Hydrodynamic interactions between charged and uncharged Brownian colloids at a fluid-fluid interface

• Published in: Journal of colloid and interface science 2022-12, Vol.628, p.931-945
• Main Authors: Dani, Archit, Yeganeh, Mohsen, Maldarelli, Charles
• Format: Article
• Language: English
• Subjects: Capillary attraction; Electrostatic repulsion; Hydrodynamics; Langevin dynamics; Particles at interfaces
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/j.jcis.2022.08.084

[Display omitted] •Hydrodynamic interactions (HI) affect the aggregation dynamics of colloids straddling a fluid–fluid interface.•For uncharged particles, HI decrease the probability of aggregate formation for all Péclet (Pe) numbers.•For charged particles, HI change the probability of aggregate formation depending on the relative magnitude and influence of electrostatic repulsive interactions. The cluster formation and self-assembly of floating colloids at a fluid/fluid interface is a delicate force balance involving deterministic lateral interaction forces, viscous resistance to relative colloid motion along the surface and thermal (Brownian) fluctuations. As the colloid dimensions get smaller, thermal forces and associated drag forces become important and can affect the self assembly into ordered patterns and crystal structures that are the starting point for various materials applications. Langevin dynamic simulations for particle pairs straddling a liquid–liquid interface with a high viscosity contrast are presented to describe the lateral interfacial assembly of particles in Brownian and non-Brownian dominated regimes. These simulations incorporate capillary attraction, electrostatic repulsion, thermal fluctuations and hydrodynamic interactions (HI) between particles (including the effect of the particle immersion depth). Simulation results are presented for neutrally wetted particles which form a contact angle θ=900 at the interface. The simulation results suggest that clustering, fractal growth and particle ordering become favorable outcomes at critically large values of the Pe numbers, while smaller Pe numbers exhibit higher probabilities of final configurations where particle motion remains uncorrelated in space and particle pairs are found to be more widely separated especially upon the introduction of HI.