| dc.description.abstract | Colloidal particles in a solution tend to adhere together due to van der Waals attraction and form aggregates of increasing size which may settle out due to gravity. The stability of a colloidal dispersion can be achieved by introducing repulsions among particles such as electrostatic and steric stabilization. For such a kinetically stable suspension, the balance between the downward gravitational force and the upward Brownian motion leads to the sedimentation equilibrium with a characteristic length kBT/?mg, where kBT represents the thermal motion and ?mg the apparent weight.
In this work, the stability of concentrated suspensions (50 wt%) such as silicon carbide powder (SiC) in ethylene glycol, used as a cutting liquid for wafer slicing, can be attained by the addition of dodecylamine (DDA, C12-NH2). In general, a suspension of particles showing no setting velocity is believed to be a dispersion stabilized by some mechanism. Since the particle size is 9 ?m and the density 3.22 g/cm3, the sedimentation length is as large as about 1 ?m. This result cannot explain the experimental observation: an apparently uniform colloidal dispersion.
A possible explanation is that such a suspension of SiC particles is a particle gel instead of a colloidal dispersion. However, the gelation of the colloidal particles is generally disrupted by gravitational collapse. The rheological property measurement shows that the storage modulus is greater than the loss modulus (G’ > G’’) and therefore confirm that the suspension is gel-like. Such colloidal gels can also be formed by SiO2, CuO, and Cu2O particles. In addition to explore the gelling mechanism such as the nature of associative bonds and microscopic structure, the influences of particle concentration, surfactant characteristics, and additives on the gel properties are investigated as well.
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