Next to the overall aggregation over time, the distribution over the various cluster sizes was evaluated (Figure ). As apparent from Figure , the percentage of dimer structures (Figure ) remains fairly constant over the course of the fuel cycle. On the contrary, the contribution of trimers (Figure ) and especially larger clusters (> 3 particles) (Figure ) changes over time and follows the trend of the overall aggregation. Larger clusters are present from the start and disappear completely upon fuel addition, while over time they slowly reassemble. The cluster structures that we observe for all samples are not entirely crystalline, but show a fractal-like open structure (Figure ). We hypothesize that this is due to the existence of a secondary minimum in the interaction potential. The formation of the fractal structures is most likely caused by an increased depletion attraction force and hence reduced probability of escape for a particle in a cluster. This phenomenon has also been observed in other research with PAA polymers used for depletion-flocculation studies of polystyrene latex particles and silica surfaces . The secondary minimum is also quite shallow, as corroborated by the presence of single particles alongside the larger clusters (Figure ). Another reason for the presence of open structures can be polymer adsorption onto the colloid surface. However, adsorption here can be ruled out since it usually happens for PAA polymers having protonated carboxylates at low pH. Furthermore, the mobility of the particles is not influenced by the fuel cycle. We confirmed this by calculating the mean squared displacement (MSD) as a function of time (see SI section Mean squared displacement from particle tracking).