Microwave Dielectric Heating of Drops in Microfluidic Devices
Original entry by Sagar Bhandari, APPHY 225 Fall 2010
Microwave Dielectric Heating of Drops in Microfluidic Devices, David Issadore, Katherine J. Humphry, Keith A. Brown, Lori Sandberg, David Weitz, Robert M. Westervelt, Lab Chip. 2009 June 21; 9(12): 1701–1706.
dielectric, microfluidics, heating, drops
In this paper, the authors present a technique to locally control the temperature of water droplets in a microfluidic device. Since water absorbs microwave power more efficiently than polymers, glass, and oils due to its permanent molecular dipole moment, microwave heating was employed for this purpose. The devices are fabricated using poly(dimethylsiloxane) (PDMS)-on-glass drop-based microfluidics. A schematic cross-section of the device is shown in Fig. 1 a.
Microwave power is locally delivered via metal electrodes that are directly integrated into the microfluidic device and that run parallel to the fluid channel.The microwaves are generated with a voltage controlled oscillator which is amplified to a maximum of 11.7 V peak to-peak with a maximum power of 26dBm. Using Finite Element simulations, the profile of electric field in the microwave heater was computed which is plotted in Fig. 1 b. The temperature of the drops is obtained by observing the temperature-dependent fluorescence of CdSe nanocrystals embedded in the drops using a ccd camera. Using a flow focused geometry , drops of diameter 50 um were created. Also, to ensure thermal isolation of the drops, they were floated on a low thermal conductivity hydrocarbon oil.
Using this microfuidic device, the drops were heated upto 30 degrees above the base temperature in just 15 ms. The average temperature change of the drops as a function of time is plotted in Fig. 3c.