DSpace Angular :: Browsing by Author "Gargallo, Ligia"

Browsing by Author "Gargallo, Ligia"

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Blends containing chitosan and poly(sodium-4-styrene sulphonate). Compatibility behavior
(ELSEVIER SCI LTD, 2011) Castro, Cristian; Gargallo, Ligia; Radic, Deodato; Kortaberria, Galder; Mondragon, Inaki
The phase behavior of blends containing chitosan (CS) and poly(sodium-4-styrene sulphonate) (PSS) was analyzed by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), fourier transform infrared spectroscopy (FOR), dielectric spectroscopy (DRS) and atomic force microscopy (AFM). FTIR and DRS analysis seem to indicate the existence of interactions between sulphonate groups of PSS and -NH2 or -OH or both groups of CS. The study of blends by AFM showed a completely different morphology when compared with that of pure components as nanocrystalline domains appeared as globular agglomerates containing more or less spherical particles instead of the independent nanodomains seen in the neat components, possibly as consequence of interactions between both polymers. (C) 2010 Elsevier Ltd. All rights reserved.
Blends of chitosan and poly(sodium-4-styrene sulphonate). Compatibilization by lysine and glutamic acid
(ELSEVIER SCI LTD, 2010) Castro, Cristian; Gargallo, Ligia; Radic', Deodato; Mondragon, Inaki; Kortaberria, Galder
Polymer blends of chitosan (CS) and poly(sodium-4-styrene sulphonate) (PSS) have been compatibilized using lysine (LYS) and glutamic acid (GLU). Blends of CS/PSS containing LYS and GLU have been studied by thermal analysis. The values of T-g for CS/PSS-LYS blends could not be detected by thermal analysis but one single T-g was found for CS/PSS-GLU blends. Thermogravimetric analysis (TGA) showed that blends decompose at lower temperatures than that of pure components. Displacements in the main absorption bands in the FT-IR spectra were not clear to discern compatibility. Atomic force microscopy (AFM) indicated that addition of lysine or glutamic acid clearly modified the compatibility of the blends. The globular domains existing in the unmodified blend changed to more or less linear and smooth crystalline domains with parallel periodicity. Dielectric analysis revealed that compatibilizer addition changed the secondary relaxation process of PSS to higher temperatures as a result of the modification on interactions. No variation on the segmental dynamics of both polymers was observed as their main relaxations remained unchanged after the addition of lysine or glutamic acid. (C) 2010 Elsevier Ltd. All rights reserved.
Dielectric and dynamic-mechanical study of the mobility of poly(t-butylacrylate) chains in diblock copolymers: Polystyrene-b-poly(t-butylacrylate)
(ELSEVIER SCI LTD, 2008) Encinar, Mario; Guzman, Eduardo; Prolongo, Margarita G.; Rubio, Ramon G.; Sandoval, Claudia; Gonzalez Nilo, Fernando; Gargallo, Ligia; Radic, Deodato
A calorimetric, dielectric and dynamic-mechanical study of the dynamics of the poly(t-butyl acrylate) (PtBa) chains has been carried out in a PtBa homopolymer and two polystyrene (PS)-b-PtBa block copolymers with different PtBa chain lengths. The DSC results show that the size of the cooperative rearranging regions is similar in the homopolymers and the copolymers, both for the PtBa rich- and the PS-rich regions. Therefore, no significant contributions are found arising from composition fluctuations in the copolymers. The relaxation map obtained from dielectric relaxation indicates that there are no differences in the temperature dependence of the a-relaxation of the PtBa block in the three samples studied. However, there are larger differences for the values obtained from DMTA experiments. Contrary to the alpha-relaxation, the relaxation map for the beta-transition shows that the characteristic times for the PtBa blocks are smaller in the homopolymer than in the copolymers. In principle, these are unexpected results because the beta-relaxations have a more local character than the alpha-ones. The width of the alpha-relaxation increases with T for all the samples, and it is slightly larger for the copolymers.
Equilibrium and Surface Rheology of Monolayers of Insoluble Polycations with Side Chains
(AMER CHEMICAL SOC, 2009) Miranda, Beatriz; Hilles, Hani M.; Rubio, Ramon G.; Ritacco, Hernan; Radic, Deodato; Gargallo, Ligia; Sferrazza, Michele; Ortega, Francisco
We have studied monolayers of poly(n-tetradecyl 4-vinylpyridinium-co-4-vinylpyridine) bromide with different degrees of quaternization at the air-water interface. The isotherms (surface pressure vs area) present several phase transitions: at low monolayer coverage, there is a phase transition over a characteristic area that increases on increasing the quaternization degree. This behavior can be rationalized in terms of a mean-field theory of 2D semiflexible polymeric chains and could be an indication of a disorder-order transition from a 2D isotropic liquid (IL) at low surface concentration to a 2D nematic phase (N) at higher concentrations, Low-frequency oscillatory strain experiments show that at low surface coverage the monolayers exhibit highly nonlinear behavior, even for low strain amplitude, whereas at higher surface coverage the response is linear for strains higher than 20%. In addition, stress relaxation experiments show a minimum in the characteristic times that coincide with the transition area. These unexpected results at low surface coverage might be characteristic of the system or related to the fact that the oscillatory experiments do not strictly correspond to constant surface-coverage conditions. However, they are in agreement with high-frequency viscoelasticity, obtained by surface quasielastic light scattering, that shows that the dilational viscosity is higher at low surface concentration than for concentrations beyond the surface phase transition. At higher coverage, there is a second phase transition, after which the isotherms present hysteresis, which is not observed below. Ellipsometry indicates that, after this transition, the monolayer thicken, which may be related to 3D growth into a multilayer.
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.
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.
Relaxational behavior of poly(4-tetrahydropyranyl) methacrylate
(WILEY, 2006) Sanchis, Maria J.; Dominguez Espinosa, Gustavo; Diaz Calleja, Ricardo; Alegria, Luz; Gargallo, Ligia; Radic, Deodato
Complex permittivity of poly(4-tetrahydropyranyl methacrylate) (P4THPMA) was measured by dielectric spectroscopy. The spectra obtained show several relaxation processes labeled as delta, gamma, beta, and alpha in increasing order of temperature. These processes have been characterized and assigned to specific molecular motions. Comparison of the dielectric activity obtained for P4THPMAwith those reported for poly(1,3-dioxan-5-yl-methacrylate) (PDMA) and poly(cyclohexyl methacrylate) (PCHMA) was performed. In fact, these three polymers have similar chemical structures with aliphatic rings in the ester residue. However, significant differences between the dielectric behavior of these polymers have been observed. In addition, complementary molecular mechanic (MM) calculations have been carried out. The energy barriers obtained by these calculations lead to energy barriers which are in relatively good agreement with those derived from the dielectric measurement by means Arrhenius plots. (c) 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys44:3135-3147,2006.
Study of Miscibility in Polymer Blends Obtained from Binary Inclusion Complexes of gamma-Cyclodextrin and Polycarbonate/Poly(Ethylene Terephthalate)
(TAYLOR & FRANCIS INC, 2012) Carrasco, Lorena; Gargallo, Ligia; Radic, Deodato
In this work the synthesis and characterization of the nanostructure of polymer blends of polycarbonate (PC) and poly(ethylene terephthalate) (PET) obtained from their inclusion complexes with gamma-cyclodextrin are reported. The blends prepared by this method present differences in their miscibility compared with those blends obtained by conventional methods like solution casting, coprecipitation, or melt blending. In order to understand the influence of molecular weight in the inclusion complex process, PCs of M-w = 64,000 and 28,000 g/mol were used. The analysis of the nanostructured blend by Fourier transform infrared (FTIR), H-1-nuclear magnetic resonance (H-1-NMR), wide-angle X-ray diffraction (WAXD), differential scanning colorimetry (DSC), and thermogravimetric analysis (TGA) suggests the existence of specific intermolecular interactions between PC and PET that promote miscibility in this normally immiscible polymer blend. Studies by FTIR confirm that the miscibility found was not due to a transesterification reaction during DSC analysis. There were also differences in the morphology of the blends, observed by optical microscopy, obtaining a more homogeneous phase for blends formed in inclusion complexes. The results obtained strongly suggest an improvement in miscibility of the PC/PET blends.
Water sorption by poly(tetrahydrofurfuril methacrylate)'s
(WILEY, 2008) Sanchis, Maria J.; Diaz Calleja, Ricardo; Garcia Bernabe, Abel; Alegria, Luz; Gargallo, Ligia; Radic, Deodato
Polymers consisting of poly(heterocyclic methacrylate)s are considered as potential materials for clinical applications such as drug delivery and cartilage repair. Much of the success of these systems has been attributed to the complex nature of their water sorption properties. Dielectric permittivity is very sensitive to water sorption. Dielectric relaxation spectroscopy studies have been carried out on two heterocyclic poly(methacrylate)s: poly(tetrahydrofurfuryl methacrylate) (PTHFMA) and poly (3-methyl tetrahydrofurfuryl methacrylate) (P3MTHFMA). The isochrones representing the dielectric losses show in both cases high conductivity at low frequencies and high temperatures. In PTHFMA two conductive processes are observed, which can be associated to the existence of two types of water sorption. These effects have been analyzed and were removed from the dielectric spectra by using classical empirical equations. Both polymers show ostensible alpha-relaxation centered in the vicinity of 350 K at 10(0) Hz. This relaxation was analyzed by means of the empirical Havriliak-Negami equation. Reminiscent beta-relaxation could also exist. Both polymers present well defined gamma and delta subglass absorptions at approximately 120 K, 160 K for PTHFMA and 125 K, 163 K for P3MTHFMA, at 10(0) Hz, associated to local intramolecular relaxations in side groups. These relaxations were analyzed using semiempirical symmetric model. (C) 2007 Wiley Periodicals, Inc.

Browsing by Author "Gargallo, Ligia"

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