Capillary rise in nanotubes coated with polymer brushes

Area of Science:

• Soft Matter Physics
• Nanofluidics
• Polymer Science

Background:

• Understanding fluid transport in nanoconfined geometries is crucial for applications in microfluidics and materials science.
• The behavior of fluids within nanoporous materials is significantly influenced by surface interactions and confinement effects.
• Polymer brushes coating capillary surfaces introduce complex interfacial phenomena affecting fluid dynamics.

Purpose of the Study:

• To investigate the spontaneous capillary rise of fluids in brush-coated nanocapillaries using molecular dynamics simulations.
• To examine the effects of varying wettability of capillary walls and polymer brushes on fluid transport.
• To determine the influence of polymer chain length on the dynamics and mechanisms of capillary filling.

Main Methods:

• Molecular dynamics (MD) simulations employing a coarse-grained model.
• Systematic variation of surface wettability (capillary walls and polymer brush).
• Analysis of fluid transport dynamics across a range of polymer chain lengths (N).

Main Results:

• Capillary filling observed in both lyophilic and lyophobic tubes when the polymer brush is wetted.
• Capillary rise follows a time-square law, with mechanisms shifting between Lucas-Washburn and diffusive propagation based on chain length (N).
• Polymer brush reorganization into channels and monomer plugs near the meniscus, influencing imbibition speed and meniscus movement.

Conclusions:

• Fluid spontaneous rise in nanocapillaries is possible even with non-wettable walls, provided the polymer brush coating is wetted.
• Polymer chain length critically dictates the capillary rise mechanism and speed, with distinct regimes observed for different N.
• The dynamic interplay between fluid, polymer brush, and capillary wall governs nanofluidic transport, leading to unique phenomena like fluid walls and negative curvature menisci.