Phase Behavior of Polyelectrolyte Block Copolymers in Mixed Solvents

We have studied the phase behavior of the poly(n-butyl acrylate)-b-poly(acrylic acid) block copolymer in a mixture of two miscible solvents, water and tetrahydrofuran (THF). The techniques used to examine the different polymers, structures and phases formed in mixed solvents were static and dynamic light scattering, small-angle neutron scattering, nuclear magnetic resonance and fluorescence microscopy. By lowering the water/THF mixing ratio X, the sequence unimers, micron-sized droplets, polymeric micelles was observed. The transition between unimers and the micron-sized droplets occurred at X = 0.75, whereas the microstructuration into core-shell polymeric micelles was effective below X = 0.4. At intermediate mixing ratios, a coexistence between the micron-sized droplets and the polymeric micelles was observed. Combining the different aforementioned techniques, it was concluded that the droplet dispersion resulted from a solvent partitioning that was induced by the hydrophobic blocks. Comparison of poly(n-butyl acrylate) homopolymers and poly(n-butyl acrylate)-b-poly(acrylic acid) block copolymers suggested that the droplets were rich in THF and concentrated in copolymers and that they were stabilized by the hydrophilic poly(acrylic acid) moieties.Comment: 11 pages, 12 figures, to appear in Macromolecule

Neutrino conversions in random magnetic fields and ν~e\tilde{\nu}_e from the Sun

The magnetic field in the convective zone of the Sun has a random small-scale component with the r.m.s. value substantially exceeding the strength of a regular large-scale field. For two Majorana neutrino flavors $\times$ two helicities in the presence of a neutrino transition magnetic moment and nonzero neutrino mixing we analyze the displacement of the allowed ($\Delta m^2- \sin^22\theta$)-parameter region reconciled for the SuperKamiokande(SK) and radiochemical (GALLEX, SAGE, Homestake) experiments in dependence on the r.m.s. magnetic field value $b$, or more precisely, on a value $\mu b$ assuming the transition magnetic moment $\mu = 10^{-11}\mu_B$. In contrast to RSFP in regular magnetic fields we find an effective production of electron antineutrinos in the Sun even for small neutrino mixing through cascade conversions $\nu_{eL}\to \nu_{\mu L}\to \tilde{\nu}_{eR}$, $\nu_{eL}\to \nu_{\mu R}\to \tilde{\nu}_{eR}$ in a random magnetic field that would be a signature of the Majorana nature of neutrino if $\tilde{\nu}_{eR}$ will be registered. Basing on the present SK bound on electron antineutrinos we have also found an excluded area in the same $\Delta m^2,~\sin^22\theta$-plane and revealed a strong sensitivity to the random magnetic field correlation length $L_0$.Comment: LaTex 36 pages including 14 PostScript figure

Foundations of the AdS_5 x S^5 Superstring. Part I

We review the recent advances towards finding the spectrum of the AdS_5 x S^5 superstring. We thoroughly explain the theoretical techniques which should be useful for the ultimate solution of the spectral problem. In certain cases our exposition is original and cannot be found in the existing literature. The present Part I deals with foundations of classical string theory in AdS_5 x S^5, light-cone perturbative quantization and derivation of the exact light-cone world-sheet scattering matrix.Comment: 161 page

Interactions between Magnetic Nanowires and Living Cells : Uptake, Toxicity and Degradation

We report on the uptake, toxicity and degradation of magnetic nanowires by NIH/3T3 mouse fibroblasts. Magnetic nanowires of diameters 200 nm and lengths comprised between 1 {\mu}m and 40 {\mu}m are fabricated by controlled assembly of iron oxide ({\gamma}-Fe2O3) nanoparticles. Using optical and electron microscopy, we show that after 24 h incubation the wires are internalized by the cells and located either in membrane-bound compartments or dispersed in the cytosol. Using fluorescence microscopy, the membrane-bound compartments were identified as late endosomal/lysosomal endosomes labeled with lysosomal associated membrane protein (Lamp1). Toxicity assays evaluating the mitochondrial activity, cell proliferation and production of reactive oxygen species show that the wires do not display acute short-term (< 100 h) toxicity towards the cells. Interestingly, the cells are able to degrade the wires and to transform them into smaller aggregates, even in short time periods (days). This degradation is likely to occur as a consequence of the internal structure of the wires, which is that of a non-covalently bound aggregate. We anticipate that this degradation should prevent long-term asbestos-like toxicity effects related to high aspect ratio morphologies and that these wires represent a promising class of nanomaterials for cell manipulation and microrheology.Comment: 21 pages 12 figure

Encapsulação de nanopartículas de Gd2O3: Eu3+ SiO2 com agentes RAFT macromoleculares de PAA

Mestrado em Ciência e Engenharia dos MateriaisO desenvolvimento de novos materiais com propriedades funcionais é uma constante necessidade para a maturação e sustentabilidade da sociedade como um todo. No que diz respeito aos nanocompósitos de matriz polimérica, uma das maiores restrições ao seu uso é a preservação e o controlo das propriedades físicas únicas das cargas de dimensões nanométricas, sendo portanto essencial manter a sua integridade e conseguir dispersões uniformes. Tal é particularmente difícil no caso de nanopartículas anisotrópicas, tais como as fibras de Gd2O3:Eu 3+ revestidas com sílica utilizadas nesta tese. Nesse sentido, estudou-se a utilização de agentes RAFT macromoleculares para preparar nanocompósitos de matriz polimérica inorgânicos quer em solução quer em emulsão. Numa primeira fase estudou-se a preparação do agente RAFT macromolecular a partir do agente RAFT ácido 2-{[(dodeciltio)carbonotioil]tio]-2- metilpropanóico (TTCA) e do ácido acrílico para diferentes graus de conversão, tendo-se obtido polímeros controlados e com distribuições de massa moleculares (PDI) estreitas. Seguidamente, verificou-se que o sistema apresenta as características de um sistema vivo por co-polimerização com o acrilato de butilo (BuA) tanto em emulsão como em solução. No entanto, não se obteve controlo no PDI, nomeadamente quando a polimerização foi realizada em emulsão. Apesar de não se ter conseguido optimizar este sistema, a sua utilização foi explorada na preparação de nanocompósitos de sílica e depois estendido a fibras de Gd2O3:Eu3+ revestidas com sílica. Com o objectivo de aumentar a afinidade entre o polímero e as cargas, as nanopartículas inorgânicas foram funcionalizadas com agentes de acoplamento à base de silano. Os nanocompósitos obtidos foram depois caracterizados por FT-IR, DSC, SEM, e PL. Os resultados obtidos por SEM e FTIR-ATR permitiram confirmar que a preparação dos nancompósitos foi bem sucedida. Porém os resultados de DSC foram inconclusivos e os de fotolumiscência indicam que após funcionalização com o 3-aminopropilo trimetoxisilano (APS) o sinal é reduzido sendo esse efeito agravado após encapsulamento na matriz polimérica. Por fim são apresentados alguns resultados relativos à preparação de filmes finos dos nanocompósitos de modo a avaliar a presença de alguma anisotropia.New materials with functional properties are a consistent necessity for the maturation and sustainability of society on a whole. One main restriction when polymer based nanocomposites are concerned is the preservation and control of the unique physical properties of the nanometric fillers. However, it is quite essential to maintain their nanoscale integrity and hitherto achieve uniform dispersions, which is extremely challenging especially when anisotropic nanoparticles are brought into the limelight, such as Gd2O3:Eu3+ fibers coated with silica studied in this thesis. In this regard, polymer nanocomposites were devised using a macroRAFT agent both in solution and emulsion. Initially, the homopolymerization of acrylic acid (AA) using 2- {[(dodecylthio)carbonothioyl]thio}-2-methylpropanoic acid (TTC-A), to yield the macroRAFT agent (PAATTC) was studied for varying degrees of conversion and narrow molar mass distributions prevailed. Next, the copolymerization of PAATTC with n-butyl acrylate (nBuA) was carried out in both emulsion and solution conditions to test the livingness of the system which was confirmed, but proved to be uncontrolled. Despite the fact that this system was not optimized, it was utilized in the preparation of silica nanocomposites and extended to the preparation of Gd2O3:Eu3+@silica nanocomposites. In order to increase the affinity between the polymer and the inorganic nanofillers, the latter was functionalized using suitable silane coupling agents. The nanocomposites obtained were characterized by FTIR, SEM, DSC, and PL. While SEM and FTIR, confirmed the successful formation of nanocomposites, the DSC results were inconclusive and the PL results of Gd2O3:Eu3+@silica showed a decrease in the signal intensity, upon functionalization with 3-aminopropyl trimethoxysilane (APS), which was further aggravated upon encapsulation in the polymeric matrix. Finally, some preliminary results regarding the preparation of composite thin films to assess the presence of any anisotropy are documented

The Aqueous Dispersion of Carbon Nanotubes

This work has focused on the use of biological molecules such as amino acids, glycolic acids, ribonucleosides and simple sugars to improve MWCNT aqueous dispersibility through both covalent and non-covalent functionalisation. Oxidative treatment of MWCNTs with 6 M nitric acid has been shown to be a mild, yet effective method for introducing carboxylic acid groups, which are known to improve their dispersion, to the surface. The subsequent ionic interactions of these carboxylic acid groups with selected acidic, basic and neutral amino acids was investigated with a view to this further increasing the aqueous dispersibility of the MWCNTs. Of the amino acids considered basic arginine was found to provide the greatest improvement with the MWCNT concentration increasing from 0.35 to 6.79 mg/mL. The carboxylic acid groups of the oxidised MWCNTs were also used to covalently attach the amino acids through formation of an amide bond. In this instance taurine was found to be the most effective amino acid with dispersibility more than doubling. Non-covalent functionalisation of the MWCNTs was also achieved with taurine functionalised poly(acrylic acid), which resulted in a vefold increase in the concentration of MWCNTs dispersed when compared with poly(acrylic acid). Diazonium chemistry is widely used for the functionalisation of CNTs with aryl groups and in this work a diazonium reaction was used to covalently functionalise MWCNTs with pyridine. These pyridine groups were then used as the basis for the covalent attachment of the sugars ribose, fructose and sucrose. Functionalisation with pyridine alone did not improve the aqueous dispersion of the MWCNTs, however the subsequent attachment of the sugars led to enhanced MWCNT dispersibility with sucrose the most effective at 20 ug/mL. The effect of functionalisation on MWCNT dispersibility was probed using UV-vis- NIR spectroscopy. The modied MWCNTs were further characterised using TGA, TEM, Raman and FTIR spectroscopy

Polyelectrolyte complexes embedding reduced graphite oxide

L'abstract è presente nell'allegato / the abstract is in the attachmen

Impaired coronary blood flow at higher heart rates during atrial fibrillation: investigation via multiscale modelling

Background. Different mechanisms have been proposed to relate atrial fibrillation (AF) and coronary flow impairment, even in absence of relevant coronary artery disease (CAD). However, the underlying hemodynamics remains unclear. Aim of the present work is to computationally explore whether and to what extent ventricular rate during AF affects the coronary perfusion. Methods. AF is simulated at different ventricular rates (50, 70, 90, 110, 130 bpm) through a 0D-1D multiscale validated model, which combines the left heart-arterial tree together with the coronary circulation. Artificially-built RR stochastic extraction mimics the \emph{in vivo} beating features. All the hemodynamic parameters computed are based on the left anterior descending (LAD) artery and account for the waveform, amplitude and perfusion of the coronary blood flow. Results. Alterations of the coronary hemodynamics are found to be associated either to the heart rate increase, which strongly modifies waveform and amplitude of the LAD flow rate, and to the beat-to-beat variability. The latter is overall amplified in the coronary circulation as HR grows, even though the input RR variability is kept constant at all HRs. Conclusions. Higher ventricular rate during AF exerts an overall coronary blood flow impairment and imbalance of the myocardial oxygen supply-demand ratio. The combined increase of heart rate and higher AF-induced hemodynamic variability lead to a coronary perfusion impairment exceeding 90-110 bpm in AF. Moreover, it is found that coronary perfusion pressure (CPP) is no longer a good measure of the myocardial perfusion for HR higher than 90 bpm.Comment: 8 pages, 5 figures, 3 table