Andreas Carlson

• Bhatt, Bidisha & Carlson, Andreas (2026). Capillary slinky: Equilibrium and dynamics of a droplet in a soft spring. Physical Review Fluids. 11(4), s. 043607-1–043607-14. doi: 10.1103/P9J4-HP5H. Fulltekst i vitenarkiv
• Al-Izzi, Sami Cameron; Du, Yao; Veenstra, Jonas; Morris, Richard G.; Souslov, Anton & Carlson, Andreas [Vis alle 8 forfattere av denne artikkelen] (2026). Nonreciprocal buckling makes active filaments polyfunctional. Proceedings of the National Academy of Sciences of the United States of America (PNAS). ISSN 0027-8424. 123(11). doi: 10.1073/pnas.2531723123. Fulltekst i vitenarkiv Vis sammendrag

  Active filaments are a workhorse for propulsion and actuation across biology, soft robotics, and mechanical metamaterials. However, artificial active rods suffer from limited robustness and adaptivity because they rely on external control, or are tethered to a substrate. Here, we bypass these constraints by demonstrating that nonreciprocal interactions lead to large-scale unidirectional dynamics in free-standing slender structures. By coupling the bending modes of a buckled beam antisymmetrically, we transform the multistable dynamics of elastic snap-through into persistent cycles of shape change. In contrast to the critical point underpinning beam buckling, this transition to self-snapping is mediated by a critical exceptional point, at which bending modes simultaneously become unstable and degenerate. Upon environmental perturbation, our active filaments exploit self-snapping for a range of functionality including crawling, digging, and walking. Our work advances critical exceptional physics as a guiding principle for programming instabilities into functional active materials.

• Kern, Vanessa R.; Moura, Marcel; Olsen, Pål E. S. & Carlson, Andreas (2026). Patterning surface textured plates with a viscoplastic fluid. Physical Review Fluids. 11(9). doi: 10.1103/1jz3-5j4d. Fulltekst i vitenarkiv Vis sammendrag

  The deposition of a viscoplastic fluid onto a substrate can be achieved by moving apart two plates initially separated by a fluid-filled gap, where the footprint shape depends on the initiation of a fingering instability. Here, we present an approach for controlled deposition of a viscoplastic fluid by designing the macroscopic structure of the solid substrate. Through experiments in a lifted Hele-Shaw cell, we explore how slot, square, pyramid, and triangular patterns affect the dynamics of liquid deposition. The substrate structures directly control the symmetry and final shape of the deposited viscoplastic footprint, while having little systematic influence on the maximal normal adhesive force or on the force-gap scaling exponents once the total entrapped volume is accounted for through an effective initial gap. We develop a scaling description for the normal force of a Herschel–Bulkley fluid, showing that the measured force decay reflects a superposition of capillary, yield stress, and viscous contributions. For experiments producing stable patterning, the measured effective exponents are consistent with the theoretical range predicted by this model. Finally, we interpret the pattern-selection mechanism through a dynamical permeability analysis where the substrate texture creates an anisotropic permeability field whose angular maxima correlate with the preferred inward propagation directions of the invading air. Our results highlight a direct link between substrate geometry, interfacial dynamics, and the final deposited morphology, showing how millimetric deposition patterns can be programed using submillimetric surface structures.

• Biswas, Uddalak; Galland, Olivier & Carlson, Andreas (2026). Laponite® RD and hydroxyethyl cellulose as host rock and magma analogue to simulate a wide range of rheological combinations in the volcanic plumbing system. Tectonophysics. ISSN 0040-1951. 937. doi: 10.1016/j.tecto.2026.231351. Fulltekst i vitenarkiv Vis sammendrag

  Analogue modelling is essential for understanding magma emplacement in the Earth’s crust and requires strict geometric, kinematic and dynamic scaling. Therefore, material selection must satisfy the scaling laws to reproduce the natural rheological variability. Although often represented by end-member rheologies, crustal rocks in nature exhibit complex rheological behaviour. In this study, we analysed two complex materials, Laponite® RD (LRD) and hydroxyethyl cellulose (HEC), to assess their effectiveness as geological analogues for country rock and magma in dyke emplacement experiments. We provide a detailed characterisation of LRD, highlighting its tuneable rheological properties via curing time (t_c). To characterise the complex rheology of the LRD gels, rotational and oscillatory tests, including flow, amplitude, frequency sweep, and creep and recovery tests, were performed at curing times (t_c) ranging from 30 to 240 min. We tested the rheology of aqueous HEC solutions at concentrations of 0.50, 0.75, and 1.00 wt%. Additionally, this study highlights the significant role of surface tension in laboratory analogue experiments, demonstrating the need to minimise interfacial tension by selecting an appropriate magma analogue fluid when using a viscoelastic host. The rheological test results showed that the storage modulus (G^') and yield stress (τ_y) increased systematically with increasing t_c. The flow and surface tension test results indicate that HEC hydrous solutions serve as robust magma analogues, offering variable viscosities with minimal alterations in surface tension and density. Combining the rheological analysis results of LRD and HEC, we propose a new methodology for simulating a wide range of rheological conditions by systematically varying the LRD curing time and employing different concentrations of HEC as a magma analogue. Our approach emphasises precise rheological characterisation together with control of magma-analogue density and surface tension, minimising the interfacial tension and buoyancy contrast with the host for accurate scaling in analogue models of volcanic plumbing systems.

• Poulain, Stephane; Koch, Timo; Mahadevan, L. & Carlson, Andreas (2026). Viscous adhesion in vibrating sheets: elastohydrodynamics with inertia and compressibility effects. Journal of Fluid Mechanics. ISSN 0022-1120. 1031. doi: 10.1017/jfm.2026.11231. Fulltekst i vitenarkiv Vis sammendrag

  Inspired by recent experiments demonstrating that vibrating elastic sheets can function as seemingly contactless suction cups, we investigate the elastohydrodynamic hovering of a thin elastic sheet vibrating near a wall. Previous theoretical work suggests that the hovering height results from a balance between the active forcing that triggers the vibrations, the bending stresses associated with the sheet’s deformation, the viscous lubrication flow between the sheet and the wall, and the sheet’s weight. Here, we extend this analysis beyond the asymptotic regime of weak forcing and explore the regime of strong forcing through numerical simulations. We identify the scalings for the equilibrium hovering height and the maximum load that can be supported. We further quantify the influence of fluid inertia and compressibility: both effects are found to introduce repulsive contributions to the net force on the sheet, which can significantly reduce its adhesive strength. Beyond providing insights into soft contactless grippers and swimming near surfaces, our analysis is relevant to the elastohydrodynamics of squeeze films and near-field acoustic levitation.

• Poulain, Stephane; Koch, Timo; Mahadevan, L. & Carlson, Andreas (2025). Hovering of an Actively Driven Fluid-Lubricated Foil. Physical Review Letters. ISSN 0031-9007. 135(21). doi: 10.1103/bs69-16nj. Fulltekst i vitenarkiv Vis sammendrag

  Inspired by recent experimental observations of a harmonically excited elastic foil hovering near a wall while supporting substantial weight, we develop a theoretical framework that describes the underlying physical effects. Using elastohydrodynamic lubrication theory, we quantify how the dynamic deformation of the soft foil couples to the viscous fluid flow in the intervening gap. Our analysis shows that the soft foil rectifies the reversible forcing, breaking time-reversal symmetry; the spatial distribution of the forcing determines whether the sheet is attracted to or repelled from the wall. A simple scaling law predicts the time-averaged equilibrium hovering height and the maximum weight the sheet can sustain before detaching. Numerical simulations of the governing equation corroborate our theoretical predictions, are in qualitative agreement with experiments, and might explain the behavior of organisms while providing design principles for soft robotics.

• Dhaliwal, Runepal Singh Sørensen; Liu, Jingbang & Carlson, Andreas (2025). Stochastic elastohydrodynamics of contact and coarsening during membrane adhesion. Journal of Fluid Mechanics. ISSN 0022-1120. 1024. doi: 10.1017/jfm.2025.10872. Fulltekst i vitenarkiv Vis sammendrag

  Contact between fluctuating, fluid-lubricated soft surfaces is prevalent in engineering and biological systems, a process starting with adhesive contact, which can give rise to complex coarsening dynamics. One representation of such a system, which is relevant to biological membrane adhesion, is a fluctuating elastic interface covered by adhesive molecules that bind and unbind to a solid substrate across a narrow gap filled with a viscous fluid. This flow is described by the stochastic elastohydrodynamic thin film equation, which incorporates thermal fluctuations into the description of viscous nanometric thin-film flow coupled to elastic membrane deformation. The average time it takes the fluctuating elastic membrane to adhere is predicted by the rare event theory, increasing exponentially with the square of the initial gap height. When the forces arising from spring-like adhesive molecules are included in the simulations, thermal fluctuations initiate phase separation of domains of bound and unbound molecules. The coarsening process of these unbound pockets displays close similarities to classical Ostwald ripening; however, the inclusion of hydrodynamics affects power-law growth. In particular, we identify a new bending-dominated coarsening regime, which is slower than the well-known tension-dominated case.

• Zhang, Xinyu; Pedersen, Christian; Zhu, Haoqi; Wang, Siming; Fu, Yuchen & Dai, Liang [Vis alle 9 forfattere av denne artikkelen] (2025). Surface Mobility of a Glass-Forming Polymer in an Ionic Liquid. Macromolecules. ISSN 0024-9297. 58(24), s. 13119–13124. doi: 10.1021/acs.macromol.5c01895. Fulltekst i vitenarkiv Vis sammendrag

  The free surface of glassy polymers exhibits enhanced segmental dynamics compared to the bulk, forming a liquid-like layer that lowers the glass transition temperature (Tg) in nanometer-sized polymer samples. Recent studies have shown that immersing polymers in ionic liquids can suppress this enhanced surface dynamics. To investigate how ionic liquids influence polymer dynamics near the ionic–liquid–polymer interface, we measure the surface leveling of nanometer-sized stepped polystyrene films immersed in ionic liquids, and compared the results to the case of films in vacuum. Our results reveal that ionic liquids significantly slow the leveling process both above and below Tg. However, our results indicate that the liquid-like surface layer below Tg does exist in ionic liquids. Numerical solutions of the thin-film equation, incorporating appropriate boundary conditions, show that the surface mobility of PS films in ionic liquids can match that of PS films in vacuum. Thus, while ionic liquids alter the polymer flow process, they do not eliminate the dynamical heterogeneity inherent to glassy polymers.

• Moura, Marcel; Kern, Vanessa Ruth; Måløy, Knut Jørgen; Carlson, Andreas & Flekkøy, Eirik Grude (2025). Droplet spreading in a wedge: a route to fluid rheology for power-law liquids. Soft Matter. ISSN 1744-683X. 21(36), s. 7014–7020. doi: 10.1039/d5sm00286a. Fulltekst i vitenarkiv Vis sammendrag

  Measuring the rheology of liquids typically requires precise control over shear rates and stresses. Here, we describe an alternative route for predicting the characteristic features of a power-law fluid by simply observing the capillary spreading dynamics of viscous droplets in a wedge-shaped geometry. In this confined setting, capillary and viscous forces interact to produce a spreading dynamics described by anomalous diffusion, a process where the front position grows as a power-law in time with an exponent that differs from the value 1/2 found in classical diffusion. We derive a nonlinear diffusion equation that captures this behavior, and we show that the diffusion exponent is directly related to the rheological exponent of the fluid. We verify this relationship by using both experiments and simulations for different power-law fluids. As the predictions are independent from flow-specific details, this approach provides a robust tool for inferring rheological properties from the spreading dynamics.

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• Kern, Vanessa Ruth; Moura, Marcel; Olsen, Pål Eivind & Carlson, Andreas (2026). Complex Fluids in confinement: instabilities in textured lifting Hele-Shaw cells. Fulltekst i vitenarkiv
• Moura, Marcel; Lanza, Federico; Kern, Vanessa Ruth; Olsen, Pål Eivind; Carlson, Andreas & Måløy, Knut Jørgen [Vis alle 7 forfattere av denne artikkelen] (2026). Instabilities in textured lifted Hele-Shaw cells and bubbly flows in a pipe. Fulltekst i vitenarkiv
• Kern, Vanessa Ruth; Moura, Marcel; Olsen, Pål Eivind & Carlson, Andreas (2026). Instabilities and Pattern Formation in Textured Lifting Hele-Shaw Cells with Viscoplastic Fluids. Fulltekst i vitenarkiv
• Biswas, Uddalak; Galland, Olivier & Carlson, Andreas (2026). Formation of various geometry by viscous magma intruding into visco-elasto-plastic deep crust: a 2D analogue experiment. Fulltekst i vitenarkiv Vis sammendrag

  Magma ascends to the Earth's surface for eruption by traversing the crust, which is the uppermost layer above the mantle, where the magma originates. As this substantial volume of magma moves through the crust, it deforms the crustal rocks, facilitating its progression toward the surface and subsurface. The resulting geometry, which may manifest as thin sheets, branching fingers, or blunt lobes, is set by the competition between the intruding fluid and the mechanical response of the host material. These deformation mechanisms, which control the geometry of the magmatic bodies, are essential for assessing hazards related to volcanic eruptions, seismic activity due to volcanism, and the localisation of economically valuable ore deposits. As the deformation of the crustal rocks by the intruding magma occurs at a certain depth and natural exposures record only the end state of this strongly dynamic process, the mechanics behind this process can’t be inferred directly. To address this gap, researchers have employed analogue modelling as a tool to simulate a simplified analogous intrusion process of magma at a laboratory scale for decades. Conventionally, in these analogue experiments, crustal rocks have been modelled using elastic or plastic Coulomb materials, whereas magma has been represented as a viscous fluid by previous researchers. However, recent studies have shown that deep crustal rocks exhibit a complex visco-elastic to visco-elasto-plastic rheology in nature. To simulate the crustal rocks more accurately, in this study, we approached the problem by injecting a viscous fluid as a magma analogue into an aqueous Laponite® RD (LRD) gel, which acted as a model host rock, confined in a two-dimensional Hele-Shaw cell. The LRD gel exhibits diverse rheological properties, transitioning progressively from a viscous liquid to a viscoelastic state, and ultimately to an elastico-viscous solid, as its curing time (tc) increases. Considering this property of the LRD gel, we used tc = 30, 60, 90, 150, and 240 min to represent crustal rock under different physical and chemical conditions. On the other hand, magma in nature exhibits variable viscosity depending on its composition, temperature and volatile content. In parallel, we varied the injected fluid using water and hydroxyethyl cellulose solutions at 0.50 and 0.75wt%, to span the range of viscosity. Injection was carried out at a fixed volumetric flow rate of 10 ml/min up to a maximum injected volume of 50 ml, so that the flow rate is held constant while the rheology of the host and viscosity of the fluid are varied. Additionally, polyamide tracer particles with a diameter of 60 μm were embedded in the gel, enabling particle image velocimetry (PIV) to simultaneously resolve the deformation field of the host as the intrusion expanded. The experiments produced distinct intrusion geometries that systematically depended on host rheology and the viscosity of the injected fluid. The velocimetry fields from the PIV analysis further show that intrusions of broadly similar shapes can be accommodated by clearly different velocity and strain distributions within the host. Combining the evolving geometry with the accompanying strain pattern therefore offers a route toward identifying which deformation mechanism accommodated a given volume of magma, and this diagnostic can in principle be applied to interpret the intrusion patterns observed in the field.

• Biswas, Uddalak; Galland, Olivier & Carlson, Andreas (2026). Magma emplacement mechanism in visco-elasto-plastic crustal rock: an insight from quantitative 2D analogue experiments. doi: 10.5194/egusphere-egu26-18980. Fulltekst i vitenarkiv Vis sammendrag

  Magma generated at depth ascends through the crust and erupts at the surface. In this process, the magma volume creates space by deforming the crustal rock. To study this process, researchers have employed analogue experiments for decades. Conventionally, most analogue models assume the crustal rock as a purely elastic, brittle (Coulomb), or viscous material. However, natural rocks exhibit more complex visco-elasto-plastic behaviours, with rheological properties transitioning from elastic-plastic to visco-elasto-plastic with increasing depth. Conversely, magma itself behaves as a Newtonian fluid, exhibiting a range of viscosities influenced by factors such as silica and volatile content. In this study, we conducted scaled 2D analogue magma emplacement experiments using Laponite® RD (LRD), a complex visco-elasto-plastic rheological material, as a host rock analogue. The rheological properties of LRD were systematically varied by changing the curing time (tc) from tc = 30 min to tc = 240 min to simulate a broad range of crustal rheological behaviours, corresponding to different depths from viscous to visco-elasto-plastic regimes. Food-coloured water and hydroxyethyl cellulose (HEC) aqueous solutions, with concentrations of 0.50 wt% and 0.75 wt%, are used to simulate magma with varying viscosities. Polyamide seeding particles (PSPs) of 60µm diameter were incorporated inside the LRD solution to quantify host-rock deformation during magma emplacement via particle image velocimetry (PIV). Our experimental results show that magma intrusions exhibit various shapes, ranging from straight-edged fractures in the case of low-viscosity water and viscoelastic LRD of high tc to bulbous, rounded forms in high-viscosity HEC and viscous LRD of low tc. Furthermore, PIV data enabled the identification of domains exhibiting distinct deformation types, thereby delineating changes in deformation regimes attributable to variations in the rheological properties of the host rock. Finally, by integrating geometric and PIV analyses, we established a relationship between the intrusion morphology and host rock rheology, and propose a mechanical model that elucidates the deformation mechanisms operative within the host during magma emplacement across different rheological combinations of host and magma materials.

• Moura, Marcel; Kern, Vanessa Ruth; Olsen, Pål Eivind; Carlson, Andreas; Måløy, Knut Jørgen & Flekkøy, Eirik Grude (2025). Complex fluids in confinement: spreading in a wedge and instabilities in textured lifted Hele-Shaw cells. Fulltekst i vitenarkiv
• Biswas, Uddalak; Galland, Olivier & Carlson, Andreas (2025). Variable curing time of Laponite RD: a convenient way to simulate a wide range of crustal rheology. Fulltekst i vitenarkiv Vis sammendrag

  Crustal rocks exhibit complex and highly variable rheological behaviors, which are challenging to account for in laboratory simulations of geological processes. The choice of relevant analogue materials is crucial for a successful laboratory experiment that can address such processes more accurately. The advent of new technologies and complex synthetic materials widens the window for the analogue experimentalist to revisit some of the problems for deeper understanding. Most of standard analogue materials used for simulating crustal rocks exhibit endmember rheology, i.e., viscous, elastic or coulomb (plastic). However,crustal rocks can exhibit a wide range of complex rheological properties, such as visco-elastic, visco-plastic, elasto-plastic and viscoelasto-plastic, during deformation under stress. In the last decade, a few researchers started using complex rheological materials, such as Carbopol, to simulate those processes more accurately. Laponite RD is one of such advanced complex rheological materials. Laponite RD is a synthetic sheet silicate mineral that resembles a natural clay mineral called hectorite. Laponite RD is used mostly as a rheological modifier in cosmetics, paint and the pharmaceutical industry. This material comes in powder form and transforms into gel when mixed with deionised water. This gel material was investigated previously by a few analogue modellers. However, these researches consist of rheological variation, either depending upon concentration (in terms of weight%, wt.%) or very long curing time. However, during the investigation of the rheological properties of Laponite RD materials, we identified that a variation in short (< 4 hours) curing time (tc) can simulate a wide range of complex rheological behaviour of crustal rock from viscous to visco-elastic to elastic. We ran rheometrical measurements (amplitude sweep test and frequency sweep test) on 3 wt.% Laponite RD gels with variable curing times from tc=30 min to tc=240 min. Note that the gels were cured within the rheometer. The test results show a consistent increase in both the storage modulus (G′) and Loss modulus (G″) of the samples with increasing tc (COULD BE GREAT TO SHOW A FIGURE). To test the reproducibility of these analyses, we ran the same analysis with fixed tc several times and found that each run yielded similar values for G′ and G″ for a specific tc. Our tests highlighted the effect of the thixotropic property of Laponite gel on its rheology: handling of the laponite to place it in the rheometer dramatically affects its rheology. Hence, our results show that it is crucial to cure the sample at the place of the experiment to simulate accurate rheological behaviour. Finally, taking an example of Laponite RD gel with variable tc as host in a magma emplacement experiment, we demonstrated the use of these gels to simulate a wide range of complex rheological behaviour of crustal rocks (refer to figure). Our study shows that Laponite RD gels are robust and easy-to-handle alternatives to Carbopol gels commonly used in analogue modelling.

• Biswas, Uddalak; Galland, Olivier & Carlson, Andreas (2025). 2D analogue models of magma emplacement in the visco-elastic crust. Fulltekst i vitenarkiv Vis sammendrag

  The Earth’s crust exhibits very complex rheology depending upon several physio-chemical conditions like temperature, pressure and lithology. This complex rheology of the crustal rocks is challenging to model. Thus, most researchers model magma propagation through crustal rocks of end-member rheologies such as viscous, coulomb (plastic) and elastic materials. These models acquire crucial information regarding the magma emplacement mechanisms. However, they are not sufficient to capture the whole spectrum of rheological behaviours of the host rock during the emplacement process. In this work, we performed a series of 2D magma injection experiments in the laboratory considering laponite RD gels as crustal rock analogues, showing complex rheological behaviour during deformation. According to the rheological analysis using a rheometer (Anton Paar MCR 702), laponite in deionised water solution exhibits a range of rheological behaviours from purely viscous to visco-elastic to purely elastic depending upon varying concentration (weight percentage, wt%) in the water. We used laponite gels of 2 wt% to 3.5 wt% to test the effects of varying rheology (yield stress = 0.597 Pa to 10.6 Pa) of the crustal rock analogue in the laboratory. These experiments used dyed oil (viscosity= 65 mPa.s) and water (viscosity= 1 mPa.s) as magma equivalents. Our 2D experiments revealed a range of intrusion shapes, from thin liquid-filled cracks of simple shapes to more massive fluid intrusions of complex shapes, indicating their varied mechanism of formation from brittle fracturing to ductile flow. To reveal the gel deformation accommodating the emplacement of the magma analogue, we implemented image analysis combining the photoelastic properties of the laponite gel and Digital Image Correlation. The resulting quantitative results allow us correlating the intrusion morphologies with the deformation mechanisms within the gel. Finally, from the experimental observations, we propose a model that connects the host rheology with the magma emplacement mechanism.

• Poulain, Stephane Albert Jules; Koch, Timo; Mahadevan, L. & Carlson, Andreas (2025). Hovering of active fluid-lubricated foil. Fulltekst i vitenarkiv
• Poulain, Stephane Albert Jules; Koch, Timo; Mahadevan, L. & Carlson, Andreas (2025). Hovering of an actively driven fluid-lubricated foil. Fulltekst i vitenarkiv
• Moura, Marcel; Kern, Vanessa Ruth; Olsen, Pål Eivind; Carlson, Andreas; Måløy, Knut Jørgen & Flekkøy, Eirik Grude (2025). Fluidos complexos em confinamento: espalhamento em cunha e instabilidades em células de Hele-Shaw texturizadas. Fulltekst i vitenarkiv

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