Screening and collective effects in randomly pinned fluids: a new theoretical framework

Area of Science:

• Physics
• Materials Science
• Physical Chemistry

Background:

• Understanding the dynamics of supercooled liquids is crucial for materials science.
• Hard-sphere systems provide a fundamental model for studying liquid behavior.
• The effect of immobile obstacles on liquid dynamics is not fully understood.

Purpose of the Study:

• To propose a theoretical framework for the dynamics of hard-sphere systems with randomly pinned particles.
• To apply this framework to supercooled water and validate it against simulations.
• To investigate the influence of pinned particles on structural relaxation dynamics.

Main Methods:

• Development of a theoretical framework for bulk isotropic hard-sphere systems.
• Inclusion of randomly pinned particles to model immobile obstacles.
• Application and validation of the theory using supercooled water simulations.
• Analysis of both local and non-local activated processes governing structural relaxation.

Main Results:

• A stronger local caging constraint emerges as the pinned fraction increases.
• Long-range collective relaxation is screened by immobile obstacles.
• The alpha relaxation time shows subtle variations with pinning and density due to differing local and cooperative motion responses.
• Theoretical predictions for water with pinned molecules align well with simulation data.
• The thermal dependence of relaxation for unpinned water matches prior experimental and computational findings.

Conclusions:

• The proposed theoretical framework accurately describes the dynamics of hard-sphere systems with pinned particles.
• Pinned particles significantly alter the relaxation dynamics of supercooled liquids, particularly water.
• The theory provides a valuable tool for understanding and predicting the behavior of complex fluids under confinement or with impurities.