Sebastijan Kovačič

Inherently reactive polyHIPE material from dicyclopentadiene

A simple formulation of a stable high internal phase emulsion of dicyclopentadiene which is cured by using properly selected ring opening metathesis polymerization initiators yields highly porous monolithic materials with paramount mechanical properties and the possibility of easy functionalisation.

Ring opening metathesis polymerisation of emulsion templated dicyclopentadiene giving open porous materials with excellent mechanical properties

Surfactant stabilized emulsions of dicyclopentadiene and 50%, 60%, 70% or 80% of water were cured using ring opening metathesis polymerisation. All formulations gave open porous architectures featuring excellent mechanical properties which change upon oxidation.

On the mechanical properties of HIPE templated macroporous poly(dicyclopentadiene) prepared with low surfactant amounts

Reducing the surfactant amount below generally accepted values in polyHIPE chemistry allowed for distinctly improving the mechanical properties of ROMP derived HIPE templated poly(dicyclopentadiene) without compromising the open cellular structure of the scaffold rendering the preparation of a ductile polymer foam with 80% porosity and a Youngs modulus of 110 MPa possible.

The Use of an Emulsion Templated Microcellular Poly(dicyclopentadiene-co-norbornene) Membrane as a Separator in Lithium-Ion Batteries

The preparation of open-cell macroporous membranes made by the ring opening metathesis polymerization (ROMP) of a mixture of norbornene and dicyclopentadiene, and their basic applicability as separators in lithium-ion batteries, is discussed. Cyclic voltammetry (CV) measurements of negative electrodes (graphite) and positive electrodes (LiCoO2 ) are performed and the results prove the absence of parasitic decomposition reactions within the membrane at high oxidative or reductive potentials. Furthermore, LiCoO2 /Li half cell cycling studies of 100 charging/discharging cycles reveal that the newly disclosed separator and conventional commercial polyolefin based separators have similar performance. These results demonstrate that a potential weakness in the newly disclosed separator, namely residual double bonds present in the polymer network, does not limit the use of this material as a separator in lithium-ion batteries.

Macroporous ZnO foams by high internal phase emulsion technique: synthesis and catalytic activity.

Zinc(II) oxide nanoparticles were used for the stabilization of dicyclopentadiene (DCPD)-water-based high internal phase emulsions (HIPEs), which were subsequently cured using ring-opening metathesis polymerization (ROMP). The morphology of the resulting ZnO-pDCPD nanocomposite foams was investigated in correlation to the nanoparticle loading and nanoparticle surface chemistry. While hydrophilic ZnO nanoparticles were found to be unsuitable for stabilizing the HIPE, oleic acid coated, yet hydrophobic ZnO nanoparticles were effective HIPE stabilizers, yielding polymer foams with ZnO nanoparticles located predominately at their surface. These inorganic/organic hybrid foam-materials were subsequently calcined at 550 °C for 15 min to obtain inorganic macroporous ZnO foams with a morphology reminiscent to the original hybrid foam, and a specific surface area of 1.5 m(2) g(-1). Longer calcination time (550 °C, 15 h) resulted in a sea urchin like morphology of the ZnO foams, characterized by higher specific surface area of 5.5 m(2) g(-1). The latter foam type showed an appealing catalytic performance in the catalytic wet air oxidation (CWAO) process for the destruction of bisphenol A.

Macroporous poly(dicyclopentadiene) γFe2O3/Fe3O4 nanocomposite foams by high internal phase emulsion templating

The high internal phase emulsion (HIPE) templating approach to macroporous poly(dicyclopentadiene) γFe2O3/Fe3O4 nanocomposite foams via ring opening metathesis polymerisation was elaborated and the influence of the formulation of the HIPE on structural and mechanical properties of the magnetic composite foams of 80% nominal porosity was studied. HIPEs solely stabilized with the nanoparticles resulted in considerably shrunken monolithic specimens characterized by an open cellular morphology with cavities bigger than 265 μm. Nanoparticles were situated in the bulk and on the surface of the polymeric foam skeleton. Precise control over the feature sizes could not be obtained in this case. In contrast, HIPE formulations co-stabilized with a surfactant yielded samples of good casting quality characterized by a fully open cellular morphology in all cases. The cavity and the window size could be controlled by the amount of surfactant in the emulsion. A low surfactant loading of 1.5 v% with respect to the monomer yielded diameters of the cavities of the order of 20 μm interconnected with windows with diameters in the order of 4 μm, while 10 v% surfactant resulted in smaller cavities (10 μm) and windows (2 μm). All these feature sizes are hardly affected by the nanoparticle loading which was varied from 1 to 30 wt%. Surfactant stabilized and cured HIPEs featured the nanoparticles predominantly on the surface of the cavities. Mechanical properties of the composite foams were assessed by stress–strain tests and revealed a strengthening of the foams prepared with 10 v% surfactant upon addition of the nanoparticles. Indicative of the strengthening is an increase of the Youngs modulus from 13 ± 2 MPa in the case of a sample without nanoparticles to 104 ± 4 MPa in the case of the composite foam with 15 wt% nanoparticles. This trend was accompanied by a decrease of the elongation at break from 21 ± 4 to less than 1%. Specimens prepared with 1.5 v% surfactant are ductile and gave the same high Youngs modulus (104 ± 9 MPa) irrespective of the nanoparticle loading and became stronger upon raising the nanoparticle amount reaching an ultimate strength of 3.4 ± 0.4 MPa at an elongation at break of 13 ± 4%.

Synthesis of hydrogel polyHIPEs from functionalized glycidyl methacrylate

Highly porous hydrogels based on functionalized glycidyl methacrylate (GMA) have been successfully prepared through the high internal phase oil-in-water emulsions. Pre-polymerization functionalization of the GMA monomer, porous structure and water uptake of highly porous hydrogels were investigated. The primary amine groups of tris(2-aminoethyl)amine (TRIS) or 1,2-diaminoethane (EDA) were found to react in three distinct reactions with the GMA, giving a mixture of methacrylate and methacrylamide as the major products with a small amount of the aza-Michael addition product. Elemental analysis revealed nitrogen loadings of 5.3 and 4.6 mmol g−1 for the hydrogel polyHIPEs prepared from the pre-functionalized GMA with TRIS and EDA, respectively. The aminated p(GMA)-based hydrogel polyHIPEs had the densities of around 0.16 g cm−3, void diameters of around 5.5 μm, water uptake up to 15 g g−1 and the specific surface area up to 55 m2 g−1. The water uptake and the specific surface area were found to be between 4 and 5 times higher than the corresponding values for the conventional GMA-based polyHIPEs prepared from the water-in-oil HIPEs. These results demonstrate a highly efficient pre-polymerization functionalization method for the preparation of GMA-based hydrogel polyHIPEs.

Synthesis and Catalytic Performance of Hierarchically Porous MIL-100(Fe)@polyHIPE Hybrid Membranes.

Metal-organic frameworks (MOFs) nanoparticles in combination with a nonionic surfactant (Pluronic L-121) are used to stabilize dicyclopentadiene (DCPD)-in-water high internal phase emulsions (HIPEs). The resulting HIPEs containing the MIL-100(Fe) nanoparticles (MIL: Materials of Institut Lavoisier) at the interface between the oil- and the water-phases are then cured, and 100 μm thick, fully open, hierarchically porous hybrid membranes are obtained. The properties of the MIL-100(Fe)@pDCPD polyHIPE membranes are characterized and it is found that up to 14 wt% of the MIL-100(Fe) nanoparticles are incorporated in the hybrid material resulting in an increase of the microporosity up to 130 m(2) g(-1). Hybrid membranes show an appealing catalytic activity in Friedel-Crafts alkylation in a batch mode as well as in a flow-through mode, thereby demonstrating the preserved accessibility of Lewis acidic sites in the MOF nanostructures.

A facile strategy towards a highly accessible and hydrostable MOF-phase within hybrid polyHIPEs through in situ metal-oxide recrystallization

HKUST-1(Cu) and MOF-5(Zn)@polyHIPE hybrid materials were prepared using a metal salt-free technique, wherein metal–organic frameworks were in situ generated from the CuO- and ZnO-nanoparticles through secondary recrystallization. The solid-to-MOF transformation has proven to be a feasible and effective technique for preparing MOF@polyHIPE hybrid materials with a high MOF content of more than 75 wt%. The MOF phase within the hybrid polyHIPEs as disclosed herein exhibits superior micropore accessibility, structure hydrostability and durable CO2 adsorption capacity under humid conditions, not achievable with any of the previously reported methods.

The influence of Ce3+ ions on the corrosion rate of stainless steel in acidic solutions of different pH-values

The corrosion resistance of AISI 420 stainless steel in 0.1 mol L−1 H2SO4 + 0.1 mol L−1 Na2SO4 solutions at different pH-values and the inhibiting effect of Ce3+ ions was studied using electrochemical polarization methods. The results reveal decreasing of the corrosion rate with an increasing the pH of the solution, which demonstrates the progressive protective character of the inhibitor used. At pH lower than 3.33, the corrosion inhibition was most probably a result of the competitive adsorption of Ce3+ with H+ ions on the cathodic sites of the electrode surface, and it was found to be dependent on the relative concentration of H+/Ce3+. The peroxide generated from the oxygen reduction reaction at pH 3.33 was found to be capable oxidize trivalent cerium (Ce) to the tetravalent state. As obtained hydroxide precipitates act as diffusion barrier hindering the corrosion processes, whereafter a spontaneous passivity occurs on the steel surface at this pH.