Molecular Simulation of Gas Solubility in Nitrile Butadiene Rubber

Area of Science:

• Materials Science
• Computational Chemistry
• Polymer Physics

Background:

• Nitrile butadiene rubber (NBR) is widely used in seals, especially in demanding environments.
• Understanding gas solubility in NBR is crucial for predicting material performance and longevity.

Purpose of the Study:

• To compute the solubility of small gases (He, CO2, H2O) in NBR using molecular simulation.
• To investigate the influence of polymer structure (acrylonitrile content) and local free volume on gas solubility.
• To analyze the impact of temperature and pressure on gas solubility in NBR.

Main Methods:

• Widom particle-insertion technique, biased by local free volume.
• Examination of method convergence with varying snapshots and insertions per snapshot.
• Analysis of acrylonitrile content and local free volume definition effects.
• Voronoi cell construction to decompose solubility contributions by atomic neighborhoods.

Main Results:

• Polar gases (CO2, H2O) exhibit enhanced solubility compared to nonpolar gases (He).
• CO2 and H2O show a strong affinity for nitrogen sites within the NBR matrix.
• Temperature decreases solubility for CO2 and H2O but increases it for He.
• Pressure generally suppresses gas solubility, with rates varying by gas-polymer interactions.

Conclusions:

• The study provides molecular-level insights into gas transport in NBR.
• Results offer valuable data for designing and using NBR seals in high-temperature and high-pressure applications.
• The findings align with experimental observations, validating the simulation approach.