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In recent years, transitional metal dichalcogenides (TMDCs) have opened a new frontier in the area of field emission devices. Due to their layered structure and the presence of thin and sharp edges with high aspect ratios the local electric field is enhanced which plays an important role in filed emission.

L. Pirker, M. Remškar in B: Višić from the Department of Condensed Matter Physics F5 together with colleagues from OTH Regensburg (Germany) published an article in Advanced Functional Materials titled MoxWx–1S2 Nanotubes for Advanced Field Emission Application, where they report on the synthesis and characterization on mixed MoWS2 nanotubes. Single nanotube field emission devices were prepared and show promising results comparable with other TMDC devices.

The 1st COST NanoSpace Scientific Meeting took place at the Jožef Stefan Institute between 9th and 11th of February 2023. The project involves astrophysicists, chemists and material scientists. The main scientific challenges on which we will try to address are (i) What nanocarbon species are present in space and how can we identify them?, (ii) What are the chemical pathways that lead to their formation and destruction?, and (iii) What is the role of nanocarbon species in non-terrestrial environments? 70 researchers coming from more than 30 countries, including Japan and Canada, attended the meeting. The JSI members of the project are Polona Umek, PhD and Prof Denis Arčon, PhD.

George Cordoyiannis, PhD from the Department of Condensed Matter Physics F5 and colleagues from Belgium and UK have published in Physical Review E the article Phase transitions study of the liquid crystal DIO with a ferroelectric nematic, a nematic, and an intermediate phase and of mixtures with the ferroelectric nematic compound RM734 by adiabatic scanning calorimetry.

We have studied phase transitions in a series of mixtures of liquid crystals RM734 and DIO exhibiting new types of ferroelectric nematic phases. RM734 exhibits a nematic (N) and a ferroelectric nematic (NF) phase, whereas DIO has an intermediate phase (Nx) between N and NF. By means of high-resolution calorimetry, we have derived the precise phase diagram as a function of mixture composition, i.e., as a function of variable ferroelectric coupling. The phase diagram is consistent with ideal mixture behavior, provided that the total enthalpy values are used in the analysis. The critical behavior of Nx–NF phase transition exhibited by the mixtures shows a systematic trend of the critical exponent values from α = 0.88 ± 0.10 for DIO towards α = 0.50 ± 0.05 (tricritical) when increasing the concentration of RM734.

The current development of soft shape-memory materials is typically restricted to the synthesis of thin-walled samples, which greatly limits their practical application. Three-dimensional specimens can be produced using complex manufacturing methods, e.g. with additive manufacturing, but these require specialized equipment, while the production output is usually very low. M. Bobnar, N. Derets, S. Umerova, N. Novak, M. Lavrič, G. Cordoyiannis, B. Zalar and A. Rešetič, together with V. Domenici from Italy developed a new composite shape-memory material made from main-chain liquid crystal elastomer microparticles (LCEs) dispersed in a silicone polymer matrix. The composite dispersions can be effortlessly molded into arbitrary shapes or sizes, most significantly, into bulk-sized solids, which is challenging to achieve using conventional synthesis methods. Shape-memory capabilities result from temperature depended mechanical properties of the LCE inclusions. These become significantly softer at higher temperatures, when the particles reach the isotropic phase, and harden while cooled back into the glassy phase. The composite material can thus be shape-programmed by deforming the material at higher temperature and cooling it into the new stable shape, fixed by the stiffened LCE inclusions. The new shape can then be reset by heating above the isotropic phase temperature. LCE particles can be additionally magnetically ordered, providing for an additional thermomechanical reversible response.… Read the rest “Article in Nature Communications”

One of the major challenges in developing materials for energy storage systems is realizing high energy density while maintaining low dielectric losses. The composite approach, where conductive particles are dispersed in the dielectric matrix, effectively increases the dielectric permittivity but also boosts the losses. An alternative approach is an operation under high electric fields, i.e. increasing the electric breakdown strength (Eb) without increasing the dielectric permittivity.

Phenyl groups are fundamental chain components of many high-temperature polymers and, depending on the polymer’s molecular structure, delocalized electrons in these groups may exhibit a partially positive or negative charge. We prepared blends of polyetherimide (PEI) and polyimide (PI) by the solution casting method and performed their extensive dielectric characterization. We demonstrated a significant enhancement of Eb in blends due to strong electrostatic interactions between different polymer chains; PEI namely contains three negatively charged phenyls, while PI has two strong positively charged phenyl groups. Electrostatic interactions (i) strongly reduce the number of space charges and (ii) lead to much higher chain packing density in blends. Since the breakdown is initiated by charges that are accelerated by an applied electric field in weak points, i.e. voids in the system, both features contribute to the enhancement of Eb.… Read the rest “Strong enhancement of the electric breakdown strength in properly matched polymer blends”