Evanescent-wave cavity ring-down investigation of polymer/solvent interactions

Area of Science:

• Materials Science
• Physical Chemistry
• Spectroscopy

Background:

• Poly(dimethylsiloxane) (PDMS) is a widely used silicone polymer with applications in various fields.
• Understanding the interfacial behavior of PDMS with different solvents is crucial for optimizing its performance.
• Evanescent-wave cavity ring-down spectroscopy (EW-CRDS) offers a sensitive method for probing thin films and interfaces.

Purpose of the Study:

• To investigate the interfacial phenomena between poly(dimethylsiloxane) (PDMS) films and solvents (methanol and water).
• To quantify the diffusion coefficients of methanol and water within PDMS films.
• To elucidate the primary causes of optical losses at the PDMS-solvent interface.

Main Methods:

• Utilized Evanescent-wave cavity ring-down spectroscopy (EW-CRDS) to monitor solvent uptake and interfacial changes in PDMS films.
• Employed bulk weight-gain measurements to determine diffusion coefficients.
• Conducted surface plasmon resonance (SPR) experiments for complementary interfacial analysis.

Main Results:

• Observed distinct uptake kinetics for methanol and water in PDMS films.
• Determined higher diffusion coefficients for methanol ((25.1 +/- 0.7) x 10(-7) cm(2)/s) compared to water ((7 +/- 2) x 10(-7) cm(2)/s) in PDMS.
• Identified film delamination from the substrate as the dominant source of optical losses for methanol-PDMS interfaces, confirmed by SPR.

Conclusions:

• Methanol exhibits faster diffusion in PDMS than water after an initial uptake period.
• Film delamination significantly contributes to optical losses at the methanol-PDMS interface.
• EW-CRDS is a valuable technique for studying solvent-polymer interactions and interfacial delamination.