  Understanding the motion of particles with ligand-receptors is important for
biomedical applications and material design. Yet, even among a single design,
the prototypical DNA-coated colloids, seemingly similar micrometric particles
hop or roll, depending on the study. We shed light on this problem by observing
DNA-coated colloids diffusing near surfaces coated with complementary strands
for a wide array of coating designs. We find colloids rapidly switch between 2
modes: they hop - with long and fast steps - and crawl - with short and slow
steps. Both modes occur at all temperatures around the melting point and over a
wide array of designs. The particles become increasingly subdiffusive as
temperature decreases, in line with subsequent velocity steps becoming
increasingly anti-correlated. Overall, crawling (or hopping) phases are more
predominant at low (or high) temperatures; crawling is also more efficient at
low temperatures than hopping to cover large distances. We rationalize this
behavior within a simple model: at lower temperatures, the number of bound
strands increases, and detachment of all bonds is unlikely, hence, hopping is
prevented and crawling favored. We thus reveal the mechanism behind a common
design rule relying on increased strand density for long-range self-assembly:
dense strands on surfaces are required to enable crawling, possibly
facilitating particle rearrangements.
