Optical coherence tomography measurement of capillary filling in porous silicon

Abstract

The use of nanoporous structures with known morphology allows studying the properties of fluids in conditions of strong spatial confinement. Alternatively, the capillary filling of nanoporous structures with simple fluids provides information on their morphology. When a liquid enters the porous structure there is an increase in the optical path of the porous layer, and measuring this optical path as a function of position and time allows evaluating the filling dynamics of the pores. In this work, we determined the capillary filling dynamics of nanostructured porous silicon (PS) by optical coherence tomography. The high spatial resolution of this technique allows one not only to follow the position of the liquid front as a function of time but also to resolve in detail the filling fraction profile of the liquid front inside the PS matrix. Moreover, these profiles contain information about the pore size distribution in the PS structure. Therefore, we show how the determination and analysis of the filling fraction profile along the advancing liquid front can be used as a method to study the pore size distribution inside PS structures.

Time-temperature indicator based on the variation of the optical response of photonic crystals upon polymer infiltration

“…Actually, when capillary-driven flows advance through periodically constricted tubes, the LW dynamics holds but the effective radius in Eq. 4 now scales as r eff ∼ r 4 min /r 3 max [43,44]. It is worth noting that this scaling ratio has been also observed in porous media with bimodal pore size distributions in the microscale [45,46].…”

Straight versus Spongy: Effect of Tortuosity on Polymer Imbibition into Nanoporous Matrices Assessed by Segmentation-Free Analysis of 3D Sample Reconstructions

“…To describe the spatiotemporal evolution of imbibition fronts during the invasion of porous matrices by wetting fluids, average positions of the imbibition fronts need to be determined and imbibition front widths need to be quantified in a statistically valid way. Imbibition fronts were, for example, inspected with the naked eye , and by averaging methods, such as small-angle X-ray scattering, dielectric spectroscopy, − neutron radiography, , gravimetry, − and opto-fluidic techniques. ,− In particular, the reliable and reproducible quantification of imbibition front widths for systems characterized by imbibition front widths ranging from a few 100 nm to a few microns has remained challenging. Recently, we reported the statistical evaluation of 3D reconstructions of AAO membranes infiltrated with polystyrene (PS), which were acquired by Zernike phase-contrast X-ray computed tomography − with submicron resolution.…”

Precursor Film Spreading during Liquid Imbibition in Nanoporous Photonic Crystals

“…The effective refractive index of the medium varies with the relative material composition (solid/air/liquid) that changes upon liquid imbibition. By using effective medium theories [32,33], the filling fraction in the microcavity can be obtained from the variation of the resonance position as, f (t) = λ(t)−λ0 λ f −λ0 , where λ(t) is the resonance wavelength at time t, while λ 0 and λ f are the resonance wavelengths at times t = 0 and t = ∞, respectively. Thus, monitoring the resonance evolution enables a simple assessment of the filling fraction as a function of time in the microcavity central layer.…”

“…This encourages us to believe that other effects than precursor film spreading on the single-channel scale that could result in a √ t spreading of the imbibition front are not dominating the kinetics here. In particular, the pore-size distribution along with the Lucas-Washburn √ t of menisci movements in non-interconnected single-pores could also result in a √ t broadening, where the prefactor (the diffusion coefficient) would be determined by the width of the pore-size distribution [19,22,33]. However, since we employed the identical nanoporous geometries with identical pore-size distributions this broadening should occur for both fluids in an identical manner, which is obviously not the case.…”