Resolving the puzzle of ferrofluid dispersants

Langmuir

Volumn 16, Issue 24, 2000, Pages 9117-9120

  Tadmor, Rafael ^a,b   Rosensweig, Ronald E ^a   Frey, Joseph ^a   Klein, Jacob ^a  

^a WEIZMANN INSTITUTE OF SCIENCE   (Israel)

^b University of California   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

OLEIC ACID; PRECIPITATION (CHEMICAL); STEARIC ACID; SURFACE ACTIVE AGENTS; SUSPENSIONS (FLUIDS); THERMODYNAMIC STABILITY;

FERROFLUID DISPERSANTS;

FERROMAGNETIC MATERIALS;

EID: 0034318866     PISSN: 07437463     EISSN: None     Source Type: Journal    
DOI: 10.1021/la0009137     Document Type: Article

References (25)

1. Rosensweig, R. E. Sci. Am. 1982, 247, 136. Rosensweig, R. E. Chem. Eng. Commun. 1986, 19, 437. Rosensweig, R. E. Annu. Rev. Fluid Mech. 1987, 79, 437.
2. Rosensweig, R. E. Sci. Am. 1982, 247, 136. Rosensweig, R. E. Chem. Eng. Commun. 1986, 19, 437. Rosensweig, R. E. Annu. Rev. Fluid Mech. 1987, 79, 437.
3. Rosensweig, R. E. Sci. Am. 1982, 247, 136. Rosensweig, R. E. Chem. Eng. Commun. 1986, 19, 437. Rosensweig, R. E. Annu. Rev. Fluid Mech. 1987, 79, 437.
4. Raj, K.; Moskowitz, B.; Casciari, R. J. Magnetism Magnetic Mater. 1995, 149, 174-180.
5. Bailey, R. L. J. Magnetism Magnetic Mater. 1983, 39, 178-182.
6. Rosensweig, R. E. Ferrohydrodynamics; Cambridge: 1985.
7. Scholten, P. C. Thermodynamics of Magnetic Fluids; Hemisphere: Washington, DC, 1978.
8. Rosensweig, R. E.; Nestor, J. W.; Timmins, R. S. Mater. Assoc. Direct Energy Convert. Proc. Symp. AIChE-I. Chem. Eng. Ser. 1968, 5, 104.
9. The STAI was prepared according to Kodawa et al., J. Phys. Chem. 1990, 94, 815, and the OTAI was prepared according to Annby et al., Chem. Scr. 1987, 27, 445; both were recrystallized twice from a methanol-acetone mixture. Elemental matches for both were confirmed with NMR analysis.
10. The STAI was prepared according to Kodawa et al., J. Phys. Chem. 1990, 94, 815, and the OTAI was prepared according to Annby et al., Chem. Scr. 1987, 27, 445; both were recrystallized twice from a methanol-acetone mixture. Elemental matches for both were confirmed with NMR analysis.
11. ii is the Hamaker constant of species i. In the present configuration, where HD liquid (3) is on top of the solid substrate (STAI coating on the mica) (2), one expects (from the values of the refractive indices and the Lifschitz relation) that this inequality holds and that for dispersion force dominance the HD should wet the solid substrate.
12. Klein, J.; Kumacheva, E. J. Chem. Phys. 1998, 108, 6996-7009.
13. Janik, J.: Tadmor, R.; Klein, J. Langmuir 1997, 13, 4466.
14. Gee, M. L.; Israelachvili, J. N. J. Chem. Soc., Faraday Trans. 1990, 86, 4049.
15. 4 across HD from the Lifschitz relation and the known refractive indices of the materials (see e.g. ref 18).
16. Hamaker, H. C. Physica IV 1937, 300, 341.
17. de Gennes, P. G. Scaling concepts in polymer physics; Cornell University Press: Ithaca, NY, 1975; p 74.
18. s, assumes the volume fraction Φ is constant during the compression (and similar to its value within the unperturbed layers). This is a reasonable approximation, since the steric repulsion rises very rapidly once the layers overlap (Figure 2b) so that the extent of compression (and δ) remains small.
19. For example, we use an expression-eq 2-developed for polymer chains while the surfactant layers consist of 18-mers only.
20. BT attraction estimated earlier from the SFB profiles arises mostly from the use of the full Hamaker expression rather than the Derjaguin approximation, which is valid only at R ≫ D, and partly from the steric contributions.
21. Israelachvili, J. N. Intermolecular and surface forces; Academic: London, 1992.
22. 18 is ∼1.65 Å.
23. 4 and thus are expected to be insensitive to the underlying substrate.
24. The hexadecane medium is a 99+% grade solvent (Aldrich i and used as received to simulate the HD used in ferrofluid dispersions; it thus probably contains an equilibrium (low) waterconcentration. Though trace water can have a marked effect on surface forces in hydrocarbon liquids (see e.g. McGown, D. N. L.; Parfitt, G. D. Kolloid Z. Z. Polym. 1967, 220, 56. Christenson, H. K.; Israelachvili, J. N. J. Colloid Interface Sci. 1987, 119, 194-202), this is generally for interacting hydrophilic surfaces and is not expected to affect the results for strongly hydrophobic surfaces, as in the present case or in the case of surfactant-coated ferrofluid particles.
25. The hexadecane medium is a 99+% grade solvent (Aldrich i and used as received to simulate the HD used in ferrofluid dispersions; it thus probably contains an equilibrium (low) waterconcentration. Though trace water can have a marked effect on surface forces in hydrocarbon liquids (see e.g. McGown, D. N. L.; Parfitt, G. D. Kolloid Z. Z. Polym. 1967, 220, 56. Christenson, H. K.; Israelachvili, J. N. J. Colloid Interface Sci. 1987, 119, 194-202), this is generally for interacting hydrophilic surfaces and is not expected to affect the results for strongly hydrophobic surfaces, as in the present case or in the case of surfactant-coated ferrofluid particles.