有限时间尺度内分子指向相关的不对称扩散研究

Asymmetrical diffusion with orientationdependence of molecules on a finite timescale

传统的经典扩散理论常常将分子和物体假设为球形,这些分子和物体的扩散是无偏移各向同性的。然而,当我们在纳米尺度去看分子和物体时,这些分子和物体呈现出各种不对称的结构。进一步,当我们观察的时间有限到小于几十纳秒时,我们会看到这些分子和物体的自由扩散表现出与它们的初始方位相关的特性。对于像甲醇分子这样的小分子,在约100 ps的有限时间内,常温下,不对称扩散能占到总扩散的10%左右。这样的不对称扩散丰富了分子的扩散理论,对生命和其他自然界现象的理解具有重要的意义,同时也可能提供一种通过控制分子的方向来驱动分子的方法。

In the classic diffusion theory, the diffusion of molecules and objects is isotro-pic, since they are usually assumed as spheres. When we see those molecules and objects down to nano-scale, most of them exhibits various asymmetrical structures instead of spheres. Correspond-ingly, the diffusion of these molecules and objects displays orientation-dependent behaviour when the observation time is less than dozens of nanoseconds. Take methanol for instance, the drift of diffusion is about 10%of the total diffusion within a finite time interval of 100 ps. This observa-tion of asymmetrical diffusion within finite time scales extends the theory of molecular diffusion and is of great importance to the understanding of life and nature phenomenon. Such asymmetrical diffusion also suggests a method for driving molecules by controlling their orientations.