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Sebastijan Kovačič, 2011, dissertation

Abstract: A new class of polyHIPE materials has been prepared using high internal phase emulsions (HIPEs) with monomers in both phases. Resulting materials, namely hybrid polyHIPE materials, are obtained consisting of hydrophobic matrix (consisted of styrene cross-linked with DVB or dicyclopentadiene) filled with hydrophilic polymer gel (polyacrylic acid or polyNIPAM) and exhibit morphology changes according to pH and temperature of the surrounding medium. Our focus with regards to the production of hybrid polyHIPE materials was the responsiveness of such materials used for flow control. This property is beneficial for controlling the flow of the solution through the monolithic polymers. Furthermore, polyHIPE materials have also been prepared by using ring opening metathesis polymerisation of monomers, such as dicyclopentadiene and norbornene. Obtained materials have Young’s moduli in the range of hundred times higher than standard polyHIPE materials with the same level of porosity which represents a very important improvement in the development of highly porous cellular polymeric materials.
Keywords: emulsions, high internal phase emulsions, polymers, polyHIPEs, hybrid, hybrid polyHIPE materials, ROMP, flow-through, styrene, DVB, acrylic acid, NIPAM
Published: 04.05.2011; Views: 2269; Downloads: 203
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Evaluation of thermal and mechanical filler gas influence on honeycomb structures behaviour
Matej Vesenjak, Andreas Öchsner, Zoran Ren, 2007, original scientific article

Abstract: In this paper the behavior of hexagonal honeycombs under dynamic in-plane loading is described. Additionally, the presence and influence of the filler gas inside the honeycomb cells is considered. Such structures are subjected to very large deformation during an impact, where the filler gas might strongly affect their behavior and the capability of deformational energy absorption, especially at very low relative densities. The purpose of this research was therefore to evaluate the influence of filler gas on the macroscopic cellular structure behavior under dynamic uniaxial loading conditions by means of computational simulations. The LS-DYNA code has been used for this purpose, where a fully coupled interaction between the honeycomb structure and the filler gas was simulated. Different relative densities, initial pore pressures and strain rates have been considered. The computational results clearly show the influence of the filler gas on the macroscopic behavior of analyzed honeycomb structures. Because of very large deformation of the cellular structure, the gas inside the cells is also enormously compressed which results in very high gas temperatures and contributes to increased crash energy absorption capability. The evaluated results are valuable for further research considering also the heat transfer in honeycomb structures and for investigations of variation of the base material mechanical properties due to increased gas temperatures under impact loading conditions.
Keywords: mechanics, cellular materials, honeycomb structure, gas filler, thermal properties, mechanical properties, dynamic loading, LS-DYNA, computational simulations
Published: 31.05.2012; Views: 1025; Downloads: 19
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The synthesis of iron-nickel alloy nanoparticles using a reverse micelle technique
Irena Ban, Mihael Drofenik, Darko Makovec, 2006, original scientific article

Abstract: Nanosized Fe0.2Ni0.8 particles were prepared by reducing their salts with sodium borohydride (NaBH4) in cationic water-in-oil (w/o) microemulsions of water/cetyl-trimethyl-amonium bromide (CTAB) and n-butanol/isooctane at 25 °C.According to the TEM and X-ray diffraction analyses, the synthesized particles were around 4-12 nm in size. Due to their nanodimensions, the particles had a primitive cubic (pc) structure rather than the body-centered cubic (BCC) structure of the bulk material. An examination of the synthesis from the reverse micelle reveals that the morphology of the iron-nickel alloy nanoparticles depends mainly on the microemulsion`s composition. The magnetization of the nanoparticles was much lower than that of the bulk material, reflecting the influence of the nanodimensions on the particlesć magnetizations.
Keywords: magnetic materials, nickel/iron alloys, nanoparticles, synthesis, microemulsions, magnetic properties, reverse micelles
Published: 31.05.2012; Views: 1196; Downloads: 64
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Highly porous open-cellular monoliths from 2-hydroxyethyl methacrylate based high internal phase emulsions (HIPEs) : preparation and void size tuning
Sebastijan Kovačič, Dejan Štefanec, Peter Krajnc, 2007, original scientific article

Abstract: Preparation of highly porous (up to 80% pore volume) open-cellular monolithic cross-linked polymers from 2-hydroxyethyl methacrylate is reported. Oil-in-water and water-in-oil high internal phase emulsions are applied as porosity templates, resulting in an interconnected porous structure with void diameters between 550 nm and 18 m. Significantly larger voids were obtained inthe case of oil-in-water emulsions (between 5 and 18 m) as opposed to water in oil emulsions (approx 600 nm). Controlled coarsening exploiting limited kinetical stability of emulsions was used to obtain monoliths with larger voids, diameters being enlarged 3-fold.
Keywords: organic chemistry, polymerization, monolithic polymers, HIPE, emulsions, porous materials, methacrylates
Published: 31.05.2012; Views: 1333; Downloads: 41
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Behaviour of cellular materials under impact loading
Matej Vesenjak, Zoran Ren, Andreas Öchsner, 2008, original scientific article

Abstract: The paper describes experimental and computational testing of regular open-cell cellular structures behaviour under impact loading. Open-cell cellular specimens made of aluminium alloy and polymer were experimentally tested under quasi-static and dynamic compressive loading in order to evaluate the failure conditions and the strain rate sensitivity. Additionally, specimens with viscous fillers have been tested to determine the increase of the energy absorption due to filler effects. The tests have shown that brittle behaviour of the cellular structure due to sudden rupture of intercellular walls observed in quasi-static and dynamic tests is reduced by introduction of viscous filler, while at the same time the energy absorption is increased. The influence of fluid filler on open-cell cellular material behaviour under impact loading was further investigated with parametric computational simulations, where fully coupled interaction between the base material and the pore filler was considered. The explicit nonlinear finite element code LS-DYNA was used for this purpose. Different failure criteria were evaluated to simulate the collapsing of intercellular walls and the failure mechanism of cellular structures in general. The new computational models and presented procedures enable determination of the optimal geometric and material parameters of cellular materials with viscous fillers for individual application demands. For example, the cellular structure stiffness and impact energy absorption through controlled deformation can be easily adapted to improve the efficiency of crash absorbers.
Keywords: mechanics, porous materials, cellular materials, impact loading, mechanical testing, fluid-structure interaction, failure mechanism
Published: 31.05.2012; Views: 1000; Downloads: 44
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Characterization of open-cell cellular material structures with pore fillers
Matej Vesenjak, Andreas Öchsner, Zoran Ren, 2008, original scientific article

Abstract: Due to their mechanical properties, cellular material structures are often used in automotive, aerospace, ship and railway industries, as elements for deformational energy absorption. New advanced cellular material structures have been evaluated and characterised in the scope of this study in order to determine their energy absorption capability through the deformation process. Parametric computational simulations in the framework of the finite element method have been used for this purpose. Newly developed computational models of regular open-cell cellular material structures considering viscous pore fillers have been developed and their response under impact conditions was analysed using the explicit code LS-DYNA. The results of the performed study show that introduction of viscous fillers indeed increases the energy absorption capability of open-cellular material structures. Additionally, it was determined that the size of the cellular material (number of cells) dramatically influences the cellular structure response and that the filler influence is stronger in cellular structures with higher relative density.
Keywords: cellular materials, computer simulation, deformation, mechanical properties
Published: 31.05.2012; Views: 921; Downloads: 49
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Zeta potential determination of polymeric materials using two differently designed measuring cells of an electrokinetic analyzer
Hermina Bukšek, Thomas Luxbacher, Irena Petrinić, 2010, original scientific article

Abstract: The so-called zeta potential can be determined through electrokinetic measurements and indicates the status regarding surface charges along the interface between solids and liquids. Surface charge gives us information about the condition, quality, and characteristics of a macroscopic surface in the polar medium. In our study the zeta potential was determined using a 'SurPASS' electrokinetic analyzer based on the streaming current and streaming potential measurements. The aim of the research was to compare the results of two differently designed measuring cells ('Adjustable Gap Cell' and 'Clamping Cell') but operating on the same principle. In order to investigate this problem, the zeta potential was determined for the three polymeric materials: poly(ethylene terephthalate) foil, thin-film polyamide composite membranes for nanofiltration and reverse osmosis. The results obtained with 'Clamping Cell' versus 'Adjustable Gap Cell' showed differences in zeta potential, where the 'Adjustable Gap Cell' gave more reproducible results. One reason for this behaviour could be the different geometries of the streaming channels. A more likely reason is the design of the 'Clamping Cell', that requires a sample size larger than necessary for zeta potential determination.
Keywords: electrical double layer, zeta potential, electrokinetic analyser, streaming current potential, polymeric materials
Published: 31.05.2012; Views: 902; Downloads: 65
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Use of AFM force spectroscopy for assessment of polymer response to conditions similar to the wound, during healing
Uroš Maver, Tina Maver, Andrej Žnidaršič, Zdenka Peršin, Miran Gaberšček, Karin Stana-Kleinschek, 2011, original scientific article

Abstract: Force spectroscopy is a very promising technique for the evaluation of interactions within different environments. Knowledge about them is especially important during the design and preparation of those modern wound dressings in contact with a changing wound-environment over a prolonged time. Such exposure can cause a drastic decrease in the materialćs mechanical performance, and can lead to degradation, thus lowering the success of any healing process. Our study tries to establish a model system, which would enable us to assess the applicability of the mentioned technique for the evaluation of any interaction changes between polymer molecules and a chosen surface, after exposure to different environments. Our proposed experimental setup consists of two representative polymers, a model silicon surface, and two solutions of various pHs and ionic strengths, respectively. Within the chosen range of parameters, we are confident that we can prove the usefulness of force spectroscopy for further research into polymer suitability, for the development of novel wound dressings.
Keywords: force spectroscopy, AFM, wound dressings, polymer materials, model system
Published: 01.06.2012; Views: 1083; Downloads: 51
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