溶液中的膠體粒子因為凡得瓦引力的作用會趨向相互靠近，當膠體粒子體直徑增加時，粒子形成聚集且受眾力影響而沉降。膠體分散的穩定性是由於粒子間的排斥力所造成，如靜電斥力及空間斥力。對於這種動力學的穩定懸浮而言，造成粒子沉降的重力及向上懸浮的布朗運動達成平衡，其特徵長度為kBT/Δmg，其中kBT代表熱擾動而Δmg為表觀重量。 本研究中所使用的系統為高濃度粒子如碳化矽（SiC） 懸浮於乙二醇中，此為晶圓切片時所使用之切削液，添加dodecylamine（DDA, C12-NH2）可達到穩定懸浮。一般而言，粒子的均勻懸浮一定有其特殊機制。本研究所使用的碳化矽粒子直徑為9.5 μm，密度為3.22 g/cm3，遠大於膠體懸浮之特徵長度1μm，此機制恐不適用。 因此本研究認為碳化矽粒子之懸浮並非之前所提之膠體懸浮，而是類似於凝膠狀之結構，然而此凝膠結構會因重力影響而崩壞。此懸浮液透過其流變性質發現其儲存模數會大於其損失模數（G' > G'），證實其為凝膠結構。其它粒子如二氧化矽（SiO2）、氧化銅（CuO）、氧化亞銅（Cu2O）等皆可得到此種凝膠結構。另外，除了研究此凝膠膠結構的形成機制外，本研究亦探討微結構及其相互間之鍵結、界面活性劑對凝膠結構的影響、凝膠之其它特殊性質等。 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.
