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Langmuir 1994,10, 3250-3254
Interaction between Aerosol OT and Poly(vinylpyrro1idone)on Alumina Kunio Esumi,* Yukiko Takaku, and Hidenori Otsuka Department of Applied Chemistry and Znstitute of Colloid and Znterface Science, Science University of Tokyo, Kagurazaka, Shinjuku-ku, Tokyo 162, Japan Received March 4, 1994. Zn Final Form: June 13, 1994@ The adsorption of a double-chained surfactant, sodium bis(2-ethylhexyl) sulfosuccinate (aerosol OT), and poly(vinylpyrro1idone)(PVP) from their mixed aqueous solutions on alumina has been studied by measuringadsorbed amount, (-potential, ESR, and dispersionstability. The adsorption ofPVP was enhanced by the presence of aerosol OT due to formation of a surface complex of PVP and aerosol OT, and this enhancement is proportional to the feed concentration of PVP. The conformation of PVP adsorbed was estimated using a spin-labeled polymer, and it changed from loops and tails to trains with increasing aerosol OT concentration. The portion of train segmentsbecomes smaller with increasingfeed concentration of PVP. The addition of aerosol OT enhances remarkably the adsorption of PVP in comparison with a single-chained anionic surfactant.
Introduction The adsorption and orientation of polymers and surfactants at the solidhquid interfacel-10 have been studied to understand the mechanisms of stabilization and flocculation of dispersion and emulsions. We reportedlo that poly(vinylpyrro1idone) (PVP) adsorption increased significantly in the presence of single-chained surfactants on alumina where the conformation of PVP adsorbed was markedly affected. On the other hand, any synergic effects have not been observed on adsorption of PVP on silica in the presence of a single-chained cationic surfaCtant.*Thus, it was found4J0that the single-chained anionic surfactants interact appreciably with PVP at the solidiliquid interface, probably due to the formation of a surface polymersurfactant complex. Actually, properties of aqueous solutions containing sodium dodecyl sulfate and PVP such as surface tension, equivalent conductivity, and viscosity have been examined.l1-l3 These studies suggest that the primary mechanism for the formation of the surfactant-polymer complex is a self-assembling of surfactant and polymer molecules driven by hydrophobic interaction or by a force similar to those encountered in the formation of surfactant micelles. Factors influencing surfactant-polymer association, such as temperature, salt, surfactant chain length, polymer structure, hydrophobicity, and a variety of surfactants, have been In particular, the effect of surfactant structure on the formation of the @
Abstract published inAdvanceACSAbstracts,August 15,1994.
(1)Somasundaran,P. J . Colloid Interface Sci. 1969,31,557. (2) Tadros, Th. F. J . Colloid Interface Sci. 1974,46,528. (3) Chibowski, S. J . Colloid Interface Sci. 1980,76,371. (4)Ma, C.; Li, C. J. Colloid Interface Sci. 1989,131,485. (5) Esumi, K.; Meguro, K. J . Colloid Interface Sci. 1989,129,217. (6) Maltesh, C.; Somasundaran, P. J . Colloid Interface Sci. 1992, 153,298. (7) Tanaka, R.; Williams, P. A,; Meadows, J.;Phillips, G. 0. Colloids Surf. 1992,66,63. ( 8 ) Esumi, K.; Oyama, M. Langmuir 1993,9,2020. (9) Esumi, K.; Matsui, H. Colloids Surf. 1993,80,273. (10)Otsuka, H.; Esumi, K. Langmuir 1994,10,45. (11)Lange, H. Kolloid 2.2.Polym. 1971,243,101. (12) Fadnavis, N. W.; Engbert, J. B. F.N. J . A m . Chem. SOC.1984, 106,2636. (13) Murata, M.; Arai, H. J . Colloid Interface Sci. 1973,44, 475. (14) Chari, K.; Lenhart, W. C. J . Colloid Interface Sci. 1990,137, 204. (15)Shirahama, K.;Ide, N. J . Colloid Interface Sci. 1971,54,450. (16) Witte, F. M.; Buwalda, P. L.; Engberts, J. B. F. N. ColloidPolym. Sci. 1987,265,42. (17) Saito, S. J . Colloid Interface Sci. 1960,15,283.
0743-7463/94l2410-3250$04.50l0
surfactant-polymer complex is of interest. On the basis of C13 NMR spectroscopy and surface tension measurements made by Chari and Lenhart,14 it is suggested that the behavior in aqueous solutions of PVP and SDS is very similar to that in aqueous solutions containing PVP and a double-chained surfactant, such as sodium bis(2ethylhexyl) sulfosuccinate (aerosol OT). The object of this paper is to investigate the interaction between a double-chained anionic surfactant, aerosol OT, and PVP on alumina and to compare with the results obtained from the single-chained anionic surfactant and PVP.
Experimental Section The spin-labeled PVP was preparedz3by polymerizing N vinylpyrrolidone and allylamine in ethanol using tert-butyl perbenzoate as an initiator, followed by a reaction with 4-isothiocyanato-2,2,6,6-tetramethylpiperidine-l-oxyl in dichloromethane at 40 "C. The obtained labeled PVP was purified with ethyl ether. The molar ratio of N-vinylpyrrolidone to allylamine in the labeled PVP determined by NMR was about 100:3. The molecular weight of the labeled polymer determined by static light scattering was about 16 000. Aerosol OT was obtained from Nikko Chemical Co. and was purified as follows. Aerosol OT was dissolved into benzene and then water was added. After the sample was shaken, the water phase was eliminated. This procedurewas repeated three times. Finally, aerosol OT was obtained by evaporating the benzene solution. a-Alumina was supplied by Showa Denko K.K., and the average diameter and specific surface area were 0.5pm and 10.0 mz g-l, respectively. The water used in all experiments was purified by a Milli-Q System (Nihon Millipore Co.) in which the specific conductivity of water fell below 0.1 pS cm-l. The adsorption of aerosol OT and PVP was obtained by measuring their concentration in solution before and after adsorptionat 25 "C. All suspensions in the presence of 10 mmol dm-3 NaCl were adjusted at about pH 3.5 and shaken to reach an equilibriumcondition for 24 h. The solids were separated by centrifugation,and the supernatant was analyzed using an ESR (18)Zana, R.; Lang, J.;Lianos, P. InPolymer Scienceand Technology; Microdomains in Polymer Solutions; Dubin, P., Ed.; Plenum Press: New York, 1985; Vol. 30, p 357. (19) Canabe, B. J . Phys. Chem. 1977,81,1639. (20) Goddard, E. D. Colloids Surf. 1986,19,225. (21) Hoffmann, H.; Huber, G. Colloids Surf. 1989,40,181. (22) Thalberg, K.; Lindman, B. J . Phys. Chem. 1989,93,1478. (23) Fox, K. K.; Robb, I . D.; Smith, R. J . Chem. Soc., Faraday Trans 1 1974,70,1186.
0 1994 American Chemical Society
Aerosol OT and PVP on Alumina
1994 3251
en (a)
4040
E 4:: 3 0
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2otI 6
01, 0
,
, 1
I
,
,
2
,
,
3
Equilibrium concn. of Aerosol OT / mmol dm
0
I
I
I
1
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1 -3
Equilibrium concn.of PVP / g dm -3
Figure 1. Adsorption isotherms of (a)aerosol OT and (b)PVP on alumina.
techniqueloto obtain the PVP concentration and using a dye methodz4to obtain the aerosol OT concentration. The ESR spectra were recorded on a JEOL JES 3-X spectrometer utilizing a 100-kHz field modulation and X-band microwaves. The slurries for the ESR measurements were prepared by centrifugation of the adsorption samples. A free polymer remaining slightly in the slurries did not significantly affect their ESR spectra at the soliMiquid interface. The
