In short, the comparison between the pristine flow tests, those with NaCl, and those with CTAB suggest two main conclusions. Particle-particle aggregation is nearly negligible in the pristine tests: the slightly negative surface charge likely provides a sufficient energetic barrier against aggregation. Further, adhesion in the pristine tests does happen, but much more rarely than when interactions are dominated by van der Waals or electrostatic attraction. In pristine flow tests, particles do not stick in the inlet region. Any adhesion is qualitatively different from that observed when the particles are suspended in a salt solution (see Video S1 in SI) or when electrostatic attractions are induced between the particles and channel walls (see Video S3 in SI). When electrostatic repulsion is screened away and van der Waals attractions dominate, adhesion is severe . Adhesion events do still occur even in pristine tests, but to a minimal degree. This suggests that van der Waals forces are not negligible, even in pristine conditions.