Materiali Politiofenici Otticamente Attivi

Much effort has been devoted in the recent years to the investigation of optically active polythiophenes characterized by the presence of a chiral moiety linked to the 3-position of the aromatic ring. In addition to their potential technological applications as materials for enantioselective electrodes and membranes, chiral poly(thiophene)s offer the possibility of studying the structural changes accompanying the transition from the disordered state by following the variation of their chiroptical properties by circular dichroism (CD). In solution of a good solvent, that kind of polythiophenes doesn’t display any optical activity arising from the presence of dissymmetric conformation of the backbone, as shown by circular dichroism (CD) spectra. When the macromolecules begin to aggregate, as it occurs e.g. by addition of a poor solvent, or lowering the solution temperature, or when the macromolecules are assembled in the solid state as thin films obtained by solution casting or spin coating, significant CD bands are observed in the spectral region related to the electronic absorptions of the aromatic polythiophene chromophore. These CD bands are indicative of a chiral macromolecule arrangement of one prevailing chirality. The synthesis of -substituted polythiophenes can be carried out starting from the corresponding -substituted mono- or oligomeric thiophenic monomers under regioselective or regiospecific conditions in order to minimize or avoid the formation of head-to-head dyads unfavourably affecting the presence of coplanar conformations of thiophene rings as a consequence of steric interactions between the side-chain substituents, both in solution and in the solid state. To this regard, non-symmetrically substituted monomers require therefore to perform the polymerization in the presence of highly demanding catalysts and reaction condition, whereas with symmetrically substituted oligothiophenic monomers containing the -substituents located far apart from the reacting sites, it is instead possible to obtain regioregular macromolecules by adopting more simple and economic polymerization methods, such as, e. g., the chemical oxidative polymerization with iron (III) trichloride. In order to verify how the polymer structure affects its optical activity, further poly-3-alkylthiophenes, substituted by an enantiomerically pure chiral alkyl group, namely poli[3,3”-di[2((S)-(+)-2-methylbutoxy)ethyl]-2,2’:5’,2”-terthiophene] (PDMBOETT), poli[3,3’di[2((S)-(+)-2-methylbutoxy)ethyl]-2,2’-bitiofene] (PDMBOEBT), poli[3,3””-didodecyl-4’,3”’-di(S)-(+)-2-methylbutyl-2,2’:5’,2”:5”,2”’:5”’,2””-quinquethiophene (PDDDMBQT) have been synthesized and characterized by instrumental techniques. The spectroscopic behaviour of thin films of poly(DDDMBQT) has been investigated in the solid state under different sample preparation procedures. It was also compared with the behaviour of polymers previously made. The experimental results are interpreted in terms of influence of the side-chain substituents on the extent of planarity of the polymeric chains and the formation of optically active chiral aggregates. In recent years conjugated block copolymers have received considerable attention. It is well known that conjugated block copolymers composed of two electronically different blocks can have morphologic and optical properties, that differ from those of their homopolymers. A recent study has also shown that the electronic properties and the supramolecular organization of one conjugated block can also be influenced by the other block. In order to study better this behavior, a new conjugated block copolymers, composed of a regioregular hydrophylic block and a regioregular hydrophobic block namely poli[3[2-(2-metossietossi)etossi]metiltiofene]-co- poli[3(1-octilossi)tiofene], has been synthesized and characterized.

Conductive Polymer Composites

In recent years, nanotechnologies have led to the production of materials with new and sometimes unexpected qualities through the manipulation of nanoscale components. This research aimed primarily to the study of the correlation between hierarchical structures of hybrid organic-inorganic materials such as conductive polymer composites (CPCs). Using a bottom-up methodology, we could synthesize a wide range of inorganic nanometric materials with a high degree of homogeneity and purity, such as thiol capped metal nanoparticles, stoichiometric geomimetic chrysotile nanotubes and metal dioxide nanoparticles. It was also possible to produce inorganic systems formed from the interaction between the synthesized materials. These synthesized materials and others like multiwalled carbon nanotubes and grapheme oxide were used to produce conductive polymer composites. Electrospinning causes polymer fibers to become elongated using an electric field. This technique was used to produce fibers with a nanometric diameter of a polymer blend based on two different intrinsically conducting polymers polymers (ICPs): polyaniline (PANI) and poly(3-hexylthiophene) (P3HT). Using different materials as second phase in the initial electrospun polymer fibers caused significant changes to the material hierarchical structure, leading to the creation of CPCs with modified electrical properties. Further study of the properties of these new materials resulted in a better understanding of the electrical conductivity mechanisms in these electrospun materials.

Polimeri tiofenici funzionali e loro applicazioni nel fotovoltaico

Recentemente, sempre più attenzione è stata rivolta all' utilizzo di coloranti organici come assorbitori di luce per la preparazione di strati fotoattivi in celle solari organiche (OPV). I coloranti organici presentano un'elevata abilità nella cattura della luce solare grazie all'elevato coefficiente di estinzione molare e buone proprietà fotofisiche. Per questi motivi sono eccellenti candidati per l'incremento della conversione fotoelettrica in OPV. In questa tesi viene descritta una nuova strategia per l'incorporazione di derivati porfirinici in catena laterale a copolimeri tiofenici. Gli studi svolti hanno dimostrato che poli(3-bromoesil)tiofene può essere variamente funzionalizzato con idrossitetrafenilporfirina (TPPOH), per l'ottenimento di copolimeri utilizzabili come materiali p-donatori nella realizzazione di OPV. I copolimeri poli[3-(6-bromoesil)tiofene-co-(3-[5-(4-fenossi)-10,15,20-trifenilporfirinil]esil tiofene] P[T6Br-co-T6TPP] contenenti differenti quantità di porfirina, sono stati sintetizzati sia con metodi non regiospecifici che regiospecifici, con lo scopo di confrontarene le proprietà e di verificare se la strutture macromolecolare che presenta una regiochimica di sostituzione sempre uguale, promuove o meno il trasporto della carica elettrica, migliorando di conseguenza l'efficienza. E' stato inoltre effettuato un ulteriore confronto tra questi derivati e derivati simili P[T6H-co-T6TPP] che non contengono l'atomo di bromo in catena laterale con lo scopo di verificare se l'assenza del gruppo reattivo, migliora o meno la stabilità termica e chimica dei film polimerici, agendo favorevolmete sulle performance dei dispositivi fotovoltaici. Tutti i copolimeri sono stati caratterizzati con differenti tecniche: spettroscopia NMR, FT-IR e UV-Vis, analisi termiche DSC e TGA, e GPC. Le celle solari Bulk Heterojunction, preparate utilizzando PCBM come materiale elettron-accettore e i copolimeri come materilai elettron-donatori, sono state testate utilizzando un multimetro Keithley e il Solar Simulator.

Design of biobased additives for tuning the properties of biopolymers

This work mainly arises from the necessity to support the rapid introduction of different biobased polymers that the industrial sector has been facing lately. Indeed, while considerable efforts are being made to find environmentally and economically sustainable materials, less attention is paid to their need to be properly compounded to fulfil increasingly rigorous technical and quality requirements. Therefore, there is a strong demand for the development of a novel generation of compatible additives able to improve the properties of biobased polymers while respecting sustainability. With this in mind, a new class of biobased plasticizers is herein proposed. Five different ketal-diesters were selectively synthesized starting from levulinic acid, a promising renewable chemical platform. These molecules were added to poly(vinyl chloride) as model polymer to test their plasticizing effectiveness. Complete morphological, thermal and viscoelastic characterizations showed a clear correlation between the structural features of the ketal-esters and the properties of the material. In addition, no significant leaching was found in both hydrophilic and lipophilic environments. Importantly, the proposed ketal-diesters performed comparably and, in some cases, even better than commercial plasticizers. The same molecules were then added to bacterial poly(3-hydroxybutyrate), a semicrystalline polyester characterized by poor thermal and mechanical properties. Morphology assessments showed no phase separation and the plasticizing effectiveness was confirmed by thermal and viscoelastic analyses, while leaching tests showed low extraction values. Readily usable fractions with controlled structure and tailored properties were obtained from highly heterogeneous industrial grade Kraft lignin. These fractions were then added to poly(vinyl alcohol). Promising preliminary results in terms of compatibility were achieved, with thermograms showing only one glass transition temperature. Finally, a fully biobased glycerol-trilevulinate was successfully synthesized by means of a mild and solvent-free route. Its plasticizing effectiveness was evaluated on poly(vinyl chloride), showing a significant decrease of the glass transition temperature of the material.

New functional polythiophene based materials: fine-tuning of photovoltaic or chiroptical properties

There is a remarkable level of interest in the development of π-conjugated polymers (ICPs) which have been employed, thanks to their promising optical and electronic properties, in numerous applications including photovoltaic cells, light emitting diodes and thin-film transistors. Although high power conversion efficiency can be reached using poly(3-alkylthiophenes) (P3ATs) as electron-donating materials in polymeric solar cells of the Bulk-Heterojunction type (BHJ), their relatively large band gap limits the solar spectrum fraction that can be utilized. The research work described in this dissertation thus concerns the synthesis, characterization and study of the optical and photoactivity properties of new organic semiconducting materials based on polythiophenes. In detail, various narrow band gap polymers and copolymers were developed through different approaches and were characterized by several complementary techniques, such as gel permeation chromatography (GPC), NMR spectroscopy, thermal analyses (DSC, TGA), UV-Vis/PL spectroscopy and cyclic voltammetry (CV), in order to investigate their structural and chemical/photophysical properties. Moreover, the polymeric derivatives were tested as active material in air-processed organic solar cells. The activity has also been devoted to investigate the behavior of polythiophenes with chiral side chain, that are fascinating materials capable to assume helix supramolecular structures, exhibiting optical activity in the aggregated state.

Exploring New Material and Analytical Method for Characterization and Conservation of Artifacts

In this dissertation, we focus on developing new green bio-based gel systems and evaluating both the cleaning efficiency and the release of residues on the treated surface, different micro or no destructive techniques, such as optical microscopy, TGA, FTIR spectroscopy, HS-SPME and micro-Spatially Offset Raman spectroscopy (micro-SORS) were tested, proposing advanced analytical protocols. In the first part, a ternary PHB-DMC/BD gel system composed by biodiesel, dimethyl carbonate and poly-3 hydroxybutyrate was developed for cleaning of wax-based coatings applied on indoor bronze. The evaluation of the cleaning efficacy of the gel was carried out on a standard bronze sample which covered a layer of beeswax by restores of Opificio delle Pietre Dure in Florence, and a real case precious indoor bronze sculpture Pulpito della Passione attributed to Donatello. Results obtained by FTIR analysis showed an efficient removal of the wax coating. In the second part, two new kinds of combined gels based on electrospun tissues (PVA and nylon) and PHB-GVL gel were developed for removal of dammar varnish from painting. The electrospun tissue combined gels exhibited good mechanical property, and showed good efficient in cleaning over normal gel. In the third part, green deep eutectic solvent which consists urea and choline chloride was proposed to produce the rigid gel with agar for the removal of proteinaceous coating from oil painting. Rabbit glue and whole egg decorated oil painting mock-ups were selected for evaluating its cleaning efficiency, results obtained by ATR analysis showed the DES-agar gel has good cleaning performance. Furthermore, we proposed micro-SORS as a valuable alternative non-destructive method to explore the DES diffusion on painting mock-up. As a result, the micro-SORS was successful applied for monitoring the liquid diffusion behavior in painting sub-layer, providing a great and useful instrument for noninvasive residues detection in the conservation field.

Smart Textile Sensors for Healthcare Monitoring

Wearable electronic textiles are an emerging research field playing a pivotal role among several different technological areas such as sensing, communication, clothing, health monitoring, information technology, and microsystems. The possibility to realise a fully-textile platform, endowed with various sensors directly realised with textile fibres and fabric, represents a new challenge for the entire research community. Among several high-performing materials, the intrinsically conductive poly(3,4-ethylenedioxythiophene) (PEDOT), doped with poly(styrenesulfonic acid) (PSS), or PEDOT:PSS, is one of the most representative and utilised, having an excellent chemical and thermal stability, as well as reversible doping state and high conductivity. This work relies on PEDOT:PSS combined with sensible materials to design, realise, and develop textile chemical and physical sensors. In particular, chloride concentration and pH level sensors in human sweat for continuous monitoring of the wearer's hydration status and stress level are reported. Additionally, a prototype smart bandage detecting the moisture level and pH value of a bed wound to allow the remote monitoring of the healing process of severe and chronic wounds is described. Physical sensors used to monitor the pressure distribution for rehabilitation, workplace safety, or sport tracking are also presented together with a novel fully-textile device able to measure the incident X-ray dose for medical or security applications where thin, comfortable, and flexible features are essential. Finally, a proof-of-concept for an organic-inorganic textile thermoelectric generator that harvests energy directly from body heat has been proposed. Though further efforts must be dedicated to overcome issues such as durability, washability, power consumption, and large-scale production, the novel, versatile, and widely encompassing area of electronic textiles is a promising protagonist in the upcoming technological revolution.

Design, synthesis and photovoltaic properties of some thiophene-based conjugated polymers for organic solar cells

The current issue of the resource of energy combined with the tendency to give a green footprint to our lifestyle have prompted the research to focus the attention on alternative sources with great strides in the optimization of polymeric photovoltaic devices. The research work described in this dissertation consists in the study of different semiconducting π-conjugated materials based on polythiophenes (Chapter I). In detail, the GRIM polymerization was deepened defining the synthetic conditions to obtain regioregular poly(3-alkylthiophene) (Chapter II). Since the use of symmetrical monomers functionalized with oxygen atom(s) allows to adopt easy synthesis leading to performing materials, disubstituted poly(3,4-dialkoxythiophene)s were successfully prepared, characterized and tested as photoactive materials in solar cells (Chapter III). A “green” resource of energy should be employed through sustainable devices and, for this purpose, the research work was continued on the synthesis of thiophene derivatives soluble in eco-friendly solvents. To make this possible, the photoactive layer was completely tailored starting from the electron-acceptor material. A fullerene derivative soluble in alcohols was successfully synthetized and adopted for the realization of the new devices (Chapter IV). New water/alcohol soluble electron-donor materials with different functional groups were prepared and their properties were compared (Chapter V). Once found the best ionic functional group, a new double-cable material was synthetized optimizing the surface area between the different materials (Chapter VI). Finally, other water/alcohol soluble materials were synthetized, characterized and used as cathode interlayers in eco-friendly devices (Chapter VII). In this work, all prepared materials were characterized by spectroscopy analyses, gel permeation chromatography and thermal analyses. Cyclic voltammetry, X-ray diffraction, atomic force microscopy and external quantum efficiency were used to investigate some peculiar aspects.

Development of textile wearable chemical sensors

In this elaborate, a textile-based Organic Electrochemical Transistor (OECT) was first developed for the determination of uric acid in wound exudate based on the conductive polymer poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), which was then coupled to an electrochemically gated textile transistor consisting of a composite of iridium oxide particles and PEDOT:PSS for pH monitoring in wound exudate. In that way a sensor for multiparameter monitoring of wound health status was assembled, including the ability to differentiate between a wet-dry status of the smart bandage by implementing impedance measurements exploiting the OECT architecture. Afterwards, for both wound management as well as generic health status tracking applications, a glass-based calcium sensor was developed employing polymeric ion-selective membranes on a novel architecture inspired by the Wrighton OECT configuration, which was later converted to a Proof-of-Concept textile prototype for wearable applications. Lastly, in collaboration with the King Abdullah University of Science and Technology (KAUST, Thuwal, Saudi Arabia) under the supervision of Prof. Sahika Inal, different types of ion-selective thiophene-based monomers were used to develop ion-selective conductive polymers to detect sodium ion by different methods, involving standard potentiometry and OECT-based approaches. The textile OECTs for uric acid detection performances were optimized by investigating the geometry effect on the instrumental response and the properties of the different textile materials involved in their production, with a special focus on the final application that implies the operativity in flow conditions to simulate the wound environment. The same testing route was followed for the multiparameter sensor and the calcium sensor prototype, with a particular care towards the ion-selective membrane composition and electrode conditioning protocol optimization. The sodium-selective polymer electrosynthesis was optimized in non-aqueous environments and was characterized by means of potentiostatic and potentiodynamic techniques coupled with Quartz Crystal Microbalance and spectrophotometric measurements.