Papers by George Voyiatzis
Bulletin of the American Physical Society, Mar 22, 2011
Greece, G.A. VOYIATZIS, Institute of Chemical Engineering and High Temperature Chemical Processes... more Greece, G.A. VOYIATZIS, Institute of Chemical Engineering and High Temperature Chemical Processes, Patras, Greece -The structure of nanohybrid materials as well as the chain conformation under confinement is investigated in hydrophilic polymer / layered silicate nanocomposites. A series of PEO / sodium montmorilonite hybrids was synthesized utilizing melt intercalation with compositions covering the whole range from pure polymer to pure clay. Intercalated nanocomposites with mono-and bi-layers of PEO chains are obtained in all cases. The intercalated chains as well as the ones adsorbed on the outer surface of the clay particles remain purely amorphous; nevertheless, their conformations exhibit different characteristics from those of the amorphous bulk material with the intercalated PEO chains adopting preferably gauche conformations. It is only for compositions where a large amount of excess polymer exists outside the completely full galleries that the polymer crystallinity is recovered. Sponsored by NATO's Scientific Affairs Division, by the Greek GSRT and by the EU.
Polymers, Nov 16, 2022
Wood and wood-based products are extensively used in the building sector due to their interesting... more Wood and wood-based products are extensively used in the building sector due to their interesting combination of properties. Fire safety and fire spread, however, are of utmost concern for the protection of buildings. Therefore, in timber structures, wood must be treated with fireretardant materials in order to improve its reaction to fire. This article highlights the flame retardancy of novel hybrid organic-inorganic halogen-free coatings applied on plywood substrates. For this purpose, either a huntite-rich mineral (H5) or its modified nano-Mg (OH) 2 type form (H5-m), acting as an inorganic (nano) filler, was functionalized with reactive oligomers (ROs) and incorporated into a waterborne polymeric matrix. A water-soluble polymer (P (SSNa-co-GMAx)), combining its hydrophilic nature with functional epoxide groups, was used as the reactive oligomer in order to enhance the compatibility between the filler and the matrix. Among various coating compositions, the system composed of 13% polymeric matrix, 73% H5 and 14% ROs, which provided the best coating quality and flame retardancy, was selected for the coating of plywood on a larger scale in one or two layers. The results indicated that the novel plywood coating systems with the addition of ecological coating formulations (WF-13, WF-14 and WF-15), prepared at two layers, reached Euroclass B according to EN13501-1, which is the best possible for fire systems applied to wood.
Advanced device materials, Sep 18, 2017
The current work attempts to provide a proof of concept for the achievement of semi-quantitative ... more The current work attempts to provide a proof of concept for the achievement of semi-quantitative measurements by applying Surface Enhanced Raman Scattering (SERS) on thermally dewetted Au-films. In order to probe the anticipated advanced (device) material, Mitoxantrone (MTX) that exhibits strong SERS signal was utilized as a relevant prototype active molecular agent. The molecule was deposited on substrates of different morphology by spin coating and after evaluation of the collected SERS spectra it is shown that there is an almost linear correlation between the SERS intensity and the concentration of the SERS active molecule. In addition the enhancements achieved depend on the substrate's morphology.
Nanomaterials, Jul 15, 2022
In the current study, we propose a simple hydrothermal pathway to synthesize nanostructured Mg(OH... more In the current study, we propose a simple hydrothermal pathway to synthesize nanostructured Mg(OH) 2 after application of thermal decomposition followed by hydration of commercial minerals based on hydromagnesite and huntite. The synthesis of nano-materials is performed without the use of any catalyst. The effect of decomposition temperature on the hydrothermal synthesis of Mg(OH) 2 is extensively studied. It is shown that the morphology of resulting structures consists typically of particles ~200 nm in diameter and ~10 nm in thickness. Study of the structure at the molecular level designates the composition and supports the nano-sized characteristics of the produced materials. The associated thermal properties combined with the corresponding optical properties suggest that the material may be used as a flame retardant filler with enhanced transparency. In this concept, the flame retardancy of composite coatings containing the produced nano-sized Mg(OH) 2 was examined in terms of limiting oxygen index (LOI), i.e., the minimum concentration of oxygen that just supports flaming combustion.
Cellulose, May 11, 2023
The modification of cotton fabrics with water-soluble cationic copolymers for salt-free dyeing ap... more The modification of cotton fabrics with water-soluble cationic copolymers for salt-free dyeing applications with reactive dyes is explored in the present work. To this end, a family of bifunctional water-soluble cationic copolymers was designed through the chemical modification of poly(4-vinyl benzyl chloride), PVBC, with triethylamine, TEAM. These copolymers were applied onto cotton fabrics in aqueous alkaline solutions at moderate temperature (60 °C). The successful cotton modification was verified through the characterization of the modified samples with Raman and XPS spectroscopy. Moreover, a polymer coverage of the fabric of the order of 0.1%
Molecules, Jun 13, 2019
The goal of this work is to model the nature of the chemical species [CdCl 2 (extractant) 2 ] tha... more The goal of this work is to model the nature of the chemical species [CdCl 2 (extractant) 2 ] that are formed during the solvent (or liquid-liquid) extraction of the toxic cadmium(II) from chloride-containing aqueous media using hydrophobic 2-pyridyl ketoximes as extractants. Our coordination chemistry approach involves the study of the reactions between cadmium(II) chloride dihydrate and phenyl 2-pyridyl ketoxime (phpaoH) in water-containing acetone. The reactions have provided access to complexes [CdCl 2 (phpaoH) ); the solid-state structures of which have been determined by single-crystal X-ray crystallography. In both complexes, phpaoH behaves as an N,N'-bidentate chelating ligand. The complexes have been characterized by solid-state IR and Raman spectra, and by solution 1 H NMR spectra. The preparation and characterization of 1•H 2 O provide strong evidence for the existence of the species [CdCl 2 (extractant) 2 ] that have been proposed to be formed during the liquid-liquid extraction process of Cd(II), allowing the efficient transfer of the toxic metal ion from the aqueous phase into the organic phase. Keywords: cadmium(II); coordination chemistry; model studies for liquid-liquid extraction; phenyl 2-pyridyl ketoxime as ligand; 2-pyridyl ketoximes as cadmium(II) extractants; Raman spectra; single-crystal X-ray structures 2-pyridyl ketoximes (including 2PC12) have also been used for copper(II) extraction from chloride solutions .
Surfaces and Interfaces, Nov 1, 2022
Surface enhanced raman scattering (SERS) technique has been widely implemented for the detection/... more Surface enhanced raman scattering (SERS) technique has been widely implemented for the detection/quantification of numerous compounds. The development of reusable SERS substrates through regeneration is a constant concern of scientists in the field, related to the sustainability of the method. Cold atmospheric plasma (CAP) is an advantageous green method well-known for its effectiveness towards the successful degradation of organic molecules and materials' activation/modification. In the present study, we explored for the first time nanosecond pulsed dielectric barrier discharge (NSP-DBD) plasma as a rapid, energy efficient method for SERS solid substrates regeneration, implemented either directly in the gas or in the liquid phase as well as through immersion of the substrates in plasma activated water (PAW). We investigated the critical cold plasma factors (e.g. feeding gas, plasma treatment and retention time) in order to propose the most cost-effective alternative and shed light on the underlying regeneration mechanisms. The different SERS analysis case scenarios (analyte's class , concentration andcross check) were considered, in order to simulate real SERS measurements conditions/requirements. In practical terms, such an approach will contribute to a significant reduction of the detection costs, revealing the NSP-DBD process as a flexible, fast, green, effective and low-cost solution towards the SERS substrates regeneration.
Inorganic Chemistry, Mar 27, 2019
Bulletin of the American Physical Society, Feb 28, 2012
ANDRIKOPOULOS, S. FOTIADOU, Aristotle University of Thessaloniki, Greece, G.A. VOYIATZIS, Institu... more ANDRIKOPOULOS, S. FOTIADOU, Aristotle University of Thessaloniki, Greece, G.A. VOYIATZIS, Institute of Chemical Engineering & High Temperature Chemical Processes, Patras, Greece -The polymer chain conformation under confinement and the polymer morphology are investigated in hydrophilic PEO/Na + -montmorilonite nanohybrids synthesized by melt and/or solution intercalation. Intercalated hybrids with mono-and bi-layers of PEO chains are obtained for all compositions covering the complete range from pure polymer to pure clay. For low polymer concentrations, where all the polymer chains are intercalated, PEO is purely amorphous. As PEO concentration increases further, the polymer chains adsorbed on the outer surface of the clay particles remain amorphous as well. It is only when there is large amount of excess polymer outside the completely filled galleries that the bulk polymer crystallinity is abruptly recovered. The conformation of the confined or adsorbed polymer chains, as probed by Raman and FTIR spectroscopies, is found more disordered that the PEO melt even at higher temperatures; this is evident by the dramatic increase of the gauche conformations of the C-C bond along the chain backbone. Sponsored by the Greek GSRT (ΣY N EP ΓAΣIA; 09ΣY N -42 -580) and by the EU (CP-IP 246095-2).
Journal of Raman Spectroscopy, Dec 27, 2012
Surface-enhanced Raman scattering (SERS) spectroscopy can be used for the determination and quant... more Surface-enhanced Raman scattering (SERS) spectroscopy can be used for the determination and quantification of biologically representative atomic ions. In this work, the detection and quantification of chloride is demonstrated by monitoring the vibrational changes occurring at a specific interface (a Cl-sensitive dye) supported on a silver-coated silica microbead. The engineered particles play a key role in the detection, as they offer a stable substrate to support the dye, with a dense collection of SERS hot spots. These results open a new avenue toward the generation of microsensors for fast ultradetection and quantification of relevant ions inside living organisms such as cells. Additionally, the use of discrete particles rather than rough films, or other conventional SERS supports, will also enable a safe remote interrogation of highly toxic sources in environmental problems or biological fluids.
Sustainability
Though an important and chronic source of dyes released to the environment, the determination of ... more Though an important and chronic source of dyes released to the environment, the determination of the release of dyes that occurs during household or industrial washing is usually disregarded. The main scope of this study is to reveal the extent of dye release through washing, and to understand if the modification of cotton fabrics with cationic polymers could reduce it. Modified cotton fabrics, dyed with Acid Blue 281 (AB) or by a mixture of the reactive dyes Novacron Yellow S-3R (NY), Novacron Ruby S-3B (NR) and Novacron Dark Blue S-GL (NDB), underwent a certified washing process. The dyed fabrics were analyzed colorimetrically, while the washing waters were analyzed spectroscopically, via UV/Vis absorption and surface enhanced Raman scattering (SERS). In the modified fabrics dyed with the acid dye, an increased dye uptake was noticed that exhibited a color intensity of K/S~16, compared to K/S~0.45 of the unmodified fabrics. The corresponding normalized dye release (dye concentrati...
Cotton cationization with low molecular-weight/polymeric cationic modifiers allows the effective ... more Cotton cationization with low molecular-weight/polymeric cationic modifiers allows the effective dyeing of fabrics with reactive dyes under salt-free and more environmentally-friendly conditions. The current work focuses on the spectroscopic study of the intermolecular interactions, which dictate the physicochemical process associated with dyeing. Water-soluble copolymers of vinyl benzyl chloride and vinyl benzyl triethylammonium chloride (VBCTEAM) have been used as cellulose cationic modifiers. Dye uptake was assessed using Remazol Brilliant Blue and Novacron Ruby dyes. The study involves ATR-FTIR, UV-Vis, fluorescence and XPS spectroscopy. The results of binary polymer-rich dye-polymer aqueous solutions or dye-polymer precipitates at stoichiometric charge-ratio revealed that the sulfonate/sulfate anions of the dyes interact with the cationic VBCTEAM units of the polymer via electrostatic interactions. Moreover, the comparative study of unmodified/modified dyed cotton indicates tha...
Coatings
Flame-retardant polymeric coatings with high limiting oxygen index (LOI) were prepared by combini... more Flame-retardant polymeric coatings with high limiting oxygen index (LOI) were prepared by combining inorganic mineral huntite (H5) and polymeric additives synthesized in the present work into a polymeric formulation. In order to improve the dispersion of the Mg- (and Ca)-based H5 particles, additives containing phosphonium and acidic groups were employed to homogenize the inorganic fillers into the polymer matrix. Specific blend combinations of the commercial matrix Ecrovin® LV 340 eco with huntite and the additives poly(benzyltriphenylphosphonium-co-4-styrene sulfonic acid) P(SSH-co-SSBTPB60) and poly(hexadecyltributylphosphonium-co-4-styrene sulfonic acid) P(SSH-co-SSTBHDPB80), combining acidic and phosphonium groups, led to LOI values of 34.5% and 33.5%, respectively. The novel flame-retardant polymeric coatings inhibited the combustion of the coated wood substrates, which is attributed to the combination of acidic groups that promote the dispersion of inorganic filler in the pol...
The modification of cotton fabrics with water-soluble cationic copolymers for salt-free dyeing ap... more The modification of cotton fabrics with water-soluble cationic copolymers for salt-free dyeing applications with reactive dyes is explored in the present work. To this end, a family of bifunctional water-soluble cationic copolymers was designed through the chemical modification of poly(4-vinyl benzyl triethylammonium chloride), PVBC, with triethylamine, TEAM. These copolymers were applied onto cotton fabrics in aqueous alkaline solutions at moderate temperature (60oC). The successful cotton modification was verified through the characterization of the modified samples with Raman and XPS spectroscopy. Moreover, a polymer coverage of the fabric of the order of 0.1% (w/w) was estimated following the polymer exhaustion through UV-vis spectroscopy of the aqueous solutions used for the modification. The modification kinetics were followed through the evolution of the Raman spectra of the modified fabrics, the polymer exhaustion of the aqueous modification solutions and, indirectly, the dy...
Global NEST International Conference on Environmental Science & Technology
A mixed microbial culture (MMC) of poly-hydroxy-alkanoates (PHAs) producers was developed in a dr... more A mixed microbial culture (MMC) of poly-hydroxy-alkanoates (PHAs) producers was developed in a draw- fill reactor (DFR) subjected to sequential nitrogen/carbon limitation stress using short chain fatty acids (SCFAs) as carbon source. The distribution of microorganisms was analyzed in the beginning of the process and after six weeks of limitation, in order to verify the domination of PHA producers in the consortium. The potential of the enhanced MMC for production of co-polymers was then evaluated in batch mode using synthetic media. The parameters tested were the C to N ratio (C/N), the propionate to butyric ratio (prop/but) and the initial pH (pHin). It was shown that the type, yields and productivity of PHAs was highly affected and the optimal yield, 40 % PHAs/dry cell weigh (DCW) (w/w), was achieved for a C/N of 200 (w/w), prop/but 10/90 (mol/mol) and pHin, 7.5. The MMC was further assessed for the production of PHAs from acidified sugary wastewater (ASW) containing SCFAs, sugars...
International Journal of Molecular Sciences
Self-healing materials and self-healing mechanisms are two topics that have attracted huge scient... more Self-healing materials and self-healing mechanisms are two topics that have attracted huge scientific interest in recent decades. Macromolecular chemistry can provide appropriately tailored functional polymers with desired healing properties. Herein, we report the incorporation of glycidyl methacrylate-based (GMA) copolymers in waterborne polyurethanes (WPUs) and the study of their potential healing ability. Two types of copolymers were synthesized, namely the hydrophobic P(BA-co-GMAy) copolymers of GMA with n-butyl acrylate (BA) and the amphiphilic copolymers P(PEGMA-co-GMAy) of GMA with a poly(ethylene glycol) methyl ether methacrylate (PEGMA) macromonomer. We demonstrate that the blending of these types of copolymers with two WPUs leads to homogenous composites. While the addition of P(BA-co-GMAy) in the WPUs leads to amorphous materials, the addition of P(PEGMA-co-GMAy) copolymers leads to hybrid composite systems varying from amorphous to semi-crystalline, depending on copolyme...
Chemical Communications, 2021
An innovative, easy, fast, one-pot, completely wet-chemistry approach has been used for the synth... more An innovative, easy, fast, one-pot, completely wet-chemistry approach has been used for the synthesis and isolation of nanowires (NWs) of a spin-crossover iron(ii) complex.
Scientific Reports, 2021
The purpose of the present study was to analyze normal and degenerated menisci with Raman methodo... more The purpose of the present study was to analyze normal and degenerated menisci with Raman methodology on thin sections of formalin fixed paraffin embedding tissues and to correlate the Raman findings with the grade of meniscus degeneration. Menisci (n = 27) were removed from human knee joints after total knee replacement or meniscectomy. Following routine histopathological analysis to determine the grade of meniscal lesions obtained from healthy and degenerated formaline fixed paraffin embedded (FFPE) meniscal sections, Raman polarization approach was applied to evaluate the orientation of collagen fibrils in different levels of the same 5 μm thick FFPE meniscal tissue sections, used for histopathological assessment. We collected Raman spectra in two different polarization geometries, v-HH and v-VV, and calculated the mean value of the v-HH/v-VV intensity ratio of two Raman bands, sensitive and non-sensitive to the molecular orientation. The collagen specific amide I band at 1665 cm...
International journal of pharmaceutics, Jan 28, 2013
The purpose of this work was to assess the colloidal stability of novel milk-based formulations. ... more The purpose of this work was to assess the colloidal stability of novel milk-based formulations. Milk-based formulations were prepared in situ by adding into milk alkaline- or ethanolic-drug solutions containing an array of drugs namely; ketoprofen, tolfenamic acid, meloxicam, tenoxicam and nimesulide, mefenamic acid, cyclosporine A, danazol and clopidogrel besylate. The produced formulations were characterized by means of dynamic lightscattering, ζ-potential studies, atomic force microscopy, fluorescence spectroscopy, Raman spectroscopy complemented with ab initio calculations and stability studies. The presence of the drugs did not induce significant changes in most cases to the particle size and ζ-potential values of the emulsions pointing to the colloidal stability of these formulations. Raman spectroscopy studies revealed interactions of the drugs and the milk at the intermolecular level. Complementary analysis with ab initio calculations confirmed the experimental observations...
Journal of Physics: Condensed Matter, 2006
We report on an inelastic (Raman) light scattering study of the local structure of amorphous GeTe... more We report on an inelastic (Raman) light scattering study of the local structure of amorphous GeTe films. A detailed analysis of the temperature-reduced Raman spectra has shown that appreciable structural changes occur as a function of temperature. These changes involve modifications of atomic arrangements such as to facilitate the rapid amorphous-to-crystal transformation, which is the major advantage of phase-change materials used in optical data storage media. A particular structural model, supported by polarization analysis, is proposed being compatible with the experimental data as regards both the structure of a-GeTe and the crystallization transition. The remarkable difference between the Raman spectrum of the crystal and the glass can thus naturally be accounted for.
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Papers by George Voyiatzis