Characterizing Fluid Properties for Micro/Nano Droplet Using High-Q Whispering Gallery Modes

CBET 1438112该项目旨在开发一种新的方法来测量微小液滴的流体性质，方法是利用光来变形液滴的形状。该方法包括使用激光器和光纤向液滴中注入光子。这些光子形成了耳语走廊模式，这是一种被液滴界面反射并在液滴赤道附近循环的光波。来自光波的辐射压力导致界面凸起，进而导致耳语走廊模式的频率改变。通过检测频率的变化，可以测量液滴形状的非常微小的变化。这些形状变化可以用来推断流体界面的表面张力和内部流体的粘度。没有其他类似的方法来测量微米级液滴的这些特性。因此，该项目将为科学家和工程师提供一种新的测量物理性质的工具，可以应用于许多制造过程和生物系统中形成的胶体系统、乳剂、气溶胶和其他悬浮液。通过光谱测量，将确定液滴中存在高Q耳语走廊模式。引起液滴变形的光学力将在实验上得到证实和表征。液滴变形将通过测量耳语走廊模式共振频率的移位来确定。结果将通过使用能够检测纳米级分辨率的界面运动的白光干涉法来测量变形来验证。通过将测量的液滴变形和变形速率与液滴的Stokes方程的边界元解进行比较，研究表面张力和粘度的作用。实验将使用水和硅油等简单的流体进行。由悬浮在液体中的纳米粒子组成的系统将被表征为模拟在更复杂的流体中耳语走廊模式诱导的液滴变形。

CBET 1438112This project aims to develop a new method to measure the fluid properties of tiny liquid droplets by using light to deform the shape of the drop. The method involves using a laser and an optical fiber to inject photons into the drop. These photons form a whispering gallery mode, which is an optical wave that is reflected by the droplet interface and circulates near the equator of the drop. The radiation pressure from the optical wave causes the interface to bulge, which, in turn, causes a change in the frequency of the whispering gallery mode. By detecting the change in frequency, extraordinarily small changes in the shape of the drop can be measured. These shape changes can then be used to deduce the surface tension of the fluid interface and the viscosity of the internal fluid. There are no other comparable methods for measuring these properties in micron-size drops. Thus, the project will provide scientists and engineers with a new tool for measuring physical properties that can be applied to colloidal systems, emulsions, aerosols and other suspensions that are formed in many manufacturing processes and biological systems.The presence of high-Q whispering gallery modes within the liquid drops will be established through optical spectrum measurements. The optical force that induces drop deformation will be experimentally confirmed and characterized. Drop deformation will be determined by measuring shifts in the whispering gallery mode resonance frequency. Results will be verified by measuring deformation with white light interferometry that is capable of detecting interface movement with nanometer scale resolution. The roles of surface tension and viscosity will be investigated by comparing the measured drop deformation and rate of deformation with boundary element solutions of the Stokes equations for the drops. Experiments will be carried out using simple fluids such as water and silicone oils. A system consisting of nanoparticles suspended in liquid will be characterized to simulate whispering gallery mode induced drop deformation in a more complex fluid.