Electrokinetic characterization of poly(dimethylsiloxane) microchannels.

Area of Science:

• Electrokinetics
• Microfluidics
• Materials Science

Background:

• Poly(dimethylsiloxane) (PDMS) is a common material for microfluidic devices.
• Understanding electrokinetic phenomena in PDMS is crucial for optimizing microchannel performance.
• Native PDMS microchannels exhibit unique electrokinetic behaviors compared to traditional materials.

Purpose of the Study:

• To characterize the fundamental electrokinetic phenomena in native PDMS microchannels.
• To compare electroosmotic flow and mobility in PDMS with fused-silica capillaries.
• To investigate the influence of pH and ionic strength on electrokinetic behavior in PDMS.

Main Methods:

• Current measurements and electroosmosis data collection in PDMS/PDMS and PDMS/glass microchannels.
• Comparison with data from fused-silica capillaries under controlled buffer conditions.
• Analysis of electroosmotic mobility dependence on ionic strength and pH using regression models.

Main Results:

• Ohm's law was observed in PDMS microchannels at higher electric field strengths than in fused-silica.
• Electroosmotic mobility in PDMS and fused-silica showed similar dependencies on ionic strength and pH.
• Native PDMS exhibited 50-70% lower electroosmotic flow magnitude than fused-silica, with reduced stability at acidic pH.

Conclusions:

• The negative surface charge in PDMS microchannels originates similarly to glass and fused-silica but with lower density.
• Electroosmotic fluid pumping in PDMS is pH-dependent and can be modeled by silanol ionization.
• Native PDMS microchannels offer distinct electrokinetic properties that differ from fused-silica, impacting their application suitability.