AFM surface force measurements conducted with silica in C(n)TACl solutions: Effect of chain length on hydrophobic force
2007 (English)In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, Vol. 300, no 3, 335-345 p.Article in journal (Refereed) Published
Surface forces were measured using an AFM with silica surfaces immersed in C(n)TACl (n = 12-18) solutions in the absence of added salt. The results showed long-range attractive forces that cannot be explained by the DLVO theory. The long-range attractions increased with increasing surfactant concentration, reaching a maximum at the point of charge neutralization (p.c.n.) and then decreased. The long-range forces decayed exponentially, with the decay lengths increasing from 3 to 32 run as the chain length of the surfactants increased from C-12 to C-18. The measured forces can be fitted to the charged-patch model of Miklavic et al. [S.J. Miklavic, D.Y.C. Chan, L.R. White, T.W. Healy, J. Phys. Chem. 98 (1994) 9022-9032] by assuming patch sizes that are much larger than the values reported in the literature. It was found that the decay length decreases linearly with the effective concentration of the CH2/CH3 groups of the C(n)TACl homologues raised to the power of -1/2, which is in line with the Eriksson et al.'s hydrophobic force model derived using a mean-field approach. It appears, therefore, that the long-range attractions observed in the present work are hydrophobic forces originating from changes in water structure across the thin surfactant solution film between the silica surfaces. It is conceivable that hydrocarbon chains in solution disrupt the surface-induced water structure and cause a decrease in hydrophobic force. This observation may also provide an explanation for the very long-range forces observed with silylated, LB-deposited, and thiol-coated surfaces.
Place, publisher, year, edition, pages
2007. Vol. 300, no 3, 335-345 p.
C(n)TACl homologues, long-range attraction, hydrophobic force, point of charge neutralization, charged patch, film tension, waterstructure
Engineering and Technology
IdentifiersURN: urn:nbn:se:kth:diva-39565DOI: 10.1016/j.colsurfa.2007.01.048ISI: 000246748500012ScopusID: 2-s2.0-34247104086OAI: oai:DiVA.org:kth-39565DiVA: diva2:442026
13th International Conference on Surface Forces Location: Moscow, Russia, Date: JUN 28-JUL 04, 2006 2011-09-202011-09-122011-09-20Bibliographically approved