Accessing fluid infiltration in nanogranular coatings is an outstanding
challenge, of relevance for applications ranging from nanomedicine to
catalysis. A sensing platform, allowing to quantify the amount of fluid
infiltrated in a nanogranular ultrathin coating, with thickness in the 10 to 40
nm range, is here proposed and theoretically investigated by multiscale
modelling. The scheme relies on impulsive photoacoustic excitation of
hypersonic mechanical breathing modes in engineered gas-phase synthesised
nanogranular metallic ultathin films and time-resolved acousto-optical read-out
of the breathing modes frequency shift upon liquid infiltration. A superior
sensitivity, exceeding 26x103 cm^2/g, is predicted upon equivalent areal mass
loading of a few ng/mm^2. The capability of the present scheme to discriminate
among different infiltration patterns is discussed. The platform is an ideal
tool to investigate nano fluidics in granular materials and naturally serves as
a distributed nanogetter coating, integrating fluid sensing capabilities. The
proposed scheme is readily extendable to other nanoscale and mesoscale porous
materials.Comment: 14 pages, 4 figure
