NER: Single File Diffusion: Application to Transport of Encapsulated Atoms and Molecules Inside Nanotubes

宾夕法尼亚大学的Khantha， mahadevan“NER：单文件扩散：应用于纳米管内封装原子和分子的传输”这一纳米级探索性研究提案研究了纳米管内封装原子和分子的单文件扩散。在一维通道中，一串“粒子”在任何时候都保持排列顺序的扩散被称为“单”文件扩散。(陕西林业局)。即使不考虑粒子通道相互作用，SFD也显示出异常（非马尔可夫）扩散特性。本探索性研究的目的是了解“粒子-通道”相互作用和通道（纳米管）内“粒子-粒子”相互作用如何影响SFD。选择了具有代表性和技术重要性的C60（富勒烯）分子和Li原子在单壁碳纳米管内扩散的体系。富勒烯分子在碳纳米管内部的相互作用以及富勒烯分子与纳米管壁的相互作用都是范德华作用。在美国国家科学基金会资助的一项研究项目中，PI们正在研究纳米管中锂原子的相互作用。目前得到的结果表明，这种相互作用类似于筛选的汤川势，而与纳米管内富勒烯的范德华相互作用有很大不同。PI将首先使用这两个势进行有限开管内输运的分子动力学模拟，以了解SFD的特征如何随粒子相互作用而变化。这些结果将为建立SFD的分析随机模型奠定基础，以回答以下基本问题：(i)原子进入开放纳米管的概率如何取决于其与纳米管的相互作用？（ii）被封装的分子链在纳米管内的平均持续时间是多少？先前对纳米管中SFD的研究主要集中在液体或气体的传输上，其中流体和纳米管壁之间的相互作用通常会导致润湿和分层转变。已知C60分子和Li原子都与碳纳米管壁有排斥性相互作用，并且有强有力的实验证据表明它们在碳纳米管内形成一维链。此外，C60分子和Li原子与纳米管的相互作用类型也不同，这是由于纳米管内部产生不同程度的电荷转移和筛选。这项探索性的研究包括数值模拟和分析模型，将在短、中、长时间尺度上建立纳米管通道内粒子输运的预测模型。通过使用真实的相互作用势，分析结果可以推广到含有内富勒烯（即富勒烯封装外来原子）、金属卤化物、金属氧化物等更复杂的填充纳米管“豆荚”体系，这些纳米结构在技术应用中具有相当大的潜力。更广泛的影响：这里讨论的纳米管中SFD的基本问题涉及到环境过程，包括纳米流体通过膜或通道的运输，工业过程，如形状选择催化，基于同位素的气体分离，以及生物进步，如纳米注射器的开发，胶囊化药物可以直接输送到细胞通道。这项研究的结果将为一个长期的研究项目奠定基础，该项目涉及复杂有机分子在纳米管中的单文件运输，其中分子的非球形形状和确认跃迁会影响运动。

Khantha, MahadevanUniversity of Pennsylvania "NER: Single File Diffusion: Application to Transport of Encapsulated Atoms and Molecules Inside Nanotubes"This Nanoscale Exploratory Research proposal examines the single file diffusion of encapsulated atoms and molecules inside nanotubes. The diffusion of a chain of "particles" in one-dimensional channels with the particles maintaining the order of their arrangement at all times is called "single" file diffusion. (SFD). The SFD displays anomalous (non-Markovian) diffusion characteristics even when particle-channel interactions are not taken into account. The objective of this exploratory research is to understand how "particle-channel" interactions and "particle-particle" interactions within the channel (nanotube) influence SFD. Representative and technologically important systems, C60 (fullerene) molecules and Li atoms, diffusing inside single wall carbon nanotubes were chosen. The interactions of fullerene molecules inside carbon nanotubes and fullerenes with nanotube walls are both of the van der Waals type. Under a current NSF funded research project, the PI's are studying the interactions of Li atoms inside nanotubes. The results obtained so far show that the interaction is similar to that of a screened Yukawa potential which is quite different from the van der Waals type interactions of fullerenes inside nanotubes. The PI's will first carry out a molecular dynamics simulation of transport within finite open tubes using these two potentials to understand how the characteristics of SFD varies with particle interactions. These results will serve as a foundation to build analytical stochastic models of SFD to answer the following basic questions: (i) How does the probability of an atom entering an open nanotube depend on its interaction with the tube? (ii) What is the average duration of time spent by the chain of encapsulated molecules inside the nanotube? Prior work on SFD in nanotubes has focused on transport of liquids or gases where theattractive interaction between fluids and the nanotube walls often lead to wetting and layering transitions. Both C60 molecules and Li atoms are known to have repulsive interactions with the carbon nanotube walls and there is strong experimental evidence to show they form one-dimensional chains inside the tubes. In addition, the interactions of C60 molecules and Li atoms with nanotubes are of different types due to the different degrees of charge transfer and screening produced within the tubes. This exploratory study involving numerical simulation and analytical models will lead to predictive models of particle transport within nanotube channels at short, intermediate and long time scales. By using realistic interaction potentials, the results of the analysis can be generalized to more complex systems of filled nanotube "peapods" containing endofullerenes (i.e., fullerenes encapsulating foreign atoms), metallic halides, metal oxides, etc., which are nanostructures of considerable potential in technological applications. Broader impacts: The fundamental problem of SFD in nanotubes addressed here has implications for environmental processes that involve nanofluidic transport through membranes or channels, industrial processes such as shape selective catalysis, isotope based separation of gases and biological advances such as development of nano-syringes with encapsulated drugs allowing direct delivery to cell channels. The results of this study will lay the groundwork for a longer-term research project which involves the transport of complex organic molecules in a single file through nanotubes where the non-spherical shape and confirmational transitions of the molecules can influence the motion.