By using the critical Casimir force, we study the attractive strength dependent aggregation of colloids with and without gravity by means of near field scattering. Significant differences were seen between microgravity and ground experiments, both in the structure of the formed fractal aggregates as well as in the kinetics of growth. In microgravity purely diffusive aggregation is observed. By using the continuously variable particle interaction potential we can for the first time experimentally relate the strength of attraction between the particles and the structure of the aggregates.
