Virtual components for droplet control using Marangoni flows :size-selective

filters, traps, channels, and pumps

Advisor: Cheng-Hsien Liu

Reporter: Y. S. Lin

Date: 2007/6/20

Amar S.Basu, Seow Yuen Yee, and Yogesh B. Gianchandani

University of Michigan, Ann Arbor, USA

MEMS2007

Outline

Introduction

Size-selective virtual channel

Single droplet trap

Guidewire pump

Conclusion

Introduction

In droplet-based microfluidic systems, droplet motion is generally guided by microfabricated patterned surfaces

Disadvantages - Droplet contact with solid surfaces and sample adsorption to channel walls or other surfaces - Actuators contact the liquid that has contamination concerns

Introduction

Several virtual microfluidic components, including channels, filters, traps, and pumps on unpatterned substrates, accomplish their function entirely by localized Marangoni flows by heat sources suspended just above the liquid surface

IntroductionMarangoni flow on a liquid surface driven by surface tension gradients

Temperature gradient causes surface tension gradients and flow directed from high to low temperature

MicroTAS05

Size-selective channel

Two heated wires parallel to the liquid surface

Recirculating flows occurring as a result of the Marangoni effect are shown with arrows

Size-selective channel500um diameters droplets entering the channel while a smaller one is rejected

S=600um, the minimum diameter for entry into the channel is 250umS=970um, the minimum diameter is 350um

Nearly 100% exclusion of off-sized droplet is shown

Single droplet trap

The single droplet trap is implemented using a ring-shaped annular heat source

Metal pin (s=600um) that a 700um diameter droplet is actively pulled into the trap

Guidewire pumpA triangular heat flux projected on the fluid surface pulls droplets in and along its longitudinal axis

The droplet achieves a maximum velocity of 196 um/sec

Conclusion Several components for droplet manipulation were presented, all of which operate without physical structures solely by localized Marangoni flows

Advantages -It is a non-contact method of actuation -Droplets do not make contact with solid surfaces -It does not require patterned substrates

These virtual components are building blocks toward a microsystem for droplet-based assays

Thanks for your listening !!

Droplet mixing

The four droplets (φ=200-400 um) merge together, one by one, eventually forming a single, φ=600 um droplet in 9 seconds.

MicroTAS05

Surface tension & Marangoni effect

t=t0(1-bT) t0 、 b ：隨液體而定之常數 T ：溫度 t ：表面張力

Ma=|dt/dT|α-1μ-1ΔTR2L-1 Ma ： Marangoni number 熱對流強度 dt/dT ：表面張力對溫度的變化率 α ：熱擴散係數 ΔT ：溫度差 μ ： 黏滯性 L ：流動區長度 R ：流動區半徑

Size-selective channel