Microscopic Movement of Slow-Diffusing Nanoparticles in Cylindrical Nanopores Studied with Three-Dimensional Tracking

Area of Science:

• Physics
• Materials Science
• Physical Chemistry

Background:

• Understanding mass transport in confined spaces is crucial for various applications.
• Slow diffusion in nanopores can arise from different physical mechanisms.
• Distinguishing these mechanisms is key to controlling transport phenomena.

Purpose of the Study:

• To develop and apply a 3D single-particle localization technique for tracking particle movement in nanopores.
• To investigate the distinct effects of solvent viscosity and pore wall affinity on particle diffusion.
• To differentiate the mechanisms underlying slow mass transport in confined environments.

Main Methods:

• Utilized a three-dimensional (3D) single-particle localization technique.
• Tracked microscopic particle movements within cylindrical nanopores.
• Analyzed particle behavior under conditions of increased solvent viscosity and increased pore wall affinity.

Main Results:

• Particles were retained longer in pores under both increased solvent viscosity and pore wall affinity.
• Increased solvent viscosity led to a proportional decrease in particle step size, causing slow diffusion.
• Increased pore wall affinity resulted in limited reduction of step sizes, with restricted diffusion being the primary cause of slow diffusion.

Conclusions:

• The study successfully differentiated slow diffusion mechanisms in confined environments.
• Solvent viscosity and pore wall interactions impact particle transport differently.
• The developed technique provides a method to distinguish between these distinct diffusion-limiting factors.