1. Splay nematic phaseerAlenka Mertelj, Luka Cmok, Nerea Sebastián Ugarteche, Richard J. Mandle, Rachel R. Parker, Adrian C. Whitwood, J. W. Goodby, Martin Čopič, 2018, original scientific article Published in DiRROS: 15.09.2025; Views: 311; Downloads: 74
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3. Antiferroelectric order in nematic liquids : flexoelectricity versus electrostaticsPeter Medle Rupnik, Ema Hanžel, Matija Lovšin, Natan Osterman, Calum Jordan Gibb, Richard J. Mandle, Nerea Sebastián Ugarteche, Alenka Mertelj, 2025, original scientific article Abstract: 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, with flexoelectric and electrostatics effects proposed as competing mechanisms. By controlling the magnitude of electrostatic forces through ion addition in two representative ferroelectric nematic materials, it is shown that the primary mechanism for the emergence of antiferroelectric order is the flexoelectric coupling between electric polarization and splay deformation of the nematic director. The addition of ions significantly expands the temperature range over which the antiferroelectric phase is observed, with this range increasing with increasing ion concentration. Polarizing optical microscopy studies and second harmonic generation (SHG) microscopy reveal the splayed structure modulated in 2D, while SHG interferometry confirms its antiferroelectric character. The model previously used to describe pretransitional behavior is extended by incorporating the electrostatic contribution of ions. The model shows qualitative agreement with the experiments, accurately reproducing the phase diagram and temperature-dependent evolution of the modulation period of the observed structure.
Keywords: ferroelectric nematic liquids, flexoelectricity, antiferroelectric order
Published in DiRROS: 15.09.2025; Views: 243; Downloads: 108
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5. Room-temperature multiferroic liquids: ferroelectric and ferromagnetic order in a hybrid nanoparticle–liquid crystal systemHajnalka Nádasi, Peter Medle Rupnik, Darja Lisjak, Nerea Sebastián Ugarteche, Alenka Mertelj, Alexey Eremin, 2025, original scientific article Abstract: 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, an example of a liquid is demonstrated that simultaneously displays both ferroelectric and ferromagnetic types of order. This material is a nanostructured liquid crystalline hybrid comprising ferrimagnetic barium hexaferrite nanoplatelets suspended in a ferroelectric nematic host. Director-mediated interactions drive the self-assembly of nanoplatelets in an intricate network. Due to the coupling between the polar electric and magnetic types of order, this material demonstrates magnetically driven electric and nonlinear optical responses, as well as electrically driven magnetic response. Such multiferroic liquids are highly promising for applications in energy harvesting, nonlinear optics, and sensors.
Keywords: liquid crystals, multiferroics, ferroelectric materials, ferromagnetic materials
Published in DiRROS: 19.08.2025; Views: 387; Downloads: 175
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6. Nonconductive ferrofluids from permanently magnetic nanoplatelets hybridized with polar phosphonic ligandsAli Tufani, Nina Popov, Janez Kovač, Stanislav Čampelj, Andraž Mavrič, Tomas Landovsky, Martin Cigl, Petra Vaňkátová, Martin Loula, Vladimíra Novotná, Matic Poberžnik, Gabriela Herrero-Saboya, Layla Martin-Samos, Alenka Mertelj, Darja Lisjak, 2025, original scientific article Abstract: Ferrofluids composed of permanently magnetic nanoplatelets of barium hexaferrite (BHF NPLs) represent a remarkable class of materials that can form a ferromagnetic liquid state at sufficiently high concentrations. To date, the surfactant dodecylbenzenesulfonic acid (DBSA) has demonstrated an excellent colloidal stability of the BHF NPLs in alcohols. However, a key limitation of DBSA is its labile adsorption onto the NPLs, meaning that the surface coverage by surfactant molecules is highly sensitive to various factors. In this study, we demonstrate that polar ligands based on phosphonic acids and phosphonate esters offer a viable alternative to DBSA, providing enhanced robustness and colloidal stability in low-polar solvents. Phosphonic ligands with the different electron-withdrawing groups and alkyl chain lengths of the terminal chain and linker were synthesized. Their attachment to the surface of the BHF NPLs was studied for various conditions and followed by a combination of spectroscopic techniques, thermogravimetry, and electrokinetic measurements. The results confirmed the theoretically predicted surface condensation of the ligands onto the BHF NPLs surfaces at 120 °C in 1-hexanol, whereas at lower temperatures or in more polar solvents the ligands were mostly physisorbed. The NPL hybrids with chemisorbed ligands having surface densities of at least 0.4 molecules per nm2 formed stable ferrofluids in 1-hexanol. Due to the relatively low polarity of 1-hexanol, the ligands remain protonated and the ferrofluids have negligible electric conductivity and are suitable for the development of novel magneto-optic sensors that can operate under an electric field.
Published in DiRROS: 21.05.2025; Views: 652; Downloads: 196
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8. Skyrmions in blue phases of chiral liquid crystalsJaka Pišljar, Matevž Marinčič, Sharmistha Ghosh, Srikanth Turlapati, Nandiraju V. S. Rao, Andriy Nych, Miha Škarabot, Alenka Mertelj, Andrej Petelin, Anja Pusovnik, Miha Ravnik, Igor Muševič, 2023, published scientific conference contribution Keywords: liquid crystals, chiral nematics, blue phases, skyrmions
Published in DiRROS: 12.05.2025; Views: 375; Downloads: 139
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9. Calorimetric and optical investigation of the nematic, splay-nematic, and ferroelectric nematic phases of RM734 liquid crystalMarta Lavrič, Nerea Sebastián Ugarteche, Calum Jordan Gibb, Richard J. Mandle, Alenka Mertelj, Nikola Novak, George Cordoyiannis, 2025, original scientific article Abstract: RM734 is one of the first two liquid crystal compounds reported to exhibit the ferroelectric nematic phase. At the early stage of its characterisation, a direct nematic – to – ferroelectric nematic phase transition was reported for this compound. However, subsequent studies revealed the presence of an intermediate phase between the nematic and ferroelectric nematic ones. Here, we provide additional evidence on the calorimetric signature and the optical texture of this intermediate phase, referred to as the splay-nematic phase. Next, we briefly comment on the nature of the transitions between the nematic, splay-nematic, and ferroelectric nematic phases, and the substantially different transition temperatures reported in the literature for RM734.
Published in DiRROS: 08.04.2025; Views: 561; Downloads: 168
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10. Saturation magnetisation as an indicator of the disintegration of barium hexaferrite nanoplatelets during the surface functionalisationDarja Lisjak, Iztok Arčon, Matic Poberžnik, Gabriela Herrero‑Saboya, Ali Tufani, Andraž Mavrič, Matjaž Valant, Patricija Hribar Boštjančič, Alenka Mertelj, Darko Makovec, Layla Martin‑Samos, 2023, original scientific article Published in DiRROS: 02.02.2023; Views: 1913; Downloads: 1261
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