Sains Ma1aysiana 28: 101-118 (1999)                                                                             Sains Fizis dan Gunaan/

                                                                                                                                            Physical and Applied Science

Negative Surface Viscosities in Fluid-Fluid Interfaces

with Adsorbed Insoluble Surfactants

D.M.A. Buzza

Department of Physics, Astronomy and Polymer

I.RC. University of Leeds

Leeds LS2 9JT United Kingdom

ABSTRACT

Recent measurements of the surface viscoelasticity of liquid surfaces with adsorbed surfactant using surface light scattering have yielded negative dilational viscosities (ε’ < 0). In this paper, we present a physical explanation for this phenomenon by constructing a molecularly based theory for the interfacial viscoelasticity of an insoluble surfactant monolayer. Using the interfacial viscoelasticity, we then calculate the resultant surface light scattering from the interface. Our microscopic theory predicts the presence of two additional surface elastic constants neglected in current treatments, namely a bending modulus, κ and a coupling constant λ. We show that for thick monolayers, the coupling constant λ can lead to apparent negative values of ε’. This is the first time that this result has been explained for insoluble monolayers using a physically realistic model.

ABSTRAK

Pengukuran kelikatkenyalan permukaan yang terkini terhadap permukaan cecair dengan surfaktant terjerap melalui penyerakan cahaya telah menunjukkan kelikatan dilatasi negatif (ε’ < 0). Kertas kerja ini memberikan pemerihalan fizis fenomena ini dengan membina satu teori berasaskan molekul bagi kelikatkenyalan antaramuka dalam satu surfaktant monolapisan tak larut. Dengan menggunakan kelikatkenyalan antaramuka ini, hasil serakan cahaya permukaan dari antaramuka ini telah dikira. Teori mikroskopik ini menjangka kewujudan dua pemalar kekenyalan permukaan yang tidak diambilkira dalam pengiran semasa iaitu modulus membengkok κ dan pemalar gandingan λ. Dalam kertas ini ditunjukkan bahawa untuk monolapisan yang tebal, pemalar gandingan boleh memberikan nilai ε’ yang nampak negatif. Kertas ini memberikan pemerihalan pertama untuk monolapisan tidak larut dengan menggunakan model fizik yang realistik.

RUJUKAN/REFERENCES

Alexander, S. 1997 Adsorption of Chain Molecules with a Polar Head a Scaling Description J. Phys. (Les Ulis, Fr.) 38: 983-987

Buzza, D. M. A., Jones, J. L., McLeish, T. C. B. & Richards, R. W. 1998 Theory of Surface Light Scattering from a Fluid-Fluid Interface with Adsorbed Polymeric Surfactants J. Chem. Phys. 109: 5008-5024

Buzza, D. M. A., Lu, C.-Y. D. & Cates, M. E. 1995. Linear Shear Rheology of Incompressible Foams. J. Phys. II France 5: 37-52

deGennes, P.-G. 1976. Scaling Theory of Polymer Adsorption. J. Phys (Les Ulis, Fr.) 37, 1445-1452; deGennes, P. -G. 1980 Conformations of Polymers Attached to an Interface Macromolecules 13: 1069-1075

Earnshaw, J. C. & McCoo, E. 1995. Surface Light-Scattering Studies of Surfactant Solutions, Langmuir 11: 1087-1100

Earnshaw, J. C., McGivern, R. c., McLaughlin, A. C & Winch P. J. 1990. Light-Scattering Studies of Surface Viscoelasticity: Direct Data Analysis. Langmuir 6: 649-666   

Earnshaw, J. C. & McLaughlin, A.C. 1989. The Surface Viscoelasticity of Surfactant Solutions and High Frequency Capillary Waves. Prog. Colloid. Polym. Sci. 79: 155-161

Earnshaw, J. C. & McLaughlin, A. C. 1993. Waves at Liquid Surfaces II. Surfactant Action and Coupled Oscillators. Proc. R. Soc. London A 440: 519-535

Earnshaw, J. C. & Sharpe, D. J. 1996. Surface Viscoelasticity of a Foam-forming Solution J. Chem. Soc. Faraday Trans. 92(4): 611-618

Forster, D. 1975. Hydrodynamic Fluctuations, Broken Symmetry. and CorrelationFunctions. Reading, Massachusetts: W. A. Benjamin Inc.

Goodrich, F. C. 1962. On the Damping of Water Waves by Monomolecular Films.J. Phys. Chem. 66: 1858-1863

Goodrich, F. C. 1981. The Theory of Capillary Excess Viscosities. Proc. R. Soc. London A 374: 341-370

Hennenberg, M., Chu, X. -L., Sanfeld, A. & Velarde, M. G. 1992. Transverse and Longitudinal Waves at the Air-Liquid Interface in the Presence of an Adsorption Barrier. J. Colloid Interface Sci. 150: 7-21

Kats, E. I. & Lebedev, V. V. 1988. Dynamics of Langmuir Films Soviet Phys. JETP 67: 940-948

Kramer, L. 1971. Theory of Light Scattering from Fluctuations of Membranes and Monolayers. J. Chem. Phys. 55: 2097-2105

Landau, L. D. & Lifshitz, E. M. 1987. Fluid Mechanics. Oxford: Pergamon Press.

Landau, L. D. & Lifshitz, E. M. 1989. Statistical Physics. Oxford: Pergamon Press.

Langevin, D., Meunier, J. & Chatenay, D. 1984. In Surfactants in Solution, Mittal K.L. & Lindman, B. eds. Vol. 3

Langevin, D., Ed. 1992. Light Scattering by Liquid Surfaces and Complementary Techniques. New York: Marcel Dekker.

Levich, V. G. 1962. Physicochemical Hydrodynamics. Englewood Cliffs, N.J: Prentice Hall.

Lucassen, J. 1968. Longitudinal Capillary Waves Trans. Faraday. Soc. 64: 2221-2229

Lucassen, J. & van den Tempel, M. 1972. Chem. Eng. Sci. 27: 1283

Lucassen-Reynders, E. H. & Lucassen, J. 1969 Properties of Capillary Waves. Advan. Colloid lnterface Sci. 2: 347-395

Milner, S. T. & Witten, T. A. 1988. Bending Moduli of Polymeric Surfactant Interfaces. J. Phys. France 49: 1951-1963

Milner, S. T., Witten, T. A. & Cates, M. E. 1988. Theory of the Grafted Polymer       Brush. Macromolecules 21(8): 2610-2619

Peace, S. K. & Richards, R. W. 1996. Capillary Wave Fluctuations of Spread Films of an Amphiphilic Graft Copolymer at the Air-water Interface Polymer. 37(22): 4945-4951

Peace, S. K., Richards, R. W., Taylor, M. R, Webster, J. R. P. & Williams, N. 1998. Organization of an Amphiphilic Graft Copolymer at the Air-water Interface: A Neutron Reflectometry Study. Macromolecules 31(4): 1261-1268

Peace, S. K., Richards, R. W. & Williams, N. 1998. Surface Quasi-Elastic Light Scattering from an Amphiphilic Graft Copolymer at the Air-Water Interface. Langmuir 14: 667-678

Pippard, A. B. 1988. The Physics of Vibration, Vol. 1. Cambridge, England: Cam­bridge University Press.    

Richards, R W. & Taylor, M. R. 1996. Long-wavelength Dynamics of Spread Films of Poly(methyl methacrylate) and Poly(ethylene oxide) at the Air/water Inter­face. J. Chem. Soc. Faraday Trans. 92: 601-610

Richards, R. W. & Taylor, M. R. 1997. Relaxation Processes in Surface Excess Layers of Aqueous Solutions of Poly (ethylene oxide). Macromolecules 30(13): 3892-3899

Sharpe, D. & Eastoe, J. 1996. Properties of Surfactant Monolayers Studied by Surface Light Scattering. Langmuir 12: 2303-2307

van den Tempel, M. & Lucassen-Reynders, E. H. 1983. Relaxation Processes at Fluid Interfaces. Advan. Colloid Interface Sci. 18: 281-301.