Degrado e protezione del calcestruzzo armato

Il presente lavoro si propone di analizzare il calcestruzzo armato come materiale da costruzione, in particolare focalizzando l’attenzione sulle tecniche di prevenzione di alcuni tipi di degrado con l’utilizzo di trattamenti superficiali. Il calcestruzzo è uno dei materiali da costruzione più utilizzati in quanto presenta molteplici vantaggi come la libertà di forma, il basso costo dei materiali ed il buon comportamento strutturale. Nonostante quanto detto, si possono evidenziare delle criticità inerenti all’utilizzo di questo materiale, il tema centrale di questo lavoro è quello di analizzare nuove tecniche di protezione atte a salvaguardare la struttura da tre diverse tipologie di degrado, valutandone l’effettiva efficacia nell’ottenere quello per cui sono state previste. Nei primi capitoli si esaminerà il calcestruzzo come materiale da costruzione e saranno spiegati i processi che il conglomerato cementizio deve compiere per diventare un materiale indurito e resistente. Nel terzo capitolo si affronteranno, senza entrare nella descrizione puntuale di ciascuna di esse, le diverse cause di degrado del calcestruzzo armato. Infine nel quarto ed ultimo capitolo, verranno esposti tre casi studio: il primo tratta di un tipo di degrado spesso non preso in considerazione ma causante ingenti danni all’aspetto paesaggistico e al patrimonio storico: si analizzano i rivestimenti da poter applicare al calcestruzzo per rendere più semplificato il processo di rimozione dai graffiti. Il secondo si ripromette di analizzare l’efficacia nel proteggere le armature di acciaio dalla corrosione per mezzo un nuovo tipo di pigmenti core-shell poco costosi ma soprattutto ecosostenibili. Infine si porrà lo sguardo su un problema non indifferente ovvero quello della protezione del calcestruzzo armato dalle alte temperature anche in questo caso utilizzando un trattamento superficiale volto a migliorare le performance del calcestruzzo durante l’incendio.

Fracture Toughening and Self-Healing of Composite Laminates by Nanofibrous Mats Interleaving

Composite laminates present important advantages compared to conventional monolithic materials, mainly because for equal stiffness and strength they have a weight up to four times lower. However, due to their ply-by-ply nature, they are susceptible to delamination, whose propagation can bring the structure to a rapid catastrophic failure. In this thesis, in order to increase the service life of composite materials, two different approaches were explored: increase the intrinsic resistance of the material or confer to them the capability of self-repair. The delamination has been hindered through interleaving the composite laminates with polymeric nanofibers, which completed the hierarchical reinforcement scale of the composite. The manufacturing process for the integration of the nanofibrous mat in the laminate was optimized, resulting in an enhancement of mode I fracture toughness up to 250%. The effect of the geometrical dimensions of the nano-reinforcement on the architecture of the micro one (UD and woven laminates) was studied on mode I and II. Moreover, different polymeric materials were employed as nanofibrous reinforcement (Nylon 66 and polyvinylidene fluoride). The nano toughening mechanism was studied by micrograph analysis of the crack path and SEM analysis of the fracture surface. The fatigue behavior to the onset of the delamination and the crack growth rate for woven laminates interleaved with Nylon 66 nanofibers was investigated. Furthermore, the impact behavior of GLARE aluminum-glass epoxy laminates, toughened with Nylon 66 nanofibers was investigated. Finally, the possibility of confer to the composite material the capability of self-repair was explored. An extrinsic self-healing-system, based on core-shell nanofibers filled with a two-component epoxy system, was developed by co-electrospinning technique. The healing potential of the nano vascular system has been proved by microscope electron observation of the healing agent release as result of the vessels rupture and the crosslinking reaction was verified by thermal analysis.

Electrospun hierarchical artificial muscle for soft robotics applications

Nowadays, one of the most ambitious challenges in soft robotics is the development of actuators capable to achieve performance comparable to skeletal muscles. Scientists have been working for decades, inspired by Nature, to mimic both their complex structure and their perfectly balanced features in terms of linear contraction, force-to-weight ratio, scalability and flexibility. The present Thesis, contextualized within the FET open Horizon 2020 project MAGNIFY, aims to develop a new family of innovative flexible actuators in the field of soft-robotics. For the realization of this actuator, a biomimetic approach has been chosen, drawing inspiration from skeletal muscle. Their hierarchical fibrous structure was mimicked employing the electrospinning technique, while the contraction of sarcomeres was designed employing chains of molecular machines, supramolecular systems capable of performing movements useful to execute specific tasks. The first part deals with the design and production of the basic unit of the artificial muscle, the artificial myofibril, consisting in a novel electrospun core-shell nanofiber, with elastomeric shell and electrically conductive core, coupled with a conductive coating, for the realization of which numerous strategies have been investigated. The second part deals instead with the integration of molecular machines (provided by the project partners) inside these artificial myofibrils, preceded by the study of several model molecules, aimed at simulating the presence of these molecular machines during the initial phases of the project. The last part concerns the realization of an electrospun multiscale hierarchical structure, aimed at reproducing the entire muscle morphology and fibrous organization. These research will be joined together in the near future like the pieces of a puzzle, recreating the artificial actuator most similar to biological muscle ever made, composed of millions of artificial myofibrils, electrically activated in which the nano-scale movement of molecular machines will be incrementally amplified to the macro-scale contraction of the artificial muscle.

A glassful of graphene: graphene-based materials for drinking water remediation

Modern world suffers from an intense water crisis. Emerging contaminants represent one of the most concerning elements of this issue. Substances, molecules, ions, and microorganisms take part in this vast and variegated class of pollutants, which main characteristic is to be highly resistant to traditional water purification technologies. An intense international research effort is being carried out in order to find new and innovative solutions to this problem, and graphene-based materials are one of the most promising options. Graphene oxide (GO) is a nanostructured material where domains populated by oxygenated groups alternate with interconnected areas of sp2 hybridized carbon atoms, on the surface of a one-atom thick nanosheets. GO can adsorb a great number of molecules and ions on its surface, thanks to the variety of different interactions that it can express, such as hydrogen bonding, p-p stacking, and electrostatic and hydrophobic interaction. These characteristics, added to the high superficial area, make it an optimal material for the development of innovative materials for drinking water remediation. The main concern in the use of GO in this field is to avoid secondary contaminations (i.e. GO itself must not become a pollutant). This issue can be faced through the immobilization of GO onto polymeric substrates, thus developing composite materials. The use of micro/ultrafiltration polymeric hollow fibers as substrates allows the design of adsorptive membranes, meaning devices that can perform filtration and adsorption simultaneously. In this thesis, two strategies for the development of adsorptive membranes were investigated: a core-shell strategy, where hollow fibers are coated with GO, and a coextrusion strategy, where GO is embedded in the polymeric matrix of the fibers. The so-obtained devices were exploited for both fundamental studies (i.e. molecular and ionic behaviour in between GO nanosheets) and real applications (the coextruded material is now at TRL 9).

Sintesi assistita al microonde di nanoparticelle Au/Pt per applicazioni catalitiche

Negli ultimi decenni la necessità di salvaguardare l’ambiente ha portato ad un importante sviluppo dei processi catalitici con particolare attenzione agli aspetti di sostenibilità e impatto ambientale. Le nanoparticelle metalliche, note per le ottime proprietà catalitiche, ricoprono un ruolo fondamentale nel settore della catalisi. Al fine di innescare effetti sinergici e ottenere catalizzatori più performanti, la ricerca si sta orientando verso lo studio di nanoparticelle bimetalliche o multicomponente. Questo lavoro di tesi presenta la sintesi di nanoparticelle di Au, Pt e AuPt applicabili in catalisi e preparate mediante un processo a basso impatto ambientale assistito da microonde. Un’estesa caratterizzazione chimicofisica dei prodotti (DLS/ELS, UV-VIS, ICP-OES, XRD; TEM-EDS) ha consentito di ottimizzare le sintesi rispetto a distribuzione granulometrica, stabilità colloidale, resa di reazione e composizione di fase. Per AuPt NPs si sono sviluppate due preparazioni finalizzate all’ottenimento di diverse nanostrutture, core-shell e leghe. Infine, le prestazioni catalitiche dei campioni preparati sono state valutate mediante idrogenazione di 4-nitrofenolo (4-NP) a 4-amminofenolo (4-AP) in presenza di NaBH4, una reazione modello utilizzata per testare l'attività catalitica di nanometalli. Il campione in lega, Au97.5Pt2.5, e il campione core-shell, Au90@Pt10, hanno evidenziato effetti sinergici positivi con una migliore attività catalitica rispetto ai monometalli.

Caratterizzazione delle proprietà elettriche di nanocompositi a matrice epossidica additivata con Quantum Dots

Questo elaborato prevede la caratterizzazione delle proprietà elettriche di nanocompositi a matrice epossidica additivata con Quantum Dots. Inizialmente sono state presentate le caratteristiche fondamentali dei materiali polimerici con particolare attenzione alle proprietà elettriche. In seguito, sono stati descritti i temi pratici e teorici delle misure che permettono di ottenere i risultati utili alla caratterizzazione, nello specifico: Spettroscopia Dielettrica, metodo Pulsed Electro-Acustic (PEA), Prova di Conducibilità e metodo Thermally Simulated Depolarization Current (TSDC). Le misure sono state effettuate su dei provini di resina epossidica vergine e nanocompositi Epoxy/QDsCS. Sono stati esposti i processi fondamentali che portano alla realizzazione dei diversi provini e di seguito sono stati mostrati i risultati delle misure precedentemente elencate. L’analisi e l’elaborazione dei dati ha portato alla caratterizzazione finale e permette di concludere che l’inserzione di Quantum Dots Core-Shell non provoca variazioni della conducibilità del materiale ma ne modifica le proprietà dielettriche, quali profondità di trappola e carica di spazio.

In situ studies of titania-supported Au shell-Pd core nanoparticles for the selective aerobic oxidation of crotyl alcohol

The thermal evolution of titania-supported Au shell–Pd core bimetallic nanoparticles, prepared via colloidal routes, has been investigated by in situ XPS, DRIFTS, EXAFS and XRD and ex situ HRTEM. As-prepared nanoparticles are terminated by a thin (∼5 layer) Au shell, encapsulating approximately 20 nm diameter cuboctahedral palladium cores, with the ensemble stabilised by citrate ligands. The net gold composition was 40 atom%. Annealing in vacuo or under inert atmosphere rapidly pyrolyses the citrate ligands, but induces only limited Au/Pd intermixing and particle growth <300 °C. Higher temperatures promote more dramatic alloying, accompanied by significant sintering and surface roughening. These changes are mirrored by the nanoparticle catalysed liquid phase selective aerobic oxidation of crotyl alcohol to crotonaldehyde; palladium surface segregation enhances both activity and selectivity, with the most active surface alloy attainable containing ∼40 atom% Au.

Involvement of dopaminergic mechanisms in the nucleus accumbens core and shell subregions in the expression of fear conditioning

The involvement of dopamine (DA) mechanisms in the nucleus accumbens (NAC) in fear conditioning has been proposed by many studies that have challenged the view that the NAC is solely involved in the modulation of appetitive processes. However, the role of the core and shell subregions of the NAC in aversive conditioning remains unclear. The present study examined DA release in these NAC subregions using microdialysis during the expression of fear memory. Guide cannulae were implanted in rats in the NAC core and shell. Five days later, the animals received 10 footshocks (0.6 mA, 1 s duration) in a distinctive cage A (same context). On the next day, dialysis probes were inserted through the guide cannulae into the NAC core and shell subregions, and the animals were behaviorally tested for fear behavior either in the same context (cage A) or in a novel context (cage B). Dialysates were collected every 5 min for 90 min and analyzed by high-performance liquid chromatography. The rats exhibited a significant fear response in cage A but not in cage B. Moreover, increased DA levels in both NAC subregions were observed 5-25 min after the beginning of the test when the animals were tested in the same context compared with accumbal DA levels from rats tested in the different context. These findings Suggest that DA mechanisms in both the NAC core and shell may play an important role in the expression of contextual fear memory. (c) 2008 Elsevier Ireland Ltd. All rights reserved.

Influence of nucleus accumbens core or shell stimulation on early long-term potentiation in the dentate gyrus of freely moving rats

Magdeburg, Univ., Fak. für Naturwiss., Diss., 2010

Nonmesonic weak decay of Λ-hypernuclei within independent-particle shell-model

After a short introduction to the nonmesonic weak decay (NMWD) ΛN→nN of Λ-hypernuclei we discuss the long-standing puzzle on the ratio Γn/Γp, and some recent experimental evidences that signalized towards its final solution. Two versions of the Independent-Particle-Shell-Model (IPSM) are employed to account for the nuclear structure of the final residual nuclei. They are: (a) IPSM-a, where no correlation, except for the Pauli principle, is taken into account, and (b) IPSM-b, where the highly excited hole states are considered to be quasi-stationary and are described by Breit-Wigner distributions, whose widths are estimated from the experimental data. We evaluate the coincidence spectra in Λ 4He, Λ 5He, Λ 12C, Λ 16O, and Λ 28Si, as a function of the sum of kinetic energies EnN=En+EN for N=n, p. The recent Brookhaven National Laboratory experiment E788 on Λ 4He, is interpreted within the IPSM. We found that the shapes of all the spectra are basically tailored by the kinematics of the corresponding phase space, depending very weakly on the dynamics, which is gauged here by the one-meson-exchange- potential. In spite of the straightforwardness of the approach a good agreement with data is achieved. This might be an indication that the final-state- interactions and the two-nucleon induced processes are not very important in the decay of this hypernucleus. We have also found that the π+K exchange potential with soft vertex-form-factor cutoffs (Λπ≈0. 7GeV, ΛK≈0.9GeV), is able to account simultaneously for the available experimental data related to Γp and Γn for Λ 4H, and Λ 5He. © 2010 American Institute of Physics.

Scale Up of PLA Nanoparticle Synthesis by Solvent Displacement and Functionalization of the Particles with a Silica Shell for Targeted Drug Delivery Applications

Biodegradable polymer nanoparticles have the properties necessary to address many of the issues associated with current drug delivery techniques including targeted and controlled delivery. A novel drug delivery vehicle is proposed consisting of a poly(lactic acid) nanoparticle core, with a functionalized, mesoporous silica shell. In this study, the production of PLA nanoparticles is investigated using solvent displacement in both a batch and continuous manner, and the effects of various system parameters are examined. Using Pluronic F-127 as the stabilization agent throughout the study, PLA nanoparticles are produced through solvent displacement with diameters ranging from 200 to 250 nm using two different methods: dropwise addition and in an impinging jet mixer. The impinging jet mixer allows for easy scale-up of particle production. The concentration of surfactant and volume of quench solution is found to have minimal impact on particle diameter; however, the concentration of PLA is found to significantly impact the diameter mean and polydispersity. In addition, the stability of the PLA nanoparticles is observed to increase as residual THF is evaporated. Lastly, the isolated PLA nanoparticles are coated with a silica shell using the Stöber Process. It is found that functionalizing the silica with a phosphonic silane in the presence of excess Pluronic F-127 decreases coalescence of the particles during the coating process. Future work should be conducted to fine-tune the PLA nanoparticle synthesis process by understanding the effect of other system parameters and in synthesizing mesoporous silica shells.

The pollen tube: a soft shell with a hard core

Plant cell expansion is controlled by a fine-tuned balance between intracellular turgor pressure, cell wall loosening and cell wall biosynthesis. To understand these processes, it is important to gain in-depth knowledge of cell wall mechanics. Pollen tubes are tip-growing cells that provide an ideal system to study mechanical properties at the single cell level. With the available approaches it was not easy to measure important mechanical parameters of pollen tubes, such as the elasticity of the cell wall. We used a cellular force microscope (CFM) to measure the apparent stiffness of lily pollen tubes. In combination with a mechanical model based on the finite element method (FEM), this allowed us to calculate turgor pressure and cell wall elasticity, which we found to be around 0.3 MPa and 20–90 MPa, respectively. Furthermore, and in contrast to previous reports, we showed that the difference in stiffness between the pollen tube tip and the shank can be explained solely by the geometry of the pollen tube. CFM, in combination with an FEM-based model, provides a powerful method to evaluate important mechanical parameters of single, growing cells. Our findings indicate that the cell wall of growing pollen tubes has mechanical properties similar to rubber. This suggests that a fully turgid pollen tube is a relatively stiff, yet flexible cell that can react very quickly to obstacles or attractants by adjusting the direction of growth on its way through the female transmitting tissue.