Radial profiling of microdroplets using cavity-enhanced Raman spectroscopy

Area of Science:

• Physical Chemistry
• Spectroscopy
• Droplet Dynamics

Background:

• Understanding droplet evaporation is crucial for atmospheric science and industrial processes.
• Previous methods lacked the spatial resolution to probe droplet composition changes.
• Methanol-water mixtures are common in various applications, necessitating detailed study.

Purpose of the Study:

• To radially resolve the composition of methanol-water droplets.
• To investigate the evaporation dynamics of these droplets.
• To validate theoretical models of droplet evaporation.

Main Methods:

• Utilized cavity-enhanced Raman spectroscopy (CERS) for high-sensitivity analysis.
• Employed a 514.5-nm laser to excite optical cavity modes within 7.7-microm-radius droplets.
• Analyzed spontaneous Raman scattered light to determine species identity and concentration.

Main Results:

• Successfully achieved radial resolution of methanol and water concentrations within droplets.
• Observed distinct radial zones corresponding to different optical cavity modes.
• Measured methanol concentration profiles showed good agreement with a diffusion-limited evaporation model.

Conclusions:

• CERS is a powerful technique for probing the internal composition of microdroplets.
• The evaporation of methanol-water droplets is governed by diffusion limitations.
• This study provides experimental validation for evaporation models at the microscale.