  Liquid adsorption in nanoporous materials induces their deformation due to
strong capillary forces. The linear relationship between the liquid pressure
and the solid strain (pore-load modulus) provides an experimental technique to
determine the mechanical properties of nanosized solids. Puzzling experimental
results have often been reported, leading to a severe reconsideration of the
mechanical properties of the thin walls, the introduction of surface stresses,
and the suggestion of a mutual influence of fluid adsorption and matrix
deformation. This work presents a molecular simulation examination of the
fundamentals of the pore-load measurement technique. The pore-load protocol is
reproduced as in experiments by measuring the solid deformation in presence of
the liquid ("numerical experiment"), and the result is compared to the expected
mechanical response of the solid. Focusing on a single nanoplatelet mimicking
silicon stiffness, we show that the pore-load protocol is valid as long as the
liquid in the pores remains liquid. However, when an ordered layer can form at
the solid surface, it significantly affects the pore-load measurement. It is
shown that this may happen above the freezing point even for moderately strong
fluid-solid interactions. This observation could help for the interpretation of
experimental data, in particular in porous silicon, where the expected presence
of atomically smooth surfaces could favor the formation of highly ordered fluid
layers.
