Influence of wettability on diffusion limited nanoparticle adsorption at gas-liquid interfaces

This study investigates the influence of hydrophobicity on particle adsorption by examining the behavior of hydrophobized silica particles at air-water interfaces. Langmuir-Blodgett (LB) trough studies of butanol (‘SiO-butane’) and hexanol (‘SiO-hexane’) esterified particles provided contrasting behavior. The SiO-butane particles formed weaker particle layers that underwent partial collapse with compression, leading to formations significantly below hexagonal close-packed estimates. In contrast, the SiO-hexane particles exhibited improved monolayer behavior and longer-range stability. Droplet surface tensions demonstrated that the hydrophobic particles significantly altered the dynamic tension during adsorption, when methyl isobutyl carbinol (MIBC) was added as a co-surfactant. Short-term modeling elucidated the role of diffusion and energy barriers on adsorption dynamics, with SiO-hexane having reduced diffusion coefficients with respect to SiO-butane and unmodified particles. Despite this reduced diffusion, long-term modeling allowed calculation of adsorption coefficients (k<inf>a</inf>), which for SiO-hexane particles were ∼200 × greater than for unmodified particles at low 0.1 wt% particle concentrations and over 1000 × greater at 2 wt%. Overall, the results provide quantitative insights into the profound influence of hydrophobicity on particle adsorption, particularly in crowded surface environments. Importantly, a diffusion-only mechanism is inadequate to explain adsorption dynamics for these larger colloids and the gravity-driven contribution must be considered in early-stage kinetics.