Comparative Particle Size Analysis - ACS Symposium Series (ACS

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.


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


16.

KOEHLER AND PROVDER

Comparative Particle Size Analysis


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


233


234


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

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Μ DC DW TURB I D I Τ Y QELS S F F F DW DCP DW TEM DW

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68B 68A 73B 93A 8A 8C

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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



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




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

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Comparative Particle Size Analysis - ACS Symposium Series (ACS

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