| Summary: |
The advent of soft photolithography has made possible the development of miniature devices to control tiny amounts of fluids, a new technology useful to a wide variety of applications: sensors, flow control and flow focusing (as in printers), delivery of drugs and chemicals, isolation and tagging of biological material, in a word, the "lab-on-a-chip" concept. These small scale flows typically involve polymer additives for two main reasons:
either they are part of the application itself (case of biopolymers) or they are used to dramatically change the flow dynamics. Indeed, the very low Reynolds number flows of Newtonian fluids are reversible whereas the addition of minor amounts of high molecular weight polymer chains impart elasticity to the fluids and make their flows asymmetric.
Miniature flows with viscoelastic fluids thus have the potential for logic devices, but the flow dynamics in these systems needs to be extensively investigated because the small scales change the equilibrium of forces and effects in comparison with large scales. This is particularly true of viscoelastic fluids, where almost everything remains to be done at microfluidic scales. This is the motivation for this proposal: to investigate in detail, experimentally as well as numerically, the flow of viscoelastic fluids in a number of geometries that have asymmetric behavior in order to clarify the role of fluid Rheology and flow geometry into the observed fluid dynamical performance.
Two cases are investigated here: (1) the microfluidic diode, a channel made of a chain of identical triangle segments connected by bottleneck contractions, the behaviour of which depends on flow direction and (2) a smooth expansion with a side entrance/exit.
To obtain these geometries, classical lithography is used first to make a set of metallic masks. From these, the microchannels are fabricated out of an elastomer using soft lithography in a clean room (spincoat, expose and dissolve). The other elements m  |
Summary
The advent of soft photolithography has made possible the development of miniature devices to control tiny amounts of fluids, a new technology useful to a wide variety of applications: sensors, flow control and flow focusing (as in printers), delivery of drugs and chemicals, isolation and tagging of biological material, in a word, the "lab-on-a-chip" concept. These small scale flows typically involve polymer additives for two main reasons:
either they are part of the application itself (case of biopolymers) or they are used to dramatically change the flow dynamics. Indeed, the very low Reynolds number flows of Newtonian fluids are reversible whereas the addition of minor amounts of high molecular weight polymer chains impart elasticity to the fluids and make their flows asymmetric.
Miniature flows with viscoelastic fluids thus have the potential for logic devices, but the flow dynamics in these systems needs to be extensively investigated because the small scales change the equilibrium of forces and effects in comparison with large scales. This is particularly true of viscoelastic fluids, where almost everything remains to be done at microfluidic scales. This is the motivation for this proposal: to investigate in detail, experimentally as well as numerically, the flow of viscoelastic fluids in a number of geometries that have asymmetric behavior in order to clarify the role of fluid Rheology and flow geometry into the observed fluid dynamical performance.
Two cases are investigated here: (1) the microfluidic diode, a channel made of a chain of identical triangle segments connected by bottleneck contractions, the behaviour of which depends on flow direction and (2) a smooth expansion with a side entrance/exit.
To obtain these geometries, classical lithography is used first to make a set of metallic masks. From these, the microchannels are fabricated out of an elastomer using soft lithography in a clean room (spincoat, expose and dissolve). The other elements making the flow circuit (syringe pumps, reservoirs, pressure transducers) are then assembled together, fluids are rheological characterized, seeding particles are added to the fluids and the flows are visualized in a microscope.
Although the experiments at small scale are to be performed for the first time by our mutidisciplinary team, it comes as the natural continuation of an on-going collaboration with the Hatsopoulos MicroFluidics Laboratory at MIT, where the Post-Doc researcher is presently being trained on experimental microfluidics under the guidance of Prof. GH McKinley, who is also a consultant in this project.
The numerical work is an extension of our own viscoelastic numerical research at macro scales using a finite-volume methodology based code. The differential constitutive equations are multi-mode and are selected to agree with the measured fluid Rheology. At our disposal are the Oldroyd-B, PTT, Giesekus, FENE-P and FENE-CR models.
The project lasts 3 years. |