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Item type:Publication, Access status: with files , An optical study of nanofluidics in mesoporous silicon(2025); This thesis presents a novel method for studying capillary imbibition and vapor sorption in mesoporous silicon (PSi) with white light spectroscopy. By Fast-Fourier-Transformation of thin film interference and parallel analysis of an optical microcavity within the porous layer, it achieves high precision in monitoring fluid dynamics. The research includes a constriction model for capillary imbibition, the resolution of liquid menisci and a percolation mechanism for vapor sorption. Moreover, a new rapid and non-destructive technique is introduced for assessing pore pathways of PSi, by calulating the pore geometry from liquid dynamics and capillary pressure.Publicationtype: Doctoral Thesis78 54 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , On the applicability of the Maxwell Garnett effective medium model to media with a high density of cylindrical pores(Optica Publishing Group, 2024-04-01); ; ; ; The optical properties of dielectric materials with subwavelength cylindrical pores are commonly described by effective medium models. We compare the Maxwell Garnett and the Bruggeman effective medium models for porous silicon with simulations and experiments for the case of polarization orthogonal to the pore axis. The Maxwell Garnett model matches the results of the simulations even up to very high porosities. An experimental study of the effective permittivity of macroporous and mesoporous silicon is conducted by analyzing the Fabry-Pérot oscillations in the long-wavelength limit. These experimental results are also consistent with the Maxwell Garnett model. We advocate using this model for media with cylindrical pores in the future.Publicationtype: Journal Article37 59 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Polymeric liquids in mesoporous photonic structures: from precursor film spreading to imbibition dynamics at the nanoscale(American Institute of Physics (AIP), 2024-02-14); ; ; ; Polymers are known to wet nanopores with high surface energy through an atomically thin precursor film followed by slower capillary filling. We present here light interference spectroscopy using a mesoporous membrane-based chip that allows us to observe the dynamics of these phenomena in situ down to the sub-nanometer scale at milli- to microsecond temporal resolution. The device consists of a mesoporous silicon film (average pore size 6 nm) with an integrated photonic crystal, which permits to simultaneously measure the phase shift of thin film interference and the resonance of the photonic crystal upon imbibition. For a styrene dimer, we find a flat fluid front without a precursor film, while the pentamer forms an expanding molecular thin film moving in front of the menisci of the capillary filling. These different behaviors are attributed to a significantly faster pore-surface diffusion compared to the imbibition dynamics for the pentamer and vice versa for the dimer. In addition, both oligomers exhibit anomalously slow imbibition dynamics, which could be explained by apparent viscosities of six and eleven times the bulk value, respectively. However, a more consistent description of the dynamics is achieved by a constriction model that emphasizes the increasing importance of local undulations in the pore radius with the molecular size and includes a sub-nanometer hydrodynamic dead, immobile zone at the pore wall but otherwise uses bulk fluid parameters. Overall, our study illustrates that interferometric, opto-fluidic experiments with mesoporous media allow for a remarkably detailed exploration of the nano-rheology of polymeric liquids.Publicationtype: Journal Article22 11 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Maxwell Garnett effective medium model for dielectric materials with high filling fraction of cylindrical poresThe optical properties of dielectric materials with subwavelength cylindrical pores are commonly described by effective medium models. We compare the Maxwell Garnett and the Bruggeman effective medium model for porous silicon with simulations to study their applicability. We found that the Maxwell Garnett model matches the results of the simulations even up to high porosities and discuss the reasons for this. We advocate using this model for membranes with cylindrical pores in the future.Publicationtype: Conference Paper48 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , In situ optical spectroscopy during liquid imbibition into a nanoporous photonic crystal resolves precursor film spreading(Springer, 2023); ; ; ; Publicationtype: Book part13 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Capillary rise of water in nanoporous glass as revealed by X-ray tomography-based Lattice-Boltzmann simulations(Springer, 2023); ; 21 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Diffusionlike Drying of a Nanoporous Solid as Revealed by Magnetic Resonance Imaging(2022-11); ; ; Drying plays a central role in various fabrication processes and applications of functional nanoporous materials, most prominently in relation to energy storage and conversion. During such processes, liquid coexists with air inside the sample, leading to transport as a result of concentration gradients of vapor and/or liquid. Experimentally, it is extremely challenging to unravel this transport phenomenology inside the hidden geometry of porous media. Here, we observe the drying of a model nanoporous material (monolithic mesoporous silica glass, Vycor) with magnetic resonance imaging. We show that, for various boundary conditions (air-flux intensities), no dry region develops, but the sample desaturates in depth. This desaturation is almost homogeneous throughout the sample for weak air flux, while saturation gradients can be observed for sufficiently strong air flux. We demonstrate that the transport of water is mainly ensured by liquid flow towards the free surface, resulting from a gradient of vapor pressure, associated with local saturation (via the desorption curve), leading to a gradient of liquid pressure (via the Kelvin law). Assuming otherwise standard hydrodynamic characteristics of the nanoconfined liquid, this results in a diffusionlike model, which appears to represent experimental data very well in terms of the spatial distribution of water over time inside the sample for various boundary conditions (air-flux intensities). Finally, we propose a predictive model of the detailed drying characteristics of a nanomaterial from knowledge of its pore size, permeability, and desorption curve. This provides an insight into the rational design of drying-based processes employing functional nanoporous materials and allows for a mechanistic understanding of drying phenomenologies in natural nanoporous media.Publicationtype: Journal Article20 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Straight versus Spongy: Effect of Tortuosity on Polymer Imbibition into Nanoporous Matrices Assessed by Segmentation-Free Analysis of 3D Sample ReconstructionsWe comparatively analyzed imbibition of polystyrene (PS) into two complementary pore models having pore diameters of ∼380 nm and hydroxyl-terminated inorganic-oxidic pore walls, controlled porous glass (CPG) and self-ordered porous alumina (AAO), by X-ray computed tomography and EDX spectroscopy. CPG contains continuous spongy-tortuous pore systems. AAO containing arrays of isolated straight cylindrical pores is a reference pore model with a tortuosity close to 1. Comparative evaluation of the spatiotemporal imbibition front evolution yields important information on the pore morphology of a probed tortuous matrix like CPG and on the imbibition mechanism. To this end, pixel brightness dispersions in tomographic 3D reconstructions and 2D EDX maps of infiltrated AAO and CPG samples were condensed into 1D brightness dispersion profiles normal to the membrane surfaces. Their statistical analysis yielded positions and widths of the imbibition fronts without segmentation or determination of pore positions. The retardation of the imbibition front movement with respect to AAO reference samples may be used as a descriptor for the tortuosity of a tested porous matrix. The velocity of the imbibition front movements in CPG equaled two-thirds of the velocity of the imbibition front movements in AAO. Moreover, the dynamics of the imbibition front broadening discloses whether porous matrices are dominated by cylindrical neck-like pore segments or by nodes. Independent single-meniscus movements in cylindrical AAO pores result in faster imbibition front broadening than in CPG, in which a morphology dominated by nodes results in slower cooperative imbibition front movements involving several menisci. The results presented here may be relevant to applications including printing and adhesive bonding, as well as to the optimization of production and properties of engineering, construction, and hybrid materials.Publicationtype: Journal Article33 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Statistical analysis of submicron X-ray tomography data on polymer imbibition into arrays of cylindrical nanopores(Soc., 2021-12-09); ; ; ; Frozen transient imbibition states in arrays of straight cylindrical pores 400 nm in diameter were imaged by phase-contrast X-ray computed tomography with single-pore resolution. A semi-automatic algorithm yielding brightness profiles along all pores identified within the probed sample volume is described. Imbibition front positions are determined by descriptive statistics. A first approach involves the evaluation of frequency densities of single-pore imbibition lengths, a second one the evaluation of the statistical brightness dispersion within the probed volume as a function of the distance from the pore mouths. We plotted average imbibition front positions against systematically varied powers of the imbibition time and determined the optimal exponent of the imbibition time by considering the correlation coefficients of the corresponding linear fits. Thus, slight deviations from the proportionality of the average imbibition front position to the square root of the imbibition time predicted by the Lucas-Washburn theory were found. A meaningful preexponential factor in the power law relating imbibition front position and imbibition time may only be determined after ambiguities regarding the exponent of the imbibition time are resolved. The dispersion of peaks representing the imbibition front in frequency densities of single-pore imbibition lengths and in brightness dispersion profiles plotted against the pore depth is suggested as measure of the imbibition front width. Phase-contrast X-ray computed tomography allows the evaluation of a large number of infiltrated submicron pores taking advantage of phase-contrast imaging; artifacts related to sample damage by tomography requiring physical ablation of sample material are avoided.Publicationtype: Journal Article59 8 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Precursor film spreading during liquid imbibition in nanoporous photonic crystals(2020-12-01); ; ; ; When a macroscopic droplet spreads, a thin precursor film of liquid moves ahead of the advancing liquid-solid-vapor contact line. Whereas this phenomenon has been explored extensively for planar solid substrates, its presence in nanostructured geometries has barely been studied so far, despite its importance for many natural and technological fluid transport processes. Here we use porous photonic crystals in silicon to resolve by light interferometry capillarity-driven spreading of liquid fronts in pores of few nanometers in radius. Upon spatiotemporal rescaling the fluid profiles collapse on master curves indicating that all imbibition fronts follow a square-root-of-time broadening dynamics. For the simple liquid (glycerol) a sharp front with a widening typical of Lucas-Washburn capillary-rise dynamics in a medium with pore-size distribution occurs. By contrast, for a polymer (PDMS) a precursor film moving ahead of the main menisci entirely alters the nature of the nanoscale transport, in agreement with predictions of computer simulations.Publicationtype: Journal ArticleScopus© Citations 15 200 173