DSpace Angular :: Browsing by Author "Leiva, Angel"

Browsing by Author "Leiva, Angel"

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Blends based on amino acid functionalized poly (ethylene-alt-maleic anhydride) polyelectrolytes and PEO for nanofiber elaboration: Biocompatible and angiogenic polyelectrolytes
(2022) Leal, Matias; Leiva, Angel; Villalobos, Valeria; Palma, Veronica; Carrillo, Daniela; Edwards, Natalie; Maine, Arianne; Cauich-Rodriguez, Juan, V; Tamayo, Laura; Neira-Carrillo, Andronico; Urzua, Marcela
A wide variety of polymers have been electrospun to obtain nanofibers. However, obtaining nanofibers from polyelectrolytes is less frequent due to the charges of these polymers, which hinder the electrospinning process. Poly (ethylene-alt-maleic anhydride) (PEMA) was modified with a series of amino acids (Aa). The functionalization of PEMA with Aa (PEMA-Aa) was demonstrated by FT-IR, H-1 NMR, and C-13 NMR. Blends of PEMA-Aa and poly (ethylene oxide), PEO, with different ratios were prepared. Nanofibers were obtained by electrospinning using blends of 10-20% w/v of PEMA-Aa and 10% w/v of PEO. The conductivity of blends decreased, and the surface tension increased as the quantity of PEO in the blends was increased. TGA showed intermediate thermal properties compared with the blend components. Nanofibers were obtained for all PEMA-Aa/PEO blends, with diameters between 170 and 350 nm. Continuous fibers without morphological defects were obtained at concentrations of 20% w/v and 10% w/v of PEMA-Aa and PEO. Wharton's Jelly Mesenchymal Stem Cells viability, chicken embryo chorioallantoic membrane (CAM) assay and embryo viability measurements were realized for PEMA-Aa. Cytotoxicity test showed both composition and concentration-dependent behavior for PEMA-Aa, with higher WJ-MSC viability at 0.1 mg/mL at 24 h. CAM assay showed the formation of a high number of blood vessels and chicken embryo viability was close to 100% in the presence of polyelectrolytes. This, study demonstrates that electrospun nanofibers obtained from PEMA-Aa/PEO modified polyelectrolyte blends can be considered as a promising material for biomedical applications.
Chromophoric Dendrimer-Based Materials: An Overview of Holistic-Integrated Molecular Systems for Fluorescence Resonance Energy Transfer (FRET) Phenomenon
(2021) Bonardd, Sebastian; Diaz Diaz, David; Leiva, Angel; Saldias, Cesar
Dendrimers (from the Greek dendros -> tree; meros -> part) are macromolecules with well-defined three-dimensional and tree-like structures. Remarkably, this hyperbranched architecture is one of the most ubiquitous, prolific, and recognizable natural patterns observed in nature. The rational design and the synthesis of highly functionalized architectures have been motivated by the need to mimic synthetic and natural-light-induced energy processes. Dendrimers offer an attractive material scaffold to generate innovative, technological, and functional materials because they provide a high amount of peripherally functional groups and void nanoreservoirs. Therefore, dendrimers emerge as excellent candidates since they can play a highly relevant role as unimolecular reactors at the nanoscale, acting as versatile and sophisticated entities. In particular, they can play a key role in the properties of light-energy harvesting and non-radiative energy transfer, allowing them to function as a whole unit. Remarkably, it is possible to promote the occurrence of the FRET phenomenon to concentrate the absorbed energy in photoactive centers. Finally, we think an in-depth understanding of this mechanism allows for diverse and prolific technological applications, such as imaging, biomedical therapy, and the conversion and storage of light energy, among others.
Conformational Changes of Poly(Maleic Anhydride-alt-styrene) Modified with Amino Acids in an Aqueous Medium and Their Effect on Cytocompatibility and Hemolytic Response
(2023) Maine, Arianne; Tamayo, Laura; Leiva, Angel; Gonzalez, Alex; Rios, Hernan E.; Rojas-Romo, Carlos; Jara, Paul; Araya-Duran, Ingrid; Gonzalez-Nilo, Fernando; Yazdani-Pedram, Mehrdad; Santana, Paula; Leal, Matias; Gonzalez, Nicolas; Briones, Ximena; Villalobos, Valeria; Urzua, Marcela
The conformational changes of poly-(maleic anhydride-alt-styrene) (PSMA) modified with different amino acids (PSMA-Aa) were studied in an aqueous medium as a function of ionic strength and pH. The specific viscosity of PSMA-Aa decreased with increasing salt concentration due to a more compact conformation. There was a decrease in surface tension with increasing concentrations of the modified polyelectrolyte having a greater effect for the PSMA modified with l-phenylalanine at pH 7.0, demonstrating a greater surface-active character. The conformational changes were also confirmed by molecular dynamics studies, indicating that PSMA-Aa exhibits a compact structure at pH 4.0 and a more extended structure at pH 7.0. On the other hand, the conformational changes of PSMA-Aa were related to its biological response, where the higher surface-active character of the PSMA modified with l-phenylalanine correlates very well with the higher hemolytic activity observed in red blood cells, in which the surface-active capacity supports lytic potency in erythrocytes. The cytocompatibility assays indicated that there were no significant cytotoxic effects of the PSMA-Aa. Additionally, in solvent-accessible surface area studies, it was shown that the carboxylate groups of the PSMA modified with l-phenylalanine are more exposed to the solvent at pH 7.0 and high salt concentrations, which correlates with lower fluorescence intensity, reflecting a loss of mitochondrial membrane potential. It is concluded that the study of the conformational changes in PE modified with amino acids is essential for their use as biomaterials and relevant to understanding the possible effects of PE modified with amino acids in biological systems.
CuAu bimetallic plasmonic-enhanced catalysts supported on alginate biohydrogels
(2022) Ramirez, Oscar; Bonardd, Sebastian; Saldias, Cesar; Zambrano, Yadira; Diaz Diaz, David; Leiva, Angel
We describe the synthesis, characterization and catalytic properties of a series of hybrid materials composed of inorganic plasmonic mono-and bimetallic nanoparticles supported on organic bio-based hydrogel beads. The bimetallic materials showed a localized surface plasmon resonance in the visible region, with a maximum light absorption correlated to the metal composition of the alloyed systems. Thermogravimetric analysis revealed a total water content near to 90 % w/w, which was in good agreement with the free-volume calculated from mu CT scan reconstruction of lyophilized samples. Catalytic essays for the reduction of 4-nitrophenol demonstrated that alginate beads loaded with bimetallic nanoparticles exhibit a 5.4-fold higher apparent kinetic constant (k(app)) than its monometallic counterparts. Additionally, taking advantage of the plasmonic properties given by the nanoparticles is that the materials were tested as photocatalysts. The activity of the catalysts was enhanced by near 2.2 times higher in comparison with its performance in dark conditions.
Effects of the Solvent Vapor Exposure on the Optical Properties and Photocatalytic Behavior of Cellulose Acetate/Perylene Free-Standing Films
(2023) Coderch, Gustavo; Cordoba, Alexander; Ramirez, Oscar; Bonardd, Sebastian; Leiva, Angel; Haering, Marleen; Diaz, David Diaz; Saldias, Cesar
The search to deliver added value to industrialized biobased materials, such as cellulose derivatives, is a relevant aspect in the scientific, technological and innovation fields at present. To address these aspects, films of cellulose acetate (CA) and a perylene derivative (Pr) were fabricated using a solution-casting method with two different compositions. Consequently, these samples were exposed to dimethylformamide (DMF) solvent vapors so that its influence on the optical, wettability, and topographical properties of the films could be examined. The results demonstrated that solvent vapor could induce the apparent total or partial preferential orientation/migration of Pr toward the polymer-air interface. In addition, photocatalytic activities of the non-exposed and DMF vapor-exposed films against the degradation of methylene blue (MB) in an aqueous medium using light-emitting diode visible light irradiation were comparatively investigated. Apparently, the observed improvement in the performance of these materials in the MB photodegradation process is closely linked to the treatment with solvent vapor. Results from this study have allowed us to propose the fabrication and use of the improved photoactivity "all-organic" materials for potential applications in dye photodegradation in aqueous media.
Highly efficient and reusable CuAu nanoparticles supported on crosslinked chitosan hydrogels as a plasmonic catalyst for nitroarene reduction
(2024) Ramirez, Oscar; Bonardd, Sebastian; Saldias, Cesar; Leiva, Angel; Diaz, David Diaz
The synthesis of CuAu-based monometallic (MNPs) and bimetallic nanoparticles (BNPs) supported on chitosanbased hydrogels for their application as catalysts is presented. The hydrogels consisted of chitosan chains crosslinked with tripolyphosphate (TPP) in the form of beads with an approximate average diameter of 1.81 mm. The MNPs and BNPs were obtained by the adsorption of metallic ions and their subsequent reduction with hydrazine, achieving a metallic loading of 0.297 mmol per gram of dry sample, with average nanoparticle sizes that were found between 2.6 and 4.4 nm. Both processes, metal adsorption and the stabilization of the nanoparticles, are mainly attributed to the participation of chitosan hydroxyl, amine and amide functional groups. The materials revealed important absorption bands in the visible region of the light spectra, specifically between 520 and 590 nm, mainly attributed to LSPR given the nature of the MNPs and BNPs inside the hydrogels. Subsequently, the hydrogels were evaluated as catalysts against the reduction of 4-nitrophenol (4NP) into 4-aminophenol (4AP), followed by UV-visible spectroscopy. The kinetic advance of the reaction revealed important improvements in the catalytic activity of the materials by synergistic effect of BNPs and plasmonic enhancement under visible light irradiation, given the combination of metals and the light harvesting properties of the nanocomposites. Finally, the catalytic performance of hydrogels containing BNPs CuAu 3:1 showed an important selectivity, recyclability and reusability performance, due to the relevant interaction of the BNPs with the chitosan matrix, highlighting the potential of this nanocomposite as an effective catalyst, with a potential environmental application.
Hydrogel composites based on chitosan and CuAuTiO₂ photocatalysts for hydrogen production under simulated sunlight irradiation
(2024) Ramirez, Oscar; Lopez-Frances, Anton; Baldovi, Herme G.; Saldias, Cesar; Navalon, Sergio; Leiva, Angel; Diaz, David Diaz
This study explored the photocatalytic hydrogen evolution reaction (HER) using novel biohydrogel composites comprising chitosan, and a photocatalyst consisting in TiO2 P25 decorated with Au and/or Cu mono- and bimetallic nanoparticles (NPs) to boost its optical and catalytic properties. Low loads of Cu and Au (1 mol%) were incorporated onto TiO2 via a green photodeposition methodology. Characterization techniques confirmed the incorporation of decoration metals as well as improvements in the light absorption properties in the visible light interval (lambda > 390 nm) and electron transfer capability of the semiconductors. Thereafter, Au and/or Cu NP- supported TiO2 were incorporated into chitosan-based physically crosslinked hydrogels revealing significant interactions between chitosan functional groups (hydroxyls, amines and amides) with the NPs to ensure its encapsulation. These materials were evaluated as photocatalysts for the HER using water and methanol mixtures under simulated sunlight and visible light irradiation. Sample CuAuTiO2/ChTPP exhibited a maximum hydrogen generation of 1790 mu mol g(-1) h(-1) under simulated sunlight irradiation, almost 12-folds higher compared with TiO2/ChTPP. Also, the nanocomposites revealed a similar tendency under visible light with a maximum hydrogen production of 590 mu mol g(-1) h(-1) . These results agree with the efficiency of photoinduced charge separation revealed by transient photocurrent and EIS.
Hydrogen bond donor and alcohol chain length effect on the physicochemical properties of choline chloride based deep eutectic solvents mixed with alcohols
(2022) Cotroneo-Figueroa, Vincenzo P.; Gajardo-Parra, Nicolas F.; Lopez-Porfiri, Pablo; Leiva, Angel; Gonzalez-Miquel, Maria; Garrido, Jose Matias; Canales, Roberto, I
Deep eutectic solvents are mixtures typically composed by a hydrogen bond donor and a hydrogen bond acceptor. They have appeared as an alternative of ionic liquids in several processes due to their tunability, biodegradability and low cost. Recently, deep eutectic solvents have been studied as potential solvents for different applications. Then, their physicochemical properties need to be characterized for understanding the interaction between its constituents and with other compounds. Deep eutectic solvents prepared for this work are based on choline chloride mixed with ethylene glycol, 1,3-propanediol or 1,4-butanediol at a 1:3 mol ratio. FT-IR spectra was obtained for comparing the different structures of those deep eutectic solvents. Density and viscosity of the prepared deep eutectic solvents were measured from 293.15 K to 333.15 K at 101.13 kPa. Also, the same properties at the same temperature and pressure conditions were obtained for the mixtures of the three deep eutectic solvents with four alcohols: methanol, ethanol, 1-propanol or 1-butanol. Physicochemical (i.e density and excess volume) and transport properties (i.e viscosity) were measured and predicted using PC-SAFT and Free Volume Theory, respectively, for understanding the effect of the temperature variation, the length of the alcohol chain, and length of the hydrogen bond donor on the configurational aspects of the mixture. Subsequently, a prediction of the excess molar enthalpy was performed with COSMO-RS in order to assess the behavior of the same variables on different type of intermolecular interactions from the energetic point of view. The results suggest that mixing each deep eutectic solvent with an alcohol produce negative molar excess volumes and molar excess enthalpies, observing a higher affinity between unlike species. (C) 2021 Elsevier B.V. All rights reserved.
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.
Nanofibers of chitosan-polycaprolactone blends as active support for photocatalytic nanoparticles: Outstanding role of chitosan in the degradation of an organic dye in water
(2023) Cordoba, Alexander; Guernelli, Moreno; Montalti, Marco; Saldias, Cesar; Focarete, Maria Letizia; Leiva, Angel
Hybrid nanofibers of a chitosan-polycaprolactone blend containing titanium dioxide nanoparticles TiO2NPs, were prepared through electrospinning to study their adsorption and photocatalytic degradation capabilities of the model organic water pollutants, rhodamine B, RhB. To obtain uniform and bead-free nanofibers, an optimization of the electrospinning parameters was performed. The optimization was carried out by systematically adjusting the solution conditions (solvent, concentration, and polymer ratio) and instrumental parameters (voltage, needle tip-collector distance, and flow). The obtained materials were characterized by FT-IR, TGA, DSC, SEM, TEM, mechanical tensile test, and water contact angle. The photoactivity was investigated using a batchtype system by following UV-Vis absorbance and fluorescence of RhB.TiO2NPs were incorporated ex-situ into the polymer matrix, contributing to good mechanical properties and higher hydrophilicity of the material. The results showed that the presence of chitosan in the nanofibers significantly increased the adsorption of RhB and its photocatalytic degradation by TiO2NPs (5, 55 and 80 % of RhB degradation with NFs of PCL, TiO2/PCL and TiO2/CS-PCL, after 30 h of light irradiation, respectively), evidencing a synergistic effect between them. The results are attributed to an attraction of RhB by chitosan to the vicinity of TiO2NPs, favouring initial adsorption and degradation, phenomenon known as "bait-and-hook-anddestruct" effect.
New Hybrid Nanocomposites with Catalytic Properties Obtained by In Situ Preparation of Gold Nanoparticles on Poly (Ionic Liquid)/Poly (4-Vinylpyridine) Nanofibers
(2022) Ramirez, Oscar; Leal, Matias; Briones, Ximena; Urzua, Marcela; Bonardd, Sebastian; Saldias, Cesar; Leiva, Angel
In this work, we report the obtaining of new hybrid nanocomposites with catalytic activity formed by nanofibers of polymer blends and gold nanoparticles. The nanofibers were obtained by electrospinning blends of a poly (ionic liquid) (PIL) and its precursor polymer, poly (4-vinyl pyridine) (P4VPy). The characteristics of the nanofibers obtained proved to be dependent on the proportion of polymer in the blends. The nanofibers obtained were used to synthesize, in situ, gold nanoparticles on their surface by two-step procedure. Firstly, the adsorption of precursor ions on the nanofibers and then their reduction with sodium borohydride to generate gold nanoparticles. The results indicated a significant improvement in the performance of PIL-containing nanofibers over pure P4VPy NFs during ion adsorption, reaching a 20% increase in the amount of adsorbed ions and a 6-fold increase in the respective adsorption constant. The catalytic performance of the obtained hybrid systems in the reduction reaction of 4-nitrophenol to 4-aminophenol was studied. Higher catalytic conversions were obtained using the hybrid nanofibers containing PIL and gold nanoparticles achieving a maximum conversion rate of 98%. Remarkably, the highest value of kinetic constant was obtained for the nanofibers with the highest PIL content.
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.
On the Versatile Role of Electrospun Polymer Nanofibers as Photocatalytic Hybrid Materials Applied to Contaminated Water Remediation: A Brief Review
(2022) Cordoba, Alexander; Saldias, Cesar; Urzua, Marcela; Montalti, Marco; Guernelli, Moreno; Focarete, Maria Letizia; Leiva, Angel
A wide variety of materials, strategies, and methods have been proposed to face the challenge of wastewater pollution. The most innovative and promising approaches include the hybrid materials made of polymeric nanofibers and photocatalytic nanoparticles. Electrospun nanofibers with unique properties, such as nanosized diameter, large specific surface area, and high aspect ratio, represent promising materials to support and stabilize photocatalytic nanosized semiconductors. Additionally, the role performed by polymer nanofibers can be extended even further since they can act as an active medium for the in situ synthesis of photocatalytic metal nanoparticles or contribute to pollutant adsorption, facilitating their approach to the photocatalytic sites and their subsequent photodegradation. In this paper, we review the state of the art of electrospun polymer/semiconductor hybrid nanofibers possessing photocatalytic activity and used for the remediation of polluted water by light-driven processes (i.e., based on photocatalytic activity). The crucial role of polymer nanofibers and their versatility in these types of procedures are emphasized.
Poly(ionic liquid)-Based Hydrogel for Emerging Pollutant Removal and Controlled Drug Delivery
(2024) Ramirez, Oscar; Castillo, Sebastian; Bonardd, Sebastian; Saldias, Cesar; Diaz, David Diaz; Leiva, Angel
In this study, we report the synthesis and characterization of a set of poly(ionic liquid) (PIL)-based gel membranes formed by the reaction of poly(4-vinylpyridine) (P4VPy) with a terminal dibrominated poly(ethylene glycol) (PEG), which led to the formation of quaternized pyridines as cross-linking joints. First, for hydrogel synthesis, PEG terminal hydroxyls were brominated and subsequently reacted with P4VPy, resulting in the formation of ionic liquid (IL)-like moieties within the hydrogel network. Modified PEG and PIL-based membranes were characterized by Nuclear Magnetic Resonance (NMR), Fourier-Transform Infrared (FT-IR), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC), as well as their swelling and adsorption properties. FT-IR spectroscopy confirmed the quaternization of the pyridine pendant groups of P4VPy by the appearance of a band at 1639 cm-1 due to the presence of pyridinium units. Thermal characterization revealed a decrease in the thermal stability of the membranes with respect to the starting materials, probably ascribed to the presence of charged species inside the cross-linked matrix. Furthermore, DSC characterization revealed that the P4VPy:PEG ratio and degree of cross-linking strongly affected the amount of non-freezable water. Swelling experiments of the hydrogels revealed a swelling ratio value (% SW) near 297% after 2 h of hydration, showing remarkable recyclability over multiple hydration and drying cycles. Finally, sodium diclofenac (DCl) and methyl orange (MO) adsorption experiments revealed the remarkable ability of the hydrogels to remove pollutants from water, with q max values of 166.7 and 218.8 mg/g, respectively. Finally, a hydrogel loaded with DCl was used as a model system for drug release experiments, in which the hydrogel was able to release almost 70% of DCl to the medium within 1 day of exposure. This process is controlled mainly by a polymer relaxation mechanism and influenced by the temperature of the experiment, showing great potential for reuse in further experiments and also as an interesting platform for controlled drug release.
PVDF Composite Membranes with Hydrophobically-Capped CuONPs for Direct-Contact Membrane Distillation
(2021) Saldias, Cesar; Terraza, Claudio A.; Leiva, Angel; Koschikowski, Joachim; Winter, Daniel; Tundidor-Camba, Alain; Martin-Trasanco, Rudy
Water scarcity is an imminent problem that humanity is beginning to attempt to solve. Among the several technologies that have been developed to mitigate water scarcity, membrane distillation is of particular note. In the present work, CuO nanoparticles capped with 1-octanethiol (CuONPs@CH) or 1H,1H,2H,2H-perfluorodecanethiol (CuONPs@CF) are prepared. The nanoparticles are characterized by FT-IR and TGA methods. Two weight losses are observed in both cases, with the decomposition of the organic fragments beginning at 158 degrees C and 230 degrees C for CuONPs@CF and CuONPs@CH, respectively. Flat sheet PVDF composite membranes containing nanoparticles are prepared by the casting solution method using nanoparticle concentrations that ranged between 2-20% with a non-woven polyester fabric as support. The obtained membranes showed a thickness of 240 +/- 40 mu m. According to water contact angle (87 degrees for CuONPs@CH and 95 degrees for CuONPs@CF, both at 10% w.t) and roughness (12 pixel for CuONPs@CH and 14 pixels for CuONPs@CF, both at 10% w.t) determinations, the hydrophobicity of membranes changed due to a decrease in surface energy, while, for naked CuONPs, the roughness factor represents the main role. Membranes prepared with capped nanoparticles showed similar porosity (60-64%). SEM micrographs show asymmetric porous membranes with a 200-nm surface pore diameter. The largest finger-like pores in the membranes prepared with CuONPs, CuONPs@CH and CuONPs@CF had values of 63 +/- 10 mu m, 32 +/- 8 mu m, and 45 +/- 10 mu m, respectively. These membranes were submitted to a direct contact membrane distillation module and flux values of 1.8, 2.7, and 3.9 kg(m(2)center dot h)(-1) at Delta T = 30 degrees C were obtained for the CuONPs, CuONPs@CH, and CuONPs@CF, respectively. The membranes showed 100% salt rejection during the testing time (240 min).
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.
Spraying Fluorinated Silicon Oxide Nanoparticles on CuONPs@CF-PVDF Membrane: A Simple Method to Achieve Superhydrophobic Surfaces and High Flux in Direct Contact Membrane Distillation
(2022) Lenac, Zivka; Saldias, Cesar; Terraza, Claudio A.; Leiva, Angel; Koschikowski, Joachim; Winter, Daniel; Tundidor-Camba, Alain; Martin-Trasanco, Rudy
Desalinization of seawater can be achieved by membrane distillation techniques (MD). In MD, the membranes should be resistant to fouling, robust for extended operating time, and preferably provide a superhydrophobic surface. In this work, we report the preparation and characterization of a robust and superhydrophobic polyvinylidene fluoride membrane containing fluoroalkyl-capped CuONPs (CuONPs@CF) in the inner and fluorinated capped silicon oxide nanoparticles (SiO(2)NPs@CF) on its surface. SiO(2)NPs@CF with a mean diameter of 225 +/- 20 nm were prepared by the sol method using 1H,1H,2H,2H-perfluorodecyltriethoxysilane as a capping agent. Surface modification of the membrane was carried out by spraying SiO(2)NPs@CF (5% wt.) dispersed in a mixture of dimethyl formamide (DMF) and ethanol (EtOH) at different DMF/EtOH % v/v ratios (0, 5, 10, 20, and 50). While ethanol dispersed the nanoparticles in the spraying solution, DMF dissolved the PVDF on the surface and retained the sprayed nanoparticles. According to SEM micrographs and water contact angle measurements, the best results were achieved by depositing the nanoparticles at 10% v/v of DMF/EtOH. Under these conditions, a SiO(2)NPs covered surface was observed with a water contact angle of 168.5 degrees. The water contact angle was retained after the sonication of the membrane, indicating that the modification was successfully achieved. The membrane with SiO(2)NPs@CF showed a flux of 14.3 kg(m(2)center dot h)(-1), 3.4 times higher than the unmodified version. The method presented herein avoids the complicated modification procedure offered by chemical step modification and, due to its simplicity, could be scalable to a commercial membrane.
Synthesis of new poly(itaconate)s containing nitrile groups as high dipolar moment entities for the development of dipolar glass polymers with increased dielectric constant. Thermal and dielectric characterization
(2019) Bonardd, Sebastian; Alegria, Angel; Saldias, Cesar; Leiva, Angel; Kortaberria, Galder
This work presents the synthesis of new poly(itaconate)s containing one or two nitrile pendant groups through conventional radical polymerization. To the best of our knowledge, this is the first time in which the synthesis of poly(itaconate)s containing nitrile groups is reported in the literature. The effect of nitrile groups on the main properties is analyzed. Polymer structures were confirmed by Fourier transform infrared spectroscopy (FTIR), H-1 and C-13 NMR. Molecular weights were measured by size exclusion chromatography (SEC), while thermal characterization was achieved by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Dielectric properties were measured using broadband dielectric spectroscopy at different temperatures. Polymers with one or two nitrile groups presented dielectric constant values (at 25 degrees C and 1 kHz) of around 7 and 12.5, respectively, with relatively low dielectric losses with values below 0.02. BDS measurements showed notorious sub-glass transitions attributed to the movement of the dipolar groups under the electric field, even below - 100 degrees C, allowing to achieve dielectric constant values above the average for polymers even at extremely low temperatures. Therefore, these materials could be considered as good candidates for energy storage applications.
The Effect of the Addition of Copper Particles in High-Density Recycled Polyethylene Matrices by Extrusion
(2022) Arcos, Camila; Munoz, Lisa; Cordova, Deborah; Munoz, Hugo; Walter, Mariana; Azocar, Manuel I.; Leiva, Angel; Sancy, Mamie; Rodriguez-Grau, Gonzalo
In this study, the effect of the recycling process and copper particle incorporation on virgin and recycled pellet HDPE were investigated by thermo-chemical analysis, mechanical characterization, and antibacterial analysis. Copper particles were added to pellet HDPE, virgin and recycled, using a tabletop single screw extruder. Some copper particles, called copper nano-particles (Cu-NPs), had a spherical morphology and an average particle size near 20 nm. The others had a cubic morphology and an average particle size close to 300 nm, labeled copper nano-cubes (Cu-NCs). The thermo-chemical analysis revealed that the degree of crystallization was not influenced by the recycling process: 55.38 % for virgin HDPE and 56.01% for recycled HDPE. The degree of crystallization decreased with the addition of the copper particles. Possibly due to a modification in the structure, packaging organization, and crystalline ordering, the recycled HDPE reached a degree of crystallization close to 44.78% with 0.5 wt.% copper nano-particles and close to 36.57% for the recycled HDPE modified with 0.7 wt.% Cu-NCs. Tensile tests revealed a slight reduction in the tensile strength related to the recycling process, being close to 26 MPa for the virgin HDPE and 15.99 MPa for the recycled HDPE, which was improved by adding copper particles, which were near 25.39 MPa for 0.7 wt.% copper nano-cubes. Antibacterial analysis showed a reduction in the viability of E. coli in virgin HDPE samples, which was close to 8% for HDPE containing copper nano-particles and lower than 2% for HDPE having copper nano-cubes. In contrast, the recycled HDPE revealed viability close to 95% for HDPE with copper nano-particles and nearly 50% for HDPE with copper nano-cubes. The viability of S. aureus for HDPE was lower than containing copper nano-particles and copper nano-cubes, which increased dramatically close to 80% for recycled HDPE with copper nano-particles 80% and 75% with copper nano-cubes.
UiO-66(Zr) as drug delivery system for non-steroidal anti-inflammatory drugs
(2024) Salazar, Javier; Hidalgo-Rosa, Yoan; Burboa, Pia C.; Wu, Yi-nan; Escalona, Nesor; Leiva, Angel; Zarate, Ximena; Schott, Eduardo
The toxicity for the human body of non-steroidal anti-inflammatory drugs (NSAIDs) overdoses is a consequence of their low water solubility, high doses, and facile accessibility to the population. New drug delivery systems (DDS) are necessary to overcome the bioavailability and toxicity related to NSAIDs. In this context, UiO-66(Zr) metal-organic framework (MOF) shows high porosity, stability, and load capacity, thus being a promising DDS. However, the adsorption and release capability for different NSAIDs is scarcely described. In this work, the biocompatible UiO-66(Zr) MOF was used to study the adsorption and release conditions of ibuprofen, naproxen, and diclofenac using a theoretical and experimental approximation. DFT results showed that the MOF-drug interaction was due to an intermolecular hydrogen bond between protons of the groups in the defect sites, (mu 3 - OH, and - OH2) and a lone pair of oxygen carboxyl functional group of the NSAIDs. Also, the experimental results suggest that the solvent where the drug is dissolved affects the adsorption process. The adsorption kinetics are similar between the drugs, but the maximum load capacity differs for each drug. The release kinetics assay showed a solvent dependence kinetics whose maximum liberation capacity is affected by the interaction between the drug and the material. Finally, the biological assays show that none of the systems studied are cytotoxic for HMVEC. Additionally, the wound healing assay suggests that the UiO-66(Zr) material has potential application on the wound healing process. However, further studies should be done.

Browsing by Author "Leiva, Angel"

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