PROPOSAL NO.: CTS-0625622 PRINCIPAL INVESTIGATOR: SANDRA M. TROIAN INSTITUTION: PRINCETON UNIVERSITY
Droplet Manipulation by Thermocapillary Actuation for Microfluidic Applications
This grant builds upon previously funded studies in which the investigators demonstrated electronic flow control within continuous microscale films on glass or silicon substrates by a combination of substrate patterning with electronically addressable microheater arrays for generation of thermocapillary stresses. Mobilization and manipulation of discrete droplets in the 100 nl range, however, requires deeper insight into the coupling of thermocapillary and capillary forces, droplet retentive forces caused by contact angle hysteresis and pinning, the fraction of input power needed to dislodge droplets for transport, the dynamics of film rupture preceding droplet breakup on patterned substrates for scission and dispensing, and the effects of solubilized surfactants on thermocapillary flows. This current study will examine the dynamic behavior of discrete droplets modulated in space and time by thermocapillary stresses in the presence of substrates partitioned into various wetting and non-wetting geometries. Besides the stresses affecting the air-liquid interface, the liquid conformation and flow behavior are affected by surface energy and geometry. Measurements based on laser interferometry, total internal reflection fluorescence, ellipsometry and atomic force microscopy will be compared directly with predictions of hydrodynamic models based on lubrication theory. Accurate estimates of the input power required for droplet depinning and scission will allow development of more energy efficient devices. The results of these studies will prove useful to alternative microfluidic systems reliant on electrowetting and dielectrophoresis where similar capabilities for droplet actuation are being investigated by other groups. Automated microfluidic systems for droplet routing, mixing, dispensing and analysis are rapidly expanding diagnostic capabilities in fields as far ranging as genomics and drug formulation to environmental monitoring for space travel and biodefense applications. The cornerstone of these technologies involves micro-hydrodynamic flows in the presence of textured surfaces to assist in droplet dispensation and apportionment to specific sites, droplet scission and coalescence, mixing of selective droplets, and transport along electronically programmable pathways. Proper functioning relies on reproducible fabrication and operation coupled with hydrodynamic models for flow optimization. Such open architecture devices are not quite ready for commercialization, however, in part because of the limited understanding involving droplet dislocation, scission and dynamics. The PI plans to diversify strategies for (a) recruiting and retaining female graduate students and (b) guiding these students toward successful positions as postdoctoral research scholars or junior faculty. These efforts are in response to the fact that the number of women pursuing advanced study in the engineering sciences is not increasing at the expected rate (and in some fields even decreasing). As part of this study, a seminar series will be launched in which scholarly articles which speak to this problem will be discussed in depth in order to identify and overcome practices which retard the advancement of junior women in research intensive activities.
