Patchy colloidal gels under the influence of gravity

Area of Science:

• Colloid and Surface Science
• Soft Matter Physics
• Computational Materials Science

Background:

• Patchy colloidal systems form gels through specific interactions.
• Gravitational effects on colloidal gelation are not fully understood.
• Rigidity percolation criterion identifies gel-like states in colloidal systems.

Purpose of the Study:

• To investigate the influence of gravity on the structure and properties of gel-forming patchy colloidal systems.
• To determine the role of the gravitational Péclet number (Pe) and patchy coverage (χ) in colloidal aggregation.
• To understand how gravity modifies the percolating cluster and structural rigidity.

Main Methods:

• Monte Carlo computer simulations of gel-like colloidal states.
• Analysis of gel structure modification under varying gravitational fields.
• Study of patchy coverage (χ) and gravitational Péclet number (Pe) effects.

Main Results:

• A threshold Péclet number (Pe_g) was identified, dependent on patchy coverage (χ), above which gravity enhances particle bonding and aggregation.
• Smaller χ values require higher Pe_g for gravitational influence.
• Gravity alters cluster size distribution and density profiles, leading to heterogeneous gel structures and modified structural rigidity.
• In the isotropic case, increased Pe shifts critical temperature, but high Pe causes sedimentation.
• Gravity shifts the rigidity percolation threshold to lower densities.

Conclusions:

• Gravitational fields significantly influence the structure and properties of gel-forming patchy colloidal systems.
• The interplay between patchy coverage and gravitational Péclet number dictates the extent of aggregation and structural modification.
• Gravity can lead to novel heterogeneous gel states, including coexistence with dilute/dense phases or crystalline-like structures.