Rapid compressions in a captive bubble apparatus are isothermal

Area of Science:

• Biophysics
• Surface Chemistry

Background:

• Captive bubbles are standard for studying pulmonary surfactant films under changing surface area via hydrostatic pressure.
• Adiabatic compression of gas in bubbles could theoretically cause >100°C temperature increases, which is not experimentally observed.

Purpose of the Study:

• To accurately measure the gas phase temperature (Tg) changes in captive bubbles during rapid compressions.
• To investigate the influence of interfacial films on Tg during compression.

Main Methods:

• Monitored pressure (P) and volume (V) during rapid compressions (<1 s) of bubbles with and without interfacial films.
• Utilized the P x V product to evaluate Tg, accounting for gas molecule solubility.
• Determined temporal variations in gas moles (n) and extrapolated back to calculate Tg immediately post-compression.

Main Results:

• P x V decreased during and after compressions, indicating reduced gas moles (n) due to increased solubility at higher pressures.
• The decrease in P x V followed first-order kinetics, consistent with gas solubility.
• Measured Tg changes were <2°C for compressions up to >3 atm within 1 s, regardless of interfacial films.

Conclusions:

• Rapid compressions of captive bubbles are near-isothermal, with minimal temperature changes (<2°C).
• Gas solubility in the subphase significantly influences gas phase behavior during rapid compressions.
• The experimental method provides accurate Tg measurements for dynamic interfacial studies.