Dynamics of nanoparticle tracers in supercooled nanoparticle matrices

Area of Science:

• Colloid and interface science
• Soft condensed matter physics
• Nanoparticle dynamics

Background:

• Understanding nanoparticle transport is crucial for designing advanced materials.
• Supercooled nanoparticle matrices exhibit complex dynamics influenced by particle interactions and size heterogeneity.
• Confocal microscopy and dynamic light scattering techniques are essential for probing nanoparticle motion.

Purpose of the Study:

• To investigate the influence of tracer nanoparticle size on dynamics within bulk supercooled nanoparticle matrices.
• To determine how tracer-to-matrix size ratios (δ) and matrix volume fractions (ϕ) affect nanoparticle mobility and relaxation.
• To elucidate the relationship between penetrant size and transport phenomena in soft porous media.

Main Methods:

• Utilized confocal microscopy for real-time tracking of fluorescent tracer nanoparticles.
• Employed particle-tracking algorithms to analyze single-particle dynamics.
• Applied differential dynamic microscopy (DDM) to characterize collective dynamics and intermediate scattering functions (ISF).

Main Results:

• Tracer nanoparticle dynamics, including mean-square displacement (MSD) and displacement distributions, are strongly dependent on tracer size (δ) and matrix volume fraction (ϕ).
• Small tracers (δ ≤ 0.36) exhibit subdiffusive behavior, while large tracers (δ ≥ 0.45) become dynamically arrested at higher matrix densities.
• Relaxation times increase with both δ and ϕ, and anomalous logarithmic decays in ISF are observed for smaller tracers over specific length scales.

Conclusions:

• Penetrant size is a critical factor governing nanoparticle transport in supercooled matrices.
• The observed dynamic arrest of larger tracers highlights the role of excluded volume effects and caging in confined soft matter.
• These findings offer fundamental insights into nanoparticle diffusion and dynamics in complex, soft porous environments.