[论文解读] Controlling morphology-structure of particles via plastically driven geometric tiny particles and effect of photons on the structures under varying process conditions

Mubarak Ali, I‐Nan Lin|arXiv (Cornell University)|May 14, 2016

Pickering emulsions and particle stabilization被引用 13

一句话总结

本研究在定制的光脉冲与电脉冲条件下，利用塑性驱动的几何微小颗粒，实现了对纳米至微米尺度胶体颗粒形态与结构的控制。通过调节双极脉冲关断与导通时间之比以及光照射量，可形成不同的各向异性形状，如连接的三角形和长条形颗粒；仅当电子扩散仍有效时，光子才能使长条形颗粒表面光滑。

ABSTRACT

Controlling morphology-structure of colloidal matter at nanoscale to micron are unusual phenomena as they may exhibit different characteristics. In this work, different morphology-structure of colloidal particles has been investigated. At air-solution interface, different geometric tiny particles are made on cropping monolayer assembly of gold atoms under tailored energy-shape photons depending on the ratio of bipolar pulse OFF to ON time. Tiny particles having connected triangles are made under suitable bipolar pulse mode, each one of them divides into two triangular-shaped tiny particles under the difference of opposite field force. However, at unipolar pulse mode triangular-shaped tiny particles are made directly. At electron-solution interface, impinging electron streams elongate to such tiny particles and packing under uniform drive at photon-solution interface result into various geometric anisotropic shaped particles. When the ratio of bipolar pulse OFF to ON time is very large, the resulting particles are distorted while those developed at smaller values of this ratio reveal geometric anisotropic shapes. When the ratio of bipolar pulse OFF to ON time is 3, resulted particles reveal lower aspect ratio to those developed at inverse value of this ratio. At longer pulse ON time, geometric tiny particles elongated more and travelling photons modified them into smooth elements whose width is less than inter-spacing distance. When elongation of tiny particles exceeds the level where diffusion of electron states of atoms is no longer workable, travelling photons do not modify them into smooth elements. We discuss morphology-structure of particles developing under uniform and non-uniform drives of plastically-driven geometric tiny particles along with roles of photons under varying conditions.

研究动机与目标

• 研究在受控电学与光学刺激下，塑性驱动的几何微小颗粒的形成机制。
• 理解光子辐照在不同脉冲条件下对颗粒生长过程中形态演变的影响。
• 确定双极脉冲关断与导通时间之比对颗粒各向异性和结构畸变的影响。
• 考察在光照射下，粗糙的长条形颗粒向光滑致密颗粒的转变过程。
• 比较单极与双极脉冲模式在引导三角形及连接三角形形状颗粒形成中的作用。

提出的方法

• 以空气-溶液界面处的单层金原子作为颗粒成核的基底。
• 施加可调制关断/导通时间比的定制双极与单极电脉冲，以诱导塑性形变与颗粒形成。
• 在电子-溶液界面处施加光子辐照，以调节颗粒形状与表面光滑度。
• 通过观察不同脉冲持续时间与光照射量下长宽比与几何各向异性的变化，监测颗粒的演化过程。
• 分析电子扩散动力学与光子诱导的表面光滑效应在长条形颗粒上的相互作用。
• 比较均匀与非均匀驱动条件下形成的颗粒结构，以评估形状控制机制。

实验结果

研究问题

• RQ1 双极脉冲关断与导通时间之比如何影响所形成颗粒的各向异性和畸变？
• RQ2 光子在将粗糙的长条形颗粒转化为光滑致密颗粒的过程中起什么作用？
• RQ3 为何单极脉冲直接生成三角形颗粒，而双极脉冲则产生连接的三角形结构？
• RQ4 在何种条件下光子无法实现颗粒表面光滑化？其限制因素是什么？
• RQ5 电子扩散如何影响光子诱导形态改性的有效性？

主要发现

• 当双极脉冲关断/导通比为3时，颗粒的长宽比低于反比情况，表明可通过脉冲时间调控实现形状控制。
• 当关断/导通比极大时，由于驱动力不足，导致颗粒生长无序，形成畸变结构。
• 在单极脉冲模式下，直接形成三角形颗粒；而在优化的双极脉冲条件下，则生成连接的三角形结构。
• 在长脉冲导通时间下形成的长条形颗粒，仅当电子态扩散仍有效时，才能通过传播光子实现表面光滑化。
• 当长条化程度超过电子态扩散极限时，光子诱导的光滑化过程失效，形态精炼无法实现。
• 光子-溶液界面的均匀驱动可形成多种几何各向异性颗粒，凸显光子能量在纳米尺度调控物质形态中的关键作用。