  Surface roughness affects many properties of colloids, from depletion [1] and
capillary interactions [2], to their dispersibility [3] and use as emulsion
stabilizers [4]. It also impacts particle-particle frictional contacts, which
have recently emerged as being responsible for the discontinuous shear
thickening (DST) of dense suspensions [5-17]. Tribological properties of these
contacts have been rarely experimentally accessed [6, 15, 17, 18], especially
for non-spherical particles. Here, we systematically tackle the effect of
nanoscale surface roughness by producing a library of all-silica,
raspberry-like colloids [19] and linking their rheology to their tribology.
Rougher surfaces lead to a significant anticipation of DST onset, both in terms
of shear rate and solid loading. Strikingly, they also eliminate continuous
thickening. DST is here due to the interlocking of asperities, which we have
identified as "stick-slip" frictional contacts by measuring the sliding of the
same particles via lateral force microscopy (LFM). Direct measurements of
particle-particle friction therefore highlight the value of an
engineering-tribology approach to tuning the thickening of suspensions.
