Publications by authors named "Gregor Primc"

27 Publications

  • Page 1 of 1

Comparison of Plasma Deposition of Carbon Nanomaterials Using Various Polymer Materials as a Carbon Atom Source.

Nanomaterials (Basel) 2022 Jan 13;12(2). Epub 2022 Jan 13.

Department of Surface Engineering, Jozef Stefan Institute, Jamova cesta 39, 1000 Ljubljana, Slovenia.

Carbon nanowalls are promising materials for various electrochemical devices due to their chemical inertness, desirable electrical conductivity, and excellent surface-to-mass ratio. Standard techniques, often based on plasma-assisted deposition using gaseous precursors, enable the synthesis of top-quality carbon nanowalls, but require long deposition times which represents a serious obstacle for mass applications. Here, an alternative deposition technique is presented. The carbon nanowalls were synthesized on titanium substrates using various polymers as solid precursors. A solid precursor and the substrate were mounted into a low-pressure plasma reactor. Plasma was sustained by an inductively coupled radiofrequency discharge in the H-mode at the power of 500 W. Spontaneous growth of carbon nanomaterials was observed for a variety of polymer precursors. The best quality of carbon nanowalls was obtained using aliphatic polyolefins. The highest growth rate of a thin film of carbon nanowalls of about 200 nm/s was observed. The results were explained by different degradation mechanisms of polymers upon plasma treatment and the surface kinetics.
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http://dx.doi.org/10.3390/nano12020246DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8778974PMC
January 2022

Rapid Functionalization of Polytetrafluorethylene (PTFE) Surfaces with Nitrogen Functional Groups.

Polymers (Basel) 2021 Dec 9;13(24). Epub 2021 Dec 9.

Institute for Chemistry and Technology of Biobased Systems, Graz University of Technology, Stremayrgasse 9, 8010 Graz, Austria.

The biocompatibility of body implants made from polytetrafluoroethylene (PTFE) is inadequate; therefore, the surface should be grafted with biocompatible molecules. Because PTFE is an inert polymer, the adhesion of the biocompatible film may not be appropriate. Therefore, the PFTE surface should be modified to enable better adhesion, preferably by functionalization with amino groups. A two-step process for functionalization of PTFE surface is described. The first step employs inductively coupled hydrogen plasma in the H-mode and the second ammonia plasma. The evolution of functional groups upon treatment with ammonia plasma in different modes is presented. The surface is saturated with nitrogen groups within a second if ammonia plasma is sustained in the H-mode at the pressure of 35 Pa and forward power of 200 W. The nitrogen-rich surface film persists for several seconds, while prolonged treatment causes etching. The etching is suppressed but not eliminated using pulsed ammonia plasma at 35 Pa and 200 W. Ammonia plasma in the E-mode at the same pressure, but forward power of 25 W, causes more gradual functionalization and etching was not observed even at prolonged treatments up to 100 s. Detailed investigation of the XPS spectra enabled revealing the surface kinetics for all three cases.
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http://dx.doi.org/10.3390/polym13244301DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8708819PMC
December 2021

Contact transmission of SARS-CoV-2 on fomite surfaces: surface survival and risk reduction.

Interface Focus 2022 Feb 10;12(1):20210042. Epub 2021 Dec 10.

School of Energy Materials, Mahatma Gandhi University, Kerala 686560, India.

There is an unprecedented concern regarding the viral strain SARS-CoV-2 and especially its respiratory disease more commonly known as COVID-19. SARS-CoV-2 virus has the ability to survive on different surfaces for extended periods, ranging from days up to months. The new infectious properties of SARS-CoV-2 vary depending on the properties of fomite surfaces. In this review, we summarize the risk factors involved in the indirect transmission pathways of SARS-CoV-2 strains on fomite surfaces. The main mode of indirect transmission is the contamination of porous and non-porous inanimate surfaces such as textile surfaces that include clothes and most importantly personal protective equipment like personal protective equipment kits, masks, etc. In the second part of the review, we highlight materials and processes that can actively reduce the SARS-CoV-2 surface contamination pattern and the associated transmission routes. The review also focuses on some general methodologies for designing advanced and effective antiviral surfaces by physical and chemical modifications, viral inhibitors, etc.
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http://dx.doi.org/10.1098/rsfs.2021.0042DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8662391PMC
February 2022

Approaches to Inactivating Aflatoxins-A Review and Challenges.

Int J Mol Sci 2021 Dec 11;22(24). Epub 2021 Dec 11.

Department of Surface Engineering, Jozef Stefan Institute, Jamova Cesta 39, 1000 Ljubljana, Slovenia.

According to the World Health Organization, the contamination of crops with aflatoxins poses a significant economic burden, estimated to affect 25% of global food crops. In the event that the contaminated food is processed, aflatoxins enter the general food supply and can cause serious diseases. Aflatoxins are distributed unevenly in food or feedstock, making eradicating them both a scientific and a technological challenge. Cooking, freezing, or pressurizing have little effect on aflatoxins. While chemical methods degrade toxins on the surface of contaminated food, the destruction inside entails a slow process. Physical techniques, such as irradiation with ultraviolet photons, pulses of extensive white radiation, and gaseous plasma, are promising; yet, the exact mechanisms concerning how these techniques degrade aflatoxins require further study. Correlations between the efficiency of such degradation and the processing parameters used by various authors are presented in this review. The lack of appropriate guidance while interpreting the observed results is a huge scientific challenge.
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http://dx.doi.org/10.3390/ijms222413322DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8704553PMC
December 2021

Non-Equilibrium Plasma Methods for Tailoring Surface Properties of Polyvinylidene Fluoride: Review and Challenges.

Polymers (Basel) 2021 Dec 3;13(23). Epub 2021 Dec 3.

Institute for Chemistry and Technology of Biobased Systems, Graz University of Technology, 8010 Graz, Austria.

Modification and functionalization of polymer surface properties is desired in numerous applications, and a standard technique is a treatment with non-equilibrium gaseous plasma. Fluorinated polymers exhibit specific properties and are regarded as difficult to functionalize with polar functional groups. Plasma methods for functionalization of polyvinylidene fluoride (PVDF) are reviewed and different mechanisms involved in the surface modification are presented and explained by the interaction of various reactive species and far ultraviolet radiation. Most authors used argon plasma but reported various results. The discrepancy between the reported results is explained by peculiarities of the experimental systems and illustrated by three mechanisms. More versatile reaction mechanisms were reported by authors who used oxygen plasma for surface modification of PVDF, while plasma sustained in other gases was rarely used. The results reported by various authors are analyzed, and correlations are drawn where feasible. The processing parameters reported by different authors were the gas pressure and purity, the discharge configuration and power, while the surface finish was predominantly determined by X-ray photoelectron spectroscopy (XPS) and static water contact angle (WCA). A reasonably good correlation was found between the surface wettability as probed by WCA and the oxygen concentration as probed by XPS, but there is hardly any correlation between the discharge parameters and the wettability.
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http://dx.doi.org/10.3390/polym13234243DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8659518PMC
December 2021

Germination of L. Seeds after a Short Treatment with a Powerful RF Plasma.

Int J Mol Sci 2021 Jun 22;22(13). Epub 2021 Jun 22.

Jožef Stefan Institute, Jamova cesta 39, 1000 Ljubljana, Slovenia.

Seeds of common bean ( L.), of the Etna variety, were treated with low-pressure oxygen plasma sustained by an inductively coupled radiofrequency discharge in the H-mode for a few seconds. The high-intensity treatment improved seed health in regard to fungal contamination. Additionally, it increased the wettability of the bean seeds by altering surface chemistry, as established by X-ray photoelectron spectroscopy, and increasing surface roughness, as seen with a scanning electron microscope. The water contact angle at the seed surface dropped to immeasurably low values after a second of plasma treatment. Hydrophobic recovery within a month returned those values to no more than half of the original water contact angle, even for beans treated for the shortest time (0.5 s). Increased wettability resulted in accelerated water uptake. The treatment increased the bean radicle length, which is useful for seedling establishment in the field. These findings confirm that even a brief plasma treatment is a useful technique for the disinfection and stimulation of radicle growth. The technique is scalable to large systems due to the short treatment times.
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http://dx.doi.org/10.3390/ijms22136672DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8268350PMC
June 2021

Recent Advances in the Plasma-Assisted Synthesis of Zinc Oxide Nanoparticles.

Nanomaterials (Basel) 2021 Apr 30;11(5). Epub 2021 Apr 30.

Department of Textiles, Graphic Arts and Design, Faculty of Natural Sciences and Engineering, University of Ljubljana, Aškerčeva 12, 1000 Ljubljana, Slovenia.

An overview of recent work on the low-temperature plasma-assisted synthesis of zinc oxide (ZnO) nanoparticles is presented and interpreted in terms of gas-phase and surface reactions with illustrated examples. The thermodynamical nonequilibrium conditions allow the formation of chemically reactive species with a potential energy of several eV, which readily interact with the Zn precursors and initiate reactions leading to the formation of nanoparticles or nanowires. The high-quality nanowires were synthesized from Zn powders only upon interaction with moderately ionized plasma in a narrow range of plasma parameters. This technique is promising for the synthesis of large quantities of nanowires with aspect ratios well above 10, but the exact range of parameters remains to be determined. Apart from the ex situ techniques, the ZnO nanoparticles can be synthesized by depositing a film of precursors (often Zn salts or Zn-containing organometallic compounds) and exposing them to oxygen plasma. This technique is useful for the synthesis of well-adherent ZnO nanoparticles on heat-sensitive objects but requires further scientific validation as it often leads to the formation of a semicontinuous ZnO film rather than nanoparticles. Both low-pressure and atmospheric plasmas are useful in converting the precursor film into ZnO nanoparticles despite completely different mechanisms.
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http://dx.doi.org/10.3390/nano11051191DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8147133PMC
April 2021

One-Step Plasma Synthesis of Nitrogen-Doped Carbon Nanomesh.

Nanomaterials (Basel) 2021 Mar 25;11(4). Epub 2021 Mar 25.

Department of Surface Engineering, Jozef Stefan Institute, Jamova Cesta 39, 1000 Ljubljana, Slovenia.

A one-step method for plasma synthesis of nitrogen-doped carbon nanomesh is presented. The method involves a molten polymer, which is a source of carbon, and inductively coupled nitrogen plasma, which is a source of highly reactive nitrogen species. The method enables the deposition of the nanocarbon layer at a rate of almost 0.1 µm/s. The deposited nanocarbon is in the form of randomly oriented multilayer graphene nanosheets or nanoflakes with a thickness of several nm and an area of the order of 1000 nm. The concentration of chemically bonded nitrogen on the surface of the film increases with deposition time and saturates at approximately 15 at.%. Initially, the oxygen concentration is up to approximately 10 at.% but decreases with treatment time and finally saturates at approximately 2 at.%. Nitrogen is bonded in various configurations, including graphitic, pyridinic, and pyrrolic nitrogen.
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http://dx.doi.org/10.3390/nano11040837DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8064338PMC
March 2021

Inactivation of Pepper Mild Mottle Virus in Water by Cold Atmospheric Plasma.

Front Microbiol 2021 28;12:618209. Epub 2021 Jan 28.

Department of Biotechnology and Systems Biology, National Institute of Biology, Ljubljana, Slovenia.

Water scarcity is one of the greatest threats for human survival and quality of life, and this is increasingly contributing to the risk of human, animal and plant infections due to waterborne viruses. Viruses are transmitted through polluted water, where they can survive and cause infections even at low concentrations. Plant viruses from the genus are highly mechanically transmissible, and cause considerable damage to important crops, such as tomato. The release of infective tobamoviruses into environmental waters has been reported, with the consequent risk for arid regions, where these waters are used for irrigation. Virus inactivation in water is thus very important and cold atmospheric plasma (CAP) is emerging in this field as an efficient, safe, and sustainable alternative to classic waterborne virus inactivation methods. In the present study we evaluated CAP-mediated inactivation of pepper mild mottle virus (PMMoV) in water samples. PMMoV is a very resilient water-transmissible tobamovirus that can survive transit through the human digestive tract. The efficiency of PMMoV inactivation was characterized for infectivity and virion integrity, and at the genome level, using test plant infectivity assays, transmission electron microscopy, and molecular methods, respectively. Additionally, the safety of CAP treatment was determined by testing the cytotoxic and genotoxic properties of CAP-treated water on the HepG2 cell line. 5-min treatment with CAP was sufficient to inactivate PMMoV without introducing any cytotoxic or genotoxic effects in the cell model system. These data on inactivation of such stable waterborne virus, PMMoV, will encourage further examination of CAP as an alternative for treatment of potable and irrigation waters, and even for other water sources, with emphasis on inactivation of various viruses including enteric viruses.
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http://dx.doi.org/10.3389/fmicb.2021.618209DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7877120PMC
January 2021

Surface Modification of Polyamides by Gaseous Plasma-Review and Scientific Challenges.

Authors:
Gregor Primc

Polymers (Basel) 2020 Dec 17;12(12). Epub 2020 Dec 17.

Department of Surface Engineering, Jozef Stefan Institute, Jamova Cesta 39, 1000 Ljubljana, Slovenia.

A review of the most significant scientific achievements in the field of surface modification of polyamides by non-equilibrium plasma treatments is presented. Most authors employed atmospheric pressure discharges and reported improved wettability. The super-hydrophilic surface finish was only achieved using a low-pressure plasma reactor and prolonged treatment time, enabling both the nanostructuring and functionalization with polar functional groups. The average increase of the oxygen concentration as probed by XPS was about 10 at%, while the changes in nitrogen concentrations were marginal in almost all cases. The final static water contact angle decreased with the increasing treatment time, and the oxygen concentration decreased with the increasing discharge power. The need for plasma characterization for the interpretation of experimental results is stressed.
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http://dx.doi.org/10.3390/polym12123020DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7767179PMC
December 2020

Defluorination of Polytetrafluoroethylene Surface by Hydrogen Plasma.

Polymers (Basel) 2020 Nov 29;12(12). Epub 2020 Nov 29.

Institute of Chemistry and Technology of Biobased Systems, Graz University of Technology, Rechbauerstraße 12, 8010 Graz, Austria.

Defluorination of polytetrafluoroethylene (PTFE) surface film is a suitable technique for tailoring its surface properties. The influence of discharge parameters on the surface chemistry was investigated systematically using radio-frequency inductively coupled H plasma sustained in the E- and H-modes at various powers, pressures and treatment times. The surface finish was probed by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The measurements of water contact angles (WCA) showed increased wettability of the pristine PTFE; however, they did not reveal remarkable modification in the surface chemistry of the samples treated at various discharge parameters. By contrast, the combination of XPS and ToF-SIMS, however, revealed important differences in the surface chemistry between the E- and H-modes. A well-expressed minimum in the fluorine to carbon ratio F/C as low as 0.2 was observed at the treatment time as short as 1 s when plasma was in the H-mode. More gradual surface chemistry was observed when plasma was in the E-mode, and the minimal achievable F/C ratio was about 0.6. The results were explained by the synergistic effects of hydrogen atoms and vacuum ultraviolet radiation.
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http://dx.doi.org/10.3390/polym12122855DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7760809PMC
November 2020

A Review of Strategies for the Synthesis of N-Doped Graphene-Like Materials.

Nanomaterials (Basel) 2020 Nov 18;10(11). Epub 2020 Nov 18.

Department of Surface Engineering, Jozef Stefan Institute, Jamova cesta 39, 1000 Ljubljana, Slovenia.

Methods for synthesizing nitrogen-doped graphene-like materials have attracted significant attention among the scientific community because of the possible applications of such materials in electrochemical devices such as fuel cells, supercapacitors and batteries, as well as nanoelectronics and sensors. The aim of this paper is to review recent advances in this scientific niche. The most common synthesis technique is nitridization of as-deposited graphene or graphene-containing carbon mesh using a non-equilibrium gaseous plasma containing nitrogen or ammonia. A variety of chemical bonds have been observed, however, it is still a challenge how to ensure preferential formation of graphitic nitrogen, which is supposed to be the most favorable. The nitrogen concentration depends on the processing conditions and is typically few at.%; however, values below 1 and up to 20 at.% have been reported. Often, huge amounts of oxygen are found as well, however, its synergistic influence on N-doped graphene is not reported. The typical plasma treatment time is several minutes. The results reported by different authors are discussed, and future needs in this scientific field are summarized. Some aspects of the characterization of graphene samples with X-ray photoelectron spectroscopy and Raman spectroscopy are presented as well.
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http://dx.doi.org/10.3390/nano10112286DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7698902PMC
November 2020

Recent Advances in Surface Activation of Polytetrafluoroethylene (PTFE) by Gaseous Plasma Treatments.

Authors:
Gregor Primc

Polymers (Basel) 2020 Oct 7;12(10). Epub 2020 Oct 7.

Jozef Stefan Institute, Jamova cesta 39, 1000 Ljubljana, Slovenia.

Fluorinated polymers are renowned for their chemical inertness and thus poor wettability and adhesion of various coatings. Apart from chemical methods employing somewhat toxic primers, gaseous plasma treatment is a popular method for the modification of surface properties. Different authors have used different plasmas, and the resultant surface finish spans between super-hydrophobic and super-hydrophilic character. Some authors also reported the hydrophobic recovery. The review of recent papers is presented and discussed. Correlations between plasma and/or discharge parameters and the surface finish are drawn and the most important conclusions are summarized. The concentration of oxygen in the surface film as probed by X-ray photoelectron spectroscopy is inversely dependent on the concentration of oxygen in gaseous plasma. The predominant mechanism leading to hydrophilic surface finish is bond scission by deep ultraviolet radiation rather than functionalization with reactive oxygen species.
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http://dx.doi.org/10.3390/polym12102295DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7601227PMC
October 2020

Investigation of Surface Modification of Polystyrene by a Direct and Remote Atmospheric-Pressure Plasma Jet Treatment.

Materials (Basel) 2020 May 26;13(11). Epub 2020 May 26.

Department of Surface Engineering, Jozef Stefan Institute, 39, 1000 Ljubljana, Slovenia.

Localized functionalization of polymer surface with an atmospheric-pressure plasma jet was investigated at various treatment conditions. Polystyrene samples were treated with the plasma jet sustained in argon under direct or remote conditions. The two-dimensional evolution of surface wettability and the spot size of the treated area was determined systematically by measuring apparent water contact angles. Modification of surface chemistry and the formation of functional groups were investigated by X-ray photoelectron spectroscopy (XPS). The saturation of surface wettability and functional groups was observed even after a second of treatment providing the sample was placed close to the exhaust of the discharge tube. The spot diameter of the modified area increased logarithmically with increasing treatment time. However, it decreased linearly when increasing the distance. At the edge of the glowing plasma, however, the modification of surface properties was more gradual, so even 30 s of treatment caused marginal effects. With a further increase in the distance from the edge of the glowing plasma, however, there were no further treatment effects. The results are explained by significant axial as well as radial gradients of reactive species, in particular hydroxyl radicals.
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http://dx.doi.org/10.3390/ma13112435DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7321248PMC
May 2020

Cold Plasma, a New Hope in the Field of Virus Inactivation.

Trends Biotechnol 2020 11 17;38(11):1278-1291. Epub 2020 Apr 17.

Department of Biotechnology and Systems Biology, National Institute of Biology, Večna Pot 111, 1000 Ljubljana, Slovenia.

Viruses can infect all cell-based organisms, from bacteria to humans, animals, and plants. They are responsible for numerous cases of hospitalization, many deaths, and widespread crop destruction, all of which result in an enormous medical, economical, and biological burden. Each of the currently used decontamination methods has important drawbacks. Cold plasma (CP) has entered this field as a novel, efficient, and clean solution for virus inactivation. We present recent developments in this promising field of CP-mediated virus inactivation, and describe the applications and mechanisms of the inactivation. This is particularly relevant because viral pandemics, such as COVID-19, highlight the need for alternative virus inactivation methods to replace, complement, or upgrade existing procedures.
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http://dx.doi.org/10.1016/j.tibtech.2020.04.003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7164895PMC
November 2020

PECVD of Hexamethyldisiloxane Coatings Using Extremely Asymmetric Capacitive RF Discharge.

Materials (Basel) 2020 May 6;13(9). Epub 2020 May 6.

Department of Surface Engineering, Jozef Stefan Institute, Jamova cesta 39, 1000 Ljubljana, Slovenia.

An extremely asymmetric low-pressure discharge was used to study the composition of thin films prepared by PECVD using HMDSO as a precursor. The metallic chamber was grounded, while the powered electrode was connected to an RF generator. The ratio between the surface area of the powered and grounded electrode was about 0.03. Plasma and thin films were characterised by optical spectroscopy and XPS depth profiling, respectively. Dense luminous plasma expanded about 1 cm from the powered electrode while a visually uniform diffusing plasma of low luminosity occupied the entire volume of the discharge chamber. Experiments were performed at HMDSO partial pressure of 10 Pa and various oxygen partial pressures. At low discharge power and small oxygen concentration, a rather uniform film was deposited at different treatment times up to a minute. In these conditions, the film composition depended on both parameters. At high powers and oxygen partial pressures, the films exhibited rather unusual behaviour since the depletion of carbon was observed at prolonged deposition times. The results were explained by spontaneous changing of plasma parameters, which was in turn explained by the formation of dust in the gas phase and corresponding interaction of plasma radicals with dust particles.
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http://dx.doi.org/10.3390/ma13092147DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7254392PMC
May 2020

Evolution of the Surface Wettability of PET Polymer upon Treatment with an Atmospheric-Pressure Plasma Jet.

Polymers (Basel) 2020 Jan 3;12(1). Epub 2020 Jan 3.

Department of Surface Engineering, Jozef Stefan Institute, Jamova cesta 39, 1000 Ljubljana, Slovenia.

A useful technique for pre-treatment of polymers for improved biocompatibility is surface activation. A method for achieving optimal wettability at a minimal thermal load and unwanted modifications of the polymer properties is elaborated in this paper. Samples of polyethylene terephthalate polymer were exposed to an atmospheric-pressure plasma jet created by a high-impedance low-frequency discharge in wet argon. Different treatment times and distances from the end of the glowing discharge enabled detailed investigation of the evolution of surface activation. A rather fast saturation of the surface wettability over the area of the order of cm was observed upon direct treatment with the glowing discharge. At a distance of few mm from the glowing discharge, the activation was already two orders of magnitude lower. Further increase of the distance resulted in negligible surface effects. In the cases of a rapid activation, very sharp interphase between the activated and unaffected surface was observed and explained by peculiarities of high-impedance discharges sustained in argon with the presence of impurities of water vapor. Results obtained by X-ray photoelectron spectroscopy confirmed that the activation was a consequence of functionalization with oxygen functional groups.
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http://dx.doi.org/10.3390/polym12010087DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7023642PMC
January 2020

Effect of Oxygen Plasma on Sprout and Root Growth, Surface Morphology and Yield of Garlic.

Plants (Basel) 2019 Oct 30;8(11). Epub 2019 Oct 30.

Jozef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia.

Depending on the climate, garlic can be planted either in the fall or spring for a harvest in the summer, but spring planting might require the strengthening of the plant by external techniques. We have used low pressure, inductively coupled, radio frequency oxygen plasma for the treatment of peeled garlic cloves of a spring-planted Slovenian autochthonous cultivar. The aim of the study was to assess the effects of plasma treatment on garlic clove shoot and root growth and, ultimately, the yield. The roles of surface chemistry, surface morphology, and water uptake in these effects were also evaluated. The plasma treatment of cloves induced increases in water uptake. The increases were explained by changes in surface morphology that were determined by using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Nanostructured epicuticular wax structures appeared at the cuticle surface. The optimal treatment parameters accelerated root growth, but not shoot growth, in a laboratory setting. After growth in the field, the trends indicated that plant height and dried bulb mass increase, but the improvements were not statistically significant.
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http://dx.doi.org/10.3390/plants8110462DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6918151PMC
October 2019

Deposition Kinetics of Thin Silica-Like Coatings in a Large Plasma Reactor.

Materials (Basel) 2019 Oct 3;12(19). Epub 2019 Oct 3.

Department of Surface Engineering, Jozef Stefan Institute, Jamova cesta 39, 1000 Ljubljana, Slovenia.

An industrial size plasma reactor of 5 m volume was used to study the deposition of silica-like coatings by the plasma-enhanced chemical vapor deposition (PECVD) method. The plasma was sustained by an asymmetrical capacitively coupled radio-frequency discharge at a frequency of 40 kHz and power up to 7 kW. Hexamethyldisilioxane (HMDSO) was introduced continuously at different flows of up to 200 sccm upon pumping with a combination of roots and rotary pumps at an effective pumping speed between 25 and 70 L/s to enable suitable gas residence time in the plasma reactor. The deposition rate and ion density were measured continuously during the plasma process. Both parameters were almost perfectly constant with time, and the deposition rate increased linearly in the range of HMDSO flows from 25 to 160 sccm. The plasma density was of the order of 10 m, indicating an extremely low ionization fraction which decreased with increasing flow from approximately 2 × 10 to 6 × 10. The correlations between the processing parameters and the properties of deposited films are drawn and discussed.
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http://dx.doi.org/10.3390/ma12193238DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6803826PMC
October 2019

Synthesis of Vertically Oriented Graphene Sheets or Carbon Nanowalls-Review and Challenges.

Materials (Basel) 2019 Sep 12;12(18). Epub 2019 Sep 12.

Department of Surface Engineering, Jozef Stefan Institute, Jamova cesta 39, 1000 Ljubljana, Slovenia.

The paper presents a review on the current methods for deposition of vertically oriented multilayer graphene sheets (often called carbon nanowalls-CNWs) on solid substrates. Thin films of CNWs are among the most promising materials for future applications in capacitors, batteries, electrochemical devices, and photovoltaics, but their application is currently limited by slow deposition rates and difficulties in providing materials of a desired structure and morphology. The review paper analyzes results obtained by various groups and draws correlations between the reported experimental conditions and obtained results. Challenges in this scientific field are presented and technological problems stressed. The key scientific challenge is providing the growth rate as well as morphological and structural properties of CNWs thin films versus plasma parameters, in particular versus the fluxes of reactive plasma species onto the substrate surface. The technological challenge is upgrading of deposition techniques to large surfaces and fast deposition rates, and development of a system for deposition of CNWs in the continuous mode.
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http://dx.doi.org/10.3390/ma12182968DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6766222PMC
September 2019

Cold Atmospheric Plasma as a Novel Method for Inactivation of Potato Virus Y in Water Samples.

Food Environ Virol 2019 09 29;11(3):220-228. Epub 2019 Apr 29.

Department of Biotechnology and Systems Biology, National Institute of Biology, Večna pot 111, 1000, Ljubljana, Slovenia.

While one of the biggest problems we are facing today is water scarcity, enormous quantities of water are still being used in irrigation. If contaminated, this water can act as an effective pathway for the spread of disease-causing agents, like viruses. Here, we present a novel, environmentally friendly method known as cold atmospheric plasma for inactivation of viruses in water used in closed irrigation systems. We measured the plasma-mediated viral RNA degradation as well as the plasma-induced loss of viral infectivity using potato virus Y as a model virus due to its confirmed water transmissibility and economic as well as biological importance. We showed that only 1 min of plasma treatment is sufficient for successful inactivation of viruses in water samples with either high or low organic background. The plasma-mediated inactivation was efficient even at markedly higher virus concentrations than those expected in irrigation waters. Obtained results point to reactive oxygen species as the main mode of viral inactivation. Our laboratory-scale experiments confirm for the first time that plasma has an excellent potential as the eukaryotic virus inactivation tool for water sources and could thus provide a cost-effective solution for irrigation mediated plant virus transmission. The outstanding inactivation efficiency demonstrated by plasma treatments in water samples offers further expansions of its application to other water sources such as reused wastewater or contaminated drinking waters, as well as other plant, animal, and human waterborne viruses, ultimately leading to the prevention of water scarcity and numerous human, animal, and plant infections worldwide.
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http://dx.doi.org/10.1007/s12560-019-09388-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6689025PMC
September 2019

Surface Functionalization of Polyethylene Granules by Treatment with Low-Pressure Air Plasma.

Materials (Basel) 2018 May 25;11(6). Epub 2018 May 25.

Faculty of Mechanical Engineering, Department of Materials Engineering, Center of Advanced Aerospace Technology, Czech Technical University in Prague, Karlovo náměstí 13, 121 35 Praha 2, Czech Republic.

Polyethylene granules of diameter 2 mm were treated with a low-pressure weakly ionized air plasma created in a metallic chamber by a pulsed microwave discharge of pulse duration 180 μs and duty cycle 70%. Optical emission spectroscopy showed rich bands of neutral nitrogen molecules and weak O-atom transitions, but the emission from N atoms was below the detection limit. The density of O atoms in the plasma above the samples was measured with a cobalt catalytic probe and exhibited a broad peak at the pressure of 80 Pa, where it was about 2.3 × 10 m. The samples were characterized by X-ray photoelectron spectroscopy. Survey spectra showed oxygen on the surface, while the nitrogen concentration remained below the detection limit for all conditions. The high-resolution C1s peaks revealed formation of various functional groups rather independently from treatment parameters. The results were explained by extensive dissociation of oxygen molecules in the gaseous plasma and negligible flux of N atoms on the polymer surface.
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http://dx.doi.org/10.3390/ma11060885DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6025483PMC
May 2018

Increase of electrodeposited catalyst stability via plasma grown vertically oriented graphene nanoparticle movement restriction.

Chem Commun (Camb) 2017 Aug;53(67):9340-9343

Universiteitsplein 1, 2610 Wilrijk, Belgium.

Beside activity, electrocatalyst stability is gaining in importance. The most common degradation mechanism is the loss of the active surface area due to nanoparticle growth via coalescence/agglomeration. We propose a particle confinement strategy via vertically oriented graphene deposition to overcome degradation of the nanoparticles.
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http://dx.doi.org/10.1039/c7cc05828dDOI Listing
August 2017

Microplasma Induced Cell Morphological Changes and Apoptosis of Ex Vivo Cultured Human Anterior Lens Epithelial Cells - Relevance to Capsular Opacification.

PLoS One 2016 10;11(11):e0165883. Epub 2016 Nov 10.

Department of Surface Engineering and Optoelectronics (F4), Jožef Stefan Institute, Ljubljana, Slovenia.

Inducing selective or targeted cell apoptosis without affecting large number of neighbouring cells remains a challenge. A plausible method for treatment of posterior capsular opacification (PCO) due to remaining lens epithelial cells (LECs) by reactive chemistry induced by localized single electrode microplasma discharge at top of a needle-like glass electrode with spot size ~3 μm is hereby presented. The focused and highly-localized atmospheric pressure microplasma jet with electrode discharge could induce a dose-dependent apoptosis in selected and targeted individual LECs, which could be confirmed by real-time monitoring of the morphological and structural changes at cellular level. Direct cell treatment with microplasma inside the medium appeared more effective in inducing apoptosis (caspase 8 positivity and DNA fragmentation) at a highly targeted cell level compared to treatment on top of the medium (indirect treatment). Our results show that single cell specific micropipette plasma can be used to selectively induce demise in LECs which remain in the capsular bag after cataract surgery and thus prevent their migration (CXCR4 positivity) to the posterior lens capsule and PCO formation.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0165883PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5104483PMC
June 2017

Degradation of Albumin on Plasma-Treated Polystyrene by Soft X-ray Exposure.

Polymers (Basel) 2016 Jun 24;8(7). Epub 2016 Jun 24.

Synchrotron-SOLEIL & Université Paris-Saclay, Saint-Aubin, BP48, Gif sur Yvette Cedex F91192, France.

Thin films of human serum albumin (HSA) were immobilized on polystyrene (PS) substrates previously functionalized either with polar or nonpolar functional groups. The functionalization was performed by treatment with cold gaseous plasma created in pure oxygen and tetrafluoromethane (CF₄) plasmas, respectively. Samples were examined with soft X-rays in the photon energy range of 520 to 710 eV in the ANTARES beam line at SOLEIL Synchrotron. NEXAFS spectra of O K-edge and F K-edge were collected at different spots of the sample, and measurements at each spot were repeated many times. A strong degradation of the HSA protein was observed. The weakly irradiated samples exhibited strong absorption at 531.5 eV associated with the O 1s→π* transitions, and a broad non distinctive peak at 540 eV was attributed to the O 1s→σ* transitions. Both peaks decreased with increasing irradiation time until they were completely replaced by a broad non-distinctive peak at around 532 eV, indicating the destruction of the original protein conformation. The shortage of the amide groups indicated breakage of the peptide bonds.
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http://dx.doi.org/10.3390/polym8070244DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6431894PMC
June 2016

Rapid Hydrophilization of Model Polyurethane/Urea (PURPEG) Polymer Scaffolds Using Oxygen Plasma Treatment.

Polymers (Basel) 2016 Apr 15;8(4). Epub 2016 Apr 15.

Jozef Stefan Institute, Jamova cesta 39, 1000 Ljubljana, Slovenia.

Polyurethane/urea copolymers based on poly(ethylene glycol) (PURPEG) were exposed to weakly ionized, highly reactive low-pressure oxygen plasma to improve their sorption kinetics. The plasma was sustained with an inductively coupled radiofrequency generator operating at various power levels in either E-mode (up to the forward power of 300 W) or H-mode (above 500 W). The treatments that used H-mode caused nearly instant thermal degradation of the polymer samples. The density of the charged particles in E-mode was on the order of 10 m, which prevented material destruction upon plasma treatment, but the density of neutral O-atoms in the ground state was on the order of 10 m. The evolution of plasma characteristics during sample treatment in E-mode was determined by optical emission spectroscopy; surface modifications were determined by water adsorption kinetics and X-ray photoelectron spectroscopy; and etching intensity was determined by residual gas analysis. The results showed moderate surface functionalization with hydroxyl and carboxyl/ester groups, weak etching at a rate of several nm/s, rather slow activation down to a water contact angle of 30° and an ability to rapidly absorb water.
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http://dx.doi.org/10.3390/polym8040144DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6431927PMC
April 2016

Effect of H₂S Plasma Treatment on the Surface Modification of a Polyethylene Terephthalate Surface.

Materials (Basel) 2016 Feb 5;9(2). Epub 2016 Feb 5.

Department of surface engineering, Jozef Stefan Institute, Jamova 39, Ljubljana 1000, Slovenia.

H₂S plasma created by an electrode-less radio-frequency discharge was used to modify the surface properties of the polymer polyethylene terephthalate. X-ray photoelectron spectroscopy, secondary ion mass spectrometry and atomic force microscopy were used to determine the evolution of the surface functionalities and morphology. A very thin film of chemically bonded sulfur formed on the surface within the first 10 s of treatment, whereas treatment for more than 20 s caused deposition of higher quantities of unbonded sulfur. The sulfur concentration reached a maximum of between 40 and 80 s of plasma treatment; at longer treatment times, the unbonded sulfur vanished, indicating instability of the deposited sulfur layer. Large differences in the surface morphology were observed.
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http://dx.doi.org/10.3390/ma9020095DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5456499PMC
February 2016
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