REVITALISATION OF RUINS AND THE IMPACT ON CONSERVATION POLICIES IN SLOVENIA. CASE STUDY OF THE CARTHUSIAN MONASTERY AT ŽIČE, SLOVENIAMateja Golež
, 2019, doktorska disertacija
Opis: The doctoral dissertation in question presents in detail the issue of protecting architectural heritage as ruins on the example of the Žiče Charterhouse complex in Slovenia. The author based her work on the history of conservation, internationally applicable charters related to architectural heritage protection and on examples taken from international conservation practice.
Although the Slovenian conservation profession, as an independent technical and scientific discipline, received its formal legal status through the emergence of independent Slovenia merely a couple of decades ago, it is possible to claim that Slovenia, with its first academically qualified conservation specialists Avguštin Stegenšek and France Stele, was in contact with active policy on heritage protection as early as before World War I, when the Slovenian territory was part of the Austro-Hungarian Empire, and also after the War, when the territory was annexed to the Kingdom of Yugoslavia. Despite long-standing efforts, Slovenians did not achieve the legal protection of architectural heritage until early 1980s, when an independent act on the protection of natural and cultural heritage was adopted in former Yugoslavia. Because of this, the tasks carried out by conservation specialists until that time primarily focused on documenting heritage and carrying out the most pressing maintenance works.
Since all major international charters related to cultural heritage protection were signed when Slovenia was part of former Yugoslavia and after it became independent, it is not possible to claim that the profession did not follow the international legal order in this field. This is why it is sometimes difficult to understand the large gap between international technical criteria and the conservation decisions made by Slovenian conservation experts when performing intervention works on structures or sites of cultural value in Slovenia. To improve this condition, it is therefore vital that buildings be treated comprehensively prior to interventions, including in terms of carrying out natural science and technical research studies that provide an insight into the materials, structural frame and building physics of a building, as shown in the doctoral dissertation on the example of the ruin of the Church of St. John the Baptist at Žiče Charterhouse. Only by carefully analysing historic materials, it is possible to make the right decision on the use of adequate substitute materials for the needs of maintaining a ruin and, only on the basis of preliminary research made into structural frames, it will be possible to monitor the vitality of ruins in future, whereby using state-of-the-art research methods from conservation science. Since the Church of St. John the Baptist has lost its original intended use and also the possibility to get it back, the author of the dissertation proposes that the structure not be reconstructed, since this would imply a major deviation from original architecture, with a shortage of adequate documentation that would provide a basis for credible reconstruction. For this reason, the author of the doctoral dissertation defends the position that the Church be protected as a ruin.
The operator of the monastery complex and the entire valley of St. John, where the remains of the lower and upper monastic houses of the Žiče Charterhouse are located, now faces quite a challenging task. It will have to prepare a management plan that will foresee expert bases for sustainable use of natural and cultural values of this site and a suitable development policy, whereby giving the key role to the local community.
Ključne besede: ruins, architectural history, legislation, international charters, revitalization, natural science research, Žiče monastery
Objavljeno: 22.01.2019; Ogledov: 16; Prenosov: 2
Polno besedilo (12,67 MB)
HAS EVOLUTION BEEN INTERRUPTED IN THE AFRICAN OIKOS?Tokunbo Laotan-Brown
, 2019, doktorska disertacija
Opis: In essence, a qualitative study revealing what the inhabitants reflect as a deep and personal relationship with and within the region, which contributes significantly to their sense of emotional security and self identity. This includes a strong conservation-orientated attitude with regard to the natural rural character of a clan, tribe or unbounded region using linguistic families, especially in the inner core. It acknowledges the journey though time of the dwellers, changes in requirements in a natural way. The principle behind this thesis is to identify the regional, cultural and environmental demands of where and how a fractal spatial function can be observed as well as how a community can be organised to maintain and preserve its culture in a natural way.
Thus, responding to specific characteristics of the local environment and climatic conditions. This lifelong interaction between the cognitive and physical realms has existed overtime. During the evolution of values inhabitants adapted form and materials to the conditions of nature; working with natural forms and climatic cycles rather than considering forces as obstacles to overcome has hermeneutic and practical values; used by intentional makers. The cultural identity in the inhabitant made the home, and then the process of home-making ‘made’ the inhabitant; a reciprocal reward. This will include their connection to the culture, region and environment while proposing a self-organizational solution. The future of conserving African tangible and intangible values, need to take lessons from the past into the future through present resolutions while documenting what maybe an interrupted progression.
To achieve the above, I modified an approach using cultural fractal organizational approach as a basis for defining; 1) The structure of research framework
using computer simulations and thus establishing linkages between space, region and
communal activities. 2) Using African linguistic families (Niger-Congo: Yoruba), as a
distinct way of documenting within the context of co-existing social and discursive practices.
3) By generating a background in ethnographic and sensory archaeological data on Yoruba
regional cities, focusing on the fractal structure of settlements in relation to the social activities that take place in and around them.
Ključne besede: Fractals, Self Similarity, Conservation, Self Organizational Approach, Cultural Heritage, Spatial Patterns, IFA, Oikos, Cultural Landscapes, Yoruba Cities, Circularity.
Objavljeno: 18.01.2019; Ogledov: 33; Prenosov: 1
Polno besedilo (24,92 MB)
Groundwater distribution in the recharge area of Ljubljanica springsMatej Blatnik
, 2019, doktorska disertacija
Opis: Porečje Ljubljanice je s svojo kraško hidrologijo že stoletja predmet proučevanja. V začetku 19. stoletja so bila dela v največji meri posvečena preprečevanju ali vsaj omilitvi poplav na Planinskem polju. Obsežne raziskave v 70. letih 20. stoletja so na območju porečja Ljubljanice razkrile okvirne poti toka podzemne vode. Bolj natančno proučevanje vodonosnika z ugotavljanjem dimenzij in razporeditve kanalov ter dinamike pretakanja pa do zdaj ni bilo izvedeno. Nove speleološke raziskave in razvoj samodejnih merilnikov ponujajo možnost postavitve kakovostne merilne mreže tudi na težje dostopnih mestih. Namen pričujočega dela je zato nadgraditi poznavanje dinamike podzemne vode na območju porečja Ljubljanice z uporabo naprednih tehnik merjenja in interpretacij.
Območje proučevanja je omejeno na severni del porečja Ljubljanice, in sicer med Planinskim poljem na jugu in izviri Ljubljanice na severu. Na tem območju je bila vzpostavljena merilna mreža s samodejnimi meritvami višine, temperature in specifične električne prevodnosti vode. Meritve so potekale na štirih požiralnikih na Planinskem polju, na treh izvirih Ljubljanice in osmih jamah z dostopom do podzemne vode. Poleg tega so bile opravljene še številne ročne meritve, na Agenciji RS za okolje (ARSO) pa so bili pridobljeni hidrološki in meteorološki podatki iz uradnih postaj.
Na novo pridobljeni podatki so bili obravnavani glede na dotedanje znanje o vodonosniku. Mnoge pretekle ugotovitve so bile potrjene, številne interpretacije pa so bile zgrajene na novo. Te so bile povečini navezane na obliko vodonosnika (razporeditve in dimenzije kanalov) in njihov vpliv na nihanje vodne gladine, kar je bilo v nadaljevanju preverjeno z izgradnjo poenostavljenih konceptualnih in numeričnih modelov. Slednji so bili zgrajeni v programu EPA SWMM (Storm Water Management Model).
V 3,5 letnem obdobju meritev je bilo veliko dogodkov s povišanim vodostajem, med njimi prek 15 takih, ko je bilo Planinsko polje poplavljeno. Dogodki so se med seboj zelo razlikovali tako po intenzivnosti kot tudi po trajanju, kar je predstavljalo raznovrstno zbirko podatkov. Najdaljši poplavni dogodek je trajal okoli tri mesece, v tem času pa se je vodna gladina v proučevanem vodonosniku dvignila do 66 m.
Raziskave so potrdile pretekle ugotovitve, da se tok vode v vodonosniku prepleta (cepi in ponovno združuje) in da voda prek severnih požiralnikov Planinskega polja povečini teče proti zahodnim izvirom Ljubljanice, voda z vzhodnih požiralnikov Planinskega polja pa povečini proti vzhodnim izvirom Ljubljanice. Ugotovitve so pokazale tudi to, da na vzhodne izvire Ljubljanice pomembno vpliva tudi neposreden tok s Cerkniškega polja, kar se odraža zlasti s temperaturnimi odstopanji.
Analiza višin podzemne vode je omogočila nove interpretacije o obliki kraškega vodonosnika. Na skoraj vseh merilnih mestih se je pokazalo obdobno upočasnjeno dviganje in spuščanje vode, kar nakazuje na prisotnost prelivnih kanalov. Takšni kanali so bili v nekaterih jamah že predhodno poznani (npr. Šerkov rov v Gradišnici, Skalni rov v Logarčku, Levi rov v Lijaku v Najdeni jami), medtem ko so v nekaterih jamah le predvideni (Veliko brezno v Grudnovi dolini, Andrejevo brezno 1).
Obsežna merilna mreža, večletno obdobje meritev, stalne in samodejne meritve, uporaba naprednih tehnik interpretacij in preverjanje z modeli so omogočili raznovrstne analize in številne ugotovitve. Postopek se je izkazal kot primeren in bi bil uporaben tudi v drugih podobnih vodonosnikih.
Podobno kot pretekle raziskave pa tudi ta pušča številna odprta vprašanja in možnosti za nadaljnje raziskave. Smiselne bi bile nadaljnje in bolj podrobne raziskave vpliva geoloških struktur, raziskave freatičnih in globokih regionalnih tokov, proučevanje vodne bilance in kakovosti vode, in nenazadnje tudi v splošnem boljše razumevanje poplavljanja Planinskega polja.
Ključne besede: kraški vodonosnik, dinamika podzemne vode, poplavljanje, modeliranje, Planinsko polje, Ljubljanica
Objavljeno: 16.01.2019; Ogledov: 53; Prenosov: 4
Polno besedilo (21,14 MB)
Correlations between photocatalytic activity and chemical structure of Cu-modified TiO2-SiO2 nanoparticle compositesT. Čižmar
, doktorska disertacija
Opis: The objective of this dissertation was to examine how copper modification can improve the photocatalytic activity of TiO2-SiO2 and to explain the correlation between Cu concentration and chemical state of Cu cations in the TiO2-SiO2 matrix, as well as the photocatalytic activity under the UV/solar irradiation.
The Cu-modified TiO2-SiO2 photocatalysts were prepared by a low temperature sol-gel method based on organic copper, silicon and titanium precursors with varied Cu concentrations (from 0.05 to 3 mol%). The sol-gels were dried at 150 °C to obtain the photocatalysts in the powder form. To test thermal stability, additional set of photocatalysts was obtained by calcinating dried samples in air at 500 °C for 1 h.
The photocatalytic activity was determined by a fluorescence-based method of terephthalic acid decomposition. Up to three times increase in photocatalytic activity of air-dried samples is obtained when TiO2-SiO2 matrix is modified with Cu in a narrow concentration range from 0.05 to 0.1 mol%. At higher Cu loadings the photocatalytic activity of Cu-modified photocatalyst is smaller than in the unmodified reference TiO2-SiO2 photocatalyst. Calcined samples showed significantly reduced photocatalytic activity compared to air-dried samples.
XRD analysis showed that all Cu-modified TiO2-SiO2 nanocomposites with different Cu concentrations have the same crystalline structure as unmodified TiO2-SiO2 nanocomposites (air-dried or calcined). The addition of Cu does not change the relative ratio between the anatase and brookite phase or unit cell parameters of the two TiO2 crystalline structures. TEM analysis showed that the addition of Cu does not change the morphology of TiO2-SiO2 catalyst dried at 150 °C.
The Cu K-edge XANES and EXAFS analysis were used to determine valence state and local structure of Cu cations in Cu-modified TiO2-SiO2 photocatalyst. The results elucidate the mechanism responsible for the improved or hindered photocatalytic activity. In the air-dried samples with low Cu content, which exhibit largest activity, Cu-O-Ti connections are formed, suggesting that the activity enhancement is due to Cu(II) cations attachment on the surface of the photocatalytically active TiO2 nanoparticles, so Cu(II) cations may act as free electron traps, reducing the intensity of recombination between electrons and holes at the TiO2 photocatalyst’s surface. At higher Cu loadings no additional Cu-O-Ti connections are formed, instead only Cu-O-Cu connections are established, indicating the formation of amorphous or nanocrystalline Cu(II) oxide, which hinders the photocatalytic activity of TiO2. Calcination of Cu-modified TiO2-SiO2 photocatalysts at 500 °C induces significant structural changes: Cu-O-Ti connections are lost, Cu partially incorporates into the SiO2 matrix and amorphous copper oxides, which again reduce the photocatalytic activity of the material, are formed.
Ključne besede: titanium dioxide, Cu-modified TiO2-SiO2 photocatalyst, photocatalytic activity, Cu K-edge XANES, EXAFS.
Objavljeno: 17.12.2018; Ogledov: 72; Prenosov: 3
Polno besedilo (3,05 MB)
ACCESSIBILITY AS A NON-PREJUDICIAL APPROACH: IS CULTURE BACK TO NORMALITY?Ilaria Bollati
, 2018, doktorska disertacija
Opis: This research explores the general and actual accessibility to cultural spaces and organizations, focusing on the network of relationships between contents, innovation, and participation. It investigates how Culture can be perceived as a normal experience, actually able to set a rich dialogue with each of us, normal ordinary people/consumers. Normality means inclusion and sharing. The proposed investigation is based on a triad of interactions among culture, economics, and design.
Assuming that Culture generates its value from a cognitive approach, or from a dynamic and context-dependent value chain that is subject to a cognitive evolution, this research acknowledges that the cultural experience is subject to a double issue of access:
- The horizontal question is related to complications associated with the structure. Believing that ‘culture is special’ implies the risk of progressively widening the gap between cultural supply and society. Culture is ‘locked’ in specific sites and a big slice of the world’s adult population has yet to be involved in any cultural experience.
- Once physically inside the cultural structure, the vertical issue is generated by the difficulty in entering in contact with the offered contents. This research focuses only on museums and multimedia exhibitions in which the learning process has changed: the research presents itself as a conversation where both ‘those who know’ and ‘those who learn’ play equally active parts in a relative process of understanding.
Starting from the existing processes, forms, previous studies and case studies, the survey yearns for their systematization in innovative models. The process, from theory to practice and vice versa, goes beyond a traditional mechanism of deduction: it moves from specific contexts to the abstraction of replicable approaches.
The question of how the narration emerges guides you toward a new method of analysis, study, and cataloguing; a schematization capable of investigating not only knowledge, but also the visitor's ‘cognitive metabolism’ (how knowledge is acquired) during the multimedia experience; an innovative multipurpose tool, useful for both the museum institution and the designer.
The research finally assesses and takes into account an actual experiment, the outcomes of which may prove to be useful in feeding theoretical implications with empirical experiences: RovelloDue - Piccolo Spazio Politecnico, a temporary multimedia space.
Ključne besede: audience development, cognitive accessibility, cultural addiction, culture, human, emotion, immersion, innovation, interactive exhibitions, participation, natural interfaces, normality, technologies
Objavljeno: 13.12.2018; Ogledov: 59; Prenosov: 3
Polno besedilo (45,89 MB)
STUDY OF ATMOSPHERIC AEROSOL PROPERTIES IN THE VIPAVA VALLEYLonglong Wang
, doktorska disertacija
Opis: The aim of the dissertation was to study aerosol loading distributions and properties over the Vipava valley, a representative hot-spot for complex mixtures of different aerosol types of both anthropogenic and natural origin.
An infrared Mie and a two-wavelength polarization Raman lidar systems
were used as main detection tools. The polarization Raman lidar, which
provides the capability to extract the extinction coefficient, backscatter coefficients, depolarization ratio, backscatter Ångström exponent, lidar ratio and
water vapor mixing ratio profiles, was itself designed, built and calibrated as
a part of this thesis. Lidar data, combined with in-situ measurements, was
used to determine detailed information on different aerosol types. Vertical
profiles of aerosol mass concentration were extracted from the Mie lidar data
taken in April 2016, where the in-situ measurements of aerosol size distribution and number concentration as well as aerosol absorption coefficient and black carbon mass concentration were used to estimate the mass extinction efficiency (MEE). Aerosol morphology and chemical composition determined by SEM-EDX on sampled particles were used for the identification
of primary aerosol types. Two cases with different atmospheric conditions
(long range mineral dust transport and local biomass burning) and different
expected the dominant presence of specific aerosol types (mineral dust and
soot) were investigated in more detail. They revealed significantly different
aerosol properties and distributions within the valley, affecting radiative heat
A more detailed investigation of aerosol properties throughout the troposphere in different atmospheric conditions was made possible by the two-wavelength polarization Raman lidar system, deployed in Ajdovščina (town
of Vipava valley) from September 2017. Using its aerosol identification capabilities, based on particle depolarization ratio and lidar ratio measurements,
it was possible to identify predominant aerosol types in the observed atmospheric structures, for example in different atmospheric layers in the case of
the stratified atmosphere. Primary anthropogenic aerosols within the valley were found to be mainly emitted from two sources: individual domestic
heating systems, which mostly use biomass fuel and traffic. Natural aerosols,
transported over large distances, such as mineral dust and sea salt, were observed both above and entering into the planetary boundary layer. Backscatter contribution of each aerosol type was separated and the corresponding
extinction contribution was derived from lidar observations.
Ključne besede: Vipava valley, aerosol distribution, aerosol characterization, lidar
remote sensing, in-situ measurements, aerosol loading.
Objavljeno: 23.10.2018; Ogledov: 255; Prenosov: 10
Polno besedilo (29,39 MB)
PHOTO-EXCITATION ENERGY INFLUENCE ON THE PHOTOCONDUCTIVITY OF ORGANIC SEMICONDUCTORSNadiia Pastukhova
, 2018, doktorska disertacija
Opis: In this work, we experimentally studied the influence of photoexcitation energy
influence on the charge transport in organic semiconductors. Organic semiconductors
were small molecules like corannulene, perylene and pentacene derivatives, polymers
such as polythiophene and benzothiophene derivatives, and graphene, along with
combinations of these materials in heterojunctions or composites.
The first part of this study is focused on the photoexcitation energy influence on
the transient photoconductivity of non-crystalline curved π-conjugated corannulene
layers. The enhanced photoconductivity, in the energy range where optical absorption
is absent, is deduced from theoretical predictions of corannulene gas-phase excited
state spectra. Theoretical analysis reveals a consistent contribution involving
transitions to Super Atomic Molecular Orbitals (SAMOs), a unique set of diffuse
orbitals typical of curved π-conjugated molecules. More, the photoconductivity of the
curved corannulene was compared to the π-conjugated planar N,N′-1H,1H-
photoexcitation energy dependence of photocurrent closely follows the optical
We next characterized charge transport in poly(3-hexylthiophene) (P3HT) layers
deposited from solution. Our results indicate that time-of-flight (TOF) mobility
depends on the photoexcitation energy. It is 0.4× 10 −3 cm 2 /Vs at 2.3 eV (530 nm) and
doubles at 4.8 eV (260 nm). TOF mobility was compared to field-effect (FET) mobility
of P3HT field-effect transistors (OFETs). The FET mobility was similar to the 2.3 eV
excitation TOF mobility. In order to improve charge mobility, graphene nanoparticles
were blended within a P3HT solution before the deposition. We found that the mobility
significantly improves upon the addition of graphene nanoparticles of a weight ratio
as low as 0.2 %. FET mobility increases with graphene concentration up to a value of
2.3× 10 −2 cm 2 /Vs at 3.2 %. The results demonstrate that phase segregation starts to
influence charge transport at graphene concentration of 0.8 % and above. Hence, the
graphene cannot form a bridged conduction channel between electrodes, which would
cancel the semiconducting effect of the polymer composite.
An alternative approach to enhance mobility is to optimize the molecular ordering
of organic semiconductors. For that purpose, we studied an innovative nanomesh
device. Free-standing nanomesh devices were used to form nanojunctions of N,N′-
iiDioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8) nanowires and crystalline
bis(triisopropylsilylethinyl)pentacene (TIPS-PEN). We characterized the photocurrent
response time of this novel nanomesh scaffold device. The photoresponse time
depends on the photon energy. It is between 4.5 − 5.6 ns at 500 nm excitation
wavelength and between 6.7 − 7.7 ns at 700 nm excitation wavelength. In addition, we
found that thermal annealing reduces charge carrier trapping in crystalline nanowires.
This confirms that the structural defects are crucial to obtaining high photon-to-charge
conversion efficiency and subsequent transport from pn junction in heterostructured
Structural defects also influence the power conversion efficiency of organic
heterostructured photovoltaics (OPVs). Anticipating that polymers with different
backbone lengths produce different level of structural defects, we examined charge
from 50 kDa to 300 kDa. We found p-type hopping transport in PTB7-Th,
characterized by 0.1 – 3× 10 −2 cm 2 /Vs mobility, which increases with temperature and
electric field. The polymer molecular weight exhibits a non-trivial influence on charge
transport. FET mobility in the saturation regime increases with molecular weight. A
similar trend is observed in TOF mobility and FET mobility in the linear regime,
except for the 100kDa polymer, which manifests in the highest mobility due to reduced
charge trapping. The lowest trapping at the dielectric interface of OFET is observed at
200 kDa. In addition, the 200 kDa polymer exhibits the lowest activation energy of the
charge transport. Although the 100 kDa polymer indicates the highest mobility, OPVs
using the 200 kDa polymer exhibit the best performance in terms of power conversion
Ključne besede: organic
photoconductivity, transient photocurrent spectroscopy, organic thin film transistors, atomic force microscopy, superatomic molecular orbitals, pn heterojunction, organic
nanowires, graphene, composites, charge mobility, charge trapping, temperature
dependence, photodetector, photovoltaic, solar cell, organic electronics
Objavljeno: 08.10.2018; Ogledov: 271; Prenosov: 18
Polno besedilo (4,56 MB)
CONTRIBUTION TO DEVELOPMENT OF MESHLESS METHODS FOR FREE AND MOVING BOUNDARY PROBLEMSNAZIA TALAT
, 2018, doktorska disertacija
Ključne besede: Two-phase flow, free and moving boundaries, computational fluid dynamics, phasefield formulation, 2D problems, axisymmetric problems, diffuse approximate
meshless method, Rayleigh-Taylor instability, Boussinesq approximation, variable
density and viscosity, flow focusing, dripping, jetting
Objavljeno: 11.09.2018; Ogledov: 219; Prenosov: 18
Polno besedilo (4,24 MB)
POLYMORPHISMS IN GENES FOR ENDOTHELIN 1, ENDOTHELIN RECEPTORS AND NITRIC OXIDE SYNTHASE 3 IN PATIENTS WITH DIABETIC RETINOPATHY AND DIABETES MELLITUS TYPE 2Dejan Bregar
, 2018, doktorska disertacija
Opis: The major causes of Diabetes Mellitus Type 2 (T2DM) are multi-factorial consequences of complex interactions between environmental, social and genetic factors. We investigated the genetic risk factors in Slovene patients with T2DM on a model of microvascular complication – Diabetic Retinopathy (DR).
Retrospective case-control study includes a T2DM Slovene population with clinical risk factors for T2DM and DR. Only some of the candidate genes with selected single nucleotid polymorphisms (SNPs) were included: (EDN1 (rs5370, rs3087459, rs1476046), EDNRA (rs5335, rs1801708), EDNRB (rs10507875, rs4885493), NOS3 (rs869109213).
By genotyping with either real-time polymerase chain reaction or standard polymerase chain reaction (PCR) we successfully identified the contribution of variable number of tandem repeats rs869109213 in DR progression (Proliferative Diabetic Retinopathy (PDR)) in Slovene patients with T2DM. The joint effect of individual genotypes of rs10507875 in EDNRB and rs869109213 in NOS3 on DR onset (DR) and DR progression (PDR) was demonstrated as well. The joint effect of the two polymorphisms on DR onset (DR) and DR progression (PDR) was greater than the individual effect of each polymorphism separately in the analyzed genetic models.
Despite genetic research contributions in DR, linkage studies, and Genome-wide association studies the identification of susceptible loci through candidate gene approaches still remains in its early stages. The frequent approach with an ultimate focus on SNP associations with phenotype is likely to underestimate the roles of genetics in human diseases by disregarding not only the joint effect of multiple loci but the complex interaction network between them. By identifying polymorphisms in genetic disorders in a more systematic way, we will be able to deepen our understanding of the regulatory mechanisms and disease etiology which should lead to a more effective development of mechanism-based therapies as well.
Ključne besede: endothelin 1, EDN1, endothelin receptor A, EDNRA, endothelin receptor B, EDNRB, nitric oxide synthase 3, NOS3, diabetic retinopathy, DR, diabetes mellitus type 2, T2DM, polymorphism, SNP, genetic model
Objavljeno: 07.09.2018; Ogledov: 193; Prenosov: 20
Polno besedilo (3,06 MB)
Amorphous nanocomposite of polycarbosilanes and aluminum oxideAndraž Mavrič
, 2018, doktorska disertacija
Opis: 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.
Ključne besede: 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
Objavljeno: 19.07.2018; Ogledov: 815; Prenosov: 43
Polno besedilo (5,07 MB)