arXiv subjects

Marina Saphiannikova

Publications and source records attributed to Marina Saphiannikova.

5 recordsLinked to original sources

arXiv2026

Influence of near-field effect on magnetic hysteresis in magneto-active elastomers

Magneto-active elastomers (MAEs) are polymer composites consisting of magnetic microparticles embedded in an elastomeric matrix. These materials exhibit strong magneto-mechanical coupling under external magnetic fields, resulting in tunable stiffness, reversible shape changes, and nonlinear magnetic responses. This study presents a multiscale theoretical framework to investigate the origin of magnetic hysteresis in MAEs, with emphasis on the evolution of the internal microstructure during magnetization and demagnetization. The total energy of the system is formulated as the sum of magnetic and micromechanical contributions, while macroscopic deformation of a cylindrical MAE sample is fully constrained. Particle interactions are modeled first via pure dipole-dipole interactions and then extended to include higher-order near-field effects at close particle separations. The results show that hysteresis in MAEs with magnetically soft particles primarily arises from trapped microstructural rearrangements, leading to distinct particle configurations under increasing and decreasing magnetic fields. Parametric studies demonstrate that particle volume fraction, sample aspect ratio, and matrix stiffness strongly influence the microstructure evolution and the width of resulting hysteresis loops. The proposed framework provides a solid foundation for modeling magnetic hysteresis, which is essential for the design and optimization of MAEs in practical applications.

cond-mat.soft↗

arXiv2026

Stress-driven photo-reconfiguration of surface microstructures via vectorial field-guided lithography

Pattern formation driven by mechanical stress plays a fundamental role in shaping structural organization in both natural and human-made systems. Using light as a vectorial stimulus may offer a powerful route to control stress-induced pattern formation in materials. However, achieving localized, programmable, and predictable control of individual microstructures via structured polarization fields has remained a major challenge. Here, we introduce vectorial field-guided lithography, a novel approach that leverages fully structured polarization fields as lithographic tools to enable the stress-driven reconfiguration of pre-patterned azopolymer microstructures with an unprecedented degree of flexibility, complexity, and diversity. By building on the Viscoplastic PhotoAlignment model, which describes the azopolymer deformation as stress response to structured light, we quantitatively demonstrate and predict complex surface architectures generated by programmable light-induced stress pathways using a digital polarization rotator implemented via a spatial light modulator. We model and experimentally achieve single-step formation of anisotropic, bent, and chiral microstructures from a single pre-patterned geometry. Our results reveal an exceptional control over local microstructure morphology and establish, for the first time, a comprehensive theoretical framework capable of quantitatively designing and fabricating target morphologies on azopolymers. This work moves beyond conventional intensity-based photopatterning and demonstrates that the full vectorial nature of light can dictate the mechanical reshaping of functional polymer surfaces, providing a new platform for the programmable design of complex micro-architectures with applications in photonics, microfluidics, and biology.

physics.optics↗

arXiv2026

All-optical Lithography for Spatiotemporal Patterning of High-Modulation Azopolymer Microreliefs

Microstructured surfaces are central to photonics, biointerfaces, and coating technologies, but they are typically fabricated through multistep workflows involving masks, molds, and postprocessing. Azopolymers offer a direct light-driven route to surface structuring, yet holographic photopatterning of flat films has mainly remain limited to smooth, shallow, and engraving-like reliefs with limited vertical modulation. Here we show that computer-generated holograms with co-designed bright and dark regions can spatially confine inward mass transport and directly generate isolated protruding microstructures with several micrometer surface modulation from pristine flat azopolymer films. Single exposures produce individual protrusions and protrusion arrays, whereas sequential tailored exposures further reshape microrelief morphology over time. Using this spatiotemporal scheme, we fabricate flattenedtop micropillars, programmable arrays, freeform continuous microreliefs, and hierarchical structures from a pristine flat film, and we demonstrate write-erase-rewrite cycles in the same surface region. These results establish an all-optical strategy for generating and reconfiguring high modulation azopolymer microreliefs through combined control of spatial and temporal degrees of freedom of holographic illumination.

physics.optics↗

arXiv2025

Light-induced deformation of side-chain azo-polymer: Insights from atomistic modeling

In this study, we apply, for the first time, the fully atomistic force field approach to modeling light-induced deformations of azo-polymers, thereby establishing a relationship between macroscopic parameters and the microscopic molecular architecture of the used azo-polymers. We apply an orientation potential to mimic the illumination of the sample, in which the action of light is represented through controlled redistribution of azo-chromophores relative to the polarization direction. This strategy allows us to capture both the microscopic details of chromophore behaviour and the collective, anisotropic response of the polymer matrix. By combining these complementary perspectives, the simulations not only resolve the local mechanism of light-induced motion but also provide a pathway to bridge molecular-scale dynamics with mesoscopic deformation phenomena in azo-polymer films.

cond-mat.soft↗

arXiv2025

Magnetically induced deformation of isotropic magneto-active elastomers and its relation to the magnetorheological effect

Can isotropic Magneto-Active Elastomers (MAEs) undergo giant magnetically induced deformations and exhibit huge magnetorheological effects simultaneously? In this experimental and theoretical study, we reveal how the macroscopic deformation of MAEs relates to the process of particle restructuring caused by application of a magnetic field. For this purpose, MAE cylinders with different aspect ratios and particle loadings are studied in uniform magnetic fields. The axial deformations of the cylinders are acquired using an optical camera. A unified mean-field model proposed in previous studies is adapted to describe the transition of initially isotropic cylinders into transversely isotropic ones. This mechanical transition is caused by the rearrangement of particles into dense columnar structures aligned with the field and is believed to result in a huge magnetorheological effect. Our model however predicts less than three-fold increase in elastic moduli when evaluated along the field direction. This prediction is based on a careful examination of the shear moduli of studied MAEs and the columnar structures. A weak magnetorheological effect explains significant axial deformations measured in the field direction. A strong magnetorheological effect would hinder axial deformations due to an increase in modulus by several orders of magnitude. Not only are the moduli and macroscopic deformations influenced by microstructure evolution, but so is the magnetization of particles, which increases as they rearrange into dense columns. With this study, we show that the unified mean-field model provides quantitative access to hidden material properties such as magnetization and stiffness in MAE samples with different shapes and evolving microstructures.

cond-mat.soft↗