  Superresolution microscopy has become a powerful tool to investigate the
internal structure of complex colloidal and polymeric systems, such as
microgels, at the nanometer scale. The ability to monitor microgels response to
temperature changes in situ opens new and exciting opportunities to design and
precisely control their behaviour for various applications. When performing
advanced microscopy experiments, interactions between the particle and the
environment can be important. Often microgels are deposited on a substrate
since they have to remain still for several minutes during the experiment. This
study uses dSTORM microscopy and advanced coarse-grained molecular dynamics
simulations to investigate, for the first time, how individual microgels
anchored on hydrophilic and hydrophobic surfaces undergo their volume phase
transition in temperature. We find that, in the presence of a hydrophilic
substrate, the structure of the microgel is unperturbed and the resulting
density profiles quantitatively agree with simulations performed in bulk
conditions. Instead, when a hydrophobic surface is used, the microgel spreads
at the interface and an interesting competition between the two hydrophobic
strengths -- monomer-monomer vs monomer-surface -- comes into play at high
temperatures. The remarkable agreement between experiments and simulations
makes the present study a fundamental step to establish this high-resolution
monitoring technique as a platform for investigating more complex systems,
being these either macromolecules with peculiar internal structure or
nanocomplexes where molecules of interest can be encapsulated in the microgel
network and controllably released with temperature.
