Jožef Stefan Institute

About: Jožef Stefan Institute is a facility organization based out in Ljubljana, Slovenia. It is known for research contribution in the topics: Liquid crystal & Dielectric. The organization has 3828 authors who have published 12614 publications receiving 291025 citations.

Partitioning of Zn, Pb and Cd in river sediments from a lead and zinc mining area using the BCR three-step sequential extraction procedure

Abstract: The extent of pollution was investigated in sediments collected along the course of the river Meža and its tributaries in the lead and zinc mining area of the Mežica valley (Slovenia) In order to evaluate the heavy metal burden, total concentrations of Zn, Pb and Cd were determined and the partitioning of these metals between the easily and sparingly soluble sediment fractions was performed by the use of the slightly modified BCR sequential extraction procedure The quality of analytical data was checked with Certified Reference Material CRM 601 Good agreement between the determined and certified or indicative metal concentrations was obtained In order to estimate the natural and anthropogenic inputs of Zn, Pb and Cd in the sediments, normalisation to Al was applied The results of the partitioning study indicate that Zn prevails in the most sparingly soluble fraction and is distributed between organic matter and sulfides, while a smaller proportion is found in the easily soluble fraction Pb is distributed mainly between organic matter and sulfides, whereas Cd is predominantly associated with the most sparingly soluble fraction Data from the normalisation procedure indicate that the anthropogenic inputs of Zn, Pb and Cd correlate with the very high total metal concentrations determined in sediments The highest total Zn, Pb and Cd concentrations (163, 93 and 013 g kg−1, respectively) were found in the sediment of the Helena rivulet, arising from former mining activities In spite of the relatively low easily soluble metal fractions in the sediment, the concentrations of metals in these fractions are high, owing to the extremely high total metal concentrations These data indicate severe pollution of the terrestrial and aquatic environment

The surface modification of cellulose fibres to create super-hydrophobic, oleophobic and self-cleaning properties

Abstract: The surface modification of cellulose fibres was performed with the use of low-pressure water vapour plasma, followed by the application of a pad-dry-cure sol-gel coating with the water- and oil-repellent organic-inorganic hybrid precursor fluoroalkyl-functional siloxane (FAS), with the aim of creating the “lotus effect” on the cotton fabric surface. The tailored “lotus effect” was confirmed by measurements of the contact angle of water (154°) and n-hexadecane (140°), as well as by measurements of the water sliding angle (7°), which were used to identify the super-hydrophobic, oleophobic and self-cleaning properties of the modified fibres. The chemical and morphological changes caused by modifications of the fibres were investigated by XPS, FTIR, AFM and SEM. The results show that the plasma pre-treatment simultaneously increased the surface polarity, average roughness, and surface area of the fabric. The application of the FAS coating after plasma pre-treatment caused only a slight increase in the surface roughness, accompanied by a decrease in the surface area, indicating that the architecture of the surface was significantly changed. This result suggests that the surface pattern affected the “lotus effect” more than the average surface roughness. The plasma pre-treatment increased the effective concentration of the FAS network on the fabric, which resulted in enhanced repellency before and after repetitive washing, compared with that of the FAS-coated fabric sample without the plasma pre-treatment. Despite the fact that the plasma pre-treatment increased the concentration of the oxygen-containing functional groups on the fabric surface, this phenomenon insignificantly contributed to the adhesion ability and, consequently, the washing fastness of the FAS coating.

Universal fine structure of nematic hedgehogs

Abstract: We study in a Landau-de Gennes approach the biaxial structure of a nematic point defect with topological charge M = + 1. We aim to illuminate the role of the confining boundaries in determining the fine structure of the defect. We show that there are different regimes associated with different values of the ratio between the typical size R of the region in space occupied by the material and the biaxial correlation length ξb. For R/ξb>20 the core structure is already qualitatively universal, that is, independent of the confining geometry, while also for R/ξb>200 any quantitative difference is unlikely to be detected.