIV on November 22, 2016 | http://pubs.acs.org Publication Date: February 12, 1987 | doi: 10.1021/bk-1987-0332.ch016
PARTICLE SIZE DISTRIBUTION
200
400
800
600
DIAMETER (nm) DCP F i g u r e 4. A p p a r e n t Number A v e r a g e P a r t i c l e L a t e x e s - S F F F v s . DCP.
S i z e s o f PMMA
•
fc£8 "*
β