Papers by Author: Arturo Ponce

Abstract: The properties of polymer/semiconducting nanoparticle (NP) composites-materials used in hybrid, bulk-heterojunction photovoltaic materials-are dependent on the interaction of the NPs and polymer. Composite films of water soluble polymers and CdS NPs have been produced both by synthesizing the NPs within the polymer matrix and by adding the CdS NPs, containing a capping agent, to the polymer. The composites have been characterized by microscopy as well as 1H, 13C and 113Cd solid-state NMR. When synthesizing the NPs within the polymer, the polymer matrix plays a role in the cadmium sulfide NP nucleation, growth and structure. In the blended system, the dominant interaction between the glycerol capping agent and sulfonated polymer is observed to be hydrogen bonding.

Abstract: In this paper, we studied the influence of the silver nanoparticles size on the electrical conductivity of PEDOT:PSS in Ag(PEDOT:PSS) films. The silver nanoparticles were synthesized in presence of PEDOT:PSS by varying the molar ratio between AgNO3 and the reducing agent (NaBH4). Both the particle size determined by TEM and the plasmon band obtained by UV-Vis spectroscopy were found to be strongly dependent on the reducing agent concentration. The electrical conductivity increases inversely with the concentration of reducing agent from 5.24 x 10-4 up to 1.63 S/cm; three orders of magnitude higher than pristine PEDOT:PSS.

Abstract: High impact polystyrene (HIPS) is considered a heterogeneous polymeric system and is constituted by a disperse phase of rubber particles within a continuous phase formed by a polystyrene (PS) matrix. During the synthesis of HIPS, PS is formed whereas some PS chains become chemically bonded to polybutadiene (PB) chains, resulting in a PB-g-PS copolymer, which decreases the interfacial tension between both incompatible phases, acting as a compatibilizer. In this study, 2 HIPS systems were evaluated by energy dispersive spectroscopy (EDS). In the first case, a HIPS composite was analyzed by EDS to locate the graft copolymer species containing Si atoms, which were previously synthesized by anionic polymerization using chloro-silane chemistry. The graft copolymer was incorporated to the HIPS synthesis from the beginning of the reaction in order to provide an improvement on the rubber phase stability. The graft copolymer was located at the interphase between the PS occlusions and the PB subdomains of the rubber particles. In the second case, HIPS was synthesized incorporating silver nanoparticles (AgNP´s) during the polymerization reaction, where the system can exhibit different types of morphology of the elastomeric phase (micelles, lamellas and core-shell). These structures overlapped the AgNP´s in the transmission electron microscopy (TEM) images, thus resulting this technique to be inadequate to establish the location of the AgNP´s. In this context EDS was used to evaluate the location and distribution of the AgNP´s by means of the elemental composition analysis. AgNP´s were preferentially detected in the PS phase as bigger clusters.

Abstract: Aluminum-based nanocomposites have been produced by mechanical milling, introducing silver nanoparticles within the matrix of a 7075 aluminum alloy using a high energy ball mill. The milled products were compacted by uniaxial load and pressure-less sintered under argon atmosphere, and finally hot extruded. Silver nanoparticles are well dispersed into the matrix of the powder particles as well as in the matrix of the extruded material. Transmission electron microscopy (TEM) analyses are used to corroborate and understand the hypothesis that second-phase particles finely and homogeneously dispersed in the matrix give greater strength to the material. In addition to the strengthening effect, the nanoparticles act like a process control agent (PCA) since the crystallite size of the nanocomposite is smaller at higher contents of nanoparticles.

Abstract: Carbon nanofibers (CNF) were surface coated with a thin layer of poly (acrylic acid) (PAA) via plasma polymerization of acrylic acid (AA). The plasma polymerization treated CNF resulted in a significant change of its surface characteristics from hydrophobic to hydrophilic due to the polar groups in PAA-coating layer. Dispersion tests in water and ethanol confirmed a marked change in the hydrophobicity of the treated CNF. In addition, FTIR results showed a new signal for the treated CNF at 1046 cm-1, assigned to C-O groups and represented the presence of PAA. Morphology results by scanning electron microscopy (SEM) revealed that the untreated CNF has a very smooth surface, whereas the treated CNF showed certain roughness on its surface due to the deposited PAA coating layer.PAA coating on the treated CNF was also observed by transmission electron microscopy (TEM) and its thickness was determined to be between 14 to 18 nm. Dynamic Light Scattering (DLS) was used to show that plasma polymerization improved the dispersion of treated CNF and prevented its agglomeration in water versus the poor dispersion observed with untreated CNF.