  We present a novel dynamic light scattering setup to probe, with time and
space resolution, the microscopic dynamics of soft matter systems confined
within millimeter-sized spherical drops. By using an ad-hoc optical layout, we
tackle the challenges raised by refraction effects due to the unconventional
shape of the samples. We first validate the setup by investigating the dynamics
of a suspension of Brownian particles. The dynamics measured at different
positions in the drop, and hence different scattering angles, are found to be
in excellent agreement with those obtained for the same sample in a
conventional light scattering setup. We then demonstrate the setup capabilities
by investigating a bead made of a polymer hydrogel undergoing swelling. The gel
microscopic dynamics exhibit a space dependence that strongly varies with time
elapsed since the beginning of swelling. Initially, the dynamics in the
periphery of the bead are much faster than in the core, indicative of
non-uniform swelling. As the swelling proceeds, the dynamics slow down and
become more spatially homogeneous. By comparing the experimental results to
numerical and analytical calculations for the dynamics of a homogeneous, purely
elastic sphere undergoing swelling, we establish that the mean square
displacement of the gel strands deviates from the affine motion inferred from
the macroscopic deformation, evolving from fast diffusive-like dynamics at the
onset of swelling to slower, yet supradiffusive, rearrangements at later
stages.
