  We study light-activated quasi-2d gels made of a colloidal network doped with
Janus particles. Following the gel formation, the internal dynamics of the gel
are monitored before, during, and after the light activation. We monitor both
the structure and dynamics, before, during and after the illumination period.
The mobility of the passive particles exhibits a characteristic scale-dependent
response. Immediately following light activation, the gel displays large-scale
reorganization, followed by progressive, short-scale displacements throughout
the activation period. Albeit subtle structural changes (including pore opening
and widening and shortening of strands) the colloidal network remains
connected, and the gel maintains its structural integrity. Once activity is
switched off, the gel keeps the memory of the structure inherited from the
active phase. Remarkably, the motility remains larger than that of the gel,
before the active period. The system has turned into a genuinely different gel,
with frozen dynamics, but with more space for thermal fluctuations. The above
conclusions remain valid long after the activity period.
