솔젤법으로 제조된 고농도 실리카 입자 분산계의 유변학적 거동

이재동; 양승만

Korean Journal of Rheology, Vol.10, No.1, 24-30, March, 1998

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솔젤법으로 제조된 고농도 실리카 입자 분산계의 유변학적 거동

Rheological Behaviors of Concentrated Silica Particle Suspensions Prepared by Sol-Gel Method

이재동, 양승만

초록

솔젤법을 이용하여 단분산의 실리카 입자를 제조하고 농도 변화에 따른 실리카 분산액의 유변학적 거동을 해석하였다. 단분산 실리카 입자의 제조는 솔젤법을 이용한 액상반응으로 제조하였고 입자의 안정화를 위하여 입자표면에 실란커플링제를 코팅하여 유기용매에서 안정성을 갖도록 하였다. 분산액의 농도에 따른 유변학적 거동을 조사하기 위하여 부피분율( )이 0.05인 희박 분산계로부터 =0.55의 고농도 분산계를 제조하였다. 솔젤법을 통하여 단분산 실리카 입자를 성공적으로 제조하였으며 실란커플링제인 γ-methacryloxypropyl triethoxysilane로 입자의 표면을 화학적 방법으로 처리하여 유기용매 상에서 알킬기의 작용에 의한 'hardsphere' 특성을 나타내도록 하였으며 동시에 분산안정성을 유지할 수 있었다. 입자 분산계는 =0.25 이하의 부피농도에서는 분산용매와 같은 뉴톤거동을 보여주었으며 이 이상의 농도에서는 비뉴톤거동인 전단 담화(shear thinning)현상과 high shear limiting viscosity를 나타내었다. 이 결과는 Krieger-Dougherty식을 따름이 확인되었으며 부피분율 -0.50 정도까지도 이 식이 잘 적용됨을 확인하였다. 부피분율 =0.50 이상의 고농도 입자 분산계는 급격한 점도의 증가와 함께 전단담화와 전단탁화(shear thickening) 현상이 모두 관찰되었다. 특히, 전단탁화를 일으키는 특성전단변형률(γ_cr) 이하의 전단변형률에서는 안정되고 빠른 점성반응(viscous response)을 보여주었으나 특성전단변형률 부근과 이상의 전단변형률 영역에서는 매우 불안한 거동이 보여짐을 확인하였다. 그러나 이러한 점도 거동은 가역적이며 전단변형률을 증가시킬 때와 감소시킬 때의 유변학적 거동이 거의 일치하였다.

Monosized silica particles were synthesized using sol-gel method and rheological behaviors of the silica suspension at various concentrations were investigated experimentally. To stabilize the silica particles in organic solvent, the surface of particle was coated through the chemical adsorption of a silane coupling agent, γ-methacryloxypropyl triethoxysilane. The effects of the concentration on the rheological properties were examined for various dispersions of different volume fractions (φ) ranging from dilute (φ=0.05)to concentrated limit (φ=0.55). The coated silica particles possessed the so-called 'hard sphere' characteristics and dispersion stability in an organic solvent with the aid of steric stabilization of the alkyl chain. When the suspensions had the volume concentration belowφ=0.25, they showed Newtonian behaviors like the medium solvent. On the other hand, non-Newtonian behavior such as shear thinning and high shear limiting viscosity were observed at the volume fraction above 0.25. These results were correlated satisfactorily with Krieger-Dougherty equation uptoφ=0.50. The highly concentrated dispersions above φ=0.50 exhibited an abrupt increase in viscosity, shear thinning and shear thickening behaviors. In particular, although the stable and fast viscous responses were observed below a critical shear rate (γ_cr at which shear thickening occurred, the rheological responses were unstable near or above γ_cr. However, these behaviors were reversible as confirmed by reversing successively the shear rate sweep tests.

Keywords:sol-gel method;silica;silane coupling agent;concentrated suspension;shear thinning;shear thickening

[References]

Brinker CJ, Scherer GW, "Sol-Gel Science," Academic Press, Inc., New York, U.S.A. (1990)
Stober W, Fink A, Bohn E, J. Colloid Interface Sci., 26, 62 (1968)
Bogush GH, Tracy MA, Zukoski CG, J. Non-Cryst. Solids, 104, 94 (1988)
van Helden AK, Jansen JW, Vrij A, J. Colloid Interface Sci., 81, 354 (1981)
Philipse AP, Vrij A, J. Colloid Interface Sci., 128, 121 (1989)
Lee JD, Yang SM, HWAHAK KONGHAK, 35(5), 782 (1997)
Lee JD, Yang SM, J. Colloid Interface Sci., to submitted (1998)
Barnes HA, Hutton JF, Walters K, "An Introduction to Rheology," Elsevier Science Publishers, New York, U.S.A. (1989)
Furth R, Cowper AD, "Investigations on the Theory of the Brownian Movement by A. Einstein," Dover Publications Inc., New York, U.S.A. (1956)
Batchelor GK, J. Fluid Mech., 41, 245 (1970)
Russel WB, Gast AP, J. Chem. Phys., 84, 1815 (1986)
Brady JF, J. Chem. Phys., 99, 567 (1993)
Krieger IM, Dougherty TJ, Trans. Soc. Rheol., 3, 137 (1959)
Metzner AB, Whitlock M, Trans. Soc. Rheol., 2, 239 (1958)
Hoffman RL, Trans. Soc. Rheol., 16, 155 (1972)
Hoffman RL, J. Rheol., 36, 947 (1992)
Boersma WH, Laven J, Stein HN, AIChE J., 36, 321 (1990)
Laun HM, Bung R, Hess S, Loose W, Hess O, Hahn K, Hadicke E, Hingmann R, Schmidt F, Lindner P, J. Rheol., 36, 743 (1992)
van Blaaderen A, Kentgens APM, J. Non-Cryst. Solids, 149, 161 (1992)
van der Werff JC, de Kruif CG, J. Rheol., 33, 421 (1989)
Bender J, Wagner NJ, J. Rheol., 40(5), 899 (1996)

[Referenced By]

[1] Brinker CJ, Scherer GW, "Sol-Gel Science," Academic Press, Inc., New York, U.S.A. (1990)

[2] Stober W, Fink A, Bohn E, J. Colloid Interface Sci., 26, 62 (1968)

[3] Bogush GH, Tracy MA, Zukoski CG, J. Non-Cryst. Solids, 104, 94 (1988)

[4] van Helden AK, Jansen JW, Vrij A, J. Colloid Interface Sci., 81, 354 (1981)

[5] Philipse AP, Vrij A, J. Colloid Interface Sci., 128, 121 (1989)

[6] Lee JD, Yang SM, HWAHAK KONGHAK, 35(5), 782 (1997)

[7] Lee JD, Yang SM, J. Colloid Interface Sci., to submitted (1998)

[8] Barnes HA, Hutton JF, Walters K, "An Introduction to Rheology," Elsevier Science Publishers, New York, U.S.A. (1989)

[9] Furth R, Cowper AD, "Investigations on the Theory of the Brownian Movement by A. Einstein," Dover Publications Inc., New York, U.S.A. (1956)

[10] Batchelor GK, J. Fluid Mech., 41, 245 (1970)

[11] Russel WB, Gast AP, J. Chem. Phys., 84, 1815 (1986)

[12] Brady JF, J. Chem. Phys., 99, 567 (1993)

[13] Krieger IM, Dougherty TJ, Trans. Soc. Rheol., 3, 137 (1959)

[14] Metzner AB, Whitlock M, Trans. Soc. Rheol., 2, 239 (1958)

[15] Hoffman RL, Trans. Soc. Rheol., 16, 155 (1972)

[16] Hoffman RL, J. Rheol., 36, 947 (1992)

[17] Boersma WH, Laven J, Stein HN, AIChE J., 36, 321 (1990)

[18] Laun HM, Bung R, Hess S, Loose W, Hess O, Hahn K, Hadicke E, Hingmann R, Schmidt F, Lindner P, J. Rheol., 36, 743 (1992)

[19] van Blaaderen A, Kentgens APM, J. Non-Cryst. Solids, 149, 161 (1992)

[20] van der Werff JC, de Kruif CG, J. Rheol., 33, 421 (1989)

[21] Bender J, Wagner NJ, J. Rheol., 40(5), 899 (1996)