Physical-chemical, thermal, and functional properties of achira (Canna indica L.) flour and starch from different geographical origin

Achira (Canna indica L.) is a plant native to the Andes in South America, a starchy source, and its cultivation has expanded to different tropical countries, like Brazil. In order to evaluate the potential of this species, starch and flours with different particle size were obtained from Brazilian achira rhizomes. Proximal analyses, size distribution, SEM, swelling power, solubility, DSC, XRD analysis, and FTIR were performed for characterization of these materials. Flours showed high dietary fiber content (16.532.2% db) and high concentration of starch in the case of the smaller particle size fraction. Significant differences in protein and starch content, swelling power, solubility, and thermal properties were observed between the Brazilian and the Colombian starch. All the studied materials displayed the B-type XRD pattern with relative crystallinity of 20.1% for the flour and between 27.0 and 28.0% for the starches. Results showed that the starch and flour produced from achira rhizomes have great technological potential for use as functional ingredient in the food industry.

ScPdZn and ScPtZn with YAlGe type structure: group-subgroup relation and 45Sc solid state NMR spectroscopy

The intermetallic compounds ScPdZn and ScPtZn were prepared from the elements by high-frequency melting in sealed tantalum ampoules. Both structures were refined from single crystal X-ray diffractometer data: YAlGe type, Cmcm, a = 429.53(8), b = 907.7(1), c = 527.86(1) pm, wR2 = 0.0375, 231 F2 values, for ScPdZn and a = 425.3(1), b = 918.4(2), c = 523.3(1) pm, wR2 = 0.0399, 213 F2 values for ScPtZn with 14 variables per refinement. The structures are orthorhombically distorted variants of the AlB2 type. The scandium and palladium (platinum atoms) build up ordered networks Sc3Pd3 and Sc3Pt3 (boron networks) which are slightly shifted with respect to each other. These networks are penetrated by chains of zinc atoms (262 pm in ScPtZn) which correspond to the aluminum positions, i.e. Zn(ScPd) and Zn(ScPt). The corresponding group-subgroup scheme and the differences in chemical bonding with respect to other AlB2-derived REPdZn and REPtZn compounds are discussed. 45Sc solid state NMR spectra confirm the single crystallographic scandium sites. From electronic band structure calculations the two compounds are found metallic with free electron like behavior at the Fermi level. A larger cohesive energy for ScPtZn suggests a more strongly bonded intermetallic than ScPdZn. Electron localization and overlap population analyses identify the largest bonding for scandium with the transition metal (Pd, Pt).

Laboratory verification of predicted permanent deformation in asphalt materials following climate change.

In the past a change in temperature of 5°C most often occurred over intervals of thousands of years. According to estimates by the IPCC, in the XXI century is expected an increase in average temperatures in Europe between 1.8 and 4.0°C in the best case caused by emissions of carbon dioxide and other GHG from human activities. As well as on the environment and economic context, global warming will have effects even on road safety. Several studies have already shown how increasing temperature may cause a worsening of some types of road surface damages, especially rutting, a permanent deformation of the road structures consisting in the formation of a longitudinal depression in the wheelpath, mostly due to the rheological behavior of bitumen. This deformation evolves during the hot season because of the heating capacity of the asphalt layers, in fact, the road surface temperature is up to 24°C higher than air. In this thesis, through the use of Wheeltrack test, it was studied the behavior of some types of asphalt concrete mixtures subjected to fatigue testing at different temperatures. The objectives of this study are: to determine the strain variation of different bituminous mixture subjected to fatigue testing at different temperature conditions; to investigate the effect of aggregates, bitumen and mixtures’ characteristics on rutting. Samples were made in the laboratory mostly using an already prepared mixtures, the others preparing the asphalt concrete from the grading curve and bitumen content. The same procedure was performed for each specimen: preparation, compaction using the roller compactor, cooling and heating before the test. The tests were carried out at 40 - 50 - 60°C in order to obtain the evolution of deformation with temperature variation, except some mixtures for which the tests were carried out only at 50°C. In the elaboration of the results were considered testing parameters, component properties and the characteristics of the mixture. Among the testing parameters, temperature was varied for each sample. The mixtures responded to this variation with a different behavior (linear logarithmic and exponential) not directly correlated with the asphalt characteristics; the others parameters as load, passage frequency and test condition were kept constant. According to the results obtained, the main contribution to deformation is due to the type of binder used, it was found that the modified bitumen have a better response than the same mixtures containing traditional bitumen; to the porosity which affects negatively the behavior of the samples and to the homogeneity ceteris paribus. The granulometric composition did not seem to have interfered with the results. Overall has emerged at working temperature, a decisive importance of bitumen composition, than the other characteristics of the mixture, that tends to disappear with heating in favor of increased dependence of rutting resistance from the granulometric composition of the sample considered. In particular it is essential, rather than the mechanical characteristics of the binder, its chemical properties given by the polymeric modification. To confirm some considered results, the maximum bulk density and the air voids content were determined. Tests have been conducted in the laboratories of the Civil Engineering Department at NTNU in Trondheim according to European Standards.

Study of materials and technology of ancient floor mosaics' substrate

Ancient pavements are composed of a variety of preparatory or foundation layers constituting the substrate, and of a layer of tesserae, pebbles or marble slabs forming the surface of the floor. In other cases, the surface consists of a mortar layer beaten and polished. The term mosaic is associated with the presence of tesserae or pebbles, while the more general term pavement is used in all the cases. As past and modern excavations of ancient pavements demonstrated, all pavements do not necessarily display the stratigraphy of the substrate described in the ancient literary sources. In fact, the number and thickness of the preparatory layers, as well as the nature and the properties of their constituent materials, are often varying in pavements which are placed either in different sites or in different buildings within a same site or even in a same building. For such a reason, an investigation that takes account of the whole structure of the pavement is important when studying the archaeological context of the site where it is placed, when designing materials to be used for its maintenance and restoration, when documenting it and when presenting it to public. Five case studies represented by archaeological sites containing floor mosaics and other kind of pavements, dated to the Hellenistic and the Roman period, have been investigated by means of in situ and laboratory analyses. The results indicated that the characteristics of the studied pavements, namely the number and the thickness of the preparatory layers, and the properties of the mortars constituting them, vary according to the ancient use of the room where the pavements are placed and to the type of surface upon which they were built. The study contributed to the understanding of the function and the technology of the pavements’ substrate and to the characterization of its constituent materials. Furthermore, the research underlined the importance of the investigation of the whole structure of the pavement, included the foundation surface, in the interpretation of the archaeological context where it is located. A series of practical applications of the results of the research, in the designing of repair mortars for pavements, in the documentation of ancient pavements in the conservation practice, and in the presentation to public in situ and in museums of ancient pavements, have been suggested.

1-, 2- and 3-dimensional phenylene-based materials for optoelectronic applications

A series of oligo-phenylene dendronised conjugated polymers was prepared. The divergent synthetic approach adopted allowed for the facile synthesis of a range of dendronised monomers from a common intermediate, e.g. first and second generation fluorene. Only the polymerisation of the first generation and alkylarylamine substituted dendronised fluorene monomers yielded high molecular weight materials, attributed to the low solubility of the remaining dendronised monomers. The alkylarylamine substituted dendronised poly(fluorene) was incorporated into an organic light emitting diode (OLED) and exhibited an increased colour stability in air compared to other poly(fluorenes). The concept of dendronisation was extended to poly(fluorenone), a previously insoluble material. The synthesis of the first soluble poly(fluorenone) was achieved by the incorporation of oligo-phenylene dendrons at the 4-position of fluorenone. The dendronisation of fluorenone allowed for a polymer with an Mn of 4.1 x 104 gmol-1 to be prepared. Cyclic voltammetry of the dendronised poly(fluorenone) showed that the electron affinity of the polymer was high and that the polymer is a promising n-type material. A dimer and trimer of indenofluorene (IF) were prepared from the monobromo IF. These oligomers were investigated by 2-dimensional wide angle x-ray spectroscopy (2D-WAXS), polarised optical microscopy (POM) and dielectric spectroscopy, and found to form highly ordered smetic phases. By attaching perylene dye as the end-capper on the IF oligomers, molecules that exhibited efficient Förster energy transfer were obtained. Indenofluorene monoketone, a potential defect structure for IF based OLED’s, was synthesised. The synthesis of this model defect structure allowed for the long wavelength emission in OLED’s to be identified as ketone defects. The long wavelength emission from the indenofluorene monoketone was found to be concentration dependent, and suggests that aggregate formation is occurring. An IF linked hexa-peri-hexabenzocoronene (HBC) dimer was synthesised. The 2D-WAXS images of this HBC dimer demonstrate that the molecule exhibits intercolumnar organisation perpendicular to the extrusion direction. POM images of mixtures of the HBC dimer mixed with an HBC with a low isotropic temperature demonstrated that the HBC dimer is mixing with the isotropic HBC.

Structure and properties of composite polyolefin materials

This thesis is based on three main studies, all dealing with structure-property investigation of semicrystalline polyolefin-based composites. Low density poly(ethylene) (LDPE) and isotactic poly(propylene) (iPP) were chosen as parts of the composites materials and they were investigated either separately (as homoploymers), either in blend systems with the composition LDPE/iPP 80/20 or as filled matrix with layered silicate (montmorillonite). The beneficial influence of adding ethylene-co-propylene polymer of amorphous nature, to low density poly(ethylene)/isotactic poly(propylene) (80/20) blend is demonstrated. This effect is expressed by the major improvement of mechanical properties of ternary blends as examined at a macroscopic size scale by means of tensile measurements. The structure investigation also reveals a clear dependence of the morphology on adding ethylene-copropylene polymer. Both the nature and the content of ethylene-co-propylene polymer affect structure and properties. It is further demonstrated that the extent of improvement in mechanical properties is to be related to the molecular details of the compatibilizer. Combination of high molecular weight and high ethylene content is appropriate for the studied system where the poly(ethylene) plays the role of matrix. A new way to characterize semicrystalline systems by means of Brillouin spectroscopy is presented in this study. By this method based on inelastic light scattering, we were able to measure the high frequency elastic constant (c11) of the two microphases in the case where the spherulites size is exhibit size larger than the size of the probing phonon wavelength. In this considered case, the sample film is inhomogeneous over the relevant length scales and there is an access to the transverse phonon in the crystalline phase yielding the elastic constant c44 as well. Isotactic poly(propylene) is well suited for this type of investigation since its morphology can be tailored through different thermal treatment from the melt. Two distinctly different types of films were used; quenched (low crystallinity) and annealed (high crystallinity). The Brillouin scattering data are discussed with respect to the spherulites size, lamellae thickness, long period, crystallinity degree and well documented by AFM images. The structure and the properties of isotactic poly(propylene) matrix modified by inorganic layered silicate, montmorillonite, are discussed with respect to the clay content. Isotactic poly(propylene)-graft-maleic anhydride was used as compatibilizer. It is clearly demonstrated that the property enhancement is largely due to the ability of layered silicate to exfoliate. The intimate dispersion of the nanometer-thick silicate result from a delicate balance of the content ratio between the isotactic poly(propylene)-graft-maleic anhydride compatibilizer and the inorganic clay.

Conjugated semiconducting organic materials for electronic applications

Since conjugated polymers, i.e. polymers with spatially extended pi-bonding system have offered unique physical properties, unobtainable for conventional polymers, significant research efforts directed to better understanding of their chemistry, physics and engineering have been undertaken in the past two and half decades. In this thesis we discuss the synthesis, characterisation and investigation of conjugated semiconducting organic materials for electronic applications. Owing to the versatile properties of metal-organic hybrid materials, there is significant promise that these materials can find use in optical or electronic devices in the future. In addressing this issue, the synthesis of bisthiazol-2-yl-amine (BTA) based polymers is attempted and their metallation is investigated. The focus of this work has been to examine whether the introduction of coordinating metal ions onto the polymer backbone can enhance the conductivity of the material. These studies can provide a basis for understanding the photophysical properties of metal-organic polymers based on BTA. In their neutral (undoped) form conjugated polymers are semiconductors and can be used as active components of plastics electronics such as polymer light-emitting diodes, polymer lasers, photovoltaic cells, field-effect transistors, etc. Toward this goal, it is an objective of the study to synthesize and characterize new classes of luminescent polymeric materials based on anthracene and phenanthrene moieties. A series of materials based on polyphenylenes and poly(phenyleneethynylene)s with 9,10-anthrylene subunits are not only presented but the synthesis and characterization of step-ladder and ladder poly(p-phenylene-alt-anthrylene)s containing 9,10-anthrylene building groups within the main chain are also explored. In a separate work, a series of soluble poly-2,7- and 3,6-phenanthrylenes are synthesized. This can enable us to do a systematic investigation into the optical and electronic properties of PPP-like versus PPV-like. Besides, the self-organization of 3,6-linked macrocyclic triphenanthrylene has been investigated by 2D wide-angle X-ray scattering experiments performed on extruded filaments in solution and in the bulk. Additionally, from the concept that donor-acceptor materials can induce efficient electron transfer, the covalent incorporation of perylene tetracarboxydiimide (PDI) into one block of a poly(2,7-carbazole) (PCz)-based diblock copolymer and 2,5-pyrrole based on push-pull type material are achieved respectively.

Nitrogen-bridged polyphenylene-based materials for electronic applications

Conjugated polymers are macromolecules that possess alternating single and double bonds along the main chain. These polymers combine the optoelectronic properties of semiconductors with the mechanical properties and processing advantages of plastics. In this thesis we discuss the synthesis, characterization and application of polyphenylene-based materials in various electronic devices. Poly(2,7-carbazole)s have the potential to be useful as blue emitters, but also as donor materials in solar cells due to their better hole-accepting properties. However, it is associated with two major drawbacks (1) the emission maximum occurs at 421 nm where the human eye is not very sensitive and (2) the 3- and 6- positions of carbazole are susceptible to chemical or electrochemical degradation. To overcome these problems, the ladder-type nitrogen-bridged polymers are synthesized. The resulting series of polymers, nitrogen-bridged poly(ladder-type tetraphenylene), nitrogen-bridged poly(ladder-type pentaphenylene), nitrogen-bridged poly(ladder-type hexaphenylene) and its derivatives are discussed in the light of photophysical and electrochemical properties and tested in PLEDs, solar cell, and OFETs. A promising trend which has emerged in recent years is the use of well defined oligomers as model compounds for their corresponding polymers. However, the uses of these molecules are many times limited by their solubility and one has to use vapor deposition techniques which require high vacuum and temperature and cannot be used for large area applications. One solution to this problem is the synthesis of small molecules having enough alkyl chain on the backbone so that they can be solution or melt processed and has the ability to form thin films like polymers as well as retain the high ordered structure characteristics of small molecules. Therefore, in the present work soluble ladderized oligomers based on thiophene and carbazole with different end group were made and tested in OFET devices. Carbazole is an attractive raw material for the synthesis of dyes since it is cheap and readily available. Carbazoledioxazine, commercially known as violet 23 is a representative compound of dioxazine pigments. As part of our efforts into developing cheap alternatives to violet 23, the synthesis and characterization of a new series of dyes by Buchwald-type coupling of 3-aminocarbazole with various isomers of chloroanthraquinone are presented.

Synthesis and surface modification of semiconductor nanocrystals

The last decade has witnessed an exponential growth of activities in the field of nanoscience and nanotechnology worldwide, driven both by the excitement of understanding new science and by the potential hope for applications and economic impacts. The largest activity in this field up to date has been in the synthesis and characterization of new materials consisting of particles with dimensions in the order of a few nanometers, so-called nanocrystalline materials. [1-8] Semiconductor nanomaterials such as III/V or II/VI compound semiconductors exhibit strong quantum confinement behavior in the size range from 1 to 10 nm. Therefore, preparation of high quality semiconductor nanocrystals has been a challenge for synthetic chemists, leading to the recent rapid progress in delivering a wide variety of semiconducting nanomaterials. Semiconductor nanocrystals, also called quantum dots, possess physical properties distinctly different from those of the bulk material. Typically, in the size range from 1 to 10 nm, when the particle size is changed, the band gap between the valence and the conduction band will change, too. In a simple approximation a particle in a box model has been used to describe the phenomenon[9]: at nanoscale dimensions the degenerate energy states of a semiconductor separate into discrete states and the system behaves like one big molecule. The size-dependent transformation of the energy levels of the particles is called “quantum size-effect”. Quantum confinement of both the electron and hole in all three dimensions leads to an increase in the effective bandgap of the material with decreasing crystallite size. Consequently, both the optical absorption and emission of semiconductor nanaocrystals shift to the blue (higher energies) as the size of the particles gets smaller. This color tuning is well documented for CdSe nanocrystals whose absorption and emission covers almost the whole visible spectral range. As particle sizes become smaller the ratio of surface atoms to those in the interior increases, which has a strong impact on particle properties, too. Prominent examples are the low melting point [8] and size/shape dependent pressure resistance [10] of semiconductor nanocrystals. Given the size dependence of particle properties, chemists and material scientists now have the unique opportunity to change the electronic and chemical properties of a material by simply controlling the particle size. In particular, CdSe nanocrystals have been widely investigated. Mainly due to their size-dependent optoelectronic properties [11, 12] and flexible chemical processibility [13], they have played a distinguished role for a number of seminal studies [11, 12, 14, 15]. Potential technical applications have been discussed, too. [8, 16-27] Improvement of the optoelectronic properties of semiconductor nanocrystals is still a prominent research topic. One of the most important approaches is fabricating composite type-I core-shell structures which exhibit improved properties, making them attractive from both a fundamental and a practical point of view. Overcoating of nanocrystallites with higher band gap inorganic materials has been shown to increase the photoluminescence quantum yields by eliminating surface nonradiative recombination sites. [28] Particles passivated with inorganic shells are more robust than nanocrystals covered by organic ligands only and have greater tolerance to processing conditions necessary for incorporation into solid state structures or for other applications. Some examples of core-shell nanocrystals reported earlier include CdS on CdSe [29], CdSe on CdS, [30], ZnS on CdS, [31] ZnS on CdSe[28, 32], ZnSe on CdSe [33] and CdS/HgS/CdS [34]. The characterization and preparation of a new core-shell structure, CdSe nanocrystals overcoated by different shells (CdS, ZnS), is presented in chapter 4. Type-I core-shell structures as mentioned above greatly improve the photoluminescence quantum yield and chemical and photochemical stability of nanocrystals. The emission wavelengths of type-I core/shell nanocrystals typically only shows a small red-shift when compared to the plain core nanocrystals. [30, 31, 35] In contrast to type-I core-shell nanocrystals, only few studies have been conducted on colloidal type-II core/shell structures [36-38] which are characterized by a staggered alignment of conduction and valence bands giving rise to a broad tunability of absorption and emission wavelengths, as was shown for CdTe/CdSe core-shell nanocrystals. [36] The emission of type-II core/shell nanocrystals mainly originates from the radiative recombination of electron-hole pairs across the core-shell interface leading to a long photoluminescence lifetime. Type-II core/shell nanocrystals are promising with respect to photoconduction or photovoltaic applications as has been discussed in the literature.[39] Novel type-II core-shell structures with ZnTe cores are reported in chapter 5. The recent progress in the shape control of semiconductor nanocrystals opens new fields of applications. For instance, rod shaped CdSe nanocrystals can enhance the photo-electro conversion efficiency of photovoltaic cells, [40, 41] and also allow for polarized emission in light emitting diodes. [42, 43] Shape control of anisotropic nanocrystals can be achieved by the use of surfactants, [44, 45] regular or inverse micelles as regulating agents, [46, 47] electrochemical processes, [48] template-assisted [49, 50] and solution-liquid-solution (SLS) growth mechnism. [51-53] Recently, formation of various CdSe nanocrystal shapes has been reported by the groups of Alivisatos [54] and Peng, [55] respectively. Furthermore, it has been reported by the group of Prasad [56] that noble metal nanoparticles can induce anisotropic growth of CdSe nanocrystals at lower temperatures than typically used in other methods for preparing anisotropic CdSe structures. Although several approaches for anisotropic crystal growth have been reported by now, developing new synthetic methods for the shape control of colloidal semiconductor nanocrystals remains an important goal. Accordingly, we have attempted to utilize a crystal phase control approach for the controllable synthesis of colloidal ZnE/CdSe (E = S, Se, Te) heterostructures in a variety of morphologies. The complex heterostructures obtained are presented in chapter 6. The unique optical properties of nanocrystals make them appealing as in vivo and in vitro fluorophores in a variety of biological and chemical investigations, in which traditional fluorescence labels based on organic molecules fall short of providing long-term stability and simultaneous detection of multiple emission colours [References]. The ability to prepare water soluble nanocrystals with high stability and quantum yield has led to promising applications in cellular labeling, [57, 58] deep-tissue imaging, [59, 60] and assay labeling [61, 62]. Furthermore, appropriately solubilized nanocrystals have been used as donors in fluorescence resonance energy transfer (FRET) couples. [63-65] Despite recent progress, much work still needs to be done to achieve reproducible and robust surface functionalization and develop flexible (bio-) conjugation techniques. Based on multi-shell CdSe nanocrystals, several new solubilization and ligand exchange protocols have been developed which are presented in chapter 7. The organization of this thesis is as follows: A short overview describing synthesis and properties of CdSe nanocrystals is given in chapter 2. Chapter 3 is the experimental part providing some background information about the optical and analytical methods used in this thesis. The following chapters report the results of this work: synthesis and characterization of type-I multi-shell and type-II core/shell nanocrystals are described in chapter 4 and chapter 5, respectively. In chapter 6, a high–yield synthesis of various CdSe architectures by crystal phase control is reported. Experiments about surface modification of nanocrystals are described in chapter 7. At last, a short summary of the results is given in chapter 8.

Structure-Property Relationships and Charge Transport Modeling of Organic Molecular Materials

From the perspective of a new-generation opto-electronic technology based on organic semiconductors, a major objective is to achieve a deep and detailed knowledge of the structure-property relationships, in order to optimize the electronic, optical, and charge transport properties by tuning the chemical-physical characteristics of the compounds. The purpose of this dissertation is to contribute to such understanding, through suitable theoretical and computational studies. Precisely, the structural, electronic, optical, and charge transport characteristics of several promising organic materials recently synthesized are investigated by means of an integrated approach encompassing quantum-chemical calculations, molecular dynamics and kinetic Monte Carlo simulations. Particular care is addressed to the rationalization of optical and charge transport properties in terms of both intra- and intermolecular features. Moreover, a considerable part of this project involves the development of a home-made set of procedures and parts of software code required to assist the modeling of charge transport properties in the framework of the non-adiabatic hopping mechanism applied to organic crystalline materials. As a first part of my investigations, I mainly discuss the optical, electronic, and structural properties of several core-extended rylene derivatives, which can be regarded to as model compounds for graphene nanoribbons. Two families have been studied, consisting in bay-linked perylene bisimide oligomers and N-annulated rylenes. Beside rylene derivatives, my studies also concerned electronic and spectroscopic properties of tetracene diimides, quinoidal oligothiophenes, and oxygen doped picene. As an example of device application, I studied the structural characteristics governing the efficiency of resistive molecular memories based on a derivative of benzoquinone. Finally, as a second part of my investigations, I concentrate on the charge transport properties of perylene bisimides derivatives. Precisely, a comprehensive study of the structural and thermal effects on the charge transport of several core-twisted chlorinated and fluoro-alkylated perylene bisimide n-type semiconductors is presented.

Structure, organization and dynamics of functional supramolecular materials studied by solid-state NMR

Functional materials have great importance due to their many important applications. The characterization of supramolecular architectures which are held together by non-covalent interactions is of most importance to understand their properties. Solid-state NMR methods have recently been proven to be able to unravel such structure-property relations with the help of fast magic-angle spinning and advanced pulse sequences. The aim of the current work is to understand the structure and dynamics of functional supramolecular materials which are potentially important for fuel-cell (proton conducting membrane materials) and solar-cell or plastic-electronic applications (photo-reactive aromatic materials). In particular, hydrogen-bonding networks, local proton mobility, molecular packing arrangements, and local dynamics will be studied by the use of advanced solid-state NMR methods. The first class of materials studied in this work is proton conducting polymers which also form hydrogen-bonding network. Different materials, which are prepared for high 1H conduction by different approaches are studied: PAA-P4VP, PVPA-ABPBI, Tz5Si, and Triazole-functional systems. The materials are examples of the following major groups; - Homopolymers with specific functional groups (Triazole functional polysiloxanes). - Acid-base polymer blends approach (PAA-P4VP, PVPA-ABPBI). - Acid-base copolymer approach (Triazole-PVPA). - Acid doped polymers (Triazole functional polymer doped with H3PO4). Perylenebisimide (PBI) derivatives, a second type of important functional supramolecular materials with potent applications in plastic electronics, were also investigated by means of solid-state NMR. The preparation of conducting nanoscopic fibers based on the self-assembling functional units is an appealing aim as they may be incorporated in molecular electronic devices. In this category, perylene derivatives have attracted great attention due to their high charge carrier mobility. A detailed knowledge about their supramolecular structure and molecular dynamics is crucial for the understanding of their electronic properties. The aim is to understand the structure, dynamics and packing arrangements which lead to high electron conductivity in PBI derivatives.

De Novo Design of Foldamers for Preparation of Nanostructured Materials

This thesis deals with the synthesis and the conformation analysis of hybrid foldamers containing the 4-carboxyoxazolidin-2-one unit or related molecules, in which an imido-type function is obtained by coupling the nitrogen of the heterocycle with the carboxylic acid moiety of the next unit. The imide group is characterized by a nitrogen atom connected to an endocyclic and an exocyclic carbonyl, which tend always to adopt the trans conformation. As a consequence of this locally constrained disposition effect, these imide-type oligomers are forced to fold in ordered conformations. The synthetic approach is highly tuneable with endless variations, so, simply by changing the design and the synthesis, a wide variety of foldamers with the required properties may be prepared “on demand”. Thus a wide variety of unusual secondary structures and interesting supramolecular materials may be obtained with hybrid foldamers. The behaviour in the solid state of some of these compounds has been analyzed in detail, thus showing the formation of different kinds of supramolecular materials that may be used for several applications. A winning example is the production of a bolaamphiphilic gelators that may also be doped with small amounts of dansyl containing compounds, needed to show the cellular uptake into IGROV-1 cells, by confocal laser scanning microscopy. These gels are readily internalized by cells and are biologically inactive, making them very good candidates in the promising field of drug delivery. In the last part of the thesis, a particular attention was directed to the search of new scaffolds that behave as constrained amino acid mimetics, showing that tetramic acids derivatives could be good candidates for the synthesis and applications of molecules having an ordered secondary structure.

Analysis of charge-transport properties in GST materials for next generation phase-change memory devices

The quest for universal memory is driving the rapid development of memories with superior all-round capabilities in non-volatility, high speed, high endurance and low power. The memory subsystem accounts for a significant cost and power budget of a computer system. Current DRAM-based main memory systems are starting to hit the power and cost limit. To resolve this issue the industry is improving existing technologies such as Flash and exploring new ones. Among those new technologies is the Phase Change Memory (PCM), which overcomes some of the shortcomings of the Flash such as durability and scalability. This alternative non-volatile memory technology, which uses resistance contrast in phase-change materials, offers more density relative to DRAM, and can help to increase main memory capacity of future systems while remaining within the cost and power constraints. Chalcogenide materials can suitably be exploited for manufacturing phase-change memory devices. Charge transport in amorphous chalcogenide-GST used for memory devices is modeled using two contributions: hopping of trapped electrons and motion of band electrons in extended states. Crystalline GST exhibits an almost Ohmic I(V) curve. In contrast amorphous GST shows a high resistance at low biases while, above a threshold voltage, a transition takes place from a highly resistive to a conductive state, characterized by a negative differential-resistance behavior. A clear and complete understanding of the threshold behavior of the amorphous phase is fundamental for exploiting such materials in the fabrication of innovative nonvolatile memories. The type of feedback that produces the snapback phenomenon is described as a filamentation in energy that is controlled by electron–electron interactions between trapped electrons and band electrons. The model thus derived is implemented within a state-of-the-art simulator. An analytical version of the model is also derived and is useful for discussing the snapback behavior and the scaling properties of the device.

Solid-state NMR investigation of phosphonic acid based proton conducting materials

In this work, new promising proton conducting fuel cell membrane materials were characterized in terms of their structure and dynamic properties using solid-state nuclear magnetic resonance (NMR) spectroscopy and X-ray diffraction. Structurally different, phosphonic acid (PA) containing materials were systematically evaluated for possible high-temperature operation (e.g. at T>100°C). Notably, 1H, 2H and 31P magic angle spinning (MAS) NMR provided insight into local connectivities and dynamics of the hydrogen bonded network, while packing arrangements were identified by means of heteronuclear dipolar recoupling techniques.rnThe first part of this work introduced rather crystalline, low molecular weight ionomers for proton conducting membranes, where six different geometries such as line, triangle, screw, tetrahedron, square and hexagon, were investigated. The hexagon was identified as the most promising geometry with high-temperature bulk proton conductivities in the range of 10-3 Scm-1 at a relative humidity of 50%. However, 2H NMR and TGA-MS data suggest that the bulk proton transport is mainly due to the presence of crystal water. Single crystal X-ray data revealed that in the tetrahedron phosphonic acids form tetrameric clusters isolating the mobile protons while the phosphonic acids in the hexagon form zigzag-type pathways through the sample.rnThe second part of this work demonstrates how acid-base pairing and the choice of appropriate spacers may influence proton conduction. Different ratios of statistical copolymers of poly (vinylphosphonic acid) and poly (4-vinylpyridine) were measured to derive information about the local structure and chemical changes. Though anhydrous proton conductivities of all statistical copolymers are rather poor, the conductivity increases to 10-2 S cm-1 when exposing the sample to relative humidity of 80%. In contrast to PVPA, anhydride formation of phosphonic acids in the copolymer is not reversible even when exposing the sample to a relative humidity of 100%.rnIn addition, the influence of both spacers and degree of backbone crystallinity on bulk proton conductivity was investigated. Unlike in systems such as poly benzimidazole (PBI), spacers were inserted between the protogenic groups along the backbone. It was found that dilution of the protogenic groups decreases the conductivity, but compared to PVPA, similar apparent activation energies for local motions were obtained from both variable temperature 1H NMR and impedance spectroscopy data. These observations suggest the formation of phosphonic acid clusters with high degrees of local proton motion, where only a fraction of motions contribute to the observable bulk proton conductivity. Additionally, it was shown that gradual changes of the spacer length lead to different morphologies.rnIn summary, applying advanced solid-state NMR and X-ray analysis, structural and dynamic phenomena in proton conducting materials were identified on a molecular level. The results were discussed with respect to different proton conduction mechanisms and may contribute to a more rational design or improvement of proton conducting membranes.rn

Inorganic-organic hybrid polymers: Solution-processible coating materials for defined surface functionalization

A new class of inorganic-organic hybrid polymers could successfully been prepared by the combination of different polymerization techniques. The access to a broad range of organic polymers incorporated into the hybrid polymer was realized using two independent approaches.rnIn the first approach a functional poly(silsesquioxane) (PSSQ) network was pre-formed, which was capable to initiate a controlled radical polymerization to graft organic vinyl-type monomers from the PSSQ precursor. As controlled radical polymerization techniques atom transfer radical polymerization (ATRP), as well as reversible addition fragmentation chain transfer (RAFT) polymerization could be used after defined tuning of the PSSQ precursor either toward a PSSQ macro-initiator or to a PSSQ macro-chain-transfer-agent. The polymerization pathway, consisting of polycondensation of trialkoxy-silanes followed by grafting-from polymerization of different monomers, allowed synthesis of various functional hybrid polymers. A controlled synthesis of the PSSQ precursors could successfully be performed using a microreactor setup; the molecular weight could be adjusted easily while the polydispersity index could be decreased well below 2.rnThe second approach aimed to incorporate differently derived organic polymers. As examples, polycarbonate and poly(ethylene glycol) were end-group-modified using trialkoxysilanes. After end-group-functionalization these organic polymers could be incorporated into a PSSQ network.rnThese different hybrid polymers showed extraordinary coating abilities. All polymers could be processed from solution by spin-coating or dip-coating. The high amount of reactive silanol moieties in the PSSQ part could be cross-linked after application by annealing at 130° for 1h. Not only cross-linking of the whole film was achieved, which resulted in mechanical interlocking with the substrate, also chemical bonds to metal or metal oxide surfaces were formed. All coating materials showed high stability and adhesion onto various underlying materials, reaching from metals (like steel or gold) and metal oxides (like glass) to plastics (like polycarbonate or polytetrafluoroethylene).rnAs the material and the synthetic pathway were very tolerant toward different functionalities, various functional monomers could be incorporated in the final coating material. The incorporation of N-isopropylacrylamide yielded in temperature-responsive surface coatings, whereas the incorporation of redox-active monomers allowed the preparation of semi-conductive coatings, capable to produce smooth hole-injection layers on transparent conductive electrodes used in optoelectronic devices.rnThe range of possible applications could be increased tremendously by incorporation of reactive monomers, capable to undergo fast and quantitative conversions by polymer-analogous reactions. For example, grafting active esters from a PSSQ precursor yielded a reactive surface coating after application onto numerous substrates. Just by dipping the coated substrate into a solution of a functionalized amine, the desired function could be immobilized at the interface as well as throughout the whole film. The obtained reactive surface coatings could be used as basis for different functional coatings for various applications. The conversion with specifically tuned amines yielded in surfaces with adjustable wetting behaviors, switchable wetting behaviors or as recognition element for surface-oriented bio-analytical devices. The combination of hybrid materials with orthogonal reactivities allowed for the first time the preparation of multi-reactive surfaces which could be functionalized sequentially with defined fractions of different groups at the interface. rnThe introduced concept to synthesis functional hybrid polymers unifies the main requirements on an ideal coating material. Strong adhesion on a wide range of underlying materials was achieved by secondary condensation of the PSSQ part, whereas the organic part allowed incorporation of various functionalities. Thus, a flexible platform to create functional and reactive surface coatings was achieved, which could be applied to different substrates. rn