Transport Properties and Non-Equilibrium Processes

Transport properties describe how mass, momentum and energy move within materials under gradients of concentration, velocity or temperature. Key parameters include viscosity, which quantifies internal friction in fluids; diffusivity, which measures molecular mixing rates; and thermal conductivity, which governs heat conduction. In systems driven far from equilibrium, such as high‐pressure magmas or fluids in confinement, these properties become strongly pressure- and temperature-dependent and may couple nonlinearly to evolving microstructure. Advances in high‐pressure experimentation, atomistic simulation and data‐driven modelling have extended accessible regimes, revealing anomalous viscosity minima, coordination changes of network‐forming elements and enhanced transport via fast species channels. Such insights inform geodynamic models of magma segregation, the design of subsurface energy storage, and the optimisation of functional materials under extreme conditions. Non‐equilibrium thermodynamics provides a framework for incorporating history-dependent flow rules and memory effects, while machine-learning interatomic potentials bridge the gap between quantum accuracy and tractable large-scale simulations.

Research from Nature Portfolio

First-principles molecular dynamics of basaltic compositions under lower-mantle pressures show an initial viscosity minimum near 6 GPa, followed by steady hardening with further compression. This behaviour arises from sharp increases in Fe and Si coordination numbers and constrains the early crystallisation of Earth’s magma ocean. Complementary simulations of hydrous Mg–Fe silicate melts reveal that water lowers density strongly at shallow depths but has negligible volumetric effect above 15 GPa. Rapid hydrogen diffusion under deep-mantle conditions enhances electrical conductivity through extended hydroxyl networks, refining our view of volatile transport and melt ponding at mantle boundaries.

Research from all publishers

High-precision measurements of dilute hydrogen diffusion in water from 298 K to 423 K at pressures up to 30 MPa resolve long-standing discrepancies and validate Stokes–Einstein correlations to within 1%. These data underpin accurate modelling of hydrogen loss in subsurface storage and guide the assessment of gas mixing effects on withdrawal purity. In parallel, empirical and numerical studies of binary hydrogen–methane diffusion in reservoir rocks at underground-storage conditions yield correlations for bulk diffusivity and tortuosity factors with relative errors below 50%. Implementation in field-scale simulators helps predict cushion-gas mixing and hydrogen retention, providing essential parameters for reliable underground energy storage.

Transport Properties and Non-Equilibrium Processes publication trend

The graph below shows the total number of articles in transport properties and non-equilibrium processes across all publications each year (not limited to Nature Index journals).

Technical terms

Viscosity: A measure of a fluid’s resistance to shear flow, reflecting momentum transport between adjacent layers.

Diffusion coefficient: A parameter quantifying the rate at which molecules spread from regions of high to low concentration.

Thermal conductivity: The capacity of a material to conduct heat, determined by energy exchange at the microscopic level.

First-principles molecular dynamics: Simulation method computing interatomic forces on-the-fly from electronic structure calculations to predict transport under extreme conditions.

Neural-network interatomic potential: A machine-learning model trained on quantum data to map atomic configurations to energies and forces, enabling large-scale, accurate dynamics.

Coordination number: The number of nearest-neighbour atoms bonded to a central atom, influencing melt structure and transport properties.

References

1. Hydrous silicate melts and the deep mantle H2O cycle. Earth and Planetary Science Letters (2022).
2. Insights into magma ocean dynamics from the transport properties of basaltic melt. Nature Communications (2022).
3. Structure and Density of H2O‐Rich Mg2SiO4 Melts at High Pressure From Ab Initio Simulations. Journal of Geophysical Research: Solid Earth (2020).
4. Diffusion Coefficients of N2O and H2 in Water at Temperatures between 298.15 and 423.15 K with Pressures up to 30 MPa. Journal of Chemical & Engineering Data (2023).
5. Empirical and Numerical Modelling of Gas–Gas Diffusion for Binary Hydrogen–Methane Systems at Underground Gas Storage Conditions. Transport in Porous Media (2023).
6. New Approach to Modeling Non-equilibrium Processes.