Insights into Ionic Diffusion in C-S-H Gel Pore from Molecular Dynamics Simulations: Spatial Distributions, Energy...

Area of Science:

• Materials Science
• Physical Chemistry
• Nanotechnology

Background:

• Understanding nanoscale transport in confined environments like cementitious materials is crucial but poorly understood at the molecular level.
• Ionic and water diffusion mechanisms within nanopores significantly impact material properties and durability.

Purpose of the Study:

• To investigate the molecular-level mechanisms of sodium (Na+), chloride (Cl-), and water diffusion in nanoconfined calcium-silicate-hydrate (C-S-H) pores.
• To analyze the spatial heterogeneity of transport behavior, thermal kinetics, and structure within cementitious nanopores.

Main Methods:

• Utilized molecular dynamics (MD) simulations to model ion and water diffusion in a 4 nm C-S-H pore channel.
• Performed spatially resolved analysis of diffusivity, activation energy barriers, and structural properties across the pore width.
• Introduced a total coordination strength (TCS) descriptor to link local liquid structure with molecular mobility.

Main Results:

• Observed significant suppression of diffusivity near the solid-liquid interface, recovering towards the pore center.
• Quantified spatial variations in activation energy and mobility, revealing distinct confinement effects.
• Identified a transition from structure-controlled to hydrodynamics-controlled transport regimes with increasing distance from the pore surface.

Conclusions:

• The study provides the first comprehensive MD resolution of transport heterogeneity in cementitious nanopores.
• Findings deepen the understanding of nanoscale transport phenomena and their dependence on pore structure and interfacial chemistry.
• Tailoring nanochannel structure and interfacial chemistry offers a strategy to suppress ionic ingress and enhance cement-based material durability.