Blanka Skipina - Academia.edu (original) (raw)

Papers by Blanka Skipina

Contemporary materials, Jun 27, 2023

This article reports on photodielectric properties of hydrocolloids of TiO 2 particles and Au/TiO... more This article reports on photodielectric properties of hydrocolloids of TiO 2 particles and Au/TiO 2 hybrid particles of lateral dimension of ∼200 nm. Illumination of the colloids with visible light did not cause measurable changes in their electrical conductivity, while the application of UV (365 nm) light led to photoinduced increase in conductivity of up to 2%. The photogeneration of ions in water, regardless of the presence of the particles, makes a dominant contribution to the photoinduced increase in conductivity of the colloids.

Универзитет у Београду, Oct 19, 2018

Materials Science Forum, Sep 1, 2005

ABSTRACT In our previous work we investigated the conductivity and dielectric relaxation phenomen... more ABSTRACT In our previous work we investigated the conductivity and dielectric relaxation phenomena in heteropoly acids and their salts. In this work, we have studied the conductivity of grains and grain boundaries in compressed powders of 12-tungstophosphoric acid (WPA) salts with univalent and bivalent ions. The method of impedance spectroscopy has been employed in the frequency range from 5 Hz to 500 kHz. We obtained grains and grain boundaries conductivities as well as corresponding activation energies. Grain conductivity in all investigated salts is always higher than the grain boundary conductivity.

Book of Abstracts, 2022

Targeting sonic hedgehog pathway in combination with proton radiation or gamma irradiation decrea... more Targeting sonic hedgehog pathway in combination with proton radiation or gamma irradiation decreases viability of glioma cell lines .

Wood Science and Technology, Feb 8, 2018

Modified cellulose materials are finding increasing application in electronics, because of the ne... more Modified cellulose materials are finding increasing application in electronics, because of the need for more environmental-friendly electronic circuits. The papers prepared from poly(ethyleneimine)-TiO 2-anthocyanin-modified cellulose fibres are completely environmentally friendly and can be applied to the construction of photocells or photo-/humidity sensors. To better understand the mechanisms of electrical conductivity of the said cellulose composites, the effect of humidity (RH = 9% → 100%) on its dielectric properties is presented in this article. The possibility of trapping the negative and positive charges in the composite under different humidity conditions is also examined. A large number of studies suggest that proton conductivity, stimulated by humidity, is the dominant mechanism of electrical conductivity in cellulose-based materials. The results presented in this paper indicate that the electronic conductivity mechanisms also play a significant role in papers prepared from poly(ethyleneimine)-TiO 2-anthocyanin-modified cellulose fibres.

Hemijska Industrija, 2010

U ovom radu su ispitivane dielektrične osobine kompozita od polietilena niske gustine (PENG) i ča... more U ovom radu su ispitivane dielektrične osobine kompozita od polietilena niske gustine (PENG) i čađi u zavisnosti od temperature i frekvencije. Pošto je većina dielektričnih fenomena u polimernim kompozitima vezana za amorfno stanje, snimljeni su spektri u temperaturnom intervalu u kome se dešavaju dielektrične relaksacije. U skladu sa tim analizirani su dielektrični gubici u funkciji temperature (od 120 do 355 K) i frekvencije (od 80 kHz do 13 MHz). Mjerenja su vršena na uzorcima PENG sa različitim koncentracijama čađi. Sa povećanjem koncentracije čađi u PENG-u uočava se povećanje realnog i imaginarnog dijela provodljivosti pri čemu je oblast perkolacije provodnosti široka i nije jasno definisana. Dielektrični gubitci pokazuju porast sa porastom koncentracije čađi.

High surface texture of textile materials is rougher than other printing substrates which can cau... more High surface texture of textile materials is rougher than other printing substrates which can cause excessive macro non-uniformity. Adding metal oxides into the ink to enhance material properties usually add to surface roughness and increase print mottle. In this paper copper(I)oxide particles and different amounts of Pinus sylvestris L. plant extract were added to modified alginate paste (CHT-NV) prior to printing. The aim of this paper is to inspect the influence of added metal oxide and plant extract on the print quality of linen based material via surface macro non-uniformity GLCM determination method. In the pattern recognition phase, the co-occurrence matrix is applied to calculate the texture characteristics, such as contrast, correlation, energy, entropy and homogeneity. The research results indicated that the metal oxide particles have had a negative influence on macro uniformity of printed linen. Increasing of the concentration of extract leads to a dilution of the printing paste, and thus to a greater penetration of copper ions between the threads of the fabric, as well as into the yarn itself.

Contemporary materials, Jan 10, 2018

In this paper, we report surface dielectric and photodielectric properties of low density polyeth... more In this paper, we report surface dielectric and photodielectric properties of low density polyethylene (LDPE)/Emodin composite. Emodin was extracted from Fallopia japonica plant. The composite was obtained from the xylene solution. Dielectric measurements were performed in the frequency range from 240 Hz to 4 kHz and the temperature range from 20 °C-70 °C. Irradiations of the sample were applied before and during measurement with selected wavelengths from UV to the visible range. Surface dielectric conductance and susceptance of the LDPE/Emodin composite is higher then value of conductance and susceptance of pure LDPE. We found an increase, by one order of magnitude, in conductance and susceptance of the LDPE/Emodin composite with increase of measurement frequency. Furthermore, the surface conductance and susceptance increase due to UV radiation in mentioned temperature range, but during visible radiation at frequency 1 kHz (except in the case green LED lamp) we observed the enhance of conductance only at temperature range up to 50 °C.

ABSTRACT A microscopic theory of optical properties of ideal ultrathin molecular films, was formu... more ABSTRACT A microscopic theory of optical properties of ideal ultrathin molecular films, was formulated in bosonic and nearest-neighbor approximation. Calculating of dynamical permittivity by the single-pole Green's functions have shown that the threshold of light absorption, refraction, reflection and transmission can be moved along frequencies, changing the film thickness. This can give a great contribution to practical ultrathin film engineering, especially to construction of drug delivery nanoparticles in nanomedicine.

Contemporary materials, Jan 10, 2021

In this paper, cotton, polyester and cotton/polyester fabrics were modified by using herbal extra... more In this paper, cotton, polyester and cotton/polyester fabrics were modified by using herbal extract of Picea omorika and copper ferrite nanoparticles and their antibacterial and dielectric properties were investigated. Antibacterial activities of all samples were examined against Escherichia coli and Staphylococcus aureus. Most of the fabrics modified by copper ferrite showed antibacterial activities against Escherichia coli, while the addition of the herbal extract improved their antibacterial protection. Dielectric properties were measured in frequency range from 24 Hz to 75 kHz at room temperature and the results showed that the modification of all three fabrics with copper ferrite caused increase in their electrical conductivity. The obtained results point to the possibility of using investigated fabrics for antibacterial protection as well as for the electromagnetic shielding application.

$Research paper thumbnail of Refractive Properties of Molecular Crystalline Superlattices$

Journal of Nonlinear Optical Physics & Materials, Sep 1, 2013

In this paper, we continue the theoretical study of changes in optical characteristics of superla... more In this paper, we continue the theoretical study of changes in optical characteristics of superlattices as a consequence of some specific behavior of excitons. Based on the particular dispersion law and the spectral distribution of excitons, we have formulated and calculated the refractive indices of these structures and defined how refractive indices change with external electromagnetic field. It was determined that among wide variety of parameters governing calculus, only two parameters have a significant effect on exciton energy spectra and calculated optical quantities: (a) the number of film layers which constitute superlattice; (b) ratio of the exciton energy transfer between the layers of one film and on the boundary between two different films.

Optical Materials, Sep 1, 2011

We study the dynamics of a single Frenkel exciton in a disordered molecular chain. The coherentpo... more We study the dynamics of a single Frenkel exciton in a disordered molecular chain. The coherentpotential approximation (CPA) is applied to the situation when the single-molecule excitation energies as well as the transition dipole moments, both their absolute values and orientations, are random. Such model is believed to be relevant for the description of the linear optical properties of one-dimensional J aggregates. We calculate the exciton density of states, the linear absorption spectra and the exciton coherence length which reveals itself in the linear optics. A detailed analysis of the low-disorder limit of the theory is presented. In particular, we derive asymptotic formulas relating the absorption linewidth and the exciton coherence length to the strength of disorder. Such expressions account simultaneously for all the above types of disorder and reduce to well-established form when no disorder in the transition dipoles is present. The theory is applied to the case of purely orientational disorder and is shown to agree well with exact numerical diagonalization.

Journal of Applied Polymer Science, Feb 16, 2011

ABSTRACT Electrical conductivities of low-density polyethylene (LDPE)–carbon black (CB) composite... more ABSTRACT Electrical conductivities of low-density polyethylene (LDPE)–carbon black (CB) composites were studied using high resistance meter at room temperature (DC conductivity) and dielectric spectroscopy (AC conductivity) in the frequency range between 90 kHz and 13 MHz and temperature range from 120 to 355 K. DC measurements revealed a percolation threshold at about 20 wt % of CB content, whereas AC measurements show two conductivity peaks at about 15% and 23% of CB content. The presence of two percolation thresholds was attributed to different dispersions of CB particles in structural inhomogeneities of LDPE. The experimental data were analyzed using the model of Efros and Shklovskii, which describes the critical behavior of a complex conductivity using critical indexes. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Journal of Macromolecular Science, Part B, Jan 6, 2023

ABSTRACT A microscopic theory of dielectric properties of symmetrical ultrathin molecular films, ... more ABSTRACT A microscopic theory of dielectric properties of symmetrical ultrathin molecular films, was formulated in bosonic and nearest-neighbor approximation. The dispersion law of harmonic exciton states were calculated using the method of two-time, temperature dependent Green's functions. It has been shown that two types of excitations can be occur: bulk and surface exciton states. Exciton spectral weights and space distribution along the direction of broken symmetry were analyzed as well. Calculating dynamical permittivity by the single-pole Green's functions it was shown that the threshold of light absorption can be moved along frequencies, changing the film thickness and the intensity of boundary perturbations. This can give a great contribution to practical ultrathin film engineering.

Contemporary Materials, 2019

Dielectric characterization of materials in the RF domain is usually carried out on samples with ... more Dielectric characterization of materials in the RF domain is usually carried out on samples with applied electroconductive electrodes. A high-quality contact between a sample and the measuring electrodes provides a stable current flow through the sample and information on the exact value of the electric field in which the sample is located. It also enables a simple measuring instrument to determine the dielectric parameters of the material being tested. However, the presence of contact potentials and the exchange of charge between the test material and the applied electrodes can mask some electrical phenomena in the material or significantly affect how we perceive these phenomena. In order to detect weak electrical processes in the material, for example the photoelectric response of non-polar polymers, contactless dielectric measurements must be carried out. The literature on non-contact dielectric measurements in the RF domain is poor, and because of that, this paper presents the m...

Contemporary Materials, 2016

We have investigated transport properties of higher acenes pentacene and hexacene and compared it... more We have investigated transport properties of higher acenes pentacene and hexacene and compared it with the transport properties of their BN analogues. Charge hopping from one structure to another was investigated through calculations of reorganization energies based on DFT and Marcus semiempiric approach, while the investigation of charge transport along the investigated structures was based on DFT calculations and non-equilibrium Green's function (NEGF) method. Attention was also paid to the energy separation between the lowest excited singlet (S1) and triplet (T1) state, which is quantity that is important for the field of thermally activated delayed fluorescence (TADF). The obtained results indicate that both groups of investigated structures have certain advantages and drawbacks. According to the reorganization energies and I-V characteristics, pentacene and hexacene have better properties, while from the aspect of TADF, BN analogues of pentacene and hexacene have better pro...

Surfaces and Interfaces, 2020

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Dyes and Pigments, 2017

The article describes the influence of humidity on the surface photodielectric properties of pape... more The article describes the influence of humidity on the surface photodielectric properties of papers prepared from poly(ethyleneimine)-TiO 2 nanoparticles-anthocyanin modified cellulose fibres. The anthocyanins were extracted from purple cabbage, beetroot , plum peel, red wine and red currant juice. The samples were conditioned to various relative humidities (from 9 to 100%) and illuminated with white visible light, l ! 405 nm. The poly(ethyleneimine)-TiO 2-anthocyanin modified samples showed similar photodielectric behaviour that can be clearly distinguished from the samples modified solely with poly(ethyleneimine)-TiO 2. Generally, an increase in humidity enhances the conductivity of the samples and induces an increase in the amount of photo-induced charge. Also, at higher humidities (above 80%), the samples with anthocyanin showed significantly higher values of photo-induced charges with respect to anthocyanin free samples. The presented results suggest that the presence of water molecules promotes electron-injection processes from the anthocyanin to the semiconductor surface.

Acta Physica Polonica A, 2010

This paper represents an overview about exciton systems in the molecular nanostructures (ultra th... more This paper represents an overview about exciton systems in the molecular nanostructures (ultra thin films and superlattices) and their implications on optical properties, primarily on absorption coefficient, which is given in the form of dielectric permittivity. With utilization of Green's function method, we have calculated dispersion law, spectral weight of exciton states and dielectric permittivity for every type of nanostructures. All obtained results are compared with optical properties in bulk crystals. Dielectric permittivity in all types of nanostructures shows very narrow and discrete dependence of external electromagnetic field frequency, which is a consequence of the expressed quantum effects, very thin thickness in these structures (or at least one dimension confinement) and boundary conditions.