联系我们  |  网站地图  |  English   |  移动版  |  中国科学院 |ARP
站内搜索:
首页 简介 管理部门 科研部门 支撑部门 研究队伍 科研成果 成果转化 研究生教育 党建与创新文化 科普 信息公开 办公内网
科技信息
北大工学院在钙钛矿微型激...
北京大学工学院在压电材料...
浙江大学课题组发现超快光...
Hydrogen power moves a s...
Microparticles created b...
不会爆炸的水基锂离子电池
砒霜可变治疗慢性白血病良方
科学家研发自驱动超灵敏脉...
New microscopy method fo...
Researchers lay groundwo...
锂—液态多硫流动电池实现...
等离子体燃料新方法可产生...
热释电红外传感器的成本优...
A new way to directly co...
New liquid-metal membran...
现在位置:首页>新闻动态>科技信息
New insights into nanocrystal growth in liquid
2017-09-18 09:18:39 | 编辑: | 【 【打印】【关闭】

 

Mica the mineral flakes off in fine sheets. Credit: Wikimedia Commons

  Many seashells, minerals, and semiconductor nanomaterials are made up of smaller crystals, which are assembled together like the pieces of a puzzle. Now, researchers have measured the forces that cause the crystals to assemble, revealing an orchestra of competing factors that researchers might be able to control.

  The work has a variety of implications in both discovery and applied science. In addition to providing insights into the formation of minerals and semiconductor nanomaterials, it might also help scientists understand soil as it expands and contracts through wetting and drying cycles. In the applied realm, researchers might use the principles to develop new materials with unique properties for energy needs.

  The results, published in the Proceedings of the National Academy of Sciences in July, describe how the arrangement of the atoms in the crystals creates forces that pull them together and align them for docking. The study reveals how the attraction becomes stronger or weaker as water is heated or salt is added, both of which are common processes in the natural world.

  The multinational team, led by chemists Dongsheng Li and Jaehun Chun from the Department of Energy's Pacific Northwest National Laboratory, explored the attractive forces between two crystal particles made from mica. A flaky mineral that is commonly used in electrical insulation, this silicon-based mineral is well-studied and easy to work with because it chips off in flat pieces with nearly-perfect crystal surfaces.

  Forces and faces 

  Crystallization often occurs through assembly of multi-faceted building blocks: some faces on these smaller crystals line up better with others, like Lego blocks do. Li and Chun have been studying a specific crystallization process called oriented attachment. Among other distinguishing characteristics, oriented attachment occurs when smaller subunits of fledgling crystals align their best matching faces before clicking together.

  The process creates various nonlinear forms: nanowires with branches, lattices that look like complicated honeycombs, and tetrapods—tiny structures that look like four-armed toy jacks. The molecular forces that contribute to this self-assembly are not well understood.

  Molecular forces that come into play can attract or repel the tiny crystal building blocks to or from each other. These include a variety of textbook forces such as van der Waals, hydrogen bonding, and electrostatic, among others.

  To explore the forces, Li, Chun and colleagues milled flat faces on tiny slabs of mica and put them on a device that measures the attraction between two pieces. Then they measured the attraction while twisting the faces relative to each other. The experiment allowed the mica to be bathed in a liquid that includes different salts, letting them test real-world scenarios.

  The difference in this work was the liquid setup. Similar experiments by other researchers have been done dry under vacuum; in this work, the liquid created conditions that better simulate how real crystals form in nature and in large industrial methods. The team performed some of these experiments at EMSL, the Environmental Molecular Sciences Laboratory, a DOE Office of Science User Facility at PNNL.

  Twist and salt 

  One of the first things the team found was that the attraction between two pieces of mica rose and fell as the faces twisted relative to each other, like when trying to make a sandwich out of two flat refrigerator magnets (go on, try it). In fact, the attraction rose and fell every 60 degrees, corresponding with the internal architecture of the mineral, which is almost hexagonal like a honeycomb cell.

  Although other researchers more than a decade ago had predicted this cyclical attraction would happen, this is the first time scientists had measured the forces. Knowing the strength of the forces is key to manipulating crystallization in a research or industrial setting.

  But other things were abuzz in the mica face-off as well. Between the two surfaces, the liquid environment housed electrically charged ions from salts, normal elements found during crystallization in nature. The water and the ions formed a somewhat stable layer between the surfaces that partly kept them separated. And as they moved toward each other, the two mica surfaces paused there, balanced between molecular attraction and repulsion by water and ions.

  The team also found they could manipulate the strength of that attraction by changing the type of ions, their concentration, and the temperature. Different types of ions and their concentrations changed electrostatic repulsion between the mica surfaces. The size of the ions and how many charges they carried also created more or less space within the meddling layer.

  Lastly, higher temperatures increased the strength of the attraction, contrary to how temperature behaves in simpler, less complex scenarios. The researchers built a model of the competing forces that included van der Waals, electrostatic, and hydration forces.

  In the future, the researchers say, the principles gleaned from this study can be applied to other materials, which would be calculated for the material of interest. For example, manipulating the attraction might allow researchers to custom-build crystals of desired sizes and shapes and with unique properties. Overall, the work provides insights into crystal growth through nanoparticle assembly in synthetic, biological, and geochemical environments.

  Explore further: For first time, researchers measure forces that align crystals and help them snap together 

  More information: Dongsheng Li et al, Trends in mica–mica adhesion reflect the influence of molecular details on long-range dispersion forces underlying aggregation and coalignment, Proceedings of the National Academy of Sciences (2017). DOI: 10.1073/pnas.1621186114   

版权所有 中国科学院上海硅酸盐研究所 沪ICP备05005480号
长宁园区地址:上海市长宁区定西路1295号 电话:86-21-52412990 传真:86-21-52413903 邮编:200050
嘉定园区地址:上海市嘉定区和硕路585号  电话:86-21-69906002 传真:86-21-69906700 邮编:201899