Alenka Mertelj

Alenka Mertelj
Jožef Stefan Institute | IJS · Complex Matter

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100
Publications
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Publications

Publications (100)
Preprint
Full-text available
Sessile droplets of a ferroelectric nematic liquid crystalline material were exposed to surface electric fields produced by pyroelectric and photogalvanic (photovoltaic) effects in X-cut iron-doped lithium niobate crystals. The resulting dynamic processes were monitored by polarization optical (video)microscopy (POM). During heating/cooling cycles,...
Article
Ferrofluids are colloidal suspensions of magnetic nanoparticles. Ferromagnetic ordering – with spontaneous net magnetization in the absence of external fields – has been described for a system of permanently magnetic nanoplatelets suspended in n-butanol, concentrated enough to undergo the transition to the nematic phase. Such material shows magneti...
Article
This Letter describes a miniature Fabry–Perot, contactless, magneto-optic sensor for angular position measurement. The sensor utilizes a magneto-optic fluid comprising barium hexaferrite nanoplatelets that become birefringent in the presence of an external magnetic field and a compact fiber-optic sensor system for tracking the liquid’s optical axis...
Article
Recent experimental realization of ferroelectric nematic liquid crystalline phases stimulated material development and numerous experimental studies of these phases, guided by their fundamental and applicative interest. In this Perspective, we give an overview of this emerging field by linking history and theoretical predictions to a general outloo...
Preprint
Full-text available
We investigated the effect of a photovoltaic field generated on the surface of iron-doped lithium niobate crystals on droplets of a ferroelectric nematic liquid crystalline and a standard nematic liquid crystalline material deposited on this surface. When such assembly is illuminated with a laser beam, a wide range of dynamic phenomena are initiate...
Article
Full-text available
Magnetic nanoplatelets (NPLs) based on barium hexaferrite (BaFe12O19) are suitable for many applications because of their uniaxial magneto-crystalline anisotropy. Novel materials, such as ferroic liquids, magneto-optic composites, and contrast agents for medical diagnostics, were developed by specific surface functionalization of the barium hexafer...
Article
Dense dispersions of ferrimagnetic bariumhexaferrite nanoplatelets form colloidal nematic phases even in the isotropic solvent such as n-butanol. The transition into the nematic phases is marked by developing the long-range orientational and magnetic correlations between the particles. Here we explore the magnetic dynamics in such dispersions in th...
Preprint
Recent experimental realization of ferroelectric nematic liquid crystalline phases stimulated material development and numerous experimental studies of these new phases, guided by their fundamental and applicative interest. In this Perspective, we give an overview of this emerging field by linking history and theoretical predictions to a general ou...
Article
Full-text available
Skyrmions are topologically protected, vortexlike formations of a field that cannot be removed by any smooth transformation and emerge in a range of fundamentally different, either quantum or classical systems, from spin textures to chiral ferromagnets and chiral complex fluids. Notably, they are generally observed in thin ordered or disordered qua...
Article
Alcohol ferrofluids made of ferrimagnetic barium hexaferrite (BHF) nanoplatelets (NPLs) form a unique example of a dipolar fluid – a liquid magnet. Its formation is induced at a high enough concentration of the NPLs. The key interactions between the NPLs are long-ranged dipolar magnetic and screened anisotropic electrostatic. Herein, we report the...
Article
Full-text available
Janus particles, which have two surfaces exhibiting different properties, are promising candidates for various applications. For example, magneto-optic Janus particles could be used for in-vivo cancer imaging, drug delivery, and photothermal therapy. The preparation of such materials on a relatively large scale is challenging, especially if the Jan...
Article
Full-text available
Nematic liquid crystals have been known for more than a century, but it was not until the 60s–70s that, with the development of room temperature nematics, they became widely used in applications. Polar nematic phases have been long-time predicted, but have only been experimentally realized recently. Synthesis of materials with nematic polar orderin...
Article
Full-text available
The recent discovery of the ferroelectric nematic phase has opened the door to experimental investigation of one of the most searched liquid crystal phases in decades, with high expectations for future applications. However, at this moment, there are more questions than answers. In this work, we examine the formation and structure of large polar ne...
Article
Full-text available
Ferrofluids most often consist of three components, they are: solid particles, the liquid in which they are dissolved and a substance that is supposed to prevent sedimentation - called surfacant. The biggest problem with ferrofluids is their stability. Mixtures in which one of the phases is a solid phase have a natural tendency to sedimentation. As...
Poster
Full-text available
Is it our great pleasure to invite you all to participate and submit your contributions to the 18th International Conference on Ferroelectric Liquid Crystals – Polarity and Chirality in Soft Matter, which will be held from 6th to 10th of September 2021 in Ljubljana (Slovenia). You are invited to submit the abstracts via our online submission form...
Preprint
The recent discovery of the ferroelectric splay nematic phase has opened the door to experimental investigation of one of the most searched liquid crystal phases in decades, with high expectations for future applications. However, at this moment, there are more questions than answers. In this work, we examine the formation and structure of large po...
Poster
Full-text available
Dear Friends and Colleagues, Is it our great pleasure to invite you all to participate in the 18th International Conference on Ferroelectric Liquid Crystals – Polarity and Chirality in Soft Matter, which will be held from 6th to 10th of September 2021 in Ljubljana (Slovenia). We are looking forward to welcoming you in Ljubljana. The conference wi...
Preprint
Nematic liquid crystals have been known for more than a century, but it was not until the 60s-70s that, with the development of room temperature nematics, they became widely used in applications. Polar nematic phases have been long-time predicted, but have only been experimentally realized recently. Synthesis of materials with nematic polar orderin...
Article
Full-text available
Amorphous coatings formed with mono-, di-, and tetra-phosphonic acids on barium hexaferrite (BHF) nanoplatelets using various synthesis conditions. The coatings, synthesized in water with di- or tetra-phosphonic acids, were thicker than that could be expected from the ligand size and the surface coverage, as determined by thermogravimetric analysis...
Article
Full-text available
By employing a combination of Molecular Dynamics simulations and experimental SAXS studies, we investigate low-concentration suspensions of polydisperse magnetic platelets with dipole moments perpendicular to the platelets' plane. Exploiting the precise control of platelet size and shape in simulation, we are also able to contrast these results wit...
Article
Full-text available
Pre-hydrolysed/condensed tetraethyl orthosilicate (TEOS) was added to a solution of methyl methacrylate (MMA) and 3-methacryloxypropyltrimethoxysilane (MAPTMS), and then copolymerised for various times to study the influence of the latter on the structure of hybrid sol-gel coatings as corrosion protection of aluminium alloy 7075-T6. The reactions t...
Article
The twist-bend nematic phase (N TB) is characterized by a conically twisting director and by a dramatic softening of the bend elastic constant before the transition to the N TB phase. In the recently found splay nematic phase (N S) the splay elastic constant tends to zero, resulting in a splay modulation perpendicular to the director. We model both...
Article
Ferroelectric ordering in liquids is a fundamental question of physics. Here, we show that ferroelectric ordering of the molecules causes the formation of recently reported splay nematic liquid-crystalline phase. As shown by dielectric spectroscopy, the transition between the uniaxial and the splay nematic phase has the characteristics of a ferroel...
Preprint
Ferroelectric ordering in liquids is a fundamental question of physics. Here, we show that ferroelectric ordering of the molecules causes formation of recently reported splay nematic liquid-crystalline phase. As shown by dielectric spectroscopy, the transition between the uniaxial and the splay nematic phase has the characteristics of a ferroelectr...
Preprint
The twist-bend nematic phase (NTB) is characterized by a conically twisting director and by a dramatic softening of the bend elastic constant before the transition to NTB phase. In the recently found splay nematic phase (NS) the splay elastic constant tends to zero, resulting in a splay modulation perpendicular to the director. We model both phases...
Article
A comparative experimental investigation of the dependence of second harmonic generation (SHG) on an applied external voltage between the standard nematic liquid crystalline material and an analogue ferromagnetic nematic liquid crystalline material was performed by using a fundamental optical beam at 800 nm wavelength. For the ferromagnetic materia...
Preprint
A comparative experimental investigation of the dependence of second harmonic generation (SHG) on applied external voltage between the standard nematic liquid crystalline material and an analogue ferromagnetic nematic liquid crystalline material was performed by using a fundamental optical beam at 800 nm wavelength. For a ferromagnetic material, th...
Article
Full-text available
In a room-temperature liquid magnet, barium hexaferrite (BHF) nanoplatelets suspended in 1-butanol spontaneously order and form a ferromagnetic nematic phase. In such concentrated suspension, the nanoplatelets align in large macroscopic regions, forming magnetic domains. The key parameter for the suspension stability and the formation of the ferrom...
Article
Full-text available
Modulated nematic liquid crystal phases, which lack positional order but have some periodic variation in the direction of average orientation present in a classical nematic, have attracted significant interest. In the recently discovered splay nematic (NS) phase the average orientational order is augmented with a periodic splay deformation of orien...
Article
This paper first reports random laser action in dye-doped ferromagnetic nematic liquid crystals, which act as a randomly distributed cavity. The random laser intensity of the ferromagnetic nematic liquid crystals can be controlled by a weak magnetic field (∼1 mT). Moreover, the magnetic switching of random laser is attributed to the direction and p...
Article
The Front Cover shows an occlusion in an artery which is marked by bimodal nanoparticles and detected by optical coherence tomography, while being exposed to a magnetic field, thereby improving the signal. More information can be found in the Article by J. Hu et al.
Article
The front cover artwork is provided by Universidad Autónoma de Madrid, Spain, the Jožef Stefan Institute Ljubljana, Slovenia, and the university hospitals Gregorio Marañon and La Princesa in Madrid, Spain. The image shows an occlusion in an artery which is marked by bimodal nanoparticles and detected by optical coherence tomography, while being exp...
Preprint
p>Modulated nematic liquid crystal phases, which lack positional order but have some periodic variation in the direction of average orientation present in a classical nematic, have attracted significant interest. In the recently discovered splay nematic (N<sub>S</sub>) phase the average orientational order is augmented with a periodic splay deforma...
Article
Suspensions of magnetic nanoplatelets in isotropic solvents are very interesting examples of ferrofluids. It has been shown that above a certain concentration ΦNI such suspensions form a ferromagnetic nematic phase, which makes this system a unique example of a dipolar fluid. The formation of a nematic phase is driven by anisotropic electrostatic a...
Preprint
Suspensions of magnetic nanoplatelets in isotropic solvents are very interesting examples of ferrofluids. It has been shown that above a certain concentration {\Phi}NI such suspensions form a ferromagnetic nematic phase, which makes this system a unique example of a dipolar fluid. The formation of a nematic phase is driven by anisotropic electrosta...
Article
Improving clinical techniques for cardiovascular imaging is important for better diagnosis / treatment of cardiovascular diseases, a main cause of mortality in western countries. One problem is a lack of contrast and hence the difficult interpretation of intracoronary images, especially those achieved by optical techniques, such as intracoronary op...
Article
Full-text available
Transmission optical diffraction gratings composed of periodic slices of a ferromagnetic liquid crystal and a conventional photoresist polymer are demonstrated. Dependence of diffraction efficiencies of various diffraction orders on an in-plane external magnetic field is investigated. It is shown that diffraction properties can be effectively tuned...
Article
Full-text available
Evaporation heat transfer with ferrofluids has the potential to improve heat and mass transfer compared to conventional two-phase systems. The ferromagnetic nanoparticles which control the rheology and heat transfer properties of the ferrofluid, must be coated with a dispersing agent, also referred to as a surfactant, to prevent particle agglomerat...
Article
Full-text available
Different liquid crystalline phases with long-range orientational but not positional order, so-called nematic phases, are scarce. New nematic phases are rarely discovered, and such an event inevitably generates much interest. Here, we describe a transition from a uniaxial to a novel nematic phase characterized by a periodic splay modulation of the...
Article
Successful realization of ferromagnetic nematic liquid crystals has opened up the possibility to experimentally study a completely new set of fundamental physical phenomena. In this contribution we present a detailed investigation of some aspects of the static response and the complex dynamics of ferromagnetic liquid crystals under the application...
Conference Paper
Nanocomposites with a high and uniform loading of magnetic nanoparticles are very desirable for various applications. In this study, a simple and scalable route for preparing nanocomposites with a high and uniform loading of magnetic nanoparticles is presented. The magnetic iron-oxide nanoparticles were functionalized with a methacrylate-based mono...
Preprint
Different liquid crystalline phases with long-range orientational but not positional order, so-called nematic phases, are scarce. It rarely occurs that a new nematic phase is discovered and such event is inevitably accompanied by a great interest. Here, we describe a transition from uniaxial to novel nematic phase characterized by a periodic splay...
Article
Full-text available
Nanocomposites with a high, uniform loading of magnetic nanoparticles are very desirable for applications such as electromagnetic shielding and cancer treatment based on magnetically induced hyperthermia. In this study, a simple and scalable route for preparing nanocomposites with a high, uniform loading of magnetic nanoparticles is presented. The...
Data
Additional experimental information.
Article
Magnetic nanoparticles (MNPs) are of great scientific interest because of the size effect associated with their magnetic properties and, even more so, because of their wide-ranging application potential in technology and biomedicine. In this review we focus on anisotropic MNPs that exhibit (i) elongated shapes and (ii) plate-like shapes. This is be...
Article
We investigate dynamic magneto-optic effects in a ferromagnetic nematic liquid crystal experimentally and theoretically. Experimentally we measure the magnetization and the phase difference of the transmitted light when an external magnetic field is applied. As a model we study the coupled dynamics of the magnetization, M, and the director field, n...
Article
The pioneering realization of suspensions of ferroelectric nanoparticles in a nematic host was one of excellent contributions of Yuri Reznikov to the science of liquid crystals [Y. Reznikov et al., Appl. Phys. Lett. 82 (2003) 191]. This achievement created great excitement as it entailed the enhancement of materials' dielectric properties and incre...
Article
Full-text available
One of the advantages of anisotropic soft materials is that their structures and, consequently, their properties can be controlled by moderate external fields. Whereas the control of materials with uniform orientational order is straightforward, manipulation of systems with complex orientational order is challenging. We show that a variety of struc...
Article
Hydrodynamics of complex fluids with multiple order parameters is governed by a set of dynamic equations with many material constants, of which only some are easily measurable. We present a unique example of a dynamic magneto-optic coupling in a ferromagnetic nematic liquid, in which long-range orientational order of liquid crystalline molecules is...
Article
This review presents experimental realization and behaviour of the ferromagnetic nematic phase, which is observed in different suspensions of magnetic nanoplatelets. After a general introduction, the challenges in the synthesis of magnetic nanoplatelets and preparation of the nematic suspensions are discussed. A brief explanation of a simple macros...
Article
Full-text available
We report magnetic field tuning of the structure and Whispering Gallery Mode lasing from ferromagnetic nematic liquid crystal micro-droplets. Microlasers were prepared by dispersing a nematic liquid crystal, containing magnetic nanoparticles and fluorescent dye, in a glycerol-lecithin matrix. The droplets exhibit radial director structure, which sh...
Article
Understanding the adsorption of amino acids (AAs) onto the magnetic iron-oxide nanoparticles (SPIONs) is important not only for the preparation of the aqueous suspensions, but also for understanding the interactions at the bio-nano interface. In this investigation the adsorption of aspartic acid (Asp) and lysine (Lys) onto SPIONs was studied, based...
Data
Supplementary Figures 1-9, Supplementary Notes 1-6 and Supplementary References
Article
Full-text available
The role is reported of zirconium tetrapropoxide (ZTP) and methacrylic acid (MAA), following their combination with sol synthesized from tetraethyl orthosilicate (TEOS) and 3-methacryloxypropyl trimethoxysilane (MAPTMS). The molar content of ZTP was varied between 0.06 and 0.96 and that of MAA between 0.12 and 1.92. The synthesized sols were deposi...
Article
Full-text available
Ferrofluids are familiar as colloidal suspensions of ferromagnetic nanoparticles in aqueous or organic solvents. The dispersed particles are randomly oriented but their moments become aligned if a magnetic field is applied, producing a variety of exotic and useful magneto-mechanical effects. A longstanding interest and challenge has been to make su...
Article
Full-text available
The incorporation of magnetic barium hexaferrite nanoparticles in a transparent polymer matrix of poly(methyl methacrylate) (PMMA) is reported for the first time. The barium hexaferrite nanoplatelets doped with Sc3+, i.e., BaSc0.5Fe11.5O12 (BaHF), having diameters in the range 20 to 130 nm and thicknesses of approximately 5 nm, are synthesized hydr...
Article
In this paper, we demonstrate how to apply recently discovered ferromagnetic nematic liquid crystal for visualisation of magnetic fields. The material exhibits strong optical response to both external electric and magnetic fields, which gives us an opportunity to use it for the detection of an area of magnetic vector field in a way that both, the m...
Article
We report on experimental studies of the viscoelastic, magnetodielectric, and magnetoviscosity properties of ferromagnetic liquid crystals (LCs) prepared by dispersing ferromagnetic nanoparticles in a thermotropic LC. Both the splay elastic constant and rotational viscosity of the ferronematic LCs are found to be considerably lower than that of the...
Article
We report experimental studies on the phase transitions and physical properties of colloidal suspensions of BaTiO3 nanoparticles and two cyanobiphenyl liquid crystals (4-pentyl-4ʹ-cyanobiphenyl and 4-octyl-4ʹ-cyanobiphenyl). From the differential scanning calorimetric measurements, we show that the nanoparticles have antagonistic effect on the isot...
Article
Full-text available
Stable colloidal suspensions of magnetic nanoparticles called ferrofluids have attracted a lot of attention in recent years, since they can be used in numerous technological and medical applications (1-3). For biomedical applications aqueous-based ferrofluids are being tested. Besides the requirements concerning their non-toxicity and biocompatibil...
Article
Full-text available
We have studied the response of ferromagnetic liquid crystal to external magnetic and electric fields, and compared it to the usual response of nematic liquid crystals (NLCs). We have observed effects, which are not present in pure NLC and are a consequence of the coupling between the nematic director and the magnetization. Electro-optic effect, wh...
Article
The effect of the morphology of ferrite nanoparticles on their assembly in a magnetic field was studied. Thin BaFe12O19 nanoplatelets were compared with isotropic, spherical or octahedral, CoFe2O4 nanoparticles, all of which were synthesized hydrothermally. The nanoplatelets and nanoparticles assembled into a variety of hierarchical structures from...
Article
Light scattering observation of nematic director fluctuations in confined geometries can be used to obtain interaction parameters of liquid crystals with surfaces. We present the basics of the method and some examples of the results in planar and cylindrical geometries. These results were obtained after neglecting the coupling of the director motio...
Article
Full-text available
More than four decades ago, Brochard and de Gennes proposed that colloidal suspensions of ferromagnetic particles in nematic (directionally ordered) liquid crystals could form macroscopic ferromagnetic phases at room temperature. The experimental realization of these predicted phases has hitherto proved elusive, with such systems showing enhanced p...
Article
Electrooptic properties of mixtures of 4-cyano-4′-pentylbiphenyl (5CB) thermotropic liquid crystal with four different inorganic dopants: (i) MoSI nanowires, (ii) MnO2 nanorods, (iii) Ag nanowires, and (iv) WS2 nanotubes were investigated by a conventional optical measurement technique. The dopant concentrations were in the range from 0.1 to 0.5 wt...
Conference Paper
Full-text available
The focus of nanoscience and nanotechnology is increasingly shifting from the synthesis of individual components to their assembly into larger systems. Hereby, the use of external fields (electric, magnetic) has an enormous potential in the preparation of nanoparticles assemblies. We report a study on magnetically directed assembly of cobalt ferrit...
Article
Here we report the chemical induction of the twist-bend nematic phase in a nematic mixture of ether-linked liquid crystal dimers by the addition of a dimer with methylene links; all dimers have an odd number of groups in the spacer connecting the two mesogenic groups. The twist-bend phase has been identified from its optical texture and x-ray scatt...