  The reconfiguration of soft, deformable particles upon adsorption at the
interface between two fluids underpins many aspects of their dynamics and
interactions, ultimately controlling the macroscopic properties of particle
monolayers of relevance for materials, such as particle-stabilized emulsions
and foams, and processes, e. g. particle-based lithography. In spite of its
importance, experimentally determining the three-dimensional shape of soft
particles at fluid interfaces with high resolution remains an elusive task. In
this work, we take poly(N-isopropylacrylamide) (pNIPAM) microgels as model soft
particles and demonstrate that their conformation at the interface between an
aqueous and an oil phase can be fully reconstructed by means of in-situ atomic
force microscopy (AFM) imaging. We show that imaging the particle topography
from both sides of the interface allows one to characterize the in-plane
deformation of the particle under the action of interfacial tension and to
visualize the occurrence of asymmetric swelling in the two fluids.
Additionally, the technique enables investigating different fluid phases and
particle architectures, as well as studying in situ the effect of temperature
variations on particle conformation. We envisage that these results open up an
exciting range of possibilities to provide microscopic insights between the
single-particle behavior of soft objects at fluid interfaces and macroscopic
material properties of relevance for applications and fundamental studies
alike.

Soft Condensed Matter