We combine small-angle
scattering experiments and simulations to
investigate the internal structure and interactions of composite poly(N-isopropylacrylamide)–poly(ethylene glycol) (PNIPAM–PEG)
microgels. At low temperatures the experimentally determined form
factors and the simulated density profiles indicate a loose internal
particle structure with an extended corona that can be modeled as
a starlike object. With increasing temperature across the volumetric
phase transition, the form factor develops an inflection that, using
simulations, is interpreted as arising from a conformation in which
PEG chains are incorporated in the interior of the PNIPAM network.
This gives rise to a peculiar density profile characterized by two
dense, separated regions, at odds with configurations in which the
PEG chains reside on the surface of the PNIPAM core. The conformation
of the PEG chains also have profound effects on the interparticle
interactions: Although chains on the surface reduce the solvophobic
attraction typically experienced by PNIPAM particles at high temperatures,
PEG chains inside the PNIPAM network shift the onset of attractive
interaction at even lower temperatures. Our results show that by tuning
the morphology of the composite microgels, we can qualitatively change
both their structure and their mutual interactions, opening the way
to explore new collective behaviors of these objects.