Dispersion stability and microstructural transition of colloidal silica suspensions were examined by rheological measurements under either steady simple shear or oscillatory flow. Monodisperse silica particles were prepared by the so-called modified Stober method and were stabilized by either steric or electrostatic repulsive force. Depending upon the methods of stabilization, the suspension showed hard-sphere or soft-sphere response. In particular, silica suspensions exhibited hardsphere response when the silica spheres coated with 3-(trimethoxysilyl)propyl methacrylate (MPTS;CH₃O)₃Si(CH₂)₃OCOC(CH₃)=CH₂) were dispersed in a refractive-index matching solvent, tetrahydrofurfuryl alcohol. On the other hand, silica particles in aqueous media behaved like soft spheres with long-range elec-trostatic repulsive interactions when they were coated with steric layer of aminosilane coupling agent, N-[3-(trimethoxysilyl)propyl]ethylenediamine((CH₃O)₃Si(CH₂)₃NHCH₂CH₂NH₂). In this case, the electrostatic repulsion or equivalently the softness of the silica spheres was contorlled by the ionic strength using a symmetric salt KCI. Both the hardsphere and soft-sphere suspensions showed stable shear-thinning behavior without experiencing shear-induced flocculation. Moreover, the oscillatory shear rheology. showed that the electrostatically stabilized soft-sphere suspensions underwent a microstuctural transition from liquid-like to solid-like structure when either the particle loading increased or the ionic strength was recuced.

Dispersion Stability Silica Suspension Silane Coupling Agent Microstructure Phase Transition Hard Spheres Soft Spheres Rheological Behavior

Barnes HA, Hutton JF, Walters K, "An Introduction to Rheology," Elsevier Science Publishers, New York, USA (1989)
Barnes HA, J. Rheol., 33, 329 (1989) 
Bogush GH, Tracy MA, Zukoski CG, J. Non-Cryst. Solids, 104, 95 (1988) 
Brady JF, Chem. Eng. Sci., 56(9), 2921 (2001) 
Chen LB, Ackerson BJ, Zukoski CF, J. Rheol., 38(2), 193 (1994) 
Chow MK, Zukoski CF, J. Rheol., 39(1), 33 (1995) 
Chow MK, Zukoski CF, J. Rheol., 39(1), 15 (1995) 
Fagan ME, Zukoski CF, J. Rheol., 41(2), 373 (1997) 
Foss DR, Brady JF, J. Fluid Mech., 407, 167 (2000) 
Franks GV, Zhou ZW, Duin NJ, Boger DV, J. Rheol., 44(4), 759 (2000) 
Gast AP, Russel WB, Phys. Today, 51(12), 24 (1998)
Kose A, Ozaka M, Takano K, Kobayashi Y, Hachisu S, J. Colloid Interface Sci., 44, 330 (1973) 
Kose A, Hachisu S, J. Colloid Interface Sci., 55, 487 (1976) 
Larson RG, "The Structure and Rheology of Complex Fluids," Oxford University Press, New York, USA (1999)
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) 
Lee JD, Yang SM, J. Colloid Interface Sci., 205(2), 397 (1998) 
Lee JD, So JH, Yang SM, J. Rheol., 43(5), 1117 (1999) 
Lewis JA, J. Am. Ceram. Soc., 83, 2341 (2000)
Oh MH, So JH, Lee JD, Yang SM, Korean J. Chem. Eng., 16(4), 532 (1999)
Perez MQ, Femandez JC, Alvarez RH, Adv. Colloid Interface Sci., 95, 295 (2002) 
Philipse AP, Vrij A, J. Colloid Interface Sci., 128, 121 (1989) 
Quemada D, Berli C, Adv. Colloid Interface Sci., 98, 51 (2002) 
Russel WB, Saville DA, Schowalter WR, "Colloidal Dispersion," Cambridge University Press, New York, USA (1989)
So JH, Bae SH, Yang SM, Kim DH, Korean J. Chem. Eng., 18(4), 547 (2001)
So JH, Oh MH, Lee JD, Yang SM, J. Chem. Eng. Jpn., 34(2), 262 (2001) 
So JH, Yang SM, Hyun JC, Chem. Eng. Sci., 56(9), 2967 (2001) 
So JH, Yang SM, Kim C, Hyun JC, Colloids Surf. A: Physicochem. Eng. Asp., 190, 89 (2001) 
Stavov V, Zhdanov V, Meireles M, Molle C, Adv. Colloid Interface Sci., 96, 279 (2002) 
Stober W, Fink A, Bohn E, J. Colloid Interface Sci., 26, 62 (1968) 
Tadros TF, Adv. Colloid Interface Sci., 68, 97 (1996)