【作者】 孙晓燕；

【导师】 马余强； 张泽新；

【作者基本信息】 苏州大学 ， 凝聚态物理， 2014， 博士

【摘要】 作为凝聚态物理学中的两大基本问题,结晶和玻璃化转变,是近几十年来人们研究的热点话题。我们知道,胶体在一定条件下,既可以经历结晶成核过程转变为规整排列的晶体；也可以经历玻璃化过程转变为无序的胶体玻璃。尽管晶体和玻璃在生活中以及自然界中普遍存在,人们在过去的几十年中也对胶体的结晶和玻璃化转变做了大量的研究,然而人们还是不能很清楚的认识和理解胶体结晶成核过程和玻璃化转变过程。为了更好地理解胶体的相变行为,也为了能对今后材料的优化提供指导作用,本论文中,我们将用实验的方法来探究胶体结晶过程和玻璃化转变行为。1、吸引力梯度诱导的二维结晶。我们设计了一种新颖的方法,即吸引力梯度法来制备胶体晶体。我们知道水和2,6-二甲基吡啶的混合溶液在接近混合溶液相分离温度时会产生吸引力。这样的吸引力可以被用来聚集胶体粒子和生长胶体晶体。本文中,我们将利用温度梯度来产生混合溶液中的吸引力梯度。胶体晶体首先在高温区域成核,因为高温区的吸引力强,然后,沿着高温区向低温区的方向生长。我们具体通过泰勒多边形构造法,径向分布函数和方向有序参量等来描述胶体晶体的生长。我们还发现,结晶粒子的数目随着时间的增加,以恒定的速率增长,最终形成了完美的二维单晶。我们最后又通过类比于团簇束沉降法,讨论了无缺陷结晶过程的微观机理。研究表明,我们找到了一个制备无缺陷的胶体晶体的有效方法,为以后的应用,如胶体印刷技术以及三维胶体晶体的制备提供了指导作用。2、pining诱导的二维胶体晶体的玻璃化。我们从实验上研究了pinning对二维胶体晶体的结构特征和动力学行为的影响。其中,pinning的数密度是控制整个过程的关键因素。我们观察发现,随着pinning数密度的增加,体系首先从结晶态转变为多晶态,随后又从多晶态转变成玻璃态。这种结晶态-玻璃态的转变过程显现出了鲜明的结构特征：在转换点处(pinning数密度为φ=6.9%),方向有序关联函数迅速的从长程有序变为短程有序,键角有序参数极化率呈现一个最大值。体系在动力学上也出现了一个急剧地变化：对于φ<6.9%时,当pinning的数密度增加时,由于pinning周围产生了缺陷,粒子运动的快。相反地,当φ>6.9%时,随着pinning数密度的增加,pinnning运动的比较慢,这是因为pinning固定不动,如同牢笼一样将周围的可移动粒子困住了。而在转换点处,粒子运动的最快。3、表面光滑和粗糙的粒子在二元混合溶液中的自组装。我们利用水和2,6-二甲基吡啶的混合溶液在接近溶液相分离温度时会产生吸引力的方法来诱导表面光滑和粗糙的粒子之间进行自组装。从实验过程中,我们可以看出,表面光滑的粒子之间更容易聚集,表面粗糙的粒子之间不发生聚集,表面光滑和粗糙的粒子之间的聚集不稳定。更多还原

【Abstract】 As the two basic problems of the condensed matter physics, crystallization and glass transition,are a hot topic in recent decades. Under appropriate conditions, colloidal liquid can transform into both order colloidal crystals and disorder colloidal glass. Although crystal and glass exist universally in nature and our daily life, and many advances have been made in the past decades, the understanding of the microscopic mechanism of crystallization and glass transition in colloids is still far from being complete. In this thesis, we experimentally study the colloidal crystallization and glass transition and it will help us to understand the colloidal phase transition and provide reliable guidance for the optimization of the materials.1. Fabrication of large two-dimensional colloidal crystals via self-assembly in an attractive force gradient. Colloidal particles in a water-lutidine (WL) binary liquid mixture experience temperature-dependent attraction close to the mixture’s demixing temperature. This temperature-tunable interaction can be potentially harnessed to assemble colloids and grow colloidal crystals. In this article, for the first time a novel attractive force gradient method is presented to fabricate high-quality, single-domain colloidal crystals. The well-controlled attractive force gradient here arises from a temperature gradient in the WL mixture. The nucleation of colloidal crystals in such a WL mixture preferably occurs in the high-temperature region because of the stronger attraction there. Crystallization propagates from the high-temperature region to the low-temperature region in a well-controlled way. The growth of the colloidal crystal is characterized in detail by Voronoi construction, the pair correlation function, and the orientational order parameter. It is found that the number of crystal-like particles increases with time, and a single-domain2D colloidal crystal can be produced. The mechanism of the defect-free crystallization process is discussed on the basis of an analogy to cluster beam deposition methods.2. Observation of pinning-induced vitrification in two-dimensional colloidal crystal. We experimentally studied the effect of pinning on the structure and dynamics in two-dimensional colloidal crystal. The number fraction of pinning particles is the key to controlling this process. In this paper, we observe that with increasing of number fraction of the pinning particles, the system transforms firstly from a crystal to a polycrystalline state, and then into a glass. The crystal-glass transition shows structural signatures:at the transition point (the number fraction φ=6.9%), the persistence of orientational order decreases sharply from long-range to short range, and the bond orientational order parameter susceptibility exhibits a maximum. The system also shows a sharply variation in particle dynamics:For φ<6.9%, as the number fraction of pinning particles increases, particles move faster due to the generation of some defects near the pinning particles. By contrast, for φ>6.9%, particles move slower when the number fraction of pinning particles increases, because their immobility has a distinct effect (caging of the moving particles). At the transition point (φ=6.9%), the particles move fastest.3. The self-assembly of particles with smooth surface and rough surface in the binary mixture. We use the mixture of water and2,6-lutidine which can produce attraction force close to the mixture’s demixing temperature to induce the self-assembly of the particles with smooth surface and rough surface. In the experiment, we can see that, the particles with smooth surface can get together easily; the particles with rough surface can not get together; the particles with smooth surface and rough surface can get together but not very stable.更多还原