TY - JOUR
T1 - AFM surface force measurements conducted with silica in CnTACl solutions
T2 - Effect of chain length on hydrophobic force
AU - Zhang, Jinhong
AU - Yoon, Roe Hoan
AU - Eriksson, Jan Christer
N1 - Funding Information:
The authors gratefully acknowledge the financial support received from the U.S. Department of Energy (DE-FC26-01NT41091).
PY - 2007/6/15
Y1 - 2007/6/15
N2 - Surface forces were measured using an AFM with silica surfaces immersed in CnTACl (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 nm 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 CnTACl 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.
AB - Surface forces were measured using an AFM with silica surfaces immersed in CnTACl (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 nm 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 CnTACl 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.
KW - CTACl homologues
KW - Charged patch
KW - Film tension
KW - Hydrophobic force
KW - Long-range attraction
KW - Point of charge neutralization
KW - Water structure
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U2 - 10.1016/j.colsurfa.2007.01.048
DO - 10.1016/j.colsurfa.2007.01.048
M3 - Article
AN - SCOPUS:34247104086
VL - 300
SP - 335
EP - 345
JO - Colloids and Surfaces A: Physicochemical and Engineering Aspects
JF - Colloids and Surfaces A: Physicochemical and Engineering Aspects
SN - 0927-7757
IS - 3 SPEC. ISS.
ER -