陸駿逸臺灣大學:化學研究所林凡硯Lin, Fan-YenFan-YenLin2010-06-302018-07-102010-06-302018-07-102008U0001-2107200818351600http://ntur.lib.ntu.edu.tw//handle/246246/187437當以高剪切率攪動一個濃的膠體懸浮系統時，在系統內的粒子可能會因受到外力的推擠而在有限的空間中使其運動受到阻塞，這樣的動力學結果讓整體膠體系統的運動行為有如固體一般，而且系統所對應到的剪切應力會隨著時間快速增加。但是當持續以固定的剪切率量測系統時，上述所對應到的剪切應力在達到最高值後便隨著時間而逐漸衰退，因此當以時間為橫軸時，可看到相對應的剪切應力出現一個又一個的特徵峰圖形，且其峰值數倍於基準線，這樣的特徵峰代表了膠體系統出現阻塞現象。我們的研究中使用二氧化矽粒子的膠體懸浮溶液在高體積分率濃度下去研究膠體系統的阻塞現象其剪切應力和剪切率之間的關係。在特定的剪切率值之上，可發現膠體系統出現阻塞現象以及其相對應的剪切應力有劇烈地震盪。們使用不同的剪切率去研究膠體系統的動態相圖，當系統處於會發生阻塞現象的區域時，其剪切應力在以時間為橫軸時會出現巨大的特徵峰。我們試圖使用兩個遞減的指數函數去擬合阻塞特徵峰的衰退曲線，我們的系統在衰退時具有兩特徵時間，此種現象相似於Mode Coupling Theory在衰退時也具有兩特徵時間的情形。們並且將出現在時間橫軸上的特徵峰依其形狀分為四個類別。另外，在時間橫軸上第一個出現的特徵峰展現了長壽的特質，且這也代表了系統的阻塞結構具高的塑性。不同於典型易碎(fragile)的阻塞系統，我們的研究結果展現了另一種有趣的阻塞現象。When a concentrated colloidal suspension system is sheared at high shear rate, the flow might lead to the arrest of the particles to form a percolated structure so that the colloidal system becomes solid-like. The particles in the colloidal system are jammed by the external shear flow and the shear stress as a function of time increases sharply. At the fixed shear rate condition, the percolated structure will eventually break and the stress value falls to become a peak as a function of time. There are consecutive peaks in the continuous shear flow experiment. The maximal values of theses peaks are several times higher than the baseline. This signals the presence of the jamming state. In our experimental study, we use the silica suspension. The shear stress-shear rate relation is measured for the relatively high volume fraction. Above the threshold shear rate, we find that the system is in the jamming region and the shear stress will oscillate largely. We choose several different shear rates to study the dynamic phase diagram. In the jamming region, the shear stress shows giant peaks with the oscillating time evolution. e also analyze the peak relaxation. The relaxations of the jamming peak are fitted by the double exponential relaxations, where the two relaxation times are similar to the mode coupling theory of the glass. The observed peak shapes are classified into four types. Moreover, the relative long-life leading jamming peaks indicate the plastic nature of the jammed structure. Our results reveal an interesting jamming phenomenon, which is different from the classical fragile jamming systems.Contents謝 Ibstract III文摘要 Vontents VIIable Captions VIIIigure Captions IXhapter 1 Introduction 1-1 Jamming Phase Diagram 1-2 Slow dynamics of glass 5-3 Shear induce jamming 9hapter 2 Experimental Methods 13-1 Rheometer 13-2 AC-Impedance 15-3 Dynamic light scattering (DLS) 15-4 Sample preparation 15hapter 3 Results and Discussion 19-1 The effects of the solvent purity and the sampling frequency 20-1-1 Solvent purity 20-1-2 Sampling frequency 21-2 The relation of shear rate and shear stress 24-3 Relaxation fitting of time evolution of stress in different imposed shear rates 27-3-1 Relaxation before jamming happening 27-3-2 Relaxation of the jamming peaks 38-3-3 Baseline decay 48-3-4 Summary 52-4 The peak types 57-5 Peak interval time 71-6 The comparison between silica0.5588 and silica0.5625 73-7 Silica0.57 78-8 Particle size distribution 80onclusions 83eference 851055169 bytesapplication/pdfen-US膠體系統流變學阻塞現象Colloidal systemRheologyJammingthesishttp://ntur.lib.ntu.edu.tw/bitstream/246246/187437/1/ntu-97-R95223017-1.pdf