自驱动的Janus微球在具有不同障碍物的表面上的运动行为研究

自驱动粒子在靠近边界尤其是平面上障碍物的边界时,会展现出奇特的运动行为.本文通过实验研究了固定于平面上的微米级障碍物的几何效应(包括大小和形状)对双氧水驱动的Janus微球运动行为的影响.实验结果表明,当障碍物尺寸超过临界值后,自驱动的Janus微球会被其"捕获"并沿着其边界定向运动.自驱动粒子在障碍物边界的停留时间及运动速率随着双氧水浓度的增加而增大,且其在圆柱形障碍物边界和球形障碍物边界的停留时间及运动速率均随着障碍物直径的增加而增大.但在相同的双氧水浓度和障碍物直径条件下,自驱动粒子在圆柱边界上的停留时间比其在球形障碍物边界上长;在圆柱边界上的运动速率比在球形障碍物边界上小,揭示了自驱动粒子在障碍物边界上的运动行为与障碍物的几何特性密切相关.本研究有助于进一步理解自驱动粒子在不同大小及形状的障碍物中的运动特征,掌握并利用这些特征在诸如设计特殊几何形状来引导自驱动粒子的运动等领域有很好的应用价值.     

含叔胺结构高光响应性香豆素衍生物的设计合成

以环氧氯丙烷为桥接, 将具有较强给电子能力的芳叔胺(ATA)结构引入香豆素衍生物C分子中, 通过芳叔胺结构的光化学促进作用加速香豆素基元的光二聚反应. 用紫外(UV)和荧光(FL)光谱等手段对该香豆素衍生物进行表征. 结果表明, 芳叔胺结构的引入可有效增强香豆素基元在260-400 nm之间的吸收. 紫外点光源光二聚反应实验表明, 芳叔胺结构的引入使香豆素基元的光响应性能得以大幅增强, 在相同光照条件下, 其在匀速反应区间内对光照时间的依赖性的斜率高达6.47, 光二聚反应程度达到80%时所需光照时间仅为29 s.     

Molecular dynamics simulations on the dynamics of two-dimensional rounded squares

The collective motion of rounded squares with different corner-roundness ζ is studied by molecular dynamics(MD)simulation in this work. Three types of translational collective motion pattern are observed, including gliding, hopping and a mixture of gliding and hopping. Quantitatively, the dynamics of each observed ordered phase is characterized by both mean square displacement and van Hove functions for both translation and rotation. The effect of corner-roundness on the dynamics is further studied by comparing the dynamics of the rhombic crystal phases formed by different corner-rounded particles at a same surface fraction. The results show that as ζ increases from 0.286 to 0.667, the translational collective motion of particles changes from a gliding-dominant pattern to a hopping-dominant pattern, whereas the rotational motion pattern is hopping-like and does not change in its type, but the rotational hopping becomes much more frequent as ζincreases(i.e., as particles become more rounded). A simple geometrical model is proposed to explain the trend of gliding motion observed in MD simulations.     

Phase behavior of rotationally asymmetric Brownian kites containing 90° internal angles

Previous Monte Carlo simulations have shown that ordered tetratic phases can emerge in a dense two-dimensional Brownian system of rotationally asymmetric hard kites having 90° internal angles. However, there have been no experimental investigations yet to compare with these simulation results. Here, we have fabricated two types of micron-sized kites having internal angles of 72°-90°-108°-90° and 72°-99°-90°-99°, respectively, and we have experimentally studied their phase behavior in two-dimensional systems. Interestingly and in contrast to the Monte Carlo simulations, the experimental results show a phase sequence of isotropic fluid-hexagonal rotator crystal-square crystal as the area fraction φ_A increases for both types of kites. The observed square crystal displays not only a quasi-long-range translational order but also (quasi-)long-range 4-fold bond- and molecular-orientational order; these characteristics confirm that tetratic order can emerge even in dense Brownian systems of rotationally asymmetric particles. A model based on local polymorphic configurations (LPCs) is proposed to understand the origin of the square lattice order in these dense kite systems. The results in this study provide a new route to realize custom-designed self-assembly of colloids by controlling LPCs.