Shape‐Tunable Colloids from Structured Liquid Droplet Templates

Shaping colloidal building units is of paramount importance for their self‐assembly into complex objects. Continuous tuning of colloidal shapes is highly desired for understanding self‐assembly, but it still remains a challenge. Herein, we report a new template strategy for the shape‐tunable synthesis of anisotropic colloids with shapes that can be continuously tuned from discs (oblate spheroids) to spheres to theta shapes to dumbbells. This was realized by creating structured shape‐tunable droplets from patchy colloidal discs and using these droplets as templates. In particular, we found that a controlled dumbbell‐to‐eyeball droplet transformation can be used for the synthesis of eyeball‐shaped colloids. We also demonstrated the droplet transformation pathways and applied the method to the synthesis of colloidal molecules. These colloids provide possibilities for exploring their ordered packing structures, and the method based on the use of structured droplets can be adapted for the synthesis of other functional colloidal particles.     

锌蒸气的氧化行为与氧化锌的结晶形貌

用热重法测定了不同气氛下锌蒸气的氧化动力学曲线,用扫描电镜跟踪观察分析了产物的结晶形貌,结果表明,氧化动力学遵守直线规律时,产物是无定形、颗粒状和单针状的ZnO;氧化动力学为抛物线规律时,产物是四针状或多针状的ZnO.动力学转变规律的原因是锌蒸气中气态锌原子与凝聚生成的锌液滴之间存在动态平衡,气态锌原子的氧化过程遵守直线规律;而锌液滴的氧化过程分为两个阶段,分别受收缩球状界面反应模型R₃和三维扩散模型D4动力学控制,表观活化能分别为106.3～108.2和114.2～117.3kJ/mol;扩散过程实际上是锌原子通过氧化膜层由里向外扩散,扩散系数D=2.46～9.70×10^-5cm²/s.     

Formation of droplets in weightless complex plasmas

Microparticles immersed in a low-temperature plasma acquire strong negative charges and thus repel each other. Nevertheless, effective attraction between the microparticles in such a complex plasma can occur due to the interplay between the fluxes of plasma ions and the microparticles. Here, we report the observation of droplets formed in a complex plasma during a parabolic flight, and explain their formation in terms of the ion drag force that sustains the droplet. We have found a good agreement between the experimentally determined droplet size and its theoretical estimate using the ion drag force mechanism. Lower values of the electron temperature result in better agreement, as is consistent with the pulsed mechanism of discharge used experimentally.     

Electron impact ionization of CCl4 and SF6 embedded in superfluid helium droplets

Electron impact ionization of helium nano-droplets containing several 10⁴ He atoms and doped with CCl₄ or SF₆ molecules is studied with high-mass resolution. The mass spectra show significant clustering of CCl₄ molecules, less so for SF₆ under our experimental conditions. Positive ion efficiency curves as a function of electron energy indicate complete immersion of the molecules inside the helium droplets in both cases. For CCl₄ we observe the molecular parent cation CCl₄⁺ that preferentially is formed via Penning ionization upon collisions with He*. In contrast, no parent cation SF₆⁺ is seen for He droplets doped with SF₆. The fragmentation patterns for both molecules embedded in He are compared with gas phase studies. Ionization via electron transfer to He⁺ forms highly excited ions that cannot be stabilized by the surrounding He droplet. Besides the atomic fragments F⁺ and Cl⁺ several molecular fragment cations are observed with He atoms attached.     

Compartmentalization of Chemically Separated Components into Droplets

Not merely a drop in the ocean : The integration of capillary electrophoresis (CE) with droplet generation driven by electroosmotic flow enabled the compartimentalization of molecular components separated by CE in a series of droplets (see picture; the green bars represent the separated analytes). The droplet‐confined bands can be docked and studied on a chip.

     

低压蒸汽滴状冷凝过程中液滴生长特性

研究了低压条件对滴状冷凝过程液滴生长特性的影响。首先,研究了超疏水表面上空气环境和蒸汽环境中附着液滴的接触角,发现蒸汽环境中的接触角比空气环境中的小,而蒸汽压力对接触角没有显著影响。第二,实验研究了冷凝过程中的液滴的生长周期和脱落尺寸,液滴的脱落半径随压力的降低而增大,生长周期也随之延长。第三,实验研究了液滴合并生长速率,并结合理论分析直接冷凝长大的生长速率,直接冷凝生长速率随压力的减小而减小,并随过冷度的减小而下降,而实验范围内合并生长速率不受压力影响。第四,根据滴状冷凝液滴分布的时间序列模型,分析了不同压力下液滴生长的临界尺寸,随着压力的降低,液滴生长方式的临界尺寸增大。