Alenka Mertelj

Jožef Stefan Institute | IJS · Complex Matter

The recent discovery of ferroelectric nematic liquid crystalline phases marks a major breakthrough in soft matter research. An intermediate phase, often observed between the nonpolar and the ferroelectric nematic phase, shows a distinct antiferroelectric response to electric fields. However, its structure and formation mechanisms remain debated, wi...

Responsiveness to multiple stimuli and adaptivity are paramount for designing smart multifunctional materials. In soft, partially ordered systems, these features can often be achieved via self-assembly, allowing for the combination of diverse components in a complex nanostructured material. Here, we demonstrate an example of a liquid that simultane...

Spontaneous symmetry breaking and emergent polar order are each of fundamental importance to a range of scientific disciplines, as well as generating rich phase behaviour in liquid crystals (LCs). Here, we show the union of these phenomena to lead to two previously undiscovered polar liquid states of matter. Both phases have a lamellar structure wi...

The ferroelectric nematic phase (NF) has quickly become the most studied system in liquid crystal research. In this work, we investigate the origin of such polar structure by studying a compound for which the NF phase directly follows the isotropic liquid phase on cooling, making it a particularly interesting system. Our experimental results eviden...

Direct viscous mechano‐electric response is demonstrated for a room‐temperature ferroelectric nematic liquid, which combines large spontaneous electric polarization with 3D fluidity. The mechano‐electric transduction is observed in the frequency range 1 −200 Hz via a simple demonstrator device. The liquid is placed into a deformable container with...

The ferroelectric nematic phase (NF) has quickly become the most studied system in liquid crystal research. In this work, we investigate the origin of such polar structure by studying a compound for which the NF phase directly follows the isotropic liquid phase on cooling, making it a particularly interesting system. Our experimental results eviden...

A great deal of effort has been recently devoted to the study of dielectric relaxation processes in ferroelectric nematic liquid crystals, yet their interpretation remains unclear. In this work, we present the results of broadband dielectric spectroscopy experiments of a prototypical ferroelectric nematogen in the frequency range 10 Hz–110 MHz at d...

A great deal of effort has been recently devoted to the study of dielectric relaxation processes in ferroelectric nematic liquid crystals, yet their interpretation remains unclear. In this work, we present the results of broadband dielectric spectroscopy experiments of a prototypical ferroelectric nematogen in the frequency range 10 Hz-110 MHz at d...

Ferromagnetic ferrofluids are synthetic materials consisting of magnetic nanoplatelets dispersed in an isotropic fluid. Their main characteristics are the formation of stable magnetic domains and the presence of macroscopic magnetization even in the absence of a magnetic field. Here, the authors report on the experimental observation of spontaneous...

The recently discovered ferroelectric nematic liquids incorporate to the functional combination of fluidity, processability and anisotropic optical properties of nematic liquids, an astonishing range of physical properties derived from the phase polarity. Among them, the remarkably large values of second order optical susceptibility encourage to ex...

Using high-resolution microscope observations, we show that both the static cubic (BPI) and the dynamic amorphous (BPIII) blue phases consist of fractional skyrmion filaments that transform into the same quasi two-dimensional structure of ‘baby’ half-skyrmions upon confinement to ultra-thin layers. We confirm this using numerical simulations of BPI...

Barium hexaferrite nanoplatelets (BHF NPLs) are permanent nanomagnets with the magnetic easy axis aligned perpendicular to their basal plane. By combining this specific property with optimised surface chemistry, novel functional materials were developed, e.g., ferromagnetic ferrofluids and porous nanomagnets. We compared the interaction of chemical...

The recently discovered ferroelectric nematic liquids incorporate to the functional combination of fluidity, processability and anisotropic optical properties of nematic liquids, an astonishing range of physical properties derived from the phase polarity. Among them, the remarkably large values of second order optical susceptibility encourage to ex...

In complex colloidal systems, interparticle interactions strongly affect the dynamics of the constituting particles. A study of the dynamical response also provides invaluable information on the character of those interactions. Here we demonstrate how tuning the electrostatic interactions by an ionic surfactant in dispersions of magnetic nanoplatel...

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 polarisation optical (video)microscopy (POM). During heating/cooling cycles,...

Recently discovered barium hexaferrite (BaFe12O19) – based nanoplatelets form a ferromagnetic-ferrofluid which exhibits interesting magnetic properties. Manufacturing the barium hexaferrite nano-platelets via hydrothermal synthesis remains of fundamental interest and allows...

We investigated the effect of a photovoltaic field generated on the surface of iron-doped lithium niobate crystals on sessile droplets of a ferroelectric nematic liquid crystalline and a standard nematic liquid crystalline material present on this surface. When such an assembly is illuminated with a laser beam, a wide range of dynamic phenomena are...

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,...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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.

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_S) phase the average orientational order is augmented with a periodic splay deforma...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

Additional experimental information.

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...

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...

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...

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...