Persona: Esteban Pacios, María Isabel
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Esteban Pacios
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María Isabel
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Publicación Fractionation of polyacrylamide in lamellar mesopashes(2014-05-16) Agzenai Ben Salem, Yahya; Renamayor, Carmen S.; Esteban Pacios, María IsabelPublicación Fibrillar morphologies of hydrogels obtained from a lamellar medium(Elsevier, 2011-10-17) Renamayor, Carmen S.; Esteban Pacios, María IsabelHydrogels are suitable for multiple applications and their properties are strongly dependent on their morphology. Sponge-like morphologies are obtained in conventional hydrogels when the polymerization is performed in isotropic media. Fibrillar morphologies imparting new properties to hydrogels are expected when the reacting medium is anisotropic. Here, we synthesize such fibrillar hydrogels by polymerization in a lamellar medium formed by 1,4- bis(2-ethylhexyl)sodium sulfosuccinate (AOT) and water. At high surfactant content this objective is achieved, and the thickness of the obtained fibrils (0.1-1 μm) can be correlated with the physical properties of the lamellar system. At intermediate AOT concentrations, the morphology is hierarchical, with primary closed pores containing a secondary fibrillar structure that fills the pores. For low AOT concentrations, the crosslinking process is unhindered, and the hydrogels are mechanically consistent with a sponge-like morphology having large (10-102 μm) void pores. The time evolution of the mesophase as polymerization advances is followed by small angle X-ray scattering.Publicación Non-stoichiometric polymer-surfactant complexes obtained in a lamellar lyotropic medium(Springer Verlag (Germany), 2012-03-08) Agzenai Ben Salem, Yahya; Renamayor, Carmen S.; Esteban Pacios, María IsabelThe addition of a polyelectrolyte to lamellar media formed by an oppositely charged surfactant often leads to the coexistence of several phases without macroscopic phase separation, which makes their characterization difficult. Here, the effect of the polydiallyldimethylammonium chloride (PD) on the lamellar liquid crystal formed by the anionic surfactant Aerosol OT (AOT) and water is investigated. SAXS results are discussed regarding the changes in the lamellar spacing as a function on the PD or AOT concentrations. In most of the samples two lamellar phases, without macroscopic phase separation, are detected. One of them is a typical swollen phase, while the other is a collapsed phase, which corresponds to the polymer-surfactant complex. At concentrations of polymer up to 3 %wt the two lamellar phases coexist, however, at a critical concentration higher than 3 %wt, the swollen phase becomes isotropic, and a macroscopic phase separation takes place. A simple model is proposed to calculate the composition of the phases when macroscopic phase separation does not occur. The results thus calculated show that generally the polymer-surfactant complexes are non-stoichiometric containing a lesser amount of polymer than ideally expected.