CAREER: Investigation of Flow Physics at Moving Liquid-Air Interfaces in Microfluidic Devices Using Thermochromic Liquid Crystal Particles

CBET-0748294 Pottebaum这项研究测量了基于热毛细管驱动的微流控设备中移动的液-气界面上的温度梯度及其产生的力。用于在微通道中移动气泡或液滴的泵以及微图案表面上的自由表面流动等设备正变得越来越常见，其应用包括芯片实验室设备、MEMS开关和喷墨打印机喷嘴。然而，其背后的物理原理还没有完全被理解。已经测量了这些运动界面上的速度场，但由于缺乏合适的技术，驱动流动的温度梯度尚未测量到。此外，温度梯度和合力之间的关系模型也没有得到实验验证。利用封装热致变色液晶(TLC)颗粒的光学全场温度测量技术被认为是最好的选择。微尺度的几何结构将对TLC测温的成像和照明配置施加限制。测量距离散射光的界面和表面很近，这带来了额外的挑战。PI在宏观TLC测温方面的专业知识将有助于开发这项新技术。首次将圆偏振滤波应用于TLC测温。这项技术将应用于三种典型的热毛细管驱动的微流控流动：面向空气的表面上的接触线，充满水的毛细管中的孤立气泡，以及毛细管中的孤立液滴。在所有三种情况下，整个设置中的温度梯度将驱动运动。将在界面上测量随时间变化的速度场，从而确定作用在流体上的力。通过提高对液-气界面作用力的理解，这项研究将能够发明和改进用于医疗测试、电子冷却和危险物质传感的新型微流控设备。未来使用这种新测量技术的研究将通过将其扩展到更多微尺度的流动来增加影响，在这些流动中温度是重要的。PI将与当地高中科学教师合作，开发和试点新的教育经验，将工程概念和尖端应用程序带入课堂，而不仅仅是基础科学。一些高中生可能也会受到启发，在理科课程中表现得更高，并考虑从事工程工作。编写的材料和对其效果的量化分析将广泛宣传，使其影响到当地社区以外的地区。本科生还将直接参与研究工作，并可以使用相关独立项目的设施。

CBET-0748294PottebaumThis research measures the thermal gradients and the forces they produce at moving liquid-air interfaces for microfluidic devices based on thermocapillary actuation. Devices such as pumps for moving bubbles or droplets in micro-channels, and free surface flows on micro-patterned surfaces are becoming increasingly common, with applications including 'lab-on-a-chip' devices, MEMS switches, and inkjet printer nozzles. However, the underlying physics is not fully understood. The velocity fields at these moving interfaces have been measured, but the temperature gradients that drive the flows have not due to the lack of a suitable technique. Also, models of the relationship between thermal gradients and the resultant forces have not been experimentally verified. A new optical, whole-field temperature measurement technique using encapsulated thermochromic liquid crystal (TLC) particles is considered the best option. The micro-scale geometry will impose constraints on imaging and illumination configurations for TLC thermometry. The proximity of the measurements to interfaces and surfaces that scatter light creates additional challenges. The PI's expertise in TLC thermometry at the macro-scale will help develop this new technique. Circular polarization filtering will be applied to TLC thermometry for the first time. This technique will be applied to three representative thermocapillary actuated microfluidic flows: a contact line on a surface open to the air, an isolated bubble in a water-filled capillary tube, and an isolated droplet in a capillary tube. In all three cases, a temperature gradient across the setup will drive the motion. Time-dependent velocity fields will be measured at the interface, allowing the forces acting on the fluid to be determined. By improving the understanding of the forces acting on liquid-air interfaces, this research will enable the invention and refinement of new microfluidic devices used in medical testing, electronic cooling, and hazardous substance sensing. Future research using this new measurement technique will increase the impact by extending it to more micro-scale flows where temperature is important. The PI will work with local high school science teachers to develop and pilot new educational experiences to bring engineering concepts and cutting-edge applications, not just basic science, into the classroom. Some high school students may also be inspired to perform at a higher level in science courses and to consider engineering careers. The materials developed and quantitative analysis of their efficacy will be publicized widely to reach beyond the local community. Undergraduate students will also be directly involved in the research effort and will also have access to the facilities for related independent projects.