Liu Ying, Ismagilov Rustem F
Department of Chemistry and Institute for Biophysical Dynamics, The University of Chicago, 929 East 57th Street, Chicago, Illinois 60637, USA.
Langmuir. 2009 Mar 3;25(5):2854-9. doi: 10.1021/la803518b.
This manuscript analyzes the dynamics of coalescence of an incoming aqueous plug with a wetting layer above a hydrophilic surface in the chemistrode. The chemistrode is a recently described (Chen, D.; Du, W.; Liu, Y.; Liu, W.; Kuznetsov, A.; Mendez, F. E.; Philipson, L. H.; Ismagilov, R. F. Proc. Natl. Acad. Sci. U.S.A. 2008, 105, 16843-16848) microfluidic analogue of an electrode, but operating at the chemical rather than electrical level, developed with the aim of capturing local stimulus-response processes in chemistry and biology. The chemistrode consists of open-ended V-shaped microfluidic channels that can be brought into contact with a chemical or biological hydrophilic substrate. The chemistrode relies on multiphase aqueous/fluorous flow and uses plugs to achieve high temporal resolution of stimulation and sampling. Coalescence of the incoming plugs, containing the stimuli, with the liquid in the wetting layer is required for chemical exchange to take place in the chemistrode. Here, we investigate the system with triethyleneglycol mono[1H,1H-perfluorooctyl]ether RfOEG as the surfactant. This surfactant was necessary to prevent nonspecific absorption of proteins to the aqueous fluorous interface and to ensure biocompatibility of the system, but too much surfactant increased the barrier for coalescence. In this system, coalescence was controlled by the capillary number. At a higher value of the capillary number, coalescence took more time, and deformation of the interface of the incoming plug and the wetting layer was more significant. Above a critical capillary number, coalescence did not occur between the incoming plug and the wetting layer. The critical capillary number was an increasing function of surface tension but was independent of viscosity ratio. Coalescence was surprisingly reproducible, presumably because film rupture during coalescence was reliably initiated at the hydrophilic substrate. These results are useful in rational operation of the chemistrode and also provide an experimental description of deformation, film drainage, and coalescence of surfactant-coated droplets in an external flow field.
本手稿分析了化学微电极中，进入的水相液塞与亲水性表面上方的湿润层的聚并动力学。化学微电极是一种最近描述的（Chen, D.; Du, W.; Liu, Y.; Liu, W.; Kuznetsov, A.; Mendez, F. E.; Philipson, L. H.; Ismagilov, R. F. Proc. Natl. Acad. Sci. U.S.A. 2008, 105, 16843 - 16848）电极微流控类似物，但在化学而非电学层面上运行，其开发目的是捕获化学和生物学中的局部刺激 - 响应过程。化学微电极由开放式V形微流控通道组成，这些通道可与化学或生物亲水性底物接触。化学微电极依赖于多相水/氟流，并使用液塞实现刺激和采样的高时间分辨率。为了在化学微电极中进行化学交换，含有刺激物的进入液塞与湿润层中的液体需要聚并。在此，我们用三乙二醇单[1H,1H - 全氟辛基]醚RfOEG作为表面活性剂来研究该系统。这种表面活性剂对于防止蛋白质非特异性吸附到水 - 氟界面以及确保系统的生物相容性是必要的，但过多的表面活性剂会增加聚并的障碍。在该系统中，聚并由毛细管数控制。毛细管数较高时，聚并所需时间更长，进入液塞与湿润层界面的变形更显著。高于临界毛细管数时，进入液塞与湿润层之间不会发生聚并。临界毛细管数是表面张力的增函数，但与粘度比无关。聚并结果惊人地可重复，大概是因为聚并过程中的膜破裂在亲水性底物处可靠地引发。这些结果对于化学微电极的合理操作很有用，并且还提供了在外流场中表面活性剂包覆液滴的变形、膜排水和聚并的实验描述。
