| 摘要: | 溶液中的奈米粒子，會受到布朗運動的影響而均勻懸浮。懸浮液中，粒子間沒有強大的作用力，無法形成凝膠。文獻中形成膠體粒子型凝膠通常是藉由耗散力（Depletion force）的作用來構成網絡結構而形成凝膠。本文利用添加界面活性劑，使碳化矽粒子間產生氫鍵而形成膠體粒子型凝膠。發現有無添加正十二胺，在巨觀上使原本均勻分散的懸浮液，轉變成有澄清液面的懸浮液；在流變性質上，出現有儲存模數大於損失模數的特性，證實添加正十二胺後，系統具有凝膠特性。其他奈米粒子如：二氧化鈦、氧化鋁都可以藉由添加正十二胺，使其由懸浮粒子轉變成凝膠。其形成凝膠的機制是由NH2頭基形成氫鍵而形成網絡結構。使用碳鏈相同且頭基也可以形成氫鍵的正十二酸當作添加物，發現正十二酸亦可使碳化矽等懸浮粒子變成膠體粒子型凝膠。再度驗證可以藉由氫鍵作用力，使原本均勻分散的懸浮液，轉變成具有凝膠特性的膠體粒子型凝膠。 由上述可知懸浮液可藉由添加界面活性劑產生氫鍵，形成膠體粒子型凝膠。但發現有不需添加界面活性劑就可以形成凝膠的系統，如：碳化矽粒子在葵烷溶液中，以及分散在乙二醇溶液中的氧化鋅與氧化鋯奈米粒子，皆不需添加界面活性劑，即可形成膠體粒子型凝膠。本研究在探討不同界面活性劑對於形成凝膠結構的影響，及無添加界面活性劑的系統，是透過何種機制形成凝膠。 In general, nano-particles can be suspended in solution due to Brownian motion. Although van der Waals attractions between particles may lead to aggregation, they are not strong enough to form particle network. Typically, upon the addition of polymers, particle gel can be formed by depletion forces. In this work, we show that silicon carbide (SiC) particles are able to form nanoparticle gel in polar solvent ethylene glycol (EG) by the addition of hydrogen-bond forming surfactants. When the surfactant dodecylamine (DDA) is added, the SiC/EG system changes from uniform nano-particle suspension to sediment in the presence of clear solution. According to the rheological measurements, the storage modulus is greater than the loss modulus, i.e., G’ > G’’. That is, upon DDA addition, the sediment displays gel-like behavior. As two SiC particles covered with DDA are nearly in contact, hydrogen bonds can be formed between the primary amine head groups (-NH2) and thus result in interparticle attraction. On the basis of the same mechanism, we show that the addition of dodecanic acid, that possesses the same carbon chain length but different head group (-COOH) from DDA, can lead to the formation of nano-particle gel as well. In addition to the nano-particle gel induced by the addition of hydrogen-bond forming surfactants, we also observe the formation of nano-particle gel in surfactant-free solvent. The examples include SiC nano-particles in decane, ZnO nano-particles in EG, and ZrO2 nano-particles in water or EG. The possible mechanism responsible for particle gel induced by solvent is proposed. |
