Prasad A, Lin A T-H, Rao V R, Seshia A A
Nanoscience Centre, Department of Engineering, University of Cambridge, 11 JJ Thomson Avenue, Cambridge, CB3 0FF, UK.
Analyst. 2014 Nov 7;139(21):5538-46. doi: 10.1039/c4an01389a.
A bulk acoustic mode micro-electro-mechanical dual resonator platform is utilised to study the evaporation of sub-microliter water droplets from the surface of the resonator. An analytical formulation for the observed frequency shift and the measure dependence of resonant frequency on the modes of evaporation which is consistent with the optically derived data. The resonators access only a thin layer of the liquid through shear contact and, hence, the response is not affected by the bulk mass of the droplet to first order. A relationship between the droplet contact area and the elapsed time was established for the evaporation process and is used to derive a value of the diffusion coefficient of water in air that is found to be in reasonable agreement with literature values. This work introduces a new tool for the electro-mechanical monitoring of droplet evaporation with relevance to applications such as biosensing in liquid samples of sub-microliter volumes.
一种体声波模式微机电双谐振器平台被用于研究亚微升水滴从谐振器表面的蒸发。针对观测到的频率偏移以及谐振频率对蒸发模式的测量依赖性，给出了一个与光学推导数据一致的解析公式。谐振器仅通过剪切接触接触到液体的薄层，因此，一阶响应不受液滴整体质量的影响。建立了蒸发过程中液滴接触面积与经过时间之间的关系，并用于推导空气中水的扩散系数值，发现该值与文献值合理相符。这项工作引入了一种用于液滴蒸发机电监测的新工具，与诸如亚微升体积液体样品中的生物传感等应用相关。
