@article{StrausKokotKravanjaetal., author = {Straus, Izidor and Kokot, Gašper and Kravanja, Gaia and Hribar, Luka and Kriegl, Raphael and Shamonin (Chamonine), Mikhail and Jezeršek, Matija and Drevenšek-Olenik, Irena}, title = {Dynamically tunable lamellar surface structures from magnetoactive elastomers driven by a uniform magnetic field}, series = {Soft Matter}, volume = {Vol. 19}, journal = {Soft Matter}, publisher = {Royal Society of Chemistry}, doi = {10.1039/D3SM00012E}, pages = {3357 -- 3365}, abstract = {Stimuli responsive materials are key ingredients for any application that requires dynamically tunable or on-demand responses. In this work we report experimental and theoretical investigation of magnetic-field driven modifications of soft-magnetic elastomers whose surface was processed by laser ablation into lamellar microstructures that can be manipulated by a uniform magnetic field. We present a minimal hybrid model that elucidates the associated deflection process of the lamellae and explains the lamellar structure frustration in terms of dipolar magnetic forces arising from the neighbouring lamellae. We experimentally determine the magnitude of the deflection as a function of magnetic flux density and explore the dynamic response of lamellae to fast changes in a magnetic field. A relationship between the deflection of lamellae and modifications of the optical reflectance of the lamellar structures is resolved.}, language = {en} } @article{StrausKravanjaHribaretal., author = {Straus, Izidor and Kravanja, Gaia and Hribar, Luka and Kriegl, Raphael and Jezeršek, Matija and Shamonin (Chamonine), Mikhail and Drevenšek-Olenik, Irena and Kokot, Gašper}, title = {Surface Modification of Magnetoactive Elastomers by Laser Micromachining}, series = {Materials}, volume = {2024}, journal = {Materials}, number = {17 / 7}, publisher = {MDPI AG}, address = {Basel, Switzerland}, doi = {10.3390/ma17071550}, pages = {12}, abstract = {It has been recently demonstrated that laser micromachining of magnetoactive elastomers is a very convenient method for fabricating dynamic surface microstructures with magnetically tunable properties, such as wettability and surface reflectivity. In this study, we investigate the impact of the micromachining process on the fabricated material's structural properties and its chemical composition. By employing scanning electron microscopy, we investigate changes in size distribution and spatial arrangement of carbonyl iron microparticles dispersed in the polydimethylsiloxane (PDMS) matrix as a function of laser irradiation. Based on the images obtained by a low vacuum secondary electron detector, we analyze modifications of the surface topography. The results show that most profound modifications occur during the low-exposure (8 J/cm^2) treatment of the surface with the laser beam. Our findings provide important insights for developing theoretical models of functional properties of laser-sculptured microstructures from magnetoactive elastomers.}, language = {en} } @inproceedings{KrieglJezeršekKravanjaetal., author = {Kriegl, Raphael and Jezeršek, Matija and Kravanja, Gaia and Hribar, Luka and Kokot, Gašper and Drevenšek-Olenik, Irena and Shamonin (Chamonine), Mikhail}, title = {Characterization of Tunable Rebound Properties of Microstructured Magnetoactive Elastomers}, series = {ASME 2024 Conference on Smart Materials, Adaptive Structures and Intelligent Systems (SMASIS), September 9-11, 2024, Atlanta, Georgia, USA}, booktitle = {ASME 2024 Conference on Smart Materials, Adaptive Structures and Intelligent Systems (SMASIS), September 9-11, 2024, Atlanta, Georgia, USA}, publisher = {American Society of Mechanical Engineers}, address = {New York, USA}, isbn = {978-0-7918-8832-2}, doi = {10.1115/SMASIS2024-139154}, abstract = {We present a novel method to control the rebounding behavior of small mm-sized solid balls by employing magnetoactive elastomers (MAEs) with microstructured surfaces. An MAE is a composite material consisting of μm-sized ferromagnetic particles dispersed in a soft elastomer (e.g., polydimethylsiloxane) matrix. In the act of rebounding, the ball hits an MAE surface and bounces back. The MAE samples contained 75 wt.\% of iron. This composite material is known to respond to an applied magnetic field with increased stiffness (due to the magnetorheological effect) and plasticity. To adjust the rebound properties, the top layer of the MAE material was additionally modified by micromachining lamellar structures with different dimensions on the 100 μm scale via laser ablation. Due to the resulting high aspect ratio, these surface structures were sensitive to the magnetic field direction. The lamellas could stand up straight or lay down flat. The rebound behavior was evaluated by using a custom build apparatus that facilitates dropping of the balls in a precise and repeatable manner. A ball was dropped from different heights. The ball trajectory was captured with a high-speed camera to investigate the rebound properties. The recorded video was processed using a custom software written in Python. The experimental procedure and data processing algorithms are presented in detail. The results for the samples with different geometrical dimensions are provided as examples. It is made evident that the magnetic field influences the rebound properties of small non-magnetic balls impinging microstructured MAE surfaces. The change in surface topography is an effective way to control the ball rebound. The fabrication flexibility in geometrical dimensions of surface microstructures opens a convenient way to tune the desired response to magnetic fields. The presented idea may find applications in impact mitigation or small-scale sorting machinery, e.g. for recycling.}, language = {en} } @article{KrieglJezeršekKravanjaetal., author = {Kriegl, Raphael and Jezeršek, Matija and Kravanja, Gaia and Hribar, Luka and Mukhi, Soham and Kokot, Gašper and Drevenšek-Olenik, Irena and Shamonin (Chamonine), Mikhail}, title = {Tunable rebound of millimeter-sized rigid balls by magnetic actuation of elastomer-based surface microstructures}, series = {Smart Materials and Structures}, volume = {33}, journal = {Smart Materials and Structures}, number = {6}, publisher = {IOP Publishing}, doi = {10.1088/1361-665X/ad41a9}, abstract = {A novel method for controlling the rebound behavior of small balls made of Al2O3 with a radius of 2.381 mm is presented. It uses different types of micro-structured surfaces of soft magnetoactive elastomers. These surfaces were fabricated via laser micromachining and include fully ablated surfaces as well as micrometer-sized lamellas with a fixed width of 90 µm, height of 250 µm and three different gap sizes (15, 60 and 105 µm). The lamellas can change their orientation from edge-on to face-on configuration according to the direction of the external magnetic field from a permanent magnet. The orientation of the external magnetic field significantly influences the rebound behavior of the balls, from a coefficient of restitution e of to < 0.1. The highest relative change in the coefficient of restitution between zero field and face-on configuration of is observed for lamellas with a gap of 60 µm. Other characteristics of the ball rebound such as the penetration depth into an Magnetoactive elastomer and the maximum deceleration are investigated as well. The proposed method does not require a constant power supply due to the use of permanent magnets. It may find novel applications in the field of impact engineering.}, language = {en} } @article{StrausKravanjaKriegletal., author = {Straus, Izidor and Kravanja, Gaia and Kriegl, Raphael and Shamonin (Chamonine), Mikhail and Drevenšek-Olenik, Irena and Jezeršek, Matija and Kokot, Gašper}, title = {Laser Micromachining for Polymer Surface Topography Designt}, series = {JoVE journal : engineering}, journal = {JoVE journal : engineering}, publisher = {JoVE}, doi = {10.3791/68126}, pages = {15}, abstract = {Soft magnetoactive elastomers (MAEs) are smart materials that respond to external magnetic fields by dynamically altering their mechanical properties. They are composed of magnetically responsive microparticles embedded within a soft polymer matrix, exhibiting an effective shear modulus of up to 100 kPa. In recent decades, MAEs' bulk properties have been successfully exploited for applications such as dynamic vibration damping, vibration sensing, and actuation in soft robotics. Recent research has shifted to their surface properties, revealing promising results on tunable surface features such as roughness, adhesion, and wetting. Even the transport of small solid and fluid objects was demonstrated. The associated surface effects can be significantly enhanced through the precise engineering of surface topography. In this article, an efficient laser micromachining technique, with a resolution of 15 µm, is presented, which enables rapid prototyping of MAE surfaces. It allows the creation of various complex shapes and offers functionality beyond the one achievable with traditional molding techniques. Additionally, the approach is versatile and can be applied to any polymer that sufficiently absorbs the laser light. As an example, a lamellar surface micro-pattern fabrication process and its characterization by optical and scanning electron microscopies are shown. Its response to a magnetic field is demonstrated. The technique provides a flexible and fast solution for optimizing polymer surface design across a wide range of applications.}, language = {en} } @article{GeldofKopačinStrausetal., author = {Geldof, Arne and Kopačin, Jan and Straus, Izidor and Kriegl, Raphael and Kravanja, Gaia and Hribar, Luka and Jezeršek, Matija and Shamonin, Mikhail and Kokot, Gašper and Drevenšek-Olenik, Irena}, title = {Transfer of Energy and Momentum Between Magnetoactive Surface Microstructure and a Solid Object}, series = {Advanced Engineering Materials}, volume = {28}, journal = {Advanced Engineering Materials}, number = {6}, publisher = {Wiley}, doi = {10.1002/adem.202502369}, pages = {9}, abstract = {Transport systems utilizing magnetic materials are very promising for applications that require contactless operation and compatibility with biological processes. A critical parameter in these systems is the efficiency of energy and momentum transfer between the transporting platform and the objects being transported. We investigate the physical mechanisms driving directional transport of solid objects by microlamellar structures laser-inscribed on the surface of a magnetoactive elastomer (MAE). When subjected to a rotating magnetic field with a magnitude of 175 mT and a time period of 0.4 s, the lamellas reorient within a few milliseconds, reaching angular velocities up to 1100 rad s-1. This rapid motion is crucial for efficient momentum and energy transfer to objects in contact with the lamellas. The analysis of collisions of a single lamella with a lead ball with a 2.2 mm diameter shows that the lamella can transfer around 50 nJ of energy, propelling the ball to a speed of around 35 mm s-1. We show how this value sets the upper limit for the ball's transport speed on microlamellar structures. We also explain the background of three distinct transport regimes (kicking, pushing, and bouncing modes) observed on these magnetically driven "conveyor belts".}, language = {en} }