Galder Kortaberria

Effect of different aqueous synthesis parameters on the size of CdSe nanocrystals

The variation of CdSe nanoparticle size as a function of synthesis conditions is presented. Cadmium sulphate (CdSO4), cadmium chloride (CdCl2) and sodium selenosulphate (Na2SeSO3) solutions were used as precursors. Nanoparticles were synthesized by aqueous chemical methods. The synthesis parameters studied were pH, Cd:Se ratio and the type of stabilizing agent. Three different stabilizing agents were used, thioglycolic acid, mercaptoethanol and poly(vinyl pyrrolidone). Fourier transform infrared spectroscopy results confirmed the presence of the stabilizing agent on the surface of the nanoparticles. Ultraviolet visible and X-ray powder diffraction measurements were used to estimate the trend of size variations of the particles with different synthesis parameters, which agreed fairly by both techniques and the crystal structure. Additionally, the size of the nanoparticles was obtained by transmission electron microscopy measurements. Whilst the effect of pH was different for each of the different stabilizing agents due to the different chemical groups in the thiol compounds and the size of the nanoparticles varied with the used stabilizing agents, the effect of Cd:Se ratio in the size of nanoparticles showed the same tendency for the several stabilizing agents.

Crystallization of poly(l‐lactid acid) monitored by dielectric relaxation spectroscopy and atomic force microscopy

An investigation was carried out on the crystallization process of poly(l‐lactid acid) by dielectric relaxation spectroscopy and atomic force microscopy. Experimental results were generated by dielectric relaxation spectroscopy over a wide range of frequency and temperature in both the wholly amorphous state and during crystallization. The variation of the average relaxation time was studied during crystallization at 80 °C and the temperature dependence of this relaxation time for wholly amorphous and crystallized samples was analysed. This behaviour was modelled by Havriliak‐Negami and Vogel‐Fulcher equations. The sensitivity of the segmental dynamics to the degree of crystallinity was analysed, taking into account the relaxing segments and the thickness of the amorphous layer between lamellae. The morphologies obtained during crystallization processes at 80, 130 and 150 °C were monitored by atomic force microscopy at both the lamellar level and by analysing the multilayered superstructures formed. Hedrites, intermediate structures between single lamellar crystals and mature spherulites, were found to appear at the highest temperatures, whereas no evidence of hedrites was found at 80 °C, the spherulites seemed to be constructed from a framework of individual dominant lamellae that splay apart and branch. Complementary to the atomic force microscopy study, the evolution of the obtained morphologies was also followed by optical microscopy. Supporting evidence about the thermal behaviour of the polymers was obtained with differential scanning calorimetry.

Effect of CdSe nanoparticle addition on nanostructuring of PS-b-P4VP copolymer via solvent vapor exposure

The surface morphology of poly(styrene-b-4 vinyl pyridine) (PS-b-P4VP) diblock copolymer thin films after solvent vapor annealing has been studied. Morphological features can be switched upon exposure to vapors of a solvent selective for one of the blocks. Self-assembled nanostructures such as hexagonal or striped morphologies were obtained varying vapor exposure time. In addition, the effect of the presence of CdSe nanoparticles located in the P4VP block on obtained nanostructures was analyzed. Atomic force microscopy (AFM) was used for morphological characterization of the block copolymer and the nanocomposites. AFM images showed that nanostructuring was different depending on the amount of CdSe nanoparticles, due to the decrease in P4VP chain mobility.

Synthesis and characterization of nanostructured PS-b-P4VP/Fe2O3 thin films with magnetic properties prepared by solvent vapor annealing

In this work hybrid organic/inorganic nanocomposites with magnetic properties, based on a PS-b-P4VP block copolymer and Fe2O3 maghemite nanoparticles have been prepared. The nanoparticles were surface modified with PS brushes by the grafting through method. The morphology of the neat block copolymer and nanocomposites was analyzed by AFM. For nanostructuring, thin films were annealed under dioxane vapors, a selective solvent for the PS block. The morphology of the neat copolymer thin films changed from hexagonal to strips with exposure time. The addition of the nanoparticles also modified the morphology of the nanocomposites, especially the higher nanoparticle contents. For all cases the nanoparticles were selectively dispersed into PS domains. Moreover, magnetic characterization by VSM and SQUID has demonstrated that the magnetic properties of the nanoparticles have been transferred to the nanocomposites.

Synthesis and Characterization of a Branched Poly(Methacrylamide): Thermal Stability and Molecular Simulation Studies of Their Blends With Vinylic Polymers

The synthesis of a poly(diethylaminoethyl methacrylamide) (BP), based on a lineal methacrylamide with diethylaminoethyl branches was carried out. Thermal behavior was studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Relatively high thermal stability is found. Blends with poly(methylmethacrylate) (PMMA), poly(acrylic acid) (PAA) and poly(monomethyl itaconate) (PMMI) were prepared. Their thermal properties in blends were studied together with miscibility, in order to improve thermal properties of vinylic polymer blends. An increase of thermal stability was found for certain blend compositions. By FTIR analysis, higher band displacements were found for low BP compositions. AFM and molecular simulation analysis were carried out in order to elucidate the structural origin leading to thermal stability and miscibility increases. Hydrophobic interactions among methyl end groups of BP and methylene groups of vinylic polymers should be the responsible of miscibility and thermal stability increases.

PI- b -PMMA diblock copolymers: nanostructure development in thin films and nanostructuring of thermosetting epoxy systems

Poly(isoprene-block-methyl methacrylate) (PI-b-PMMA) block copolymers with different block ratios have been used to generate nanostructures both in thin films and by nanostructuring a thermosetting epoxy system. Obtained morphologies have been analyzed in terms of atomic force microscopy. The nanostructuring of thin films was carried out by thermal and solvent vapor annealing, in which the copolymer films were exposed to acetone vapors, selective solvent for methyl methacrylate (PMMA) block. By solvent vapor annealing thin films of both copolymers self-assembled into a hexagonally packed cylindrical morphology. Thermal annealing was carried out above the glass transition temperature of both blocks, obtaining worm-like and lamellar morphologies, depending on the block ratio. One of the copolymers has also been used for nanostructuring an epoxy thermosetting system. Morphologies consisting of spherical-shaped PI domains dispersed in a continuous epoxy matrix in which PMMA remained miscible were obtained, independently of the copolymer amount.

Morphological and magnetic properties of PS-b-PMMA diblock copolymer based nanocomposites

Block copolymers constitute an interesting platforms to host inorganic nanoparticles for obtaining new materials with advantageous properties. In this case, PS-b-PMMA block copolymer self-assembled into a lamellar nanostructure has been used to disperse magnetic Fe2O3 nanoparticles, resulting in a polymeric nanocomposite with magnetic properties. In order to obtain a good and selective dispersion of nanoparticles into the nanostructured block copolymer, the surface of nanoparticles has been modified both with a silane as a compatibilising agent or with poly(methyl methacrylate) (PMMA) brushes. Morphology of nanocomposites has been characterized by atomic force microscopy (AFM) while magnetic characterization has been carried out with a vibrating sample magnetometer (VSM).Block copolymers constitute an interesting platforms to host inorganic nanoparticles for obtaining new materials with advantageous properties. In this case, PS-b-PMMA block copolymer self-assembled into a lamellar nanostructure has been used to disperse magnetic Fe2O3 nanoparticles, resulting in a polymeric nanocomposite with magnetic properties. In order to obtain a good and selective dispersion of nanoparticles into the nanostructured block copolymer, the surface of nanoparticles has been modified both with a silane as a compatibilising agent or with poly(methyl methacrylate) (PMMA) brushes. Morphology of nanocomposites has been characterized by atomic force microscopy (AFM) while magnetic characterization has been carried out with a vibrating sample magnetometer (VSM).

Exploring the Self-Assembly Capabilities of ABA-Type SBS, SIS, and Their Analogous Hydrogenated Copolymers onto Different Nanostructures Using Atomic Force Microscopy

In this work, the self-assembled morphologies obtained for poly(styrene-b-butadiene-b-styrene) (SBS) and poly(styrene-b-isoprene-b-styrene) (SIS) ABA-type copolymers were investigated before and after hydrogenation of the polydiene block, which led to poly(styrene-b-ethylene)/poly(ethylene-b-styrene) (SEES) and poly(styrene-b-ethylene)/poly(propylene-b-styrene) (SEPS) copolymers, respectively. The evaluation of different morphologies was carried out using atomic force microscopy (AFM), analyzing the effect of various parameters such as the solvent and polymer concentrations employed for film casting (toluene, cyclohexane, or tetrahydrofurane with concentrations of 1 and 3 wt%), together with that of the annealing treatment (thermal annealing at room temperature, and 60, 80, and 100 °C). The effect of these parameters in combination with the chemical nature of the polydiene block led to different morphologies with different topographic aspects affecting the roughness (Ra) of the film.

Polyitaconates: a new family of “all polymer” dielectrics

This work presents the synthesis of new poly(itaconate)s containing sulfone or nitrile pendant groups through conventional radical polymerization together with their characterization and comparison with poly(methacrylate)s containing identical groups. Structural and thermal characterization has been carried out in terms of Fourier transform infrared spectroscopy, differential scanning calorimetry, nuclear magnetic resonance, and thermogravimetric analysis. Characterized by broad band dielectric spectroscopy (BDS), all polymers showed dielectric constant values between 7 and 10 (at 25 °C and 1 kHz) and relative low dielectric loss values (≈0.02). BDS measurements showed, for all the polymers analyzed, notorious subglass transitions even at temperatures below -100 °C, resulting in a broad temperature interval in which these polymers exhibit high dielectric constant and could work without high losses. Therefore, these materials seem to be good candidates for dielectric applications such as energy storage, among others.

Rheokinetic and Dynamic Mechanical Analysis of Tetrafunctional Epoxy/anhydride Mixtures. Influence of Stoichiometry and Cure Conditions

The copolymerization of hexahydrophthalic anhydride (HHPA) with N,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenylmethane (TGDDM) has been studied for several stoichiometric ratios. The rheological, thermal and dynamic mechanical behaviors of these systems were examined. Kinetic studies by differential scanning calorimetry, in both isothermal and dynamic modes, showed a first-order kinetics. Activation energies were also obtained by rheological measurements, through gelation times at different temperatures, with results in agreement with calorimetric results. The dynamic mechanical behavior was studied to analyse the influence of both stoichiometric ratio and cure schedule in the viscoelastic properties of the mixtures.