succinimide Dispersants onto Calcium Alkylarylsulfonate Colloids

Chapter 26

Irreversible Adsorption of Poly(isobutenyl)succinimide Dispersants onto Calcium Alkylarylsulfonate Colloids

Downloaded by NORTH CAROLINA STATE UNIV on August 9, 2012 | http://pubs.acs.org Publication Date: September 8, 1992 | doi: 10.1021/bk-1992-0501.ch026

B. L. Papke Texaco Research Center, P.O. Box 509, Beacon, NY 12508

The r e v e r s i b i l i t y of poly(isobutenyl)succinimide dispersant adsorption onto alkaline calcium alkylarylsulfonate c o l l o i d a l dispersions was measured using ultracentrifugation and Fourier transform infrared techniques. Adsorption techniques were used to obtain quantitative information on factors affecting the interaction r a t i o and strength; dispersant adsorption was shown to occur through interaction of the polar succinimide/amine headgroup with the sulfonate colloid. Poly(isobutenyl)succinimide/calcium sulfonate molar interaction ratios as high as 0.25 were observed. Adsorption of poly(isobutenyl)succinimide dispersants onto calcium sulfonate colloids i s shown to be irreversible in at least some cases. Evidence for the formation of a new mixed surfactant c o l l o i d was obtained by l i g h t scattering p a r t i c l e size measurements. A l k a l i n e earth a l k y l a r y l s u l f o n a t e s , the s a l t s of high m o l e c u l a r weight (ca. 450), o i l - s o l u b l e s u l f o n i c a c i d s , a r e known t o f o r m i n v e r t e d m i c e l l a r s t r u c t u r e s i n h y d r o c a r b o n media (1). These s u r f a c t a n t s c a n be u s e d t o p r e p a r e non-aqueous c o l l o i d a l d i s p e r s i o n s o f an i n o r g a n i c base (such as a carbonate o r h y d r o x i d e ) . The i n o r g a n i c b a s e ( t y p i c a l l y amorphous c a l c i u m c a r b o n a t e ) i s p r e s e n t as s m a l l submicron p a r t i c u l a t e s s o l u b i l i z e d i n h y d r o c a r b o n s o l v e n t s by an a d s o r b e d l a y e r o f t h e sulfonate surfactant. These a l k a l i n e c o l l o i d a l d i s p e r s i o n s form the b a s i s f o r a w i d e l y used c l a s s o f g a s o l i n e and d i e s e l e n g i n e l u b r i c a n t a d d i t i v e s (2), p r o v i d i n g an i n e x p e n s i v e s o u r c e o f o i l - s o l u b l e b a s e t o a i d i n the n e u t r a l i z a t i o n of c o r r o s i v e acids generated

0097-6156/92/0501-0377$06.00/0 © 1992 American Chemical Society

In Mixed Surfactant Systems; Holland, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1992.

MIXED SURFACTANT SYSTEMS


378

during engine o p e r a t i o n . The m a n u f a c t u r i n g p r o c e s s e s used t o p r e p a r e t h e s e c o l l o i d a l d i s p e r s i o n s have been d e s c r i b e d by Marsh ( 3 ) ; p a r t i c l e s i z e s and p r o p e r t i e s have been measured by s m a l l a n g l e n e u t r o n s c a t t e r i n g (4), 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 ( 5 ) , and u l t r a c e n t r i fugation sedimentation rates (6). For s i m p l i c i t y , these c o l l o i d a l d i s p e r s i o n s a r e r e f e r r e d t o as b a s i c (or alkaline) calcium sulfonates. P a r t i c l e sizes vary with m a n u f a c t u r i n g c o n d i t i o n s a n d t h e amount o f i n o r g a n i c b a s e i n c o r p o r a t e d , b u t g e n e r a l l y r a n g e f r o m 80 t o 160 Angstroms i n d i a m e t e r , i n c l u d i n g the t h i c k n e s s o f the adsorbed s u r f a c t a n t l a y e r . The p r o p e r t i e s o f s t e r i c a l l y s t a b i l i z e d , non-aqueous c o l l o i d a l d i s p e r s i o n s , such as t h e b a s i c a l k a l i n e e a r t h s u l f o n a t e s , have been w e l l documented ( 7 ) . P o l y ( i s o b u t e n y l ) s u c c i n i m i d e s , a second w i d e l y u t i l i z e d c l a s s of engine l u b r i c a n t a d d i t i v e s , are o i l - s o l u b l e s u r f a c t a n t s p r e p a r e d b y r e a c t i o n o f low m o l e c u l a r w e i g h t p o l y i s o b u t y l e n e ( P I B , c a . 1000 - 2500 a v . M . W.) w i t h m a l e i c a n h y d r i d e and a p o l y e t h y l e n e amine. F o r amines h a v i n g more t h a n one p r i m a r y n i t r o g e n , s u c h a s t r i e t h y l e n e tetramine, bisimide structures are usually prepared (Figure 1). Poly(isobutenyl)succinimides f u n c t i o n by r e d u c i n g t h e f o r m a t i o n o f o i l - i n s o l u b l e s l u d g e i n e n g i n e o p e r a t i o n , and a r e b e l i e v e d t o f u n c t i o n t h r o u g h a s t e r i c s t a b i l i z a t i o n mechanism i n v o l v i n g adsorption of the p o l a r p o r t i o n of the succinimide d i s p e r s a n t molecule onto engine sludge p a r t i c u l a t e s (8). S u c c i n i m i d e d i s p e r s a n t s may a s s o c i a t e i n h y d r o c a r b o n s o l v e n t s t o form weakly bound m i c e l l e s , b u t m i c e l l e f o r m a t i o n o c c u r s much more r e a d i l y i n t h e p r e s e n c e o f p o l a r m a t e r i a l s (such as a c i d s o r water) ( 9 ) . The s o l u b i l i z a t i o n o f a c i d s ( o r g a n i c and i n o r g a n i c ) by s u c c i n i m i d e d i s p e r s a n t s i n h y d r o c a r b o n s o l v e n t s has been described (10,11). C a l c i u m a l k y l a r y l s u l f o n a t e s and p o l y ( i s o b u t e n y l ) succinimide dispersants are both t y p i c a l l y present i n commercial e n g i n e l u b r i c a n t s , and t h e r e f o r e i t i s o f p r a c t i c a l i n t e r e s t t o understand whether p h y s i c a l i n t e r a c t i o n s o c c u r b e t w e e n t h e s e two c l a s s e s o f surfactant materials. Lubricant additive interactions may a f f e c t e n g i n e p e r f o r m a n c e , e i t h e r s y n e r g i s t i c a l l y o r a n t a g o n i s t i c a l l y (12, 1 3 ) , a n d a b e t t e r u n d e r s t a n d i n g o f f a c t o r s a f f e c t i n g engine l u b r i c a n t a d d i t i v e i n t e r a c t i o n s

0 F i g u r e 1. dispersant

polyamine

0

Idealized poly(isobutenyl)bissuccinimide structure.


26.

PAPKE

Adsorption of Poly (isobutenyl)-succinimide Dispersants

i s needed. application to identify succinimide colloids.

379

The p r e s e n t s t u d y d e s c r i b e s t h e n o v e l o f an u l t r a c e n t r i f u g a t i o n / i n f r a r e d t e c h n i q u e d i r e c t p h y s i c a l i n t e r a c t i o n s between d i s p e r s a n t s and b a s i c c a l c i u m s u l f o n a t e


EXPERIMENTAL Materials. Three s l i g h t l y d i f f e r e n t a l k a l i n e calcium a l k y l a r y l s u l f o n a t e c o l l o i d s were u s e d i n t h e p r e s e n t study. T h e s u l f o n a t e s u r f a c t a n t i n a l l c a s e s was a m i x t u r e o f a p p r o x i m a t e l y 65 wt% p e t r o l e u m s u l f o n a t e (a l a r g e l y m o n o a l k a r y l s u l f o n a t e ) a n d 35 wt% s y n t h e t i c s u l f o n a t e ( m o s t l y d i a l k y l C-12 b e n z e n e s u l f o n a t e s ) w i t h a c o m b i n e d a v e r a g e m o l e c u l a r w e i g h t o f a b o u t 1000 g / m o l e . Calcium a l k y l a r y l s u l f o n a t e surfactants i n t h i s molecular w e i g h t r a n g e a r e known t o f o r m i n v e r s e m i c e l l a r s t r u c t u r e s i n h y d r o c a r b o n media (1). A more d e t a i l e d p h y s i c a l c h a r a c t e r i z a t i o n of the calcium a l k y l a r y l s u l f o n a t e s u r f a c t a n t i s a v a i l a b l e elsewhere (14). The three a l k a l i n e calcium sulfonate c o l l o i d s i n t h i s study d i f f e r e d o n l y i n t h e amount o f s o l u b i l i z e d i n o r g a n i c b a s e they contained. The f i r s t s u l f o n a t e , r e f e r r e d t o as a " n e u t r a l " c a l c i u m s u l f o n a t e , had a 0.5:1 base:sulfonate molar r a t i o . The second c a l c i u m s u l f o n a t e c o n t a i n e d a l a r g e amount o f s o l u b i l i z e d i n o r g a n i c b a s e , a n d h a d a base:sulfonate molar r a t i o of 20:1. This sulfonate c o n t a i n e d a p p r o x i m a t e l y 38 wt% c a l c i u m c a r b o n a t e , 18 wt% c a l c i u m s u l f o n a t e a n d 44 wt% o f a n o n - p o l a r h y d r o c a r b o n carrier o i l . T h e t h i r d s u l f o n a t e was s i m i l a r t o t h e second, but had a reduced b a s e : s u l f o n a t e molar r a t i o o f 12.5:1. H e p t a n e ( A l d r i c h , 99% s p e c t r o p h o t o m e t r i c g r a d e ) was u s e d a s a n o n p o l a r s o l v e n t i n a l l s t u d i e s . S u c c i n i m i d e d i s p e r s a n t s u s e d i n t h i s s t u d y were p r e p a r e d by t h e r e a c t i o n o f p o l y i s o b u t e n y l s u c c i n i c a c i d anhydride with a polyethylene polyamine (pentaethyleneh e x a m i n e ( P E H A ) , Dow C h e m i c a l C o . , o r e t h y l e n e d i a m i n e ( E D A ) , A l d r i c h , 99%), i n a 2:1 m o l a r r a t i o . The p o l y i s o b u t e n y l s u c c i n i c a n h y d r i d e was p r e p a r e d f r o m r e a c t i o n o f p o l y i s o b u t y l e n e (PIB) w i t h m a l e i c a n h y d r i d e u s i n g e i t h e r 960 o r 2060 a v e r a g e m o l e c u l a r w e i g h t P I B (H-100 o r H - 1 5 0 0 ; Amoco C h e m i c a l C o m p a n y ) . The p r e p a r a t i o n and c h a r a c t e r i z a t i o n o f s u c c i n i m i d e d i s p e r s a n t s i s d e s c r i b e d i n t h e l i t e r a t u r e (8, 15). Succinimide d i s p e r s a n t s used i n the present study c o n t a i n e d a p p r o x i m a t e l y 30% u n r e a c t e d p o l y i s o b u t y l e n e due to incomplete conversion of the o r i g i n a l polyisobutylene to the polyisobutenyl s u c c i n i c a c i d anhydride. The s u c c i n i m i d e d i s p e r s a n t s were p r e s e n t i n a n o n - p o l a r hydrocarbon c a r r i e r o i l to f a c i l i t a t e handling; the a c t i v e d i s p e r s a n t c o n c e n t r a t i o n ( e x c l u d i n g u n r e a c t e d PIB) was a b o u t 37%. C a l c u l a t e d molecular weights f o r the d i s p e r s a n t s i n t h i s study a r e as f o l l o w s : (a) H-100 P I B / P E H A / b i s s u c c i n i m i d e - 2465 g / m o l (b) H-1500 P I B / E D A / b i s s u c c i n i m i d e - 4350 g / m o l (c) H-1500 P I B / P E H A / b i s s u c c i n i m i d e - 4750 g / m o l In Mixed Surfactant Systems; Holland, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1992.


380


Instrumentation. U l t r a c e n t r i f u g e s e p a r a t i o n s were c o n d u c t e d u s i n g a Beckman L 8 - 5 5 u l t r a c e n t r i f u g e e q u i p p e d w i t h a Beckman 5 0 . 2 T i f i x e d a n g l e r o t o r . Fourier t r a n s f o r m i n f r a r e d s p e c t r a were o b t a i n e d u s i n g a N i c o l e t 510 i n f r a r e d i n s t r u m e n t a n d 0 . 0 5 cm KC1 f i x e d p a t h l e n g t h solution cells. Light scattering studies u t i l i z e d a Nicomp 370 s u b m i c r o n p a r t i c l e a n a l y z e r s u p p l i m e n t e d w i t h a 15 mW HeNe S p e c t r a - P h y s i c s l a s e r . T h i s i n s t r u m e n t was s u p p l i e d w i t h a software package c a p a b l e o f a n a l y z i n g G a u s s i a n u n i m o d a l and n o n - G a u s s i a n m u l t i - m o d a l s i z e distributions. V o l u m e - w e i g h t e d s i z e measurements a r e reported. Procedures*. D i r e c t p h y s i c a l i n t e r a c t i o n s b e t w e e n b a s i c c a l c i u m s u l f o n a t e c o l l o i d a l d i s p e r s i o n s and p o l y ( i s o b u t e n y l ) s u c c i n i m i d e s were q u a n t i t a t i v e l y measuring u s i n g adsorption techniques (16). U l t r a c e n t r i f u g a t i o n was u s e d i n t h e p r e s e n t s t u d y a s a p h y s i c a l s e p a r a t i o n t e c h n i q u e ; t h i s t e c h n i q u e was f e a s i b l e because a l a r g e d i f f e r e n c e i n u l t r a c e n t r i f u g a t i o n s e d i m e n t a t i o n r a t e s e x i s t between t h e c a l c i u m s u l f o n a t e c o l l o i d s and t h e s u c c i n i m i d e d i s p e r s a n t s . B a s i c c a l i c u m s u l f o n a t e s c a n be removed f r o m d i l u t e l o w - d e n s i t y h y d r o c a r b o n s o l u t i o n s w i t h i n 1-3 h o u r s through u l t r a c e n t r i f u g a t i o n (6); succinimide d i s p e r s a n t s u s e d i n t h e p r e s e n t s t u d y were e s s e n t i a l l y unaffected under s i m i l a r c o n d i t i o n s . However, i n t e r a c t i o n s b e t w e e n t h e b a s i c s u l f o n a t e and s u c c i n i m i d e d i s p e r s a n t w i l l c a u s e t h e s u c c i n i m i d e d i s p e r s a n t t o be p h y s i c a l l y removed a l o n g with the calcium sulfonate c o l l o i d during u l t r a c e n t r i fugation (Figure 2). A l l a d s o r p t i o n measurements d e s c r i b e d i n t h i s p a p e r were c o n d u c t e d u s i n g t h e 20:1 (base:sulfonate) calcium sulfonate c o l l o i d . I n a t y p i c a l a d s o r p t i o n e x p e r i m e n t , a w e i g h e d amount o f t h e b a s i c c a l c i u m s u l f o n a t e c o l l o i d was m i x e d w i t h t h e succinimide d i s p e r s a n t i n petroleum ether t o ensure a c o m p l e t e l y homogeneous m i x t u r e . T h e p e t r o l e u m e t h e r was removed a t 80 C u n d e r N 2 , a n d t h e d i s p e r s a n t / d é t e r g e n t a d d i t i v e m i x t u r e was p l a c e d i n a t h e r m o s t a t e d o v e n a t 100 C f o r 4.0 h r s . A f t e r c o o l i n g , t h e a d d i t i v e m i x t u r e was d i l u t e d 1/6 ( w t / w t ) w i t h d i s t i l l e d h e p t a n e , s t i r r e d f o r a t l e a s t 30 m i n u t e s t o m i x t h r o u g h l y , a n d u l t r a c e n t r i f u g e d f o r 3 . 0 h r s a t 1 8 , 0 0 0 RPM. T r a n s l u c e n t p o l y p r o p y l e n e t u b e s were m a r k e d t o show s o l v e n t v o l u m e s p r i o r to c e n t r i f u g a t i o n ; the top eighth of the u l t r a c e n t r i f u g e d s o l u t i o n was d i s c a r d e d a n d a c u t was c a r e f u l l y t a k e n o f t h e next q u a r t e r o f t h e tube volume (using a f l a t - t i p syringe). The heptane s o l v e n t i n t h i s f r a c t i o n was s t r i p p e d u n d e r v a c u u m , a n d a s o l u t i o n c e l l i n f r a r e d s p e c t r u m o b t a i n e d on t h e r e m a i n i n g o i l s o l u t i o n . The i n t e n s i t y o f t h e s u c c i n i m i d e c a r b o n y l a d s o r p t i o n band a t 1705 cm-1 was r e c o r d e d a n d c o m p a r e d w i t h a d i s p e r s a n t



26. PAPKE


standard c a l i b r a t i o n curve to q u a n t i t a t i v e l y determine t h e amount o f r e m a i n i n g d i s p e r s a n t . L i g h t s c a t t e r i n g p a r t i c l e s i z e measurements w e r e c o n d u c t e d b o t h on t h e o r i g i n a l c a l c i u m s u l f o n a t e c o l l o i d and on m i x t u r e s o f t h e s u l f o n a t e c o l l o i d w i t h t h e s u c c i n i m i d e d i s p e r s a n t ( h e a t e d a t 100 C f o r 4 h o u r s ) . Samples were p r e p a r e d u s i n g f i l t e r e d h e p t a n e (Nucleopore 0.44 m i c r o m e t e r ) i n c o n c e n t r a t i o n s b e t w e e n 3 . 5 a n d 0 . 5 wt%, d e p e n d i n g on t h e s c a t t e r e d l i g h t i n t e n s i t y ( c a r e was t a k e n t o a v o i d c o n c e n t r a t i o n s where m u l t i p l e s c a t t e r i n g occurred). A l l s a m p l e s were f i l t e r e d i m m e d i a t e l y p r i o r t o a n a l y s i s ( N u c l e o p o r e 0.22 m i c r o m e t e r g r a v i t y filtration). A l l l i g h t s c a t t e r i n g s t u d i e s were c o n d u c t e d using the 12.5:1 (base:sulfonate) calcium sulfonate colloid. I n t e r a c t i o n r e v e r s i b i l i t y was d e t e r m i n e d u s i n g a c o m p e t i t i v e i n t e r a c t i o n between a " n e u t r a l " c a l c i u m s u l f o n a t e , a b a s i c c a l c i u m s u l f o n a t e c o l l o i d , and a succinimide dispersant. The " n e u t r a l " s u l f o n a t e h a d p a r t i c l e s i z e o f 5 0 - 6 0 A (17) a n d a s l o w s e d i m e n t a t i o n r a t e s i m i l a r to that observed f o r the succinimide dispersant. The 20:1 ( b a s e : s u l f o n a t e ) c a l c i u m s u l f o n a t e c o l l o i d h a d a p a r t i c l e s i z e o f c a . 130 A ( v o l u m e - w e i g h t e d s i z e measured by l i g h t s c a t t e r i n g ) and a r e l a t i v e l y r a p i d sedimentation rate. A n o r d e r o f a d d i t i o n s t u d y was c o n d u c t e d ( i . e . mix " n e u t r a l s u l f o n a t e + s u c c i n i m i d e , h e a t @ 100 C f o r 4 h r s ; f o l l o w e d b y a d d i t i o n o f t h e " b a s i c " s u l f o n a t e a n d r e h e a t i n g @ 100 C / 4 h r s ) , t h e p r o c e d u r e was r e v e r s e d , and t h e r e s u l t s w e r e c o m p a r e d a f t e r u l t r a c e n t i r f u g a t i o n to determine the r e v e r s i b i l i t y of the succinimide/sulfonate i n t e r a c t i o n . For i r r e v e r s i b l e i n t e r a c t i o n s , premixing the b a s i c sulfonate w i t h t h e d i s p e r s a n t i s e x p e c t e d t o r e s u l t i n a much g r e a t e r removal o f d i s p e r s a n t from s o l u t i o n ; t h e m i x i n g o r d e r w o u l d be i r r e l e v a n t f o r c o m p l e t e l y r e v e r s i b l e interactions.

RESULTS and DISCUSSION B a s i c Calcium Sulfonate / P o l y i s o b u t e n y l

Succinimide

A g g r e g a t i o n Behavior. Q u a n t i t a t i v e i n f o r m a t i o n on i n t e r a c t i o n s between b a s i c c a l c i u m s u l f o n a t e c o l l o i d s and p o l y i s o b u t e n y l s u c c i n i m i d e d i s p e r s a n t s was o b t a i n e d b y c o n s i d e r i n g t h e s u l f o n a t e c o l l o i d t o be a s o l i d adsorbent. A d s o r p t i o n c u r v e s a r e shown f o r t h e b a s i c c a l c i u m s u l f o n a t e c o l l o i d a n d two d i f f e r e n t p o l y i s o b u t e n y l b i s s u c c i n i m i d e d i s p e r s a n t s i n F i g u r e 3. The a d s o r p t i o n c u r v e s a r e a l l L a n g m u i r i a n i n shape, t h a t i s , they followed the equations: η = n

bC m

(D 1 + bC


381

382


a)

b)

No Interaction


j

Strong Interaction

Removed for FTIR Analysis

Dispersant Molecule Calcium Sulfonate Colloid Before

Before / After Ultracentrifugation

/

After

Ultracentrifugation

F i g u r e 2. U l t r a c e n t r i f u g a t i o n / F T I R method f o r screening potential additive interactions; p i c t o r i a l representation.

(a) (b)

(c)

(d) - -2-j

1

1

1

0

10

20

30

1

40 _

3

1

1

50

b0

Dispersant Cone (moles / L χ 10 ) Figure 3. Adsorption of poly(isobutenylJbissuccinimide d i s p e r s a n t s o r p o l y i s o b u t y l e n e onto a b a s i c c a l c i u m s u l f o n a t e c o l l o i d from η - h e p t a n e s o l u t i o n : (a) H - 1 0 0 P I B / P E H A / B i s i m i d e ; (b) H-1500 P I B / P E H A / B i s i m i d e ; (c) H-1500 P I B / E D A / B i s i m i d e ; (d) H-1500 P o l y i s o b u t y l e n e .



26. PAPKE

383

and C

1

1 (2)

η

n

b

η


m

m

where C i s t h e e q u i l i b r i u m d i s p e r s a n t c o n c e n t r a t i o n ( i n moles p e r l i t e r ) and η i s t h e moles o f s u c c i n i m i d e d i s p e r s a n t a d s o r b e d p e r gram o f b a s i c c a l c i u m s u l f o n a t e c o l l o i d ( c o n t a i n i n g no c a r r i e r o i l ) . As t h e d i s p e r s a n t c o n c e n t r a t i o n i s i n c r e a s e d , t h e amount o f a d s o r b e d s u c c i n i m i d e d i s p e r s a n t w i l l a p p r o a c h some l i m i t i n g v a l u e , η,ρ. T h i s v a l u e r e p r e s e n t s t h e maximum c a l c i u m s u l f o n a t e / s u c c i n i m i d e i n t e r a c t i o n r a t i o . The v a l u e o f t h e c o n s t a n t "b" i s a m e a s u r e o f t h e a d s o r p t i o n s t r e n g t h . If t r u e Langmuir a d s o r p t i o n b e h a v i o r i s o b s e r v e d , then a p l o t o f C / n v s C s h o u l d be l i n e a r , t h e s l o p e i s e q u a l t o l/n and t h e y - i n t e r c e p t e q u a l t o 1/n^b. A s shown i n F i g u r e 4, L a n g m u i r a d s o r p t i o n b e h a v i o u r was o b s e r v e d , a n d t h e v a r i o u s b and η v a l u e s a r e t a b u l a t e d i n T a b l e I . | l U

Table I Langmuir Constants f o r A d s o r p t i o n o f S u c c i n i m i d e D i s p e r s a n t s onto t h e 20:1 C a l c i u m S u l f o n a t e C o l l o i d -1 Dispersant (amine)

H-1500

η , mol g m

b, M

-1 Disp./CaSf2 molar r a t i o

bis(imides) -5

a.

EDA

4.5

x

10

550

.135

1100

.227

1700

.254

-5 b.

PEHA

H-100

7.6

X 10

bis(imides) -5

a.

PEHA

8.5

x

10

The d a t a i n F i g u r e 3 d e m o n s t r a t e s t h a t p o l y (isobutenyl)succinimide dispersant molecules i n t e r a c t s t r o n g l y with the calcium sulfonate c o l l o i d a l p a r t i c l e s . Evidence that t h i s i n t e r a c t i o n occurs through the p o l a r d i s p e r s a n t a m i n e / s u c c i n i m i d e headgroup and not t h e p o l y i s o b u t y l e n e p o l y m e r was o b t a i n e d b y s u b s t i t u t i n g a sample o f t h e n o n f u n c t i o n a l i z e d p o l y i s o b u t y l e n e polymer (2060 a v . M.W.) i n place of the succinimide dispersant i n the u l t r a c e n t r i f u g a t i o n / F T I R procedure. T h e 1230 cm-1



384


p o l y i s o b u t y l e n e IR b a n d ( a s s i g n e d t o t h e g e m - d i m e t h y l s t r u c t u r e o n t h e P I B p o l y m e r ) was u s e d t o f o l l o w t h e interaction. T h e p o l y i s o b u t y l e n e c o n c e n t r a t i o n was v a r i e d i n mixtures with the basic calcium sulfonate c o l l o i d , a n d a n a d s o r p t i o n " c u r v e " was o b t a i n e d . The r e s u l t s a r e compared w i t h t h e a d s o r p t i o n c u r v e s o b t a i n e d for the bissuccinimide dispersants. No a d s o r p t i o n o f t h e p o l y i s o b u t y l e n e p o l y m e r was o b s e r v e d ( c u r v e " d " , F i g u r e 3) d e m o n s t r a t i n g t h a t t h e p o l a r d i s p e r s a n t a m i n e / s u c c i n i m i d e headgroup i s r e s p o n s i b l e f o r d i s p e r s a n t a d s o r p t i o n onto the calcium s u l f o n a t e c o l l o i d .

P o l y i s o b u t e n y l Succinimide - Calcium S u l f o n a t e Molar I n t e r a c t i o n R a t i o s . T h e maximum m o l a r s u c c i n i m i d e / s u l f o n a t e i n t e r a c t i o n r a t i o s a r e shown i n T a b l e I . Since the b a s i c calcium sulfonate i t s e l f i s a s t e r i c a l l y s t a b i l i z e d p a r t i c l e o f c a l c i u m c a r b o n a t e w i t h an a d s o r b e d l a y e r o f c a l c i u m s u l f o n a t e , t h e most p l a u s i b l e s t r u c t u r e f o r the mixed m i c e l l a r s u c c i n i m i d e / s u l f o n a t e s t r u c t u r e i s t h a t d e p i c t e d p i c t o r i a l l y i n F i g u r e 5. No c l e a r r e l a t i o n between t h e m o l a r i n t e r a c t i o n r a t i o s and p o s s i b l e interaction r a t i o s with either calcium cations or sulfonate anions i s apparent, suggesting that these r a t i o s may be d e t e r m i n e d p r i m a r i l y b y s t e r i c p a c k i n g c o n s t r a i n t s due t o b u l k y P I B c h a i n s . No d e - s o r p t i o n o f c a l c i u m s u l f o n a t e s u r f a c t a n t o c c u r r e d , as determined by infrared spectroscopy. P h y s i c a l p r o p e r t i e s o f t h e "mixed" s u l f o n a t e / s u c c i n i m i d e c o l l o i d a r e l i k e l y t o be q u i t e d i f f e r e n t f r o m the o r i g i n a l b a s i c calcium sulfonate c o l l o i d . The s u c c i n i m i d e d i s p e r s a n t has a s u r f a c t a n t " t a i l " t h a t i s approximately f i v e times the l e n g t h (extended c o n f o r m a t i o n ) o f t h e s u l f o n a t e ( f o r a 2060 a v e r a g e molecular weight p o l y i s o b u t y l e n e ) . In a d d i t i o n , the p o l y i s o b u t y l e n e c h a i n s t r u c t u r e i s c o n s i d e r a b l y more r i g i d t h a n a s i m p l e h y d r o c a r b o n c h a i n (due t o s t e r i c r e p u l s i o n s f r o m t h e gem d i - m e t h y l g r o u p s ) , a n d h e n c e l i k e l y t o a d o p t a more e x t e n d e d c h a i n c o n f o r m a t i o n . S u r f a c e p r o p e r t i e s o f the mixed s u l f o n a t e - s u c c i n i m i d e m i c e l l e a r e t h e r e f o r e l i k e l y t o be d o m i n a t e d b y t h e p r o p e r t i e s o f t h e p o l y i s o b u t y l e n e p o l y m e r , and t h e o v e r a l l s i z e of the c o l l o i d a l d i s p e r s i o n should increase. L i g h t s c a t t e r i n g s t u d i e s demonstrate t h a t s u c c i n i m i d e d i s p e r s a n t a d s o r p t i o n r e s u l t s i n measurable i n c r e a s e s i n c o l l o i d a l p a r t i c a l s i z e s , p r o v i d i n g a d d i t i o n a l evidence t o s u p p o r t t h e p i c t o r i a l r e p r e s e n t a t i o n o f F i g u r e 5. The b a s i c c a l c i u m sulfonate c o l l o i d used i n the l i g h t s c a t t e r i n g s t u d i e s had a b a s e : s u l f o n a t e r a t i o o f 1 2 . 5 : 1 and a n a v e r a g e p a r t i c l e s i z e o f 107 A n g s t r o m s . When t h e H-100 P I B / P E H A / b i s s u c c i n i m i d e was a d d e d i n a . 1 6 : 1 m o l a r r a t i o ( r o u g h l y 40% o f s a t u r a t i o n ) , t h e m e a s u r e d p a r t i c l e s i z e i n c r e a s e d t o 114 A n g s t r o m s . Adsorption of the l a r g e r H-1500 P I B / P E H A / b i s s u c c i n i m i d e i n a 0 . 0 8 7 : 1 m o l a r



26. PAPKE

Adsorption of Poly (isobutenyl) -succinimide Dispersants

385

F i g u r e 4. Adsorption data for p o l y ( i s o b u t e n y l ) b i s s u c c i n i m i d e d i s p e r s a n t s onto a b a s i c c a l c i u m s u l f o n a t e c o l l o i d from η - h e p t a n e s o l u t i o n p l o t t e d a c c o r d i n g t o e q n . 2: (a) H-1500 P I B / E D A / B i s i m i d e ; (b) H-1500 P I B / P E H A / B i s i m i d e ; (c) H-100 P I B / P E H A / B i s i m i d e .

Calcium Carbonate Colloidal Particle F i g u r e 5. P i c t o r i a l representation of hypothesized i n t e r a c t i o n s between a c a l c i u m s u l f o n a t e c o l l o i d a l p a r t i c l e and a d s o r b e d p o l y ( i s o b u t e n y l ) b i s s u c c i n i m i d e dispersants.



386


r a t i o ( a l s o r o u g h l y 40% o f s a t u r a t i o n ) r e s u l t e d i n a n a d d i t i o n a l i n c r e a s e i n p a r t i c l e s i z e ( t o 126 A n g s t r o m s ) . A l t h o u g h t h e s e s i z e i n c r e a s e s a r e measurable and s i g n i f i c a n t , they are l e s s than those expected f o r a f u l l y e x t e n d e d P I B c h a i n c o n f o r m a t i o n ; 46 A a n d 73 À maximum s i z e i n c r e a s e s a r e p o s s i b l e f o r t h e H-100 a n d t h e H-1500 P I B d i s p e r s a n t s r e s p e c t i v e l y ( b a s e d o n a n e x t e n d e d c h a i n conformation, d i s p e r s a n t a d s o r p t i o n onto the c o l l o i d ' s i n o r g a n i c c o r e , a n d an a d s o r b e d s u l f o n a t e s u r f a c t a n t l a y e r t h i c k n e s s o f 20 À ) . T h i s d a t a s u g g e s t s t h a t a t l o w (40%) c o v e r a g e t h e P I B c h a i n s a r e i n a more c o l l a p s e d conformation over the surface of the calcium sulfonate c o l l o i d a l p a r t i c l e . Higher l e v e l s of adsorbed PIB s u c c i n i m i d e d i s p e r s a n t s h o u l d r e s u l t i n more e x t e n d e d c h a i n c o n f o r m a t i o n s and c o r r e s p o n d i n g l y l a r g e r s i z e increases. Interaction R e v e r s i b i l i t y Studies. Although the i n t e r a c t i o n between p o l y ( i s o b u t e n y l ) s u c c i n i m i d e s and basic calcium sulfonate c o l l o i d s follows t y p i c a l L a n g m u i r i a n a d s o r p t i o n b e h a v i o r , i t c a n be d e m o n s t r a t e d that the adsorption i n t e r a c t i o n i s i r r e v e r s i b l e i n at least certain cases. A d s o r p t i o n r e v e r s i b i l i t y was evaluated through a three-way competitive i n t e r a c t i o n experiment i n v o l v i n g a "neutral" calcium s u l f o n a t e , a b a s i c c a l c i u m s u l f o n a t e c o l l o i d and a s u c c i n i m i d e d i s p e r s a n t , as d e s c r i b e d i n the e x p e r i m e n t a l s e c t i o n . S i n c e the " n e u t r a l " c a l c i u m s u l f o n a t e had a v e r y slow sedimentation r a t e , d i s p e r s a n t s which i n t e r a c t " i r r e v e r s i b l y " w i t h t h i s s u l f o n a t e w i l l n o t b e removed from s o l u t i o n d u r i n g u l t r a c e n t r i f u g a t i o n . Interaction r e v e r s i b i l i t y was m e a s u r e d u s i n g a n o r d e r - o f - a d d i t i o n study; i f the dispersant adsorption i s r e v e r s i b l e , then t h e a d s o r p t i o n c u r v e s s h o u l d be i n d e p e n d e n t o f t h e a d d i t i o n order, provided s u f f i c i e n t time i s allowed f o r the mixture to reach e q u i l i b r i u m . A parallel control e x p e r i m e n t was a l s o c o n d u c t e d , s u b s t i t u t i n g a n o n - p o l a r mineral o i l f o r the neutral calcium sulfonate. The r e s u l t s , shown i n F i g u r e 6, c l e a r l y d e m o n s t r a t e that the o r d e r - o f - a d d i t i o n i s c r i t i c a l . Identical a d s o r p t i o n c u r v e s a r e o b t a i n e d when t h e " n e u t r a l " s u l f o n a t e was a d d e d l a s t o r when a n o n - i n t e r a c t i n g m i n e r a l o i l was s u b s t i t u t e d f o r t h e " n e u t r a l " s u l f o n a t e ( c u r v e s (a) a n d (b) i n F i g u r e 6 ) . H o w e v e r , when t h e n e u t r a l s u l f o n a t e a n d d i s p e r s a n t were b l e n d e d f i r s t , a much w e a k e r i n t e r a c t i o n b e t w e e n t h e d i s p e r s a n t a n d t h e b a s i c s u l f o n a t e was o b s e r v e d ( c u r v e ( c ) , F i g u r e 6 ) . If t h e d i s p e r s a n t a d s o r p t i o n were t o t a l l y r e v e r s i b l e , t h e n a l l t h r e e a d s o r p t i o n c u r e v e s s h o u l d have been i d e n t i c a l . The f a c t t h a t c u r v e s (a) a n d (b) a r e i d e n t i c a l demonstrates t h a t succinimide d i s p e r s a n t a d s o r p t i o n onto the b a s i c calcium sulfonate c o l l o i d i s essentially i r r e v e r s i b l e under the c o n d i t i o n s o f t h i s experiment.



26.

PAPKE


in

F i g u r e 6. Competitive adsorption study: (a) Ca s u l f o n a t e a d d e d l a s t ; (b) no " n e u t r a l " Ca (c) " n e u t r a l " Ca s u l f o n a t e a d d e d f i r s t .

"neutral" sulfonate;


387


388


I n t e r a c t i o n between t h e s u c c i n i m i d e d i s p e r s a n t and t h e " n e u t r a l " s u l f o n a t e , i n c o n t r a s t , a p p e a r s t o show some degree o f r e v e r s i b i l i t y . I f t h e i n t e r a c t i o n were t o t a l l y i r r e v e r s i b l e , t h e n c u r v e (c) ( F i g u r e 6) s h o u l d be a f l a t l i n e a t f i r s t ( u n t i l complete s a t u r a t i o n o f the " n e u t r a l " s u l f o n a t e has o c c u r r e d ) , f o l l o w e d by an a d s o r p t i o n c u r v e i d e n t i c a l w i t h c u r v e s (a) o r (b) ( b u t o f f s e t o n t h e dispersant concentration axis). The o b s e r v e d shape f o r a d s o r p t i o n c u r v e (c) s u g g e s t s t h a t a s l o w " r e l e a s e " o f d i s p e r s a n t f r o m t h e n e u t r a l s u l f o n a t e may o c c u r . I r r e v e r s i b l e adsorption that follows Langmuirian b e h a v i o r , as i s o b s e r v e d f o r t h e i n t e r a c t i o n between t h e p o l y i s o b u t e n y l s u c c i n i m i d e s and b a s i c c a l c i u m s u l f o n a t e c o l l o i d s , p r e s e n t s an i n t e r e s t i n g p a r a d o x ( 1 8 ) . I f the a d s o r p t i o n i s i r r e v e r s i b l e (that i s d e s o r p t i o n cannot o c c u r ) , t h e n why d o e s n ' t c o m p l e t e a d s o r p t i o n o f t h e s u c c i n i m i d e d i s p e r s a n t c o n t i n u e u n t i l t h e maximum s a t u r a t i o n of the calcium sulfonate c o l l o i d i s achieved? The a n s w e r t h a t h a s b e e n p r o p o s e d t o t h i s p a r a d o x i s t h a t two a d s o r p t i o n i n t e r a c t i o n s must o c c u r - a l a b i l e (reversible) i n i t i a l i n t e r a c t i o n ( r e s u l t i n g i n the o b s e r v e d L a n g m u i r i a n b e h a v i o r ) and an i r r e v e r s i b l e a d s o r p t i o n which o c c u r s o v e r a l o n g e r t i m e p e r i o d and i n v o l v e s some t y p e o f " a g i n g " t r a n s f o r m a t i o n ( 1 8 ) . In t h e p r e s e n t s t u d y , one p l a u s i b l e m o d e l i s t h a t t h e i n i t i a l (reversible) interaction involves physia d s o r p t i o n o f the succinimide d i s p e r s a n t onto the s u l f o n a t e c o l l o i d , f o l l o w e d by a s l o w e r i r r e v e r s i b l e i n t e r a c t i o n (perhaps an a m i n e / c a t i o n c o m p l e x a t i o n interaction). Additional studies are required to f u l l y explore the i m p l i c a t i o n s of the observed i r r e v e r s i b i l i t y between t h e p o l y ( i s o b u t e n y l ) s u c c i n i m i d e d i s p e r s a n t s and calcium sulfonate c o l l o i d s .

CONCLUSIONS P h y s i c a l i n t e r a c t i o n s between b a s i c c a l c i u m a l k y l a r y l s u l f o n a t e c o l l o i d s and p o l y ( i s o b u t e n y l ) s u c c i n i m i d e d i s p e r s a n t s have been i d e n t i f i e d u s i n g an ultracentrifugation/FTIR technique. Succinimide d i s p e r s a n t s a r e shown t o a d s o r b o n t o c a l c i u m s u l f o n a t e c o l l o i d a l p a r t i c l e s ; the p o l a r succinimide dispersant h e a d g r o u p i s shown t o be r e s p o n s i b l e f o r t h e o b s e r v e d adsorption. Succinimide a d s o r p t i o n onto s u l f o n a t e c o l l o i d s i s i r r e v e r s i b l e under c e r t a i n c o n d i t i o n s ; c o m p l e x a t i o n between t h e p o l y a m i n e a n d / o r t h e s u c c i n i m i d e f u n c t i o n a l i t i e s w i t h t h e c a l c i u m c a t i o n may b e t h e d r i v i n g force behind t h i s i n t e r a c t i o n . Interactions between s u c c i n i m i d e d i s p e r s a n t s and c a l c i u m s u l f o n a t e c o l l o i d s r e s u l t i n t h e f o r m a t i o n o f new m i x e d s u r f a c t a n t c o l l o i d s , as e v i d e n c e d by measurable i n c r e a s e s i n colloidal particle sizes.


26. PAPKE


389

ACKNOWLEDGEMENTS The a u t h o r t h a n k s T e x a c o I n c . f o r p e r m i s s i o n t o p u b l i s h t h i s w o r k , and w i s h e s t o a c k n o w l e d g e t h e a s s i s t a n c e o f Dr. C. A. M i g d a l and M r . J . F . L u c a s i n p r e p a r i n g t h e d i s p e r s a n t s a m p l e s , and M s . A . T . A r r u z a f o r c o n d u c t i n g t h e a d s o r p t i o n and l i g h t s c a t t e r i n g s t u d i e s .


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(3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17)

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