nanoconfinement

Nanoconfinement is the confinement of matter to dimensions on the nanometer scale, typically within pores, channels, or films whose characteristic size ranges from a few to several tens of nanometers. In these restricted geometries, the physical properties of liquids, polymers, and soft matter depart from bulk behavior because surface interactions become dominant and the system's dimensionality is effectively reduced.

Nanoconfinement is observed in a variety of materials systems, including liquids in nanoporous silica or carbon, polymers inside mesoporous matrices, water confined in zeolites or carbon nanotubes, and ion transport through nanochannels. The confinement length scale and surface chemistry can strongly influence structure, dynamics, and phase behavior.

Confinement can modify phase transitions: melting points may be depressed, crystallization can be suppressed or altered, and new ordering can emerge in confined layers. Diffusion and viscosity become anisotropic; in the narrowest pores transport may be governed by Knudsen diffusion or surface hopping. Layering, preferential adsorption, and orientational ordering are common near walls, and in liquids or liquid crystals confinement can induce changes in dielectric properties and reactivity.

Characterization and theory employ neutron, x-ray, and light scattering; nuclear magnetic resonance diffusometry; calorimetry; electron microscopy; and spectroscopy. Molecular simulations and continuum models help interpret how confinement geometry, surface chemistry, and interfacial forces govern observed behavior.

Nanoconfinement is exploited in catalysis within porous supports, energy storage and conversion in nanoporous electrodes, desalination and filtration membranes, drug delivery using mesoporous carriers, and nanofluidic devices where transport occurs through nanoscale channels. Ongoing research aims to understand fundamental size effects and to tailor confinement for targeted applications.