| 摘要: | 粒狀材料無論是在工業界中或是日常生活上都扮演著舉足輕重的腳色，在此論文中，我們研究了乾粒狀材料（以空氣為介質）以及濕粒狀材料（以溶劑為介質）的特性及行為，甚至添加界劑於其中以改變其性質。我的研究分為三個部份，詳述如下： 高濃度的碳化矽粒子懸浮液通常應用在切割矽晶圓的切削液中，因此，如何使其穩定懸浮乃是一重要的議題。微米級的碳化矽粒子在乙二醇溶劑中非常容易沉降，即使粒子的聚集並未發生。然而，藉由添加正十二胺此種界劑將會形成粒子型的凝膠而使粒子穩定懸浮。透過流變性質的量測，我們發現儲存模數約為損失模數的三倍，此外，我們也可以觀察到由粒子間的作用力所造成的網狀結構，此結構的強度可由降伏應力來表示。界劑濃度對降伏應力的影響可區分為兩個區域：在較低的界劑濃度時，凝膠高度與降伏應力都會隨著界劑濃度上升而增加，然而當界劑濃度超過一特定值之後，凝膠高度與降伏應力則隨界劑濃度上升而下降。形成粒子型凝膠的機制如下：因正十二胺的尾鏈並不喜歡存在於溶劑，界劑分子會傾向利用尾鏈接在粒子的表面上，而粒子間的引力會透過吸附在不同粒子上界劑頭基的分子間氫鍵所構成。添加一般典型的界劑如SDS並無法形成粒子型凝膠，此外，在溶劑中添加鹽酸使其酸化也會破壞粒子型凝膠的生成。 粒狀材料包含許多肉眼可見的顆粒，其廣泛應用於許多領域之中且流動行為相當重要。然而，奈米粒狀材料的流動行為及特性則大大地迥異於一般的粒狀材料，奈米粒狀材料可在空氣中形成體積分率很低（5%）的粒子型凝膠，且其並不會受重力驅使而導致流動。我們發現奈米粒狀材料擁有很高的壓縮度，與氣體相似；但由於高的降伏應力及黏度，奈米粒狀材料也十分不易流動。此凝膠的形成是由於粒子間的凡得瓦耳作用力，此作用力可支撐奈米粒子的重量且抵抗剪切應力的破壞。 由於毛細作用力的影響，部分濕潤的粒狀材料大多具有可朔性。然而，我們發現完全濕潤的奈米粒狀材料有同樣具有可朔性，此性質是藉由凡得瓦耳引力所造成，此外，根據所使用溶劑的不同，奈米粒狀材料會形成所謂的凝膠態或玻璃態。當溶劑所造成的引力主導時，我們發現奈米粒狀材料在溶劑中會形成相分離，此狀態就是所謂的粒子凝膠狀態；相反地，當圍籠效應主導時，我們則可得到玻璃狀態。透過界劑的添加，我們也可使原本應形成玻璃狀態的系統轉換成凝膠狀態。 Granular material plays an important role in our daily life as well as in engineering and science. In my study, I investigate the behaviors and properties of dry granular materials and wet granular materials. Furthermore, the properties of granular materials can be changed by addition of the surfactants. There are three main topic in my paper, described as follow: The concentrated suspension of silicon carbide (SiC) particles are often used as cutting fluids for Si-wafer. How to maintain suspended states is thus essential. The suspension of micron-sized SiC particles in ethylene glycol (EG) is liable to sedimentation although the particles do not aggregate. By addition of surfactant dodecylamine, however, we show that the suspension can form particle gel. According to rheological measurements, the ratio of storage to loss modulus is about 3, indicating a weak gel. Moreover, the observation of dynamic yield stress reveals the existence of the structure caused by the particle-particle attraction. The influence of surfactant concentration on the gel properties can be classified into two regimes. At low concentration, both gel height and yield stress grow with increasing surfactant concentration. However, as the concentration exceeds a certain value, they decline with increasing surfactant concentration. A gelling mechanism has been proposed and examined. Since the tails of alkyl amines are solvophobic, the surfactant molecules in EG prefer to stay on the particle with the tail orienting toward the surface. The attraction between particles originates from hydrogen bonds formed between surfactant molecules adsorbed on different particles. Thus gelation fails when typical surfactants such as sodium dodecyl sulfate are employed. Acidification by HCl also hinders the gel formation by alkyl amine. Granular materials consisting of macroscopic grains have commercial applications and their flow behavior plays key role in geophysics. However, flow characteristics of nano-granules differ significantly from those of granules. The latter can form low-volume fraction (5%) particle gels in air and is difficult to exhibit gravity-driven granular flow. It is found that although dry nano-granules possess a high compressibility, close to gases, they are less susceptible to flow than granules due to high yield stress and viscosity. Such differences can be attributed to van der Waals attractions, which support the weight of nanoparticles to form aerogels and resist shearing deformation. The rheology of granular materials is relevant to many areas of nature and industry, from mountain avalanches and mud slides, to grain transport and storage. Partially wet granular medium is a mouldable material due to capillary cohesion and its behavior plays key roles in geophysics. However, completely wet nanogranules may also demonstrate mouldable properties via van der Waals attraction and they exhibit colloidal glass or gel characteristics, depending on the solvent. As solvent-enhanced attractions prevail, phase separation is observed and nanogranular gel can be obtained. In contrast, as cage effects dominate, the stable slurry is seen and the nanogranular glass can be prepared. Upon surfactant addition, however, the arrested glass state changes into colloidal gel due to the formation of hydrogen bonds between nanogranules. |
