Browsing by Author "Leiva, Angel"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Monolayers and Thin Films of Dextran Hydrophobically Modified
    (SOC BRASILEIRA QUIMICA, 2010) Leiva, Angel; Munoz, Natalia; Urzua, Marcela; Gargallo, Ligia; Radic, Deodato
    A series of biodegradable graft copolymers were synthesized by grafting epsilon-caprolactone over dextran of different molecular weights. The obtained copolymers were characterized by Fourier transform infrared spectroscopy FTIR, proton nuclear magnetic resonance H-1 NMR, thermogravimetry and elemental analysis. Stable monolayers at the air-water interface and spin coated thin films were prepared and characterized by the Langmuir technique and by contact angle measurements respectively. The compressibility and static surface elasticity of the monolayers and the surface energy of copolymer thin films show dependence with the epsilon-caprolactone content. From these results it can be concluded that the surface properties of grafted copolymers can be modulated by their composition. Additionally, according to the obtained results, epsilon-caprolactone grafted-dextrans show potential for being used in different applications where surface properties are important.
  • Thumbnail Image
    Item
    New three-arm amphiphilic and biodegradable block copolymers composed of poly(6-caprolactone) and poly(N-vinyl-2-pyrrolidone). Synthesis, characterization and self-assembly in aqueous solution
    (ACADEMIC PRESS INC ELSEVIER SCIENCE, 2007) Leiva, Angel; Quina, Frank H.; Araneda, Emilio; Gargallo, Ligia; Radic, Deodato
    The synthesis, characterization and the self-assembly process of a novel biodegradable block copolymer containing a poly (epsilon-caprolactone), PCL, central block and three poly(N-vinyl-2-pyrrolidone), PVP, arms are reported. Three samples with different amounts of PVP were investigated. The copolymers were characterized by FTIR spectroscopy, H-1 NMR and viscosity measurements. The composition and the molecular weights of the block copolymers were established using size exclusion chromatography SEC and H-1 NMR. Micelle formation by these copolymers was monitored by using the vibrational fine structure of pyrene monomer fluorescence and the critical aggregation concentrations, cac, of the copolymers in aqueous solution were determined using sigmoid Boltzmann-type fitting of the fluorescence data. Dynamic light scattering measurements showed a bimodal size distribution for the copolymers in solution, indicating that the micellization is an intermolecular process. Partitioning coefficients of pyrene between copolymer micelles and water were also determined and increase in magnitude with increasing 8-caprolactone content of the copolymer. (c) 2007 Elsevier Inc. All rights reserved.
  • Thumbnail Image
    Item
    Spontaneous Adsorption of Gold Nanoparticles by Polyelectrolyte Thin Films
    (AMER SCIENTIFIC PUBLISHERS, 2012) Urzua, Marcela; Leiva, Angel; Espinoza Beltran, Francisco J.; Briones, Ximena; Saldias, Cesar; Pino, Maximiliano
    Nanocomposed films constituted by gold nanoparticles immobilized onto polyelectrolytes were obtained and studied. To obtain the films, amino terminated silicon wafer surfaces were put in contact with aqueous solution of polyelectrolytes derived from Poly(maleic anhydride-alt-styrene) containing aryl and amine-alkyl groups in the side chains, in this condition the adsorption of macromolecules was achieved. The effects of the chemical nature of the side chains and ionic strength on the amounts of adsorbed polyelectrolytes were studied by ellipsometry. The adsorption of polyelectrolytes increases with increasing ionic strength in agreement with the screening-enhanced adsorption regime; the results are discussed considering the steric hindrance of the side chains and flexibility of the polymers. A spontaneous adsorption process of nanoparticles onto polyelectrolyte films took place when these last were immersed in a gold nanoparticles suspension. The adsorption amounts were qualitatively evaluated by SEM and AFM and these showed to be dependent on chemical structure of polyelectrolytes.