Study of capillary phenomena in nanoporous media by digital holographic microscopy

M. SALLESE; N. BUDINI; P. PSOTA; R. URTEAGA

Buenos Aires

Congreso; III Brazil-Argentine Microfluidics Congress, VI Congreso de Microfluídica Argentina; 2022

In this work, digital holographic microscopy (DHM) is implemented to study capillary filling phenomena in nanoporous structures such as porous silicon (PS). This technique is particularly useful for studying nanoporous materials whose morphology cannot be examined by conventional optical methods in the visible spectrum, providing a more precise and complex characterization method based on phenomena involving capillary condensation and evaporation on these nanostructures. We implemented a transmission DHM setup to study the condensation and evaporation dynamics around a drop of distilled water deposited onto a 5 µm-thick layer of PS on glass. Around the edge of the droplet a completely filled PS region (halo) develops due to the fact that condensation rate outruns evaporation rate. Farther from the edge of the drop this scenario is reverted and evaporation outruns condensation, which gives place to a region with a decreasing filling fraction. By digitally registering and numerically reconstructing holograms of the droplet it is possible to obtain a phase map that provides quantitative two-dimensional information of the filling fraction profile. Combining this information with fluid dynamic models allows for a morphological characterization of the porous structure. At the same time, the characterization of porous materials using simple fluids provides the basis for studying the behavior of more complex fluids under high spatial confinement conditions.