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Polymer Nanoparticle Sizes from Dynamic Light Scattering and Size Exclusion Chromatography: The Case Study of Polysilanes.
Artem Badasyan, Andraž Mavrič, Irena Kralj Cigić, Tim Bencik, Matjaž Valant, 2018, izvirni znanstveni članek

Opis: Dynamic Light Scattering (DLS) and Size Exclusion Chromatography (SEC) are among the most popular methods for determining polymer sizes in solution. Taking dendritic and network polysilanes as a group of least soluble polymer substances, we critically compare and discuss the difference between nanoparticle sizes, obtained by DLS and SEC. Polymer nanoparticles are typically in poor solution conditions below the theta point and are in globular conformation therefore. Determination of particle sizes in presence of attractive interactions is not a trivial task. The only possibility to measure aggregation-free, a true molecular size of polymer nanoparticles in such regime of solution, is to operate with the dilute solution of globules (below theta point and above the miscibility line). Basing on results of our polysilane measurements, we come to a conclusion that DLS provides more reliable results than SEC for the dilute solution of globules. General implications for the size measurements of polymer nanoparticles in solutions are discussed.
Ključne besede: Polymer Nanoparticle, Dynamic Light Scattering, Size Exclusion Chromatography, Polysilanes
Objavljeno v RUNG: 16.05.2018; Ogledov: 4643; Prenosov: 16
.pdf Celotno besedilo (3,17 MB)

Unusual magnetodielectric effects in La2CuMnO6 induced by a dynamic crossover in dielectric relaxation at TC
Jasnamol Pezhumkattil Palakkal, Cheriyedath Raj Sankar, Ajeesh Parayancheri Paulose, Matjaž Valant, Artem Badasyan, Manoj Raama Varma, 2018, izvirni znanstveni članek

Opis: A series of fixed frequency dielectric measurements shows dielectric relaxation in La2CuMnO6, with a dynamic (Arrhenius to Arrhenius) crossover at TC. The external magnetic field alters the relaxation parameters in the vicinity of crossover and induces an unusual trend in the magnetodielectric coupling around TC. A large magnetodielectric coupling of 55% (at 68 K, 4 kHz) and 61% (at 105 K, 285.8 kHz) under a small magnetic field of 5 kOe is discovered. Presence of ferromagnetic short-range correlations above TC and a sign reversal of magnetoresistance around TC are observed. Specific heat analysis revealed the presence of ferromagnetic, variable range hopping active charge localized state. The presence of ferromagnetic short-range correlations and the influence of a core-grain dominated magnetoresistance on the Maxwell-Wagner interfacial polarization are responsible for the observed large magnetodielectric effect. Both the magnetic ordering and external magnetic field control the electric dipole relaxation in the material.
Ključne besede: Double perovskite Griffiths-like phase Dielectric Magnetoresistance Magnetodielectric
Objavljeno v RUNG: 03.01.2018; Ogledov: 4098; Prenosov: 0
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Artem Badasyan, Boštjan Mavrič, Matjaž Valant, objavljeni povzetek znanstvenega prispevka na konferenci

Opis: Conformations of polymer molecules in solution crucially depend on the sign of the effective potential energy of interaction between the monomers, also known as the quality of solvent. Therefore in “poor” solvent regime, when effective attraction overwhelms, the experimental measurements of polymer sizes are complicated by the agglomeration of macromolecules, followed by precipitation. This phenomenon, also known as spinodal decomposition, causes serious problems when the goal is to determine properties of individual macromolecules. Interestingly, while in the case of carbon-based polymers the precipitation-related problems can be easily avoided with dilution, this is not the case for polysilanes, i.e. polymeric chains on basis of silicon. Although the linear polysilanes were first synthesized in early 1920’s, the aggregationrelated problems have hampered their studies and applicability until recently. In the Materials Research Laboratory of University of Nova Gorica we have developed a technology to strengthen the scratch-resistance nanocoating for glass on the basis of polysilane dendritic polymers we synthesized. Through the prism of the Flory-Huggins theory, that provides a miscibility phase diagram in temperature-volume fraction variables, the quality of polymer solution can be manipulated by changing the temperature. Using Dynamic Light Scattering (DLS) and Differential Scanning Calorimetry (DSC) we have managed to show, that at temperatures in the range of 40- 50 C the deagglomeration of the dendritic polysilane takes place in tetrahydrofuran (THF) [1], and the system becomes a true molecular dispersion with particles 20 nm in size [2]. Introducing such molecular dispersion into the alumina precursor solution yields an amorphous nanocomposite stabilized by a high level of strain. This resulted in an extraordinary increase of hardness and scratch resistance of the alumina – polymer nanocomposite coating that can be used for glass protection [3].
Ključne besede: Polysilane, dendrimer, solubility
Objavljeno v RUNG: 12.09.2017; Ogledov: 4670; Prenosov: 0
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The electrochemical synthesis of dendritic polymethylsilane
Andraž Mavrič, Artem Badasyan, Gregor Mali, Matjaž Valant, 2017, objavljeni povzetek znanstvenega prispevka na konferenci

Ključne besede: electropolymerization, polysilane, dendrimer
Objavljeno v RUNG: 11.09.2017; Ogledov: 4533; Prenosov: 0
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Efficient de-agglomeration of polysilane macromolecules in solution and their molecular size
Andraž Mavrič, Artem Badasyan, Mattia Fanetti, Matjaž Valant, 2017, objavljeni povzetek znanstvenega prispevka na konferenci

Ključne besede: polysilane, solubility, de-agglomeration, dynamic light scattering
Objavljeno v RUNG: 03.07.2017; Ogledov: 4841; Prenosov: 0
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Growth mechanism and structure of electrochemically synthesized dendritic polymethylsilane molecules
Andraž Mavrič, Artem Badasyan, Gregor Mali, Matjaž Valant, 2017, izvirni znanstveni članek

Opis: 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.
Ključne besede: Polymethylsilane Dendritic polymer Electropolymerization
Objavljeno v RUNG: 20.03.2017; Ogledov: 4643; Prenosov: 14
.pdf Celotno besedilo (705,04 KB)

Physics behind the Conformational Transitions in Biopolymers. Demystification of DNA melting and Protein Folding
Artem Badasyan, predavanje na tuji univerzi

Opis: Biophysics is the area of research, devoted to the studies of physical problems related to living systems. Animal cell is the smallest unit of an organism and mainly contains water solutions of structurally inhomogeneous polymers of biological origin: polypeptides (proteins) and polynucleotides (DNA, RNA). Statistical physics of macromolecules allows to describe the conformations of both synthetic and bio-polymers and constitutes the basis of Biophysics. During the talk I will report on the biophysical problems I have solved with numerical simulations (Langevin-based Molecular Dynamics of Go-like protein folding model and Monte Carlo with Wang-Landau sampling) and analytical studies of spin models (formula evaluation by hand, enforced with computer algebra systems). The direct connections with the theory of phase transitions, algebra of non-commutative operators and decorated spin models will be elucidated.
Ključne besede: Biophysics, protein folding, helix-coil transition, spin models
Objavljeno v RUNG: 13.12.2016; Ogledov: 6153; Prenosov: 0
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