Aleksander Zidanšek

Terahertz spectroscopic identification of explosive and drug simulants concealed by various hiding techniques.

Terahertz time-domain spectroscopy and imaging is used to study the effects of various hiding techniques of spectral features of drug and explosive simulants in combination with different paper and textile barriers. Results show that rapid detection and identification of concealed simulants is possible in the frequency range from 1.5 to 4.0 THz by using an organic-crystal-based terahertz time-domain system and the spectral peak analysis method.

Different modulated structures of topological defects stabilized by adaptive targeting nanoparticles

It is demonstrated that interactions between nanoparticles and topological defects induce a twist-grain boundary phase in a chiral liquid crystal. The occurrence of this phase, the analogue of the Shubnikov phase in type-II superconductors, is driven by direct interactions between surface-functionalized CdSe quantum dots and screw dislocations. It is shown that, within an adaptive-defect-core-targeting mechanism, nanoparticles of appropriate size and functionalization adapt to qualitatively different cores of topological defects such as disclination lines and screw dislocations. This mechanism enables the effective reduction of the energetically costly, singular defect core volume, while the surrounding phase ordering remains relatively weakly affected. The findings suggest new pathways towards the controlled assembly of superstructures in diverse, symmetry-broken, condensed-matter systems, ranging from nanoparticle-decorated liquid crystals to superconductors.

Presmectic wetting and supercritical-like phase behavior of octylcyanobiphenyl liquid crystal confined to controlled-pore glass matrices.

The influence of controlled-pore glass (CPG) confinement on the phase behavior of octylcyanobiphenyl liquid crystal (LC) is studied by means of x-ray scattering and high precision calorimetry. For CPG samples with pore diameter 2R>24 nm, the smectic order parameter temperature dependence eta(T) reveals apparent presmectic ordering far above the bulk smectic A-nematic (SmA-N) phase transition for both nontreated and silane-treated CPG matrices. The behavior of eta(T) is qualitatively similar in all samples, well obeying the mean field approach (MFA) in which the surface wetting tendency plays the dominant role. In contrast, the critical fluctuations remain important in the specific heat data, which cannot be described within the MFA. We show experimentally that randomness and surface wetting become dominant over finite-size effects for 2R approximately<10 nm, in agreement with theoretical analysis. In nontreated samples, the noncritical character of the static disorder and the interfacial LC-CPG coupling almost completely suppress the quasi-SmA-N and nematic-isotropic phase transitions at 2R approximately 15.1 and approximately 7.5 nm, respectively.

The effect of graphene on liquid-crystalline blue phases

The stabilization of liquid-crystalline blue phases is recently attracting considerable interest because of the envisioned applications in fast optical displays and tunable photonic crystals. We report on the effect of surface-functionalized graphene nanosheets on the blue phase range of a chiral liquid crystal. Calorimetric and optical measurements, reproducible on heating and cooling, demonstrate that the resulting soft nanocomposite exhibits an increased blue phase temperature stability range for a minute concentration of dispersed graphene. The impact is stronger on the ordered, cubic structured blue phase I. These findings suggest that anisotropic nanoparticles may be of great usefulness for stabilizing blue phases.

Applications of Terahertz Spectroscopy in the Field of Construction and Building Materials

Abstract: In last two decades, rapid development in the field of terahertz (THz) technology has opened new possibilities for creating innovative imaging and sensing systems. Although the applications of THz technology in different sectors constantly increase, the construction industry lags behind them. The aim of this article is to review the current applications of THz spectroscopy in research and industry related to construction and building materials, along with the key drawbacks of technology and recommendations for future use. The review concludes that THz spectroscopy and imaging have promising potential and provide many opportunities for applications in construction and building materials characterization.

Dimensional crossover and scaling behavior of a smectic liquid crystal confined to controlled-pore glass matrices

The structural and thermodynamic phase behavior of the thermotropic liquid crystal dodecylcyanobiphenyl (12CB) confined in controlled-pore glasses (CPGs) has been studied by means of high-resolution calorimetry and small-angle X-ray scattering. Non-treated CPG matrices have been used with a characteristic pore size R ranging from nanometre to micrometre scale. Even in the case of the strongest confinement the isotropic-to-smectic-A (I-SmA) transition was pronounced. Both the smectic pretransitional ordering and the broadening of the specific heat capacity anomaly were relatively weak. This signals the secondary importance of the surface interaction potential and of the disorder upon phase behavior. We claim that the surface interaction is dominated by the coupling between surface-frozen and volume liquid crystal molecules. This coupling is weak due to the flexible long alkyl chains which dominantly influence the phase behavior of 12CB. The depression of the phase transition temperature Tc is dominated by smectic elastic compressibility distortions. The observed anomalous Tc(R) dependence is explained by allowing surface rearrangement processes. In severely-confined samples the 1st order I-SmA phase transition tends to be replaced by a 2nd order one. This phenomenon is attributed to a dimensional-crossover which, in 12CB samples, is not masked by surface interactions as it is in case of similar liquid crystals with shorter alkyl chains. The observed behavior is explained using scaling and dimensional analysis within the Landau–Ginzburg–de Gennes mesoscopic approach.

Phase transitions in 8CB liquid crystal confined to a controlled-pore glass: Deuteron NMR and small angle X-ray scattering studies

We present results of the deuteron nuclear magnetic resonance (NMR) and small-angle X-ray scattering (SAXS) study of ordering and phase transition behavior of octylcyanobiphenyl (8CB) liquid crystal confined to a controlled-pore glass (CPG) with nontreated and silanes-treated pore surfaces. The deuteron NMR spectra allowed to determine the degree of nematic liquid crystal ordering and also provided an indirect information on the confined 8CB smectic ordering via its influence on the nematic ordering. For the smectic phase these data are supplemented with measurements of the temperature dependence of the first-order SAXS diffraction pattern. The NMR results indicate that the average nematic and smectic order parameters of 8CB in the nontreated CPG are only weakly perturbed by the confinement. The SAXS data further suggest that in confined 8CB for both nontreated and silane-treated CPG a domainlike pattern appears in accordance with the Imry-Ma theorem.

Qualitative and quantitative analysis of calcium-based microfillers using terahertz spectroscopy and imaging

In different industrial applications, several strictly defined parameters of calcium-based microfillers such as average particle size, particle size distribution, morphology, specific surface area, polymorphism and chemical purity, play a key role in the determination of its usefulness and effectiveness. Therefore, an analytical tool is required for rapid and non-destructive characterization of calcium-based microfillers during the synthesis process or before its use in a further manufacturing process. Since spectroscopic techniques are preferred over microscopy and thermogravimetry, particularly due to its non-destructive nature and short analysis time, we applied terahertz (THz) spectroscopy to analyse calcite microfillers concentration in polymer matrix, its granulation and chemical treatment. Based on the analysis of peak absorbance amplitude, peak frequency position, and the appearance of additional spectral features, quantitative and qualitative analysis was successfully achieved. In addition, THz imaging was also applied for both quantitative and qualitative analysis of calcium-based microfillers. By using spatial distribution map, the inhomogeneity in concentration of calcium carbonate in polymer matrix was characterized. Moreover, by THz spectroscopy and imaging different calcium compounds were detected in binary mixtures. Finally, we demonstrated that the applied spectroscopic technique offers valuable results and can be, in combination with other spectroscopic and microscopic techniques, converted to a powerful rapid analytical tool.

Greenhouse gas and air pollution emissions and options for reducing from the Kosovo transportation sector‐dynamic modelling

Purpose – The purpose of this investigation is the dynamic modelling of greenhouse gas (GHG) and air pollution emissions, to identify technology and policy options for reducing GHG and air pollution, and to explain how these options might affect the different variables of mobile source emission systems in Kosovo.Design/methodology/approach – For modelling impacts of the technology and policy options for reducing GHG and air pollution, the model STELLA software has been used. The annual total emission for air pollutants (CO, NOx, CHx, SO2 and dust) and GHG (CO2) from the year 2000 up to 2025 is calculated. 2000 is taken as the base year for emission. Initial data value for vehicle population is taken from MEM and from World Bank ESTAP Project for Kosovo. Projection for the total number of vehicles in Kosovo is calculated with the WB Atlas Method, while the projection for emission factors and total annual emission for Air Pollutants and GHG (CO2) are calculated with US EPA methodology.Findings – From the re...

Smectic ordering of octylcyanobiphenyl confined to control porous glasses

We performed an x-ray scattering study of the smectic A (SmA) ordering of the liquid crystal 8CB (octylcyanobiphenyl) confined to a control porous glass with a typical void radius R = 0.2 µm. The voids were either nontreated or covered with silane. The results reveal a strong influence of spatial restriction and surface treatment on the temperature evolution of smectic ordering. The observations are qualitatively reproduced using the Landau-Ginsburg approach.