Imaging of Pressure- and Electrokinetically Driven Flows through Open Capillaries

Area of Science:

• Microfluidics
• Optical Imaging
• Fluid Dynamics

Background:

• Accurate characterization of fluid dynamics within microscale structures is crucial for advancements in various scientific and engineering fields.
• Existing methods for imaging scalar transport and velocity fields in microchannels often face limitations in resolution, distortion, or applicability.

Purpose of the Study:

• To introduce and validate a new optical imaging tool for simultaneous measurement of scalar transport and velocity fields in microscale liquid flows.
• To demonstrate the tool's capability in visualizing complex flow patterns within microchannels.

Main Methods:

• Employing an ultraviolet laser pulse to uncage a fluorescent dye, creating a traceable pattern within the liquid flow.
• Utilizing flood illumination with visible light and a sensitive CCD camera to capture fluorescence images at selected time delays.
• Integrating the system with an oil immersion microscope to minimize optical aberrations and ensure high-contrast imaging.

Main Results:

• Successfully obtained high-contrast images of steady flow patterns driven by pressure and electrokinetic forces in micrometer-scale capillaries.
• Demonstrated the ability to reconstruct velocity profiles by analyzing time sequences of scalar images through direct inversion of the advection-convection equation.

Conclusions:

• The developed tool provides a powerful, non-invasive method for detailed analysis of microfluidic transport phenomena.
• This technique offers high spatial and temporal resolution, enabling precise characterization of flow dynamics in microscale systems.