Hydrophobic nano-asperities in control of energy barrier during particle-surface interactions

To explain differences in colloidal interactions for spherical hydrophobic particles, a theoretical analysis of the interaction potential was carried out for a model rough particle interacting with a smooth and flat surface in an electrolyte solution. The attractive hydrophobic interaction potential was added to repulsive retarded van der Waals and repulsive electrical double layer interaction potentials. The rough microscopic particles were modeled as spheres decorated with nano-sized hemispherical asperities. Parameters that reflect common flotation separation systems were selected for testing this theoretical model and computation of the energy barrier applicable to particle-surface interactions. It was found that hydrophobic asperities with the radius of only a few nanometers reduced the energy required for particle attachment to a hydrophobic surface by several times. The value of this energy barrier was reduced by as much as two orders of magnitude when the radius of nano-sized asperities increased to a few tens of nanometers. Theoretical analysis also revealed that surface coverage of microscopic particles by nano-sized asperities was not as important as the size of the asperities.