Relaxation times in single event electrospraying controlled by nozzle front surface modification

Area of Science:

• Fluid dynamics
• Surface science
• Microfluidics

Background:

• Single event electrospraying (SEE) enables precise deposition of minute fluid volumes.
• Controlling fluid behavior at the nozzle is crucial for reproducible SEE.

Purpose of the Study:

• To investigate the influence of meniscus size on SEE characteristics.
• To understand the timing limitations of SEE based on electrical and hydrodynamic factors.
• To develop a model for predicting fluid motion during SEE.

Main Methods:

• Utilizing glass capillaries with and without anti-wetting coatings (perfluorodecylsilane monolayer) to control meniscus size.
• Analyzing electrical and hydrodynamic time constants governing the SEE process.
• Developing a model for one-dimensional liquid motion within the capillary during pulsing.

Main Results:

• A significant difference in driving voltage was observed between small and large menisci.
• Hydrodynamic relaxation time was substantially reduced in capillaries with anti-wetting coatings.
• The resistor-capacitor (RC) time of the electrical circuit was identified as the primary limitation for deposition timing.
• A model was developed to estimate hydrodynamic relaxation times for meniscus-cone transitions.

Conclusions:

• Confining the meniscus to the nozzle's inner diameter allows for sub-picoliter volume deposition per SEE event.
• Understanding and controlling meniscus size is key to optimizing SEE for precise fluid handling.
• The electrical RC time constant dictates the timing limitations of the SEE process.