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Flocculation-deflocculation effect of polymer additive in nonaqueous dispersions
Flocculation-Deflocculation Effect of Polymer Additive in Nonaqueous Dispersions The flocculation-defioeculation effects of polymers in colloidal dispersions have a long h i s t o r y and our u n d e r s t a n d i n g of these effects has been enlarged by polymer research. However, m u c h seems to be unclarified for nonaqueous dispersions compared w i t h aqueous dispersions. Lyklema (1) has reviewed the effect of adsorbed layer of polymet in nonaqueous media. N a p p e r (2) and N a p p e r and N e t s c h e y (3) have studied the flocculationdeflocculation effects of polymers in b o t h aqueous and nonaqueous media and clarified the steric effects of polymers t h e r m o d y n a m i c a l l y . N a p p e r (4) has presented experimental evidence for nonaqueous systems, as well as for aqueous systems (2, 3). N a p p e r ' s investigations were m a i n l y carried out at high surface coverage of polymer except TABLE I SEDIMENTATION VOLUME RATIO (Sr) FOR Low COVERAGE SYSTEMS a
MW
1.51 )< 106 1.15 X 104
Sr = s e d i m e n t a t i o n vol in polymer solution s e d i m e n t a t i o n vol in pure solvent TABLE II 2-V[EAN PARTICLE SIZE (R) OF ANATASE PARTICLES DISPERSED AT HIGHER COVERAGE
Coverage
Sr Benzene systems
except for some detailed b e h a v i o r (5). In this note, the s t u d y on poly(n-octyl m e t h a e r y l a t e ) is given as an example. Two samples of higher and lower molecular weight polymer (1.51 X 106 and 1.15 X 104) were used. TiO2 (anatase) was used as disperse phase. Dispersions were p r e p a r e d b y shaking in a vessel containing glass balls. W a t e r c o n t e n t in the dispersion was below 20 p p m t h r o u g h o u t this study. Surface coverage was d e t e r m i n e d b y use of adsorption data. The flocculation-defloeeulation effect was e s t i m a t e d b y s e d i m e n t a t i o n volume ratio (Sr) for low coverage systems. Sr was expressed as follows :
MW
Cyclohexane ,ystems
1.29 0.81
1.26 1.08
Surface coverage: a b o u t 0.1. for a few cases in which he varied the surface coverage down to 0.57 or 0.20 (2, 4). However, at this low coverage of polymer, bridging effects m a y occur due to adsorption of a polymer molecule extending over v a c a n t sites of two particles. Hence, it is expected t h a t a polymer which s t a b i lizes a dispersion sterically b y its adsorbed layer at higher coverage m a y flocculate it b y the bridging effect at lower coverage. The bridging effect has been cited by Lyklema (1) and N a p p e r (2). However, the experimental evidence for this seems to be lacking for nonaqueous systems. We show here t h a t the same polymer yields b o t h flocculation and defloeeulation effects in nonaqueous media according to the a m o u n t of surface coverage or the c o n c e n t r a t i o n of polymer. The polymers used were poly(alkyl m e t h a e r y late)s. The alkyl group was n - b u t y l , n-oetyl or ndodeeyl, All of the polymers showed similar effects Copyright @ 1972 by Academic Press, Inc. All rights of reproduction in any form reserved.
R@m) Benzene systems
Cycbhexane systems
ca. 0.7
1.51 X 106 1.15 X 104
1.6 1.45
2.4 1.2 1.4
ca. 1.0
1.51 X 108 1.15 X 104
0.7-0.8 0.8-1.2
1.2-1.4
Since Sr's were v e r y low and h a r d l y differentiated for high coverage systems, the mean particle size (R) of dispersed particles was used for e s t i m a t i o n of floeeulation-defloeeulation effect at high coverage. R was defined as the particle radius corresponding to t h e inflexion p o i n t of the size d i s t r i b u t i o n curve o b t a i n e d w i t h the Wiegner t u b e (6). Sr and R in benzene or eyclohexane systems are shown in Tables I and II. The values of Sr > 1 in the presence of polymers (Table I) show the occurrence of further floceulation compared with the flocculation evident in pure solvents. Bridging effects may be considered as a cause of this flocculation effect of the polymer. The data support the idea of bridging in that the floceu]ating effect of the high moleeu]ar weight (MW) polymer is
Journal of Colloid and Interface Science, Vol. 41, No. 2, November 1972
383
384
NOTES
larger than that of the low MW polymer in both solvent systems (Table I). That flocculating behavior appears in the low MW solution of cyelohexane (Table I) may be due to the presence of higher MW components and the good solvency of the solvent. That the mean particle size (R) of the dispersion in the high MW polymer solution is larger than that in the low MW polymer solution at a coverage of about 0.7 (Table II) may be due to the remaining bridging effect. The steric stabilization effect of polymers explains why R at saturated coverage is smaller compared with those at lower coverage and that R for lower MW polymer is larger than those for higher MW polymer (Table II). REFERENCES 1. LYKLEMA,J., Advan. Colloid Interface Sei., 2, 67 (1968).
2. NAFPER, D. H., J. Colloid Interface Sei. 32,106 (1970). 3. NAPPER,D. H., ANDNETSCHE¥, A. J., J. Colloid Interface Sei. 37,528 (1971). 4. NAPPER, D. H., Trans. Faraday Soc. 64, 1701 (1968). 5. KITAH&RA, A., AND HASUMUMA, M., Unpublished data. 6. DANIELS, F., MA_T~IEWS, J. ~-~., WILLIAMS, J. W., BENDER, :P., AND ALBERTY~R. A., "Experimental Physical Chemistry," 6th ed., p. 312. McGraw-Hill, New York, 1962. AvAO KITA~ARA MASAO ~-IASUMUMA Science University of Tokyo Kagurazaka Shinjiku -ku To]~yo, Japan Received May 30, 1972; accepted July 18, I972
Journal o] Colloidand InterfaceScience,Vol.41, No. 2, November1972
MW
1.51 )< 106 1.15 X 104
Sr = s e d i m e n t a t i o n vol in polymer solution s e d i m e n t a t i o n vol in pure solvent TABLE II 2-V[EAN PARTICLE SIZE (R) OF ANATASE PARTICLES DISPERSED AT HIGHER COVERAGE
Coverage
Sr Benzene systems
except for some detailed b e h a v i o r (5). In this note, the s t u d y on poly(n-octyl m e t h a e r y l a t e ) is given as an example. Two samples of higher and lower molecular weight polymer (1.51 X 106 and 1.15 X 104) were used. TiO2 (anatase) was used as disperse phase. Dispersions were p r e p a r e d b y shaking in a vessel containing glass balls. W a t e r c o n t e n t in the dispersion was below 20 p p m t h r o u g h o u t this study. Surface coverage was d e t e r m i n e d b y use of adsorption data. The flocculation-defloeeulation effect was e s t i m a t e d b y s e d i m e n t a t i o n volume ratio (Sr) for low coverage systems. Sr was expressed as follows :
MW
Cyclohexane ,ystems
1.29 0.81
1.26 1.08
Surface coverage: a b o u t 0.1. for a few cases in which he varied the surface coverage down to 0.57 or 0.20 (2, 4). However, at this low coverage of polymer, bridging effects m a y occur due to adsorption of a polymer molecule extending over v a c a n t sites of two particles. Hence, it is expected t h a t a polymer which s t a b i lizes a dispersion sterically b y its adsorbed layer at higher coverage m a y flocculate it b y the bridging effect at lower coverage. The bridging effect has been cited by Lyklema (1) and N a p p e r (2). However, the experimental evidence for this seems to be lacking for nonaqueous systems. We show here t h a t the same polymer yields b o t h flocculation and defloeeulation effects in nonaqueous media according to the a m o u n t of surface coverage or the c o n c e n t r a t i o n of polymer. The polymers used were poly(alkyl m e t h a e r y late)s. The alkyl group was n - b u t y l , n-oetyl or ndodeeyl, All of the polymers showed similar effects Copyright @ 1972 by Academic Press, Inc. All rights of reproduction in any form reserved.
R@m) Benzene systems
Cycbhexane systems
ca. 0.7
1.51 X 106 1.15 X 104
1.6 1.45
2.4 1.2 1.4
ca. 1.0
1.51 X 108 1.15 X 104
0.7-0.8 0.8-1.2
1.2-1.4
Since Sr's were v e r y low and h a r d l y differentiated for high coverage systems, the mean particle size (R) of dispersed particles was used for e s t i m a t i o n of floeeulation-defloeeulation effect at high coverage. R was defined as the particle radius corresponding to t h e inflexion p o i n t of the size d i s t r i b u t i o n curve o b t a i n e d w i t h the Wiegner t u b e (6). Sr and R in benzene or eyclohexane systems are shown in Tables I and II. The values of Sr > 1 in the presence of polymers (Table I) show the occurrence of further floceulation compared with the flocculation evident in pure solvents. Bridging effects may be considered as a cause of this flocculation effect of the polymer. The data support the idea of bridging in that the floceu]ating effect of the high moleeu]ar weight (MW) polymer is
Journal of Colloid and Interface Science, Vol. 41, No. 2, November 1972
383
384
NOTES
larger than that of the low MW polymer in both solvent systems (Table I). That flocculating behavior appears in the low MW solution of cyelohexane (Table I) may be due to the presence of higher MW components and the good solvency of the solvent. That the mean particle size (R) of the dispersion in the high MW polymer solution is larger than that in the low MW polymer solution at a coverage of about 0.7 (Table II) may be due to the remaining bridging effect. The steric stabilization effect of polymers explains why R at saturated coverage is smaller compared with those at lower coverage and that R for lower MW polymer is larger than those for higher MW polymer (Table II). REFERENCES 1. LYKLEMA,J., Advan. Colloid Interface Sei., 2, 67 (1968).
2. NAFPER, D. H., J. Colloid Interface Sei. 32,106 (1970). 3. NAPPER,D. H., ANDNETSCHE¥, A. J., J. Colloid Interface Sei. 37,528 (1971). 4. NAPPER, D. H., Trans. Faraday Soc. 64, 1701 (1968). 5. KITAH&RA, A., AND HASUMUMA, M., Unpublished data. 6. DANIELS, F., MA_T~IEWS, J. ~-~., WILLIAMS, J. W., BENDER, :P., AND ALBERTY~R. A., "Experimental Physical Chemistry," 6th ed., p. 312. McGraw-Hill, New York, 1962. AvAO KITA~ARA MASAO ~-IASUMUMA Science University of Tokyo Kagurazaka Shinjiku -ku To]~yo, Japan Received May 30, 1972; accepted July 18, I972
Journal o] Colloidand InterfaceScience,Vol.41, No. 2, November1972