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Characterization of bitumen oils
Andraž Mavrič, Matjaž Valant, final research report

Found in: osebi
Keywords: izolacija, bitumen, termična analiza
Published: 14.09.2016; Views: 3319; Downloads: 0
.pdf Fulltext (1,34 MB)

Amorphous nanocomposite of polycarbosilanes and aluminum oxide
Andraž Mavrič, 2018, doctoral dissertation

Abstract: This work presents a paradigm for high temperature stabilization of bulk amorphous aluminium oxide. The thermodynamic stabilization is achieved by preparing a nanocomposite, where polymethylsilane dendritic molecules are dispersed in an aluminium hydroxide gel. Upon heat-treatment the gel transforms to the amorphous aluminium oxide that is stable up to 900°C. The dispersion of the macromolecules and their covalent bonding to the alumina matrix induce homogeneously distributed strain fields that keep the alumina amorphous. The first part of the thesis focuses on the synthesis, characterization and solubility properties of the dendritic polymethylsilane. The polymethylsilane is synthetized by electrochemical polymerization from trichloromethylsilane monomer. The polymerization mechanism, involving a single polymerization pathway, is identified. The polymer growth proceeds through reduction of the monomers to the silyl anions and their addition to the growing polymer. The solubility of three chemically related but topologically different polysilanes (linear, dendritic and network) were studied by dynamic light scattering. At room temperature the agglomerates in a range from 500 to 1300 nm are present. They undergo de-agglomeration at slightly elevated temperatures of around 40°C. The de-agglomeration results in formation of stable solutions, where a hydrodynamic diameter of the individual polymer molecules was measured to be in a range from 20 to 40 nm. The obtained diameters of two dendritic polymethylsilane macromolecules, synthesized under different electrolysis conditions, are much larger than the theoretical size estimated for an ideal dendrimer. We determined by 29Si NMR that the reason for this is in a large number of branching irregularities (defects) contained in the molecular structure. Combining the experimental values obtained by DLS and density measurements with a structural model that considers the branching irregularities, it is shown that the inclusion of the defects allows the dendritic polymer to exceed the sterical limitations and form the hyperbranched dendritic structure. The final size depends on a relative amount of the branching defects. In the second part, the synthetized polymethylsilane molecules were successfully used for the nanocomposite formation. The aluminium hydroxide gel with the dispersed polymethylsilane molecules was prepared as a precursor. Upon heat-treatment it gives the amorphous aluminium oxide stable up to 900°C. The dispersed macromolecules induce homogeneously distributed strain fields that keep the aluminium oxide amorphous during the thermal treatment the dispersed macromolecules covalently bind to the matrix, inducing the interface strain. The amorphous state was confirmed by the presence of penta-coordinated aluminium detected by 27Al NMR and a low bandgap measured by UV-vis absorption spectroscopy.
Found in: osebi
Keywords: amorphous aluminium oxide, polymethylsilane, nanocomposite, electropolymerization, solubility, agglomeration, de-agglomeration, dendrimer, hyperbranched dendritic structure, dynamic light scattering, thermal analysis, transmission electron microscopy, scanning electron microscopy, X-ray diffraction, infrared spectroscopy, UV-Vis spectroscopy
Published: 19.07.2018; Views: 4264; Downloads: 167
.pdf Fulltext (5,07 MB)

Deposition of porphyrin thin films by electrophoresis
Matjaž Valant, Changzhu Wu, Mads Nybo Sørensen, Tina Škorjanc, Andraž Mavrič, 2022, published scientific conference contribution abstract

Abstract: Porphyrins are heterocyclic macrocycles consisting of interconnected pyrrole subunits acting as ligands for metal ions. Metallised metalloporphyrins naturally occur as cofactors in a series of enzymes, acting as active sites for biochemical transformations. Mimicking nature, a variety of functionalized porphyrins have been prepared for different catalytic purposes [1]. These organometallic complexes have isolated metal centers in tailored coordination environments to drive catalytic reactions in homogeneous solutions. The activity and selectivity of isolated metal ions acting as single-atom catalysts are defined by the coordination environment. Depending on the porphyrin structure, the solubility of these macrocycles and their processability in solutions can be altered. While such adjustments to the structure might ease the processability, the catalytic properties might also be altered. Because homogenous catalysis presents challenges with the separation and recyclability of the catalyst, it is common to fix metalloporphyrins into molecular organic frameworks or deposit them onto a substrate. Commonly used deposition techniques face several challenges. For instance, thermal evaporation can cause partial or complete degradation of some thermally-labile functional groups attached to the porphyrins. Similarly, spin coating commonly results in an uneven thickness and uneven morphology of the deposited films. To overcome these difficulties, we present an alternative method for the deposition of porphyrin thin films that is suitable for a wide range of functionalized porphyrins. The electrophoresis can force the molecules to deposit on a conductive substrate such as a metal foil or transparent conductive oxide by applying the electric field generated by a DC power supply. The film thickness can be precisely controlled by changing the voltage value, deposition time, or solution concentration using even a small amount of material [2, 3]. Six different functionalized porphyrin molecules have been successfully deposited onto the copper foil substrate by optimizing key parameters, including applied electric field, the duration of electrophoresis, the size of the copper electrodes, and solvent polarity. To demonstrate the generality of our approach, we have selected a broad range of porphyrins that incorporate the following functional groups: phenyl rings, carboxylic acids, pyridyl rings, methyl benzyl ethers, methyl benzoyl esters, and cobalt (II) metalized macrocycle. The impact of this study extends above catalysis to various applications of porphyrins thin films on conductive substrates such as optoelectronics and sensors.
Found in: osebi
Keywords: porphyrin, thin film, electrophoresis
Published: 26.09.2022; Views: 22; Downloads: 0
.pdf Fulltext (27,64 MB)

Temperature induced de-agglomeration of the polysilane macromolecules
Matjaž Valant, Mattia Fanetti, Artem Badasyan, Andraž Mavrič, 2016, published scientific conference contribution abstract

Found in: osebi
Keywords: polysilane, de-agglomeration, dynamic light scattering, differential scanning calorimetry
Published: 05.10.2016; Views: 3886; Downloads: 0
.pdf Fulltext (73,71 KB)

Growth mechanism and structure of electrochemically synthesized dendritic polymethylsilane molecules
Matjaž Valant, Gregor Mali, Artem Badasyan, Andraž Mavrič, 2017, original scientific article

Abstract: The study of an electrochemical synthesis of polymethylsilane from trifunctional trichloro- methylsilane monomers identified a single polymerization pathway involving reduction of the monomer to silyl anions and their addition to the growing polymer. The sizes of the synthesized macromolecules, measured with dynamic light scattering, are much larger than the theoretical size estimated for an ideal dendrimer. The reason for this, found by NMR analysis, is in a large number of branching irregularities (defects) contained in the molecular structure, which can be described as a hyperbranched dendritic polymer. Theoretical estimates of sizes for an ideal dendrimer were corrected assuming a branching defect is a cavity with the volume of one monomer. Appropriateness of the theoretical and experimental models was confirmed with a good quantitative agreement between the experimental densities and the theoretically calculated values.
Found in: osebi
Keywords: Polymethylsilane Dendritic polymer Electropolymerization
Published: 20.03.2017; Views: 3369; Downloads: 0
.pdf Fulltext (705,04 KB)

Efficient de-agglomeration of polysilane macromolecules in solution and their molecular size
Matjaž Valant, Mattia Fanetti, Artem Badasyan, Andraž Mavrič, 2017, published scientific conference contribution abstract

Found in: osebi
Keywords: polysilane, solubility, de-agglomeration, dynamic light scattering
Published: 03.07.2017; Views: 3403; Downloads: 0
.pdf Fulltext (1,81 MB)

The electrochemical synthesis of dendritic polymethylsilane
Matjaž Valant, Gregor Mali, Artem Badasyan, Andraž Mavrič, 2017, published scientific conference contribution abstract

Found in: osebi
Keywords: electropolymerization, polysilane, dendrimer
Published: 11.09.2017; Views: 3210; Downloads: 0
.pdf Fulltext (152,81 KB)

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