Nondestructive high-throughput screening of nanopore geometry in porous membranes by imbibition

Abstract

A fluid dynamic model for imbibition into closed-end, axisymmetric pores having diameters that change as a function of the pore depth is presented. Despite the fact that liquid invasion into nonbranched closed-end pores is characterized by a wealth of different transient and/or metastable nonequilibrium stages related to precursor film formation, we show that a simple hydraulic model accounting for geometry-and air compression-induced deviations from classical Lucas-Washburn dynamics precisely describes the imbibition dynamics except at the late stage. The model was validated by laser interferometry experiments with submillisecond temporal resolution. Imbibition of three simple liquids (isopropanol, ethanol, and hexane) into self-ordered anodic alumina membranes containing arrays of parallel closed-end nanopores characterized by slight conicity was studied. The model provides an improved description of nanoscale fluid dynamics and allows geometric characterization of nanoporous membranes by their imbibition kinetics accounting for the back pressure of the compressed gas. Thus, a precise calibration of porous membranes with simple liquids becomes possible, and changes in the mean pore diameter as a function of the pore depth can be assessed.

Laser-excited elastic guided waves reveal the complex mechanics of nanoporous silicon

“…Cone-shaped pores and their significant influence on key properties like optical response and capillary pressure have already been evidenced for pSi [41][42][43][44] . A model has recently been developed to describe the pore depth-dependency in capillary rise experiments 45 . In order to outline the impact of the pore network, pSi is first compared to bulk silicon.…”

Dynamic Kerr and Pockels electro-optics of liquid crystals in nanopores for active photonic metamaterials

“…However, given the cylindrical pore wall geometry this would still result in centrosymmetric structures. Thus we suggest that the conicity of the channels, as dictated by the fabrication process, 54 results in macroscopic non-centrosymmetric polarizability along the channel axis and thus causes the Pockels effect. It is interesting to mention that a similar impact of conicity on second harmonic generation has recently been reported for chromophores embedded in conical silica nanochannels.…”

“…The conicity of the pores results from the unidirectional etching process. 54 The as-fabricated oxidic pore walls are polar, hydrophilic. 37 No surface treatment was employed before embedding the liquid crystals.…”

Dynamic Kerr and Pockels Electro-Optics of Liquid Crystals in Nanopores for Active Photonic Metamaterials

“…However, given the cylindrical pore wall geometry this would still result in centrosymmetric structures. Thus we suggest that the conicity of the channels, as dictated by the fabrication process 50 , results in a macroscopic non-centrosymmetric polarizability along the channel axis and thus causes the Pockels effect. It is interesting to mention that a similar impact of conicity on second harmonic generation has recently been reported for chromophores embedded in conical silica nanochannels 55 .…”