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

本研究测量了基于热毛细驱动的微流体装置在移动液气界面处的热梯度及其产生的力。诸如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普遍，其应用包括“片上实验室”设备，MEMS开关和喷墨打印机喷嘴。然而，其基本的物理原理还没有被完全理解。已经测量了这些运动界面的速度场，但是由于缺乏合适的技术，还没有测量驱动流动的温度梯度。此外，热梯度和合力之间关系的模型还没有得到实验验证。采用封装热致变色液晶（TLC）粒子的新型光学全场温度测量技术被认为是最佳选择。微尺度的几何结构将对薄层色谱测温的成像和照明配置施加限制。由于测量结果接近散射光的界面和表面，这也带来了额外的挑战。PI在宏观尺度TLC测温方面的专业知识将有助于开发这项新技术。圆偏振滤波将首次应用于薄层色谱测温。该技术将应用于三种具有代表性的热毛细管驱动微流：对空气开放的表面上的接触线，充满水的毛细管中的孤立气泡，以及毛细管中的孤立液滴。在这三种情况下，整个装置的温度梯度将驱动运动。将在界面处测量与时间相关的速度场，从而确定作用在流体上的力。通过提高对作用在液-气界面上的力的理解，这项研究将使新的微流体设备的发明和改进成为可能，这些设备将用于医疗测试、电子冷却和有害物质传感。使用这种新的测量技术的未来研究将通过将其扩展到温度重要的更微观尺度的流动来增加影响。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带入课堂，而不仅仅是基础科学。一些高中生也可能受到启发，在科学课程中表现得更高，并考虑从事工程职业。开发的材料和对其功效的定量分析将广泛宣传，以达到当地社区以外。本科生也将直接参与研究工作，并可以使用相关的独立项目设施。

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.