Phase transitions in nanoconfined binary mixtures of highly oriented colloidal rods

Area of Science:

• Colloidal science
• Soft matter physics
• Materials science

Background:

• Colloidal mixtures exhibit complex phase behavior, including nematic and smectic liquid crystal phases.
• Surface-induced layering (SIL) transitions are known to occur at single hard walls.
• Understanding confined systems is crucial for designing materials with specific properties.

Purpose of the Study:

• To investigate the effects of confinement on a binary mixture of colloidal hard cylinders.
• To analyze how pore width influences phase transitions and layering phenomena.
• To provide a foundational understanding for self-assembly of nanoparticles in restricted geometries.

Main Methods:

• Utilized fundamental-measure density functional theory.
• Analyzed a binary mixture of colloidal parallel hard cylinders with length ratio s=3.
• Studied systems confined within a planar slit-pore geometry.

Main Results:

• Confinement significantly alters the phase diagram, suppressing second-order nematic-smectic transitions.
• Demixing transitions are weakly affected by confinement, showing minor shifts in chemical potential.
• Confinement-induced layering (CIL) transitions can merge with demixing, and surface-induced layering (SIL) transitions are shifted.

Conclusions:

• Confinement introduces significant changes to the phase behavior of colloidal liquid crystal mixtures.
• The interplay between pore width, smectic period, and particle length ratio dictates these changes.
• This research is a crucial first step toward understanding nanoparticle self-assembly under confinement.