Colloidal interaction at the air—liquid interface: experimental results

We present some results obtained in 2D aggregation experiments. Experiments were made using a salt subphase of 2.0 M KBr and pH values ranging from 1.5 to 6.0. We used two latex polystyrene samples with different contact angles (i.e. different hydrophobic properties) and similar particle sizes. Digitised images were obtained at different aggregation times. These images were analysed to obtain the aggregates from the whole image. The aggregation results were compared using the kinetic exponents obtained from the asymptotic behaviour of the total number of aggregates as a function of time. N ∝ tz. In contrast to the 3D case, the aggregation at the air—solution interface was faster for the hydrophilic particles than for the hydrophobic ones. These experimental findings were analysed using a model of the interactions between colloidal particles at the air—liquid interface that takes an electrostatic dipolar repulsive term into account between the air-exposed parts of the particles.