  Microgels are soft colloidal particles constituted by cross-linked polymer
networks with a high potential for applications. In particular, after
adsorption at a fluid interface, interfacial tension provides two-dimensional
(2D) confinement for microgel monolayers and drives the reconfiguration of the
particles, enabling their deployment in foam and emulsion stabilization and in
surface patterning for lithography, sensing and optical materials. However,
most studies focus on systems of fluids with a high interfacial tension, e.g.
alkanes/ or air/water interfaces, which imparts similar properties to the
assembled monolayers. Here, instead, we compare two organic fluid phases,
hexane and methyl tert-butyl ether, which have markedly different interfacial
tension ($\gamma$) values with water and thus tune the elasticity and
deformation of adsorbed microgels. We rationalize how $\gamma$ controls the
single-particle morphology, which consequently modulates the structural and
mechanical response of the monolayers at varying interfacial compression.
Specifically, when $\gamma$ is low, the microgels are less deformed within the
interface plane and their polymer networks can rearrange more easily upon
lateral compression, leading to softer monolayers. Selecting interfaces with
different surface energy offers an additional control to customize the 2D
assembly of soft particles, from the fine-tuning of particle size and
interparticle spacing to the tailoring of mechanical properties.
