arXiv subjects

L. Daniel Söderberg

Publications and source records attributed to L. Daniel Söderberg.

10 recordsLinked to original sources

arXiv2026

4D Synchrotron X-Ray Multi Projection Imaging (XMPI) for studying multiphase flow dynamics and flow instabilities in porous networks

Flow instabilities such as Haines jumps in porous media are common phenomena that occur on sub-second timescales. X-rays are particularly suitable for investigating these processes because they provide non-destructive three-dimensional insight into the network structure and the liquid distribution within porous media. Studying imbibition events in four dimensions (three spatial dimensions plus time) is inherently challenging with conventional tomography because the required rapid sample rotation imposes significant centrifugal forces that alter the flow. Here, we demonstrate synchrotron X-ray multi-projection imaging (XMPI) to capture four-dimensional flow in an additively manufactured, homogeneous spherical pore network at 1.3 $μ$m effective pixel size and 50 Hz temporal resolution without the need for high rotational speeds. This enables in situ visualization of non-repeatable pore-scale events in both space and time, a capability unachievable with classical X-ray tomographic approaches. We compare the results to Shan-Chen multiphase Lattice Boltzmann simulations performed on the same geometry, finding both qualitative agreements and systematic differences in filling sequences and timescales. These discrepancies expose key limitations of current simulation methods in representing contact-line dynamics and realistic boundary conditions limitations that XMPI can directly overcome. By enabling high-resolution, real-time imaging of flow instabilities in opaque porous media, synchrotron XMPI provides a unique platform that bridges the gap between pore-scale experiments and simulations.

physics.flu-dyn↗

arXiv2026

Time-resolved X-ray radiography of through-thickness liquid transport in partly saturated needle-punched nonwovens

Nonwoven fibre networks underpin filtration, insulation and geotextiles, where liquid uptake, redistribution and release govern performance. In needle-punched felts, barbed needles mechanically entangle fibres and partially reorient them toward the thickness direction ($z$), creating out-of-plane "pillars" and heterogeneity. While mechanical and structural consequences of needling are well documented, dynamic $z$-direction transport in partly saturated networks remains difficult to access due to opacity and sub-second timescales. Here we combine micro-CT ($μ$CT) of dry structure with time-resolved X-ray radiography during droplet addition to quantify through-thickness transport as a function of saturation and needling intensity, using a compact Washburn-type descriptor for dynamics. Results show an exponential dependence of $z$-directional liquid transport on saturation, consistent with previous models for in-plane relative permeability of nonwoven networks. Additionally, increased needle-punch intensity reorients fibres toward the $z$-direction, forming preferential flow pathways that enhance through-thickness transport, even as single-phase permeability decreases. These findings underscore needle-punch as a key design parameter for tuning liquid transport in nonwoven fibre networks. The approach provides an experimental and modelling framework for dynamic, capillarity-driven transport in opaque fibrous materials.

physics.flu-dyn↗

arXiv2026

Synchrotron X-Ray Multi-Projection Imaging (XMPI) for High-Resolution 4D Characterization of Multiphase Flows

Multiphase flows where particles, bubbles, or droplets are suspended in a fluid govern critical processes in biology, medicine, materials processing, and geophysics. However, observing their microscale dynamics in opaque systems has remained a fundamental challenge. We present Synchrotron X-ray Multi-Projection Imaging (XMPI), a novel approach enabling four-dimensional (3D+time) tracking of microparticles in dense suspension flows without requiring sample rotation. By capturing simultaneous projections from multiple angles using beam-split X-rays at synchrotron facilities, we resolve instantaneous particle positions and trajectories in opaque fluids such as blood. We demonstrate the potential of XMPI through individual particle tracking velocimetry (3D PTV) in dilute conditions, as well as multi-projection optical flow analysis in dense suspensions. The methodology provides otherwise inaccessible experimental validation for particle-resolved computational fluid dynamics models and allows, e.g., observation of inertial focusing effects and microstructural dynamics relevant to suspension rheology and biomedical flows. This work paves the way for high-resolution, time-resolved 4D imaging of complex multiphase flows across a range of scientific and industrial applications. Combining XMPI with recent AI-supported 4D reconstruction algorithms opens a new spatiotemporal frontier for high-speed, rotation-free microtomography.

physics.flu-dyn↗

arXiv2023

Breaking the Reptation Trap: Escape Dynamics of Semi-Flexible Polymers in Crowded Networks

Semi-flexible polymers in crowded environments exhibit complex dynamics that play a crucial role in various biological and material design processes. Based on the classic reptation theory, it is generally believed that semiflexible polymers are trapped within static confinements. Here we demonstrate that semi-flexible polymers are indeed trapped in short-lived kinetic cages. We have developed a novel scaling law for rotational diffusion through the examination of the polymer network at the level of an individual nanofiber and quantify the onset of entanglement and entanglement itself by introducing an effective tube diameter. We also show that understanding these dynamics is critical for interpreting the macroscopic behavior of such systems, as evidenced by our micro-rheology analysis. The insight from our study provides a rectified microscopic understanding of the dynamics of semi-flexible polymers in complex environments, yielding new principles to better understand the macroscopic behavior of crowded systems, from biophysics to materials science.

cond-mat.soft↗

arXiv2022

Exploring Nanofibrous Networks with X-ray Photon Correlation Spectroscopy

Nanofibrous networks are the foundation and natural building strategy for all life forms on our planet. Apart from providing structural integrity to cells and tissues, they also provide a porous scaffold allowing transport of substances, where the resulting properties rely on the nanoscale network structure. Recently, there has been a great deal of interest in extracting and reassembling biobased nanofibers to create sustainable, advanced materials with applications ranging from high-performance textiles to artificial tissues. However, achieving structural control of the extracted nanofibers is challenging as it is strongly dependent on the extraction methods and source materials. Furthermore, the small nanofiber cross-sections and fast Brownian dynamics make them notoriously difficult to characterize in dispersions. In this work, we study the diffusive motion of spherical gold nanoparticles in semi-dilute networks of cellulose nanofibers (CNFs) using X-ray Photon Correlation Spectroscopy (XPCS). We find that the motion becomes increasingly subdiffusive with higher CNF concentration, where the dynamics can be decomposed into several superdiffusive relaxation modes in reciprocal space. Using simulations of confined Brownian dynamics in combination with simulated XPCS-experiments, we observe that the dynamic modes can be connected to pore sizes and inter-pore transport properties in the network. The demonstrated analytical strategy by combining experiments using tracer particles with a digital twin may be the key to understand nanoscale properties of nanofibrous networks.

cond-mat.soft↗

arXiv2021

Formation of colloidal threads in geometrically varying flow-focusing channels

When two miscible fluids are brought into contact with each other, the concentration gradients induce stresses. These are referred to as Korteweg stresses and are analogous to interfacial tension between two immiscible fluids, thereby acting as an effective interfacial tension (EIT) in inhomogeneous miscible systems. EIT governs the formation of a viscous thread in flow-focusing of two miscible fluids. To further investigate its significance, we have studied thread formation of a colloidal dispersion focused by its own solvent. Experiments are combined with three-dimensional numerical models to systematically expand previous knowledge utilising different flow-focusing channel setups. In the reference setup, the sheath flows impinge the core flow orthogonally while in four other channel setups, the sheath flows impinge the core flow at an oblique angle that is both positive and negative with respect to the reference sheath direction. As an initial estimate of the EIT, we fit the experimentally determined thread shape in the reference setup to a master curve that depends on EIT through an effective capillary number. By numerically reproducing these experimental results, it is concluded that the estimated EIT is within 25% of the optimal EIT value that can be deduced by iteratively fitting the numerical results to the experimental measurements. Regardless of channel setups, further numerical calculations performed using the optimal EIT evaluated from the reference setup show good agreement with the experimental findings in terms of thread shapes, wetted region morphologies, and velocity flow fields. The one-to-one comparison of numerical and experimental findings unveil the crucial role of EIT on the thread detachment from the top and bottom walls of the channel, bringing useful insights to understand the physical phenomenons involved in miscible systems with a high-viscosity contrast.

physics.flu-dyn↗

arXiv2019

Effective interfacial tension in flow-focusing of colloidal dispersions: 3D numerical simulations and experiments

An interface between two miscible fluids is transient, existing as a non-equilibrium state before complete molecular mixing is reached. However, during the existence of such an interface, which typically be at short timescales, composition gradients at the boundary between the two liquids cause stresses effectively mimicking an interfacial tension. Here, we combine numerical modelling and experiments to study the influence of an effective interfacial tension between a colloidal fibre dispersion and its own solvent on the flow in a microfluidic system. In a flow-focusing channel, the dispersion is injected as core flow that is hydrodynamically focused by its solvent as sheath flows. This leads to the formation of a long fluid thread, which is characterised in 3D using Optical Coherence Tomography and simulated using a volume of fluid method. The simulated flow and thread geometries very closely reproduce the experimental results in terms of thread topology and velocity flow fields. By varying the effective interfacial tension numerically, we show that it clearly influences threading dynamics and that it can be described by an effective capillary number. Furthermore, we demonstrate that the applied methodology provide means to measure the ultra-low but dynamically highly significant effective interfacial tension.

physics.flu-dyn↗

arXiv2018

Orientation and dynamics of stiff polymeric nanoparticles

Successful assembly of suspended nanoscale rod-like particles depends on fundamental phenomena controlling rotational and translational diffusion. Despite the significant developments in fluidic fabrication of nanostructured materials, the ability to quantify the dynamics in processing systems remains challenging. Here we demonstrate an experimental method for characterization of the orientation dynamics of nanorod suspensions in assembly flows using birefringence relaxation. The methodology is illustrated using nanocelluloses (cellulose nanocrystals and nanofibrils) as model systems, where the coupling of rotational diffusion coefficients to particle size distributions as well as flow-induced orientation mechanisms are elucidated. Our observations advance the knowledge on key fundamental nanoscale mechanisms governing the dynamics of nanotubes and nanorods allowing bottom-up assembly into hierarchical superstructures.

cond-mat.soft↗

arXiv2018

Dynamic characterization of cellulose nanofibrils in sheared and extended semi-dilute dispersions

New materials made through controlled assembly of dispersed cellulose nanofibrils (CNF) has the potential to develop into biobased competitors to some of the highest performing materials today. The performance of these new cellulose materials depends on how easily CNF alignment can be controlled with hydrodynamic forces, which are always in competition with a different process driving the system towards isotropy, called rotary diffusion. In this work, we present a flow-stop experiment using polarized optical microscopy (POM) to study the rotary diffusion of CNF dispersions in process relevant flows and concentrations. This is combined with small angle X-ray scattering (SAXS) experiments to analyze the true orientation distribution function (ODF) of the flowing fibrils. It is found that the rotary diffusion process of CNF occurs at multiple time scales, where the fastest scale seems to be dependent on the deformation history of the dispersion before the stop. At the same time, the hypothesis that rotary diffusion is dependent on the initial ODF does not hold as the same distribution can result in different diffusion time scales. The rotary diffusion is found to be faster in flows dominated by shear compared to pure extensional flows. Furthermore, the experimental setup can be used to quickly characterize the dynamic properties of flowing CNF and thus aid in determining the quality of the dispersion and its usability in material processes.

cond-mat.soft↗

arXiv2017

Evaluating alignment of elongated nanoparticles in cylindrical geometries through small angle X-ray scattering experiments

The increased availability and brilliance of new X-ray facilities have in the recent years opened up the possibility to characterize the motion of dispersed nanoparticles in various microfluidic applications. One of these applications is the process of making strong continuous filaments through hydrodynamic alignment and assembly of cellulose nanofibrils (CNF) demonstrated by Håkansson et al. [Nature communications 5, 2014]. In this process it is vital to study the alignment of the nanofibrils in the flow, as this in turn affects the final material properties of the dried filament. Small angle X-ray scattering (SAXS) is a well-suited characterization technique for this, which typically provides the alignment in a projected plane perpendicular to the beam direction. In this work, we demonstrate a simple method to reconstruct the full three-dimensional (3D) orientation distribution function (ODF) from a SAXS-experiment through the assumption that the azimuthal angle of the nanofibril around the flow direction is distributed uniformly; an assumption that is approximately valid in the flow-focusing process. For demonstrational purposes, the experimental results from Håkansson et al. (2014) have been revised, resulting in a small correction to the presented order parameters. The results are then directly compared with simple numerical models to describe the increased alignment of CNF both in the flowing system and during the drying process. The proposed reconstruction method will allow for further improvements of theoretical or numerical simulations and consequently open up new possibilities for optimizing assembly processes, which include flow-alignment of elongated nanoparticles.

cond-mat.soft↗