| Summary: | 二氧化鈦分散液其應用範圍廣泛，例如在塗料、化妝品、光催化、抗菌劑、環境方面等領域的應用日益漸增，不過由於二氧化鈦粒子與粒子之間會有凡得瓦吸引力的作用，造成團聚的現象，導致分散液穩定性變差的情況，影響其使用優點。因此如何降低分散液的二次平均粒徑及提升穩定性是一項很重要的議題。在本研究中，利用超臨界二氧化碳輔助製備二氧化鈦分散液，基礎流體使用去離子水，並添加六偏磷酸鈉做為分散劑，改變不同的超臨界二氧化碳分散條件，如溫度、壓力、飽和時間、分散液濃度與製程方式等，探討不同的分散條件與製程對二氧化鈦分散液的二次平均粒徑、均勻性和穩定性的影響，並進一步研究添加共溶劑之後，對分散液的穩定性和分散性之改變，過程中利用紫外光-可見光分光光譜儀(UV-Vis)、高速離心機、pH計、穿透式電子顯微鏡(TEM)、Zeta電位分析儀等儀器對分散液進行分析。根據以上實驗結果，本文獲得以下重要成果： (1)在分散液的二氧化鈦濃度為0.1 wt%的情況下，其TEM二次平均粒徑為366±295 nm，經過超臨界二氧化碳一次分散，且溫度為55℃，壓力為4000 psi及飽和時間為30 min的分散條件下，其TEM二次平均粒徑為148±68 nm，下降幅度達59%；而降低分散液濃度至0.005 wt%後，分散後的TEM二次平均粒徑為127±68 nm。此表示超臨界二氧化碳滲透至顆粒聚集的縫隙中，並經快速洩壓，有助於聚集的粒子分散之功效。 (2)在分散液的二氧化鈦濃度為0.1 wt% 的情況下，超臨界二氧化碳溫度為55℃，壓力為4000 psi及飽和時間為30 min的分散條件下，且經過同樣的超臨界二氧化碳條件重複分散三次後，其TEM的二次平均粒徑為126±63 nm，因為在進行第二次分散時，分散液之粒徑比第一次分散前還要小，超臨界二氧化碳能滲透至顆粒聚集更微小的縫隙中，增加其分散力。此意味著，在高濃度的情況之下，重複超臨界二氧化碳分散可以使聚集的二次平均粒徑有變小的趨勢。 (3)在分散液二氧化鈦濃度為0.005 wt%情況下，添加六偏磷酸鈉當作分散劑，經由zeta電位分析及變化pH值得知，當分散劑添加量為二氧化鈦濃度的兩倍時，最大的zeta電位為-53.7 mV，此表示添加六偏磷酸鈉作為分散劑，會解離出磷酸根離子吸附在二氧化鈦顆粒表面，因此分散液有較大負電荷的靜電排斥力而具有良好的穩定性，而超臨界二氧化碳溶於分散液中會產生弱酸性的碳酸，其較穩定的酸鹼值為6.25，呈現弱酸的現象，DLS測量的二次平均粒徑為317 nm。 (4)由UV-Vis和高速離心機測試證實，在六偏磷酸鈉的水溶液中加入適當的乙二醇，發現水和乙二醇比例為1：1的情況下，有助於提升分散液之穩定性，其穩定度增加72.7%，此因為乙二醇黏度較高，加至水溶液內可增加基礎流體的黏度，故可減緩粒子與粒子之間的碰撞，使分散液安定化。 (5)由沉澱法測試得知，利用超臨界二氧化碳分散所獲得濃度為0.1 wt%的二氧化鈦分散液，其儲存時間可超過三個星期，且添加適當的乙二醇，如比例為1：1的情況下，其分散穩定性比去離子水作為基礎流體的分散液好，也證實添加乙二醇有助於增加分散液的穩定性。 Titanium dioxide dispersion solution was widely applied for coating, cosmetic, photocatalytic, antibacterial agents, environmental and so on. However, between of particles and particles have the Van Der Waals’ forces, resulting in reduce the stability of titanium dioxide dispersion solution, and affecting their application. Therehore, how to reduce the secondary average particle size and enhance the stability of the dispersion solution is a very important issue. In this study, we preparation of titanium dioxide dispersion solution assisted by supercritical carbon dioxide.The base fluid was deionized water, and sodium hexametaphosphate was added as a dispersant, and then we changed the different dispersion conditions of supercritical carbon dioxide, such as temperature, pressure, saturation time, dispersion solution concentration, co-solvent of base fluid and the process methods to investigate the secondary average particle size and uniformity of the titanium dioxide dispersion in base fluid. Finally, we discussed the stability of titanium dioxide dispersion in solution. In the experiment, we characterized titanium dioxide dispersion solution by ultraviolet-visible absorption spectroscopy (UV-Vis), high-speed centrifugation, pH meter, transmission electron microscopy (TEM) and zeta potential instrument. As shown in the results, we surmise the following remarks: (1)When the concentration of titanium dioxide dispersion in solution with sodium hexametaphosphate was 0.1 wt%, the secondary average particle size was 366±295 nm and 148±68 nm, rescpectively, measured from the TEM before and after dispersing with supercritical carbon dioxide; and then reduced the concentration of titanium dioxide dispersion in solution to 0.005 wt%, the secondary average particle size was 127±68 nm after dispersing with supercritical carbon dioxide. It means that supercritical carbon dioxide penetrates the pores of aggregated particles, and then rapidly depressurize to separate aggregated particles in solution. (2)Under the conditions of 0.1 wt% titanium dioxide dispersion in solution, the temperature of 55℃, the pressure of 4000 psi, and the saturation time for 30 min, the dispersion of supercritical carbon dioxide was repeat by three times, which results in that the secondary average particle size was 126±63 nm measured from the TEM. This was that because the particle size of the second dispersion was smaller than that of the first dispersion, so that the supercritical carbon dioxide can penetrate the smaller pores in the aggregated particles and increase its dispersibility. It means that repeated the same conditions dispersion of supercritical carbon dioxide can decrease the secondary mean particle size of aggregates particle in solution. (3)As the concentration of titanium dioxide dispersion in solution was 0.005 wt%, and the addition of sodium hexametaphosphate was twice times of concentration of titanium dioxide, the maximum zeta potential of dispersion solution was -53.7 mV by zeta potential instrument. This suggests that the sodium hexametaphosphate as a dispersant will dissociate from the phosphate ions and adsorbed on the surface of the titanium dioxide particles, induceing that titanium dioxide dispersion in solution has a large negative charge of the electrostatic repulsive force and has good stability. And supercritical carbon dioxide dissolved in the dispersion will produce carbonic acid, which pH value was 6.25 in the dispersion solution. The secondary average particle size was 317 nm measured from the DLS. (4)By means of UV-Vis associated with high-speed centrifugation method, the addition of sodium hexametaphosphate was confirmed to enhance the dispersion of titanium dioxide in solution by supercritical carbon dioxide, which the optimal volume ratio of ethylene glycol and deionized water was 1：1 and its stability increased by 72.7%. It will help to enhance the stability of the solution. Because the viscosity of ethylene glycol was higher than deionized water, which can slow down the collision between particles and particles, so that enhance the stability of the solution. (5)The lifetime of as-prepared 0.1 wt% TiO2 dispersion solution achieve three weeks measured by sedimentation method in this study. The volume ratio of ethylene glycol and deionized water was 1：1. It will help to enhance the stability of the solution. 摘要 i Abstract iii 目錄 vi 圖目錄 ix 表目錄 xii 第一章 緒論 1 1-1 前言 1 1-2 研究動機 2 1-3 研究方法 3 1-4 論文架構 5 第二章 文獻回顧 6 2-1二氧化鈦 6 2-2分散液製備 9 2-3機械力分散 10 2-3-1 超臨界流體 12 2-3-2 超臨界二氧化碳介紹 15 2-3-3 超臨界流體分散法 17 2-4分散系統之穩定 19 2-4-1 膠體特性 20 2-4-2 粒子間的作用力 23 2-4-3 提升二氧化鈦分散液穩定性方法 25 第三章 研究方法 27 3-1二氧化鈦分散液 28 3-1-1分散劑比例最佳化 28 3-1-2 穩定性探討 30 3-2 改變超臨界二氧化碳分散條件 32 3-3 半連續式分散 39 3-4 共溶劑為基礎流體分散 43 3-5 穩定度測試 45 3-6 儀器分析 48 3-7 實驗材料與儀器設備 59 3-7-1 材料規格 59 3-7-2 儀器設備 62 第四章 結果與討論 63 4-1 二氧化鈦分散液 63 4-1-1 分散劑比例最佳化 63 4-1-2 分散液pH值與穩定性 67 4-2 改變超臨界二氧化碳分散條件 69 4-2-1 不同溫度之分散 71 4-2-2 不同壓力之分散 76 4-2-3 不同時間之分散 80 4-2-4 不同濃度與時間之分散效果 85 4-3 半連續式分散 92 4-4 共溶劑為基礎流體分散 97 4-5 分散液穩定度 105 4-5-1分散劑及超臨界二氧化碳分散穩定度 105 4-5-2去離子水和不同比例共溶劑穩定度 108 4-5-3 沉澱實驗 112 第五章 結論與未來方向 116 5-1 結論 116 5-2 未來延續工作 118 參考文獻 119
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