20 research outputs found
Single-layer and double-layer filtration materials based on polyvinylidene fluoride-co-hexafluoropropylene nanofibers coated on melamine microfibers
No full text<p>In this work, we demonstrate selected optimization changes in the simple design of filtration masks to increase particle removal efficiency (PRE) and filter quality factor by combining experiments and numerical modeling. In particular, we focus on single-layer filters fabricated from uniform thickness fibers and double-layer filters consisting of a layer of highly permeable thick fibers as a support and a thin layer of filtering electrospun nanofibers. For single-layer filters, we demonstrate performance improvement in terms of the quality factor by optimizing the geometry of the composition. We show significantly better PRE performance for filters composed of micrometer-sized fibers covered by a thin layer of electrospun nanofibers. This work is motivated and carried out in collaboration with a targeted industrial development of selected melamine-based filter nano- and micromaterials.</p>Corresponding author: Tilen Potisk ([email protected]
Martina POTISK, 2022: Medkulturnost in sodobni slovenski roman.: Maribor: Kulturni center. (Zbirka Znanstvene monografije). 217 str.
No full textThe author evaluates the scientific monograph of Martina Potisk, Medkulturnost in sodobni slovenski roman (2022).Avtorica oceni znanstveno monografijo Martine Potisk Medkulturnost in sodobni slovenski roman (2022)
Macroscopic aspects of ferromagnetic nematic phases, tetrahedral order in ferrogels, and magnetorheological fluids
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Continuum model of magnetic field induced viscoelasticity in magnetorheological fluids
No full textAn effective macroscopic model of magnetorheological fluids in the viscoelastic regime is proposed. Under the application of an external magnetic field, columns of magnetizable particles are formed in these systems. The columns are responsible for solidlike properties, such as the existence of elastic shear modulus and yield stress, and are captured by the strain field, while magnetic properties are described by the magnetization. We investigate the interplay of these variables when static shear or normal pressure is imposed in the presence of the external magnetic field. By assuming a relaxing strain field, we calculate the flow curves, i.e., the shear stress as a function of the imposed shear rate, for different values of the applied magnetic field. Focusing on the small amplitude oscillatory shear, we study the complex shear modulus, i.e., the storage and the loss moduli, as a function of the frequency. We demonstrate that already such a minimal model is capable of furnishing many of the key physical features of these systems, such as yield stress, enhancement of the shear yield stress by pressure, threshold behavior in the spirit of the frequently employed Bingham law, and several features in the frequency dependence of storage and loss moduli
Effects of flow on the dynamics of a ferromagnetic nematic liquid crystal
No full textWe investigate the effects of flow on the dynamics of ferromagnetic nematic liquid crystals. As a model we study the coupled dynamics of the magnetization, M, the director field, n, associated with the liquid crystalline orientational order and the velocity field v. We evaluate how simple shear flow in a ferromagnetic nematic is modified in the presence of small external magnetic fields and we make experimentally testable predictions for the resulting effective shear viscosity: an increase by a factor of two in a magnetic field of about 20 mT. Flow alignment, a characteristic feature of classical uniaxial nematic liquid crystals, is analyzed for ferromagnetic nematics for the two cases of a magnetization in or perpendicular to the shear plane. In the former case we find that small in-plane magnetic fields are suffcient to suppress tumbling and that thus the boundary between flow alignment and tumbling can be controlled easily. In the latter case we furthermore find a possibility of flow alignment in a regime for which one obtains tumbling for the pure nematic component. We derive the analogues of the three Miesowicz viscosities well-known from usual nematic liquid crystals, corresponding to nine different configurations. Combinations of these can be used to determine several dynamic coeffcients experimentally
Dissipative particle dynamics models of encapsulated microbubbles and nanoscale gas vesicles for biomedical ultrasound simulations
No full textUltrasound-guided drug and gene delivery (USDG) enables controlled and spatially precise delivery of drugs and macromolecules, encapsulated in microbubbles (EMBs) and nanoscale gas vesicles (GVs), to target areas such as cancer tumors. It is a noninvasive, high precision, low toxicity process with drastically reduced drug dosage. Rheological and acoustic properties of GVs and EMBs critically affect the outcome of USDG and imaging. Detailed understanding and modeling of their physical properties is thus essential for ultrasound-mediated therapeutic applications. State-of-the-art continuum models of shelled bodies cannot incorporate critical details such as varying thickness of the encapsulating shell or specific interactions between its constituents and interior or exterior solvents. Such modeling approaches also do not allow for detailed modeling of chemical surface functionalizations, which are crucial for tuning the GV−blood interactions. We develop a general particle-based modeling framework for encapsulated bodies that accurately captures elastic and rheological properties of GVs and EMBs at the mesoscopic and nanoscale levels. We use dissipative particle dynamics to model the solvent, the gaseous phase in the capsid, and the triangulated surfaces of immersed objects. Their elastic behavior is studied and validated through stretching and buckling simulations, eigenmode analysis, shear flow simulations, and comparison of predicted GV buckling pressure with published experimental data. The presented modeling approach paves the way for large-scale simulations of nanoscale and microscale encapsulated bodies of different shapes and local anisotropy, capturing their dynamics, interactions, and collective behavior
External field-induced caloric effects in liquid crystals from molecular simulation
No full textIn the search for alternative, environmentally friendly refrigeration technologies, caloric effects play an important role. Over the past years, liquid crystals have emerged as promising caloric materials. Here, we present a molecular simulation study of the electrocaloric and magnetocaloric effect in liquid crystals exhibiting a nematic–isotropic phase transition. The indirect approach for determining the caloric response is used in combination with molecular dynamics simulations based on the Gay–Berne model. The simulations confirm that the largest response is present at temperatures just above the phase transition and predict the magnitude of the electrocaloric response to be ∼1.6 kJ/kg for an applied electric field of 1600 kV/cm. A much weaker magnetocaloric response is predicted, ∼0.4 kJ/kg for an applied magnetic field of 200 T, indicating that electric fields are much more promising for use in applications than magnetic fields
Macroscopic two-fluid effects in magnetorheological fluids
No full textWe investigate macroscopic two-fluid effects in magnetorheological fluids generalizing a one-fluid model studied before. In the bulk of the paper we use a model in which the carrier fluid, with density ρ1, moves with velocity v1, while the magnetic component (density ρ2) and, therefore, the magnetization and the magneticfield-induced relaxing strain field move with velocity v2. In the framework of macroscopic dynamics we find, in particular, reversible dynamic and dissipative cross-coupling terms between the magnetization and the velocity difference. Experiments to detect some of these cross-coupling terms are suggested. We also compare the results of the two-fluid model presented here with two-fluid models available for electrorheological fluids. In two appendices we discuss the simplifying assumptions made to arrive at the model used in this paper and we also outline how to detect potential deviations from this model
