Effect of Primary Particle Size and Salt Concentration on the Structure of Colloidal Gels

Structures of colloidal gels prepared in the reaction-limited aggregation regime from fluorinated colloidal particles with two different sizes and different salt concentrations have been characterized by combining small-angle and wide-angle light scattering and small-angle neutron scattering techniques. In all cases, the scattering structure factors indicate the coexistence of two types of fractal structures at different scale lengths: a mass fractal scaling at the scale length of the clusters that constitute the gel and a surface fractal scaling for larger scale lengths. It has been found that, at the same particle volume fraction, the mass fractal dimension of the clusters in the gel increases as the primary particle size decreases. On the other hand, we show that both the mass and the surface fractal gel structures are independent of the salt concentration.