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Publicaciones científicas más recientes (desde 2010)

Autores: Puig Rigall, Joan; Blanco Prieto, María José (Autor de correspondencia); Radulescu, A.; et al.
ISSN 0021-9797  Vol. 582  2021  págs. 353-363
Hypothesis: The combination of polymeric surfactants into mixed micelles is expected to improve properties relevant to their use in drug delivery, such as micellar size, gelation, and toxicity. We investigated synergistic effects in mixtures of D-¿-Tocopheryl polyethylene glycol succinate (TPGS), an FDA-approved PEGylated derivative of vitamin E, and Tetronic surfactants, pH-responsive and thermogelling polyethylene oxide (PEO)-polypropylene oxide (PPO) 4-arm block copolymers. We hypothesized that mixed micelles would form under specific conditions and provide a handle to tune formulation characteristics. Experiments: We examined the morphology of the self-assembled structures in mixtures of TPGS with two Tetronic: T1107 and T908, using a combination of dynamic light scattering (DLS), small-angle neutron scattering (SANS), NMR spectroscopy (NOESY and diffusion NMR) and oscillatory rheology, over a range of compositions, temperatures and pH. Cell viability was assessed in NIH/3T3 fibroblasts. Findings: The combination of TPGS with either of the two Tetronic produces spherical core-shell micelles that comprise both surfactants in their structure (mixed micelles). T1107 unimers incorporate into TPGS aggregates below the critical micelle temperature of the poloxamine, while mixed micelles only form under limited conditions with T908. At high concentration/temperature, small proportions of TPGS extend the gel phase, more markedly with T1107, with similar elastic moduli (30-50 kPa) and a BCC crystalline structure. Cell viability of NIH/3T3 fibroblasts grown in the hydrogels increases significantly when the poloxamine gels are doped with TPGS, making the combination of poloxamines and TPGS a promising platform for drug delivery.
Autores: Goñi Ciaurriz, Leire; González Gaitano, Gustavo; Vélaz Rivas, Itziar (Autor de correspondencia)
ISSN 0378-5173  Vol. 588  2020  págs. 119664
Photocatalytic properties of titanium dioxide nanoparticles (TiO2 NPs) have encouraged their use as fillers in polymer-based nanocomposites for application in food packaging. The surface modification of TiO2 NPs with cyclodextrins (CDs) can improve their functionality in a large extent. With this purpose, sorbic acid (SA) and benzoic acid (BA), commonly used as antifungal and antibacterial food preservatives, respectively, have been encapsulated in CD-grafted NPs. Inclusion complex formation of SA and BA with a and beta CDs in water has been assessed first by means of H-1 NMR and UV-Vis spectroscopy to determine the affinity of the preservatives for the macrocycles and the stoichiometry of the complexes. The association constants of both preservatives were found to be lower for beta CD, however, the loading efficiency in beta CD-grafted NPs was higher than that exhibited by alpha CD-NPs. Release kinetics from the CD-grafted NPs have been carried out. In the case of SA, the alpha CD-grafted NPs showed a prolonged and sustained release profile, suggesting its application as microbial growth inhibition system if incorporated into packaging materials.
Autores: Puig Rigall, Joan; Fernández Rubio, Celia; González-Benito, J.; et al.
ISSN 0378-5173  Vol. 578  2020  págs. 119057
Miltefosine (MF), an alkylphospholipid originally developed for breast cancer treatment, is a highly active drug for the treatment against leishmaniasis, a neglected tropical disease considered the world's second leading cause of death by a parasitic agent after malaria. MF exhibits dose-limiting gastrointestinal side effects in patients and its penetration through lipophilic barriers is reduced. In this work we propose a reformulation of MF by incorporating the drug to poly(ethylene)oxide (PEO)-based polymeric micelles, specifically, D-alpha-tocopheryl polyethylene glycol succinate (TPGS) and Tetronic block copolymers (T904 and T1107). A full structural characterization of the aggregates has been carried out by SANS (small-angle neutron scattering) and dynamic light scattering (DLS), in combination with proton 1D and 2D nuclear magnetic resonance (NMR) spectroscopy, to determine the precise location of the drug. The structure of MF micelles has been characterized as a function of the temperature and concentration. In the presence of the block-copolymers, MF forms mixed micelles in a wide range of temperatures, TPGS being the co-surfactant that incorporates more MF unimers. The hydrophobic tail of MF and those of the block copolymers are in close contact within the micelles, which present a core-shell structure with a hydrophilic corona formed by the PEG blocks of the TPGS and the zwitterion head group of the MF. In order to identify the best carrier, the antileishmanicidal activity of MF in the different formulations has been tested on macrophages, promastigotes and intracellular amastigotes. The combination of the three vehicles with MF makes the formulated drug more active than MF alone against L. major promastigotes, however, only the combination with T904 increases the MF activity against intracellular amastigotes. With the aim of exploring gel-based formulations of the drug, the combination of MF and T1107 under gelation conditions has also been investigated.
Autores: Puig Rigall, Joan; Serra Gómez, Rafael; Guembe-Michel, N.; et al.
ISSN 0024-9297  Vol. 53  Nº 8  2020  págs. 3166 - 3174
Pseudopolyrotaxanes (PPRs) are supramolecular host-guest complexes constituted by the reversible threading of macrocycles along a polymer chain. We report the formation of hybrid PPRs (hPPRs), where two types of cyclodextrins (CDs) thread either simultaneously or sequentially on four-arm poly-(ethylene oxide)-poly(propylene oxide) (PEO-PPO) block copolymers (Tetronic): native alpha-CD (CD) (with higher affinity for PEO) and dimethylated beta-CD (DIMEB, with higher affinity for PPO). The competitive complexation along the chains is examined with three Tetronics, differing mainly in the length of their PEO blocks: T904, T1107, and T1307. While PPRs formed with alpha-CD are insoluble, due to the hydrogen-bond network formed between adjacent alpha-CDs, the presence of DIMEB leads to soluble hybrid PPRs, slows down the kinetics of complexation, and increases the number of alpha-CDs threaded per arm. The morphology of the constructs in solution over time is followed by time-resolved small-angle neutron scattering (TR-SANS), while their crystalline structure is studied by X-ray diffraction. Whereas the complexation of the polymeric surfactant with DIMEB shifts the unimer-micelle equilibrium toward unimers, the presence of alpha-CD slows down demicellization and reduces its extent. Overall, the co-threading of two cyclodextrins on the same polymer provides a handle to tune the complexation process and the final properties of the PPR, including solubility, kinetics of complexation, and composition of the complexes.
Autores: Vandera, K. K. A. ; Picconi, P. ; Valero, M.; et al.
ISSN 1543-8384  Vol. 17  Nº 7  2020  págs. 2354 - 2369
Gram-negative bacteria possess numerous defenses against antibiotics, due to the intrinsic permeability barrier of their outer membrane (OM), explaining the recalcitrance of some common and life-threatening infections. We report the formulation of a new drug, PPA148, which shows promising activity against all Gram-negative bacteria included in the ESKAPEE pathogens. PPA148 was solubilized by inclusion complexation with cyclodextrin followed by encapsulation in liposomes. The complex and liposomal formulation presented increased activity against E. coli compared to the pure drug when assessed with the Kirby Bauer assay. The novel formulation containing 1 mu g PPA148 reached similar efficacy levels equivalent to those of 30 mu g of pure rifampicin. A range of biophysical techniques was used to explore the mechanism of drug uptake. Langmuir trough (LT) and neutron reflectivity (NR) techniques were employed to monitor the interactions between the drug and the formulation with model membranes. We found evidence for liposome fusion with the model Gram-negative outer membrane and for cyclodextrins acting as inner membrane (IM) permeation enhancers without presenting intrinsic antimicrobial activity. An antibiotic-in-cyclodextrin-in-liposomes (ACL) formulation was developed, which targets both the bacterial OM and IM, and offers promise as a means to breach the Gram-negative cell envelope.
Autores: Benigno, E.; Lorente, M. A.; Olmos, D.; et al.
ISSN 0959-8103  Vol. 68  Nº 6  2019  págs. 1155 - 1163
Low density polyethylene ( LDPE) based nanocomposites containing multi-walled carbon nanotubes ( MWCNTs) were prepared by a two-stepprocess consisting of apre-mixture using high energy ball milling ( HEBM) and subsequent hotpressing. The effects of ball milling and the presence of the MWCNTs on some physical properties of the materials and the antimicrobial efficiency against DH5.. Escherichia coli were studied. Fourier transform infrared spectroscopy revealed that the polymer structure did not change in the final materials after the addition of MWCNTs and mixing. Differential scanning calorimetry showed small differences in the LDPEthermal behavior as a function of the type ofmaterial due to small changes in the polymer crystallization. This result was mainly ascribed to the milling process rather than to the incorporation of the MWCNTs. The presence of 1% by weight of the nanofiller increased the rigidity and hydrophobicity of the nanocomposites with respect to neat LDPE. This effect was explained by the preferential location of theMWCNTs in the surface of the material as themain factor decreasing the polar contribution to the surface free energy. A correlation between hydrophobicity, biofilm development and the shape and size of DH5.. E. coli was observed, indicating that the presence of MWCNTs leads to a biocide effect by decreasing cell adhesion and changing itsmetabolism.
Autores: Zornoza Cebeiro, Arantza; Moreno, L. ; Puig Rigall, Joan; et al.
ISSN 0167-7322  Vol. 282  2019  págs. 205 - 212
The solubilisation of methylparaben (MP), an antimicrobial agent used as a food preservative and in cosmetics and personal-care products, in two poloxamines of different Hydrophilic-Lipophilic Balance (HLB), namely Tetronic 904 (T904) and 1107 (T1107), has been studied. The influence of the preservative on the aggregation behaviour of both Tetronics has been analysed by dynamic light scattering (DLS) and small-angle neutron scattering (SANS), while the precise location of the molecule in the aggregates as well as the effects of the micellar solubilisation on the reactivity of the preservative have been elucidated by NMR and UV spectroscopies. The presence of MP reduces the critical micelle temperature (CMT) of any of the poloxamines and induces the formation of larger micelles at room temperature compared to the plain poloxamines; in addition, a remarkable temperature dependent effect on the structure of the micelles has been detected, which progressively evolve from core-shell spheres to rods as the temperature increases. The incorporation of the preservative into the micelles modifies its reactivity against alkaline hydrolysis, resulting in a decrease of its reaction rate constant in which the dominant factor for the reduction in the hydrolysis rate is the incorporation into the micelle core, with a little effect of the length of the hydrophilic polyethylene oxide (PEO) blocks.
Autores: Puig Rigall, Joan; Serra Gómez, Rafael; Stead, I.; et al.
ISSN 0024-9297  Vol. 52  Nº 4  2019  págs. 1458 - 1468
Pseudo-polyrotaxanes (PPRs) are supramolecular host-guest complexes constituted by the reversible threading of a macrocycle along a polymer chain. The resuting dynamic "molecular necklaces" offer potential applications in nanotechnology, drug delivery, and biomaterials. We report the formation of PPRs by threading of cyclodextrins (CDs), cyclic oligosaccharides, onto X-shaped PEO-PPO block copolymers with two opposite presentation of their hydrophobic and hydrophilic blocks: Tetronic 904 (T904) and its reverse counterpart Tetronic 90R4 (T90R4). We assess the effects that relative block position on the polymeric surfactants and cavity size of CD have on the composition, morphology, thermodynamics, and kinetics of PPRs by using a combination of X-ray diffraction, scanning electron microscopy, NMR, UV-vis spectroscopy, and time-resolved small-angle neutron scattering (TR-SANS). Solid PPRs with lamellar microstructure and crystalline channel-like structures are obtained with native CDs and both Tetronics above a threshold concentration of the macrocycle, which varies with the type of CD and surfactant. While gamma-CD can form PPRs with both Tetronics, alpha-CD only forms a PPR with T90R4 at high concentrations. The results can be explained in terms of the preferential complexation of alpha-CD with EO and gamma-CD with PO monomers, which also has a direct impact on the kinetics of PPR formation.
Autores: Gonzalez-Benito, J.; Olmos, D.; Teno, J.; et al.
ISSN 0021-8995  Vol. 136  Nº 10  2019  págs. 47115
Fibers of poly(vinylidene fluoride) (PVDF) filled with multiwalled carbon nanotubes (MWCNTs) were prepared by solution blow spinning (SBS). The influence of the MWCNTs on the surface morphology and mechanical behavior of single fibers was studied. The morphology of the materials prepared and the dispersion of the MWCNTs within the polymer were studied by optical microscopy (OM) and transmission electron microscopy (TEM), while atomic force microscopy (AFM) was used to inspect the topography of single fibers and to perform nanoindentation tests. OM and TEM images indicated a good dispersion of the MWCNTs within the PVDF. AFM images evidenced clear changes in the topography of the blow-spun fibers when the MWCNTs were present in the polymer. A greater amount of MWCNTs in the PVDF led to more heterogeneous fiber surfaces. The nanoindentation force curves revealed that the stiffness was practically constant along the fibers, which indicated that the mechanical response was homogeneous and, in turn, an even distribution of the MWCNTs. The incorporation of the MWCNTs produced a mechanical reinforcement of the PVDF fibers, showing increases of 31% and 49% in the elastic modulus when 1% and 5% by weight of MWCNTs were added to the polymer, respectively.
Autores: Gonzalez-Benito, J. , (Autor de correspondencia); Olmos, D.; Martinez-Tarifa, J. M.; et al.
ISSN 0021-8995  Vol. 136  Nº 29  2019  págs. 47788
Nanocomposites based on poly(vinylidene fluoride) (PVDF) filled with barium titanate, BaTiO3, (BT) particles, and multiwalled carbon nanotubes (MWCNTs) were prepared by high-energy ball milling (HEBM) and subsequent hot pressing. This method of materials preparation allowed obtaining uniform dispersions of the nanofillers. The influence of the particles on the polymer structure and morphology was studied. To understand the origin of changes in the PVDF properties, thermal and electrical behaviors of the PVDF/BT/MWCNT nanocomposites were studied as a function of composition. The addition of BT, MWCNT, or its mixture had not any influence on the PVDF polymorphism. However, calorimetric results pointed out that the presence of the nanofillers exerted nucleation mainly ascribed to the surface to volume ratio of the nanoparticles. The capacitance of the composites increased as the nanofiller content increased, being the effect mainly dependent on the surface to volume ratio of the nanoparticles. The dielectric behavior of the materials as a function of frequency was modeled by a Debye equivalent circuit only below the percolation threshold respect to the amount of MWCNT. The piezoelectric behavior of the ternary nanocomposites was highly affected by the incorporation of the nanofillers only when high dielectric losses occurred above the percolation threshold.
Autores: Uriz, A.; Sanmartín Grijalba, Carmen; Plano Amatriain, Daniel; et al.
ISSN 0927-7765  Vol. 170  2018  págs. 463 - 469
Selenium (Se) incorporated into organic frameworks has demonstrated anticancer activity against several cancer types. One of the drawbacks of most of these constructs is their poor solubility and bioavailability, which can be overcome with the use of suitable nanocarriers. We have synthesized a series of 5-substituted amide selenodiazoles, based on the parent structure of ebselen, an organoselenium drug with proven cytoprotective activity, and solubilized them in polymeric micelles of poloxamines, poly(ethylene oxide)-poly(propylene oxide) X-shaped tetrablock-copolymers. Scattering methods (SANS and DLS) were employed to characterize the micellar nanocarriers. MTT biological evaluation highlights the selectivity of the Se-compounds towards cancer cells, with MCF-7 standing as the most responsive line. The alkylation of the heterocycle with a 12-carbon hydrophobic tail displays the highest activity, showing a 100-fold increase with respect to ebselen. This compound also exhibits the greatest increase in solubility in poloxamine micelles, overall resulting in a one-fold increase in activity with respect to the non-formulated form, making it a hit compound for further optimization.
Autores: Fuentes Ramírez, Marta (Autor de correspondencia); Baigorri Ekisoain, Roberto Pedro; González Gaitano, Gustavo; et al.
ISSN 1439-0108  Vol. 18  Nº 4  2018  págs. 1389 - 1399
The traditional method to determine humic content (humic and fulvic acids) in commercial fertilizers, biostimulants, and organic materials is based on the oxidation of the organic carbon contained in the basic-soluble but acid-insoluble fraction (humic acids) and the basic-acid soluble fraction (fulvic acids) of their alkaline water extracts. This methodology, merely operational, makes it impossible to distinguish if the quantified carbon corresponds to substances with "humic" chemical nature or to non-humic organic matter but with similar solubility properties to those of humic matter. The aim of this work is to develop a new methodology that not only quantifies the humic content in commercial products (and raw materials) but also assesses the humic quality of the quantified organic matter. To this end, humic and fulvic (-like) fractions have been isolated/purified from several humic and non-humic materials and characterized by means of elemental analysis and UV-visible, fluorescence, and infrared spectroscopies, and these data have been used to perform a discriminant analysis (DA). The model obtained from the DA is able to discriminate humic and fulvic fractions from apparently humic or fulvic ones and provides discriminant classification functions that have proven to successfully predict the "humic quality" of the fractions isolated from commercial products, after their elemental and spectroscopic characterization. Therefore, the combination of the fractionation, characterization, and evaluation by the DA is proposed as an effective methodology for quantifying and assessing the quality of the humic content claimed in the labels of commercial products.
Autores: Olmos, D. ; Pontes-Quero, G. M. ; Corral, A. ; et al.
ISSN 2079-4991  Vol. 8  Nº 2  2018  págs. 60
In this work, the antimicrobial effect of silver nanoparticles in polyethylene based nanocomposites has been investigated using a non-conventional processing method to produce homogeneous materials. High energy ball milling under cryogenic conditions was used to achieve a powder of well-blended low-density polyethylene and commercial silver nanoparticles. The final composites in the form of films were obtained by hot pressing. The effect of various silver nanoparticles content (0, 0.5, 1 and 2 wt %) on the properties of low-density polyethylene and the antimicrobial effectiveness of the composite against DH5 ff Escherichia coli were studied. The presence of silver nanoparticles did not seem to affect the surface energy and thermal properties of the materials. Apart from the inhibition of bacterial growth, slight changes in the aspect ratio of the bacteria with the content of particles were observed, suggesting a direct relationship between the presence of silver nanoparticles and the proliferation of DH5 alpha ff E. coli (Escherichia coli) cells. Results indicate that these materials may be used to commercially produce antimicrobial polymers with potential applications in the food and health industries.
Autores: Monreal-Perez, P.; Isasi Allica, José Ramón (Autor de correspondencia); Gonzalez-Benito, J.; et al.
ISSN 2079-4991  Vol. 8  Nº 9  2018  págs. 642
The modification of the surface of titanium dioxide nanoparticles (TiO2 NPs) by the incorporation of cyclodextrins (CDs), cyclic oligosaccharides with a hydrophobic cavity, can largely improve the functionality of TiO2 by lodging molecules of interest in the CD to act directly on the surface of the nanoparticles or for further release. With this aim, we have synthesized beta CD-modified nanoparticles (beta CDTiO2 NPs) by a two-step reaction that involves the incorporation of a spacer and then the linking of the macrocycle, and characterized them by thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The capacity of the functionalized structures to trap model compounds (Rhodamine and 1-naphthol) has been compared to that of bare TiO2 NPs by fluorescence and Ultraviolet-visible (UV-visible) spectroscopy. The presence of the CDs on the surface of the TiO2 avoids the photo-degradation of the guest, which is of interest in order to combine the photocatalytic activity of TiO2, one of its most interesting features for practical purposes, with the delivery of compounds susceptible of being photo-degraded. The beta CDTiO2 NPs have been dispersed in polymeric matrices of frequently used polymers, polyethylene (LDPE) and polyethylene oxide (PEO), by cryogenic high energy ball milling to produce nanocomposites in the form of films. The surface modification of the nanoparticles favors the homogenization of the filler in the matrix, while the nanoparticles, either in bare or functionalized form, do not seem to alter the crystallization properties of the polymer at least up to a 5% (w/w) load of filler.
Autores: Iorio, M.; Santarelli, M. L.; González Gaitano, Gustavo; et al.
ISSN 0169-4332  Vol. 427  2018  págs. 1248 - 1256
Basalt fibers were surface treated with silane coupling agents as a method to enhance the adhesion and durability of fiber-matrix interfaces in concrete based composite materials. In particular, this work has been focused on the study of basalt fibers chemical coatings with aminosilanes and their subsequent characterization. Surface treatments were carried out after removing the original sizing applied by manufacturer and pretreating them with an activation process of surface silanol regeneration. Different samples were considered to make convenient comparisons: as received fibers (commercial), calcinated fibers (without commercial sizing), activated samples (calcinated fibers subjected to an acid process for hydroxyl regeneration), and silanized fibers with ¿-aminopropiltriethoxysilane, ¿-aminopropilmethyldiethoxysilane and a mixture of 50% by weight of both silanes. A deep characterization was carried out in terms of structure using X-ray diffraction, XRD, and Fourier transform infrared spectroscopy, FTIR, thermal properties by thermogravimetric analysis, TGA, coupled with single differential thermal analysis, SDTA, and morphology by scanning electron microscopy, SEM, and atomic force microscopy, AFM.
Autores: Iorio, M.; Teno, J.; Nicolás, M.; et al.
ISSN 0303-402X  Vol. 296  Nº 3  2018  págs. 461-469
Poly(methyl methacrylate) (PMMA) films filled with titanium oxide (TiO2) nanoparticles were prepared by solution blow spinning (SBS). The influence of the presence of nanoparticles (up to 10% by weight) in the physicochemical properties of the material was studied, focusing on the morphology, structure, and thermal properties, by scanning electron microscopy (SEM), Fourier-transformed infrared spectroscopy (FTIR), thermogravimetry (TGA), and differential scanning calorimetry (DSC). It was demonstrated that SBS allows obtaining PMMA/TiO2 nanocomposites with a relatively high amount of nanoparticles uniformly dispersed within the polymeric matrix, varying the surface characteristics of the films according to the amount of TiO2. The results indicate that the flow of the macromolecules is somewhat forced by the SBS process, and that specific interactions between the ester group of the MMA and the surface of the nanoparticles induce a preferential conformation of the functional group with respect to the PMMA backbone, at least at low loads of nanopartciles, conditions in which the self-aggregation of the nanofiller takes place in a lesser extent.
Autores: Lucio Ollauri, David; Martínez Oharriz, María Cristina; González Navarro, Carlos Javier; et al.
ISSN 0927-7765  Vol. 163  2018  págs. 64 - 72
This work describes the feasibility of poly(anhydride) nanoparticles as carriers for the oral administration of glibenclamide (GB) as well as the in vivo evaluation of their hypolipidemic effect in a C. elegans model. For this purpose, and in order to increase the GB payload, the drug was encapsulated in nanoparticles in presence of cyclodextrins (either ßCD or HPßCD). The optimized nanoparticles displayed a size of about 220¿nm and a negative zeta potential (-40¿mV), with a drug loading up to 52¿¿g/mg. Small-angle neutron scattering studies suggested an internal fractal-like structure, based on the repetition of spherical blocks of polymeric units (about 5¿nm) grouped to form the nanoparticle. X-ray diffraction study confirmed the absence of crystalline GB molecules due to its dispersion into the nanoparticles, either entrapped in the polymer chains and/or included into cyclodextrin cavities. GB-loaded nanoparticles induced a significant reduction in the fat content of C. elegans. This hypolipidemic effect was slightly higher for the nanoparticles prepared with coencapsulated HPßCD (8.2%) than for those prepared with ßCD (7.9%) or in the absence of cyclodextrins (7.0%). In summary, the coencapsulation of cyclodextrins into poly(anhydride) nanoparticles could be an interesting strategy to develop new oral formulations of glibenclamide.
Autores: Puig Rigall, Joan; Obregon-Gomez, I.; Monreal-Perez, P. ; et al.
ISSN 0021-9797  Vol. 524  2018  págs. 42 - 51
Tetronics are X-shaped block-copolymers of polyethylene oxide and polypropylene oxide, which self-assemble into micelles and can undergo a sol-gel transition; these transitions are dependent on temperature, concentration but also pH, due to the central diamine group of the tetrablock. We report the nanoscale morphologies underlying these different phases and the rheology of the systems for a very large, highly hydrophilic block copolymer, Tetronic 908, through the combined use of oscillatory rheology, steadyblock-state and time-resolved fluorescence, small-angle neutron scattering (SANS), dynamic light scattering (DLS) and Fourier transform infrared attenuated total reflectance (FTIR-ATR). At low concentrations, SANS reveal core-shell micelles of ca. 10 nm radius, presenting a dehydrated core and a highly hydrated shell, with relatively small aggregation numbers (N-agg approximate to 13). The micelles are notably affected by the pH, due to the protonation of the central amine spacer at low pH (pH approximate to 2), which shifts micellization to higher temperature, with smaller micelles than at natural pH. In the intermediate concentration regime (10-15%), micelles become smaller (N-agg approximate to 5), and present a higher hydration of the core. In the high concentration regime, Tetronic 908 undergoes a sol-gel transition above a threshold temperature, which is fully inhibited at acidic pH. SANS data from the gel phase reveal a BCC order of tightly packed spheres. Temperature sweeps in oscillatory rheology show a shift of the onset of gelation towards lower temperatures as concentration increases, an increase in the elastic modulus G' and an expansion of gel region over a larger range of temperatures. SANS and rheology reveal that at pH below the natural pH (ca. 8), gelation is shifted to higher temperatures, but the morphology of the gels is similar, while under highly acidic conditions the gelation is fully suppresed. (C) 2018 Elsevier Inc. All rights reserved.
Autores: Serres-Gomez, M.; González Gaitano, Gustavo; Kaldybekov, D. B. ; et al.
ISSN 0743-7463  Vol. 34  Nº 36  2018  págs. 10591 - 10602
Polypseudorotaxanes are polymer chains threaded by molecular rings that are free to unthread; these "pearl-necklace" can self-assemble further, leading to higher-order supramolecular structures with interesting functionalities. In this work, the complexation between alpha-cyclodextrin (alpha-CD), a cyclic oligosaccharide of glucopyranose units, and poly(ethylene glycol) (PEG) grafted to silica nanoparticles was studied. The threading of alpha-CD onto the polymeric chains leads to their aggregation into bundles, followed by either the precipitation of the inclusion complex or the formation of a gel phase, in which silica nanoparticles are incorporated. The kinetics of threading, followed by turbidimetry, revealed a dependence of the rate of complexation on the following parameters: the concentration of alpha-CD, temperature, PEG length (750, 4000, and 5000 g mol(-1)), whether the polymer is grafted or free in solution, and the density of grafting. Complexation is slower, and temperature has a higher impact on PEG grafted on silica nanoparticles compared to PEG free in solution. Thermodynamic parameters extracted from the transition-state theory showed that inclusion complex formation is favored with grafted PEG compared to free PEG and establishes a ratio of complexation of five to six ethylene oxide units per cyclodextrin. The complexation yields, determined by gravimetry, revealed that much higher yields are obtained with longer chains and higher grafting density.
Autores: Gonzalez Benito, J.; Teno, J.; González Gaitano, Gustavo; et al.
ISSN 0142-9418  Vol. 58  2017  págs. 21 - 30
Thermoplastic nanocomposite materials with potential bactericide properties were prepared and their surface properties and adhesion to Streptococcus mutans, S. mutans, were characterized. Solution blow spinning was successfully used to prepare films with a fiber-like structure on the surface of nano composites based on Polyvinylidene fluoride, PVDF, filled with well dispersed TiO2 nanoparticles. PVDF/TiO2 nanocomposites were prepared varying the nanoparticles content (0%, 1%, 2%, 5% and 10% by weight). In order to understand the influence of the presence of TiO2 nanoparticles and the final surface properties on the adhesion of S. mutans to the materials, a deep characterization was carried out focusing on the morphology, roughness, surface free energy from contact angle measurements and cell adhesion by single cell force spectroscopy. It was observed that the Uniform dispersion of the nanofiber arose from nanoparticles embedded in the polymer when fibers were created during the blow spinning process. TiO2 content influenced the topography of the films probably due to a direct effect on the solvent evaporation rate. Although this factor greatly conditioned the roughness of the samples and therefore the surface free energy, S. mutant adhesion on the substrates under study was concluded to be more dependent on the specific interactions with the surface polar groups of the material.
Autores: Teno, J.; González Gaitano, Gustavo; González-Benito, J.;
ISSN 0887-6266  Vol. 55   Nº 21  2017  págs. 1575 - 1584
Solution blow spinning, SBS, was used to prepare fibrous films of thermoplastic nanocomposites with potential antibacterial properties based on polysulfone, PSF, filled with well dispersed TiO2 nanoparticles. The PSF/TiO2 nanocomposites were produced with different nanoparticles content up to 10% by weight. A wide characterization was carried out focusing on the morphology at the nanoscale, roughness, contact angles, and surface free energy. Cell adhesion was studied by inspection by scanning electron microscopy (SEM). A uniform dispersion of the nanofiller was achieved, with the nanoparticles evenly embedded in the polymer along the fibers when they were created during the blow spinning process. TiO2 content influenced the topography of the films, most likely due to a direct effect on the solvent evaporation rate. The results obtained pointed out that an increase of the surface hydrophobicity as a result of the increased roughness induced by the presence of TiO2 nanoparticles was the main contribution to the reduction of DH5¿ Escherichia coli cells adhesion.
Autores: Teno, J.; González Gaitano, Gustavo; González-Benito, J.;
ISSN 0142-9418  Vol. 60  2017  págs. 140 - 148
Solution blow spinning, SBS, a quite novel processing method, was used to obtain poly (ethylene-co-vinyl acetate), EVA, films with controlled surface properties. The influence of the surface characteristics of EVA films on the adhesion of DH5 alpha Escherichia coli was studied. In particular, the initial concentration of the EVA solution to be blow spun was varied in order to get different surface topographies. Considering the potential use of EVA based materials in applications such as food packaging or scaffolds for tissue engineering all factors affecting proliferation of microorganisms on their surfaces should be studied and understood. Structural, morphological and surface characterizations based on the use of infrared spectroscopy, FTIR, scanning electron microscopy, SEM, and contact angle measurements were performed to ascertain the main factor influencing the E. coli adhesion on the EVA films. Roughness data were determined at different scales from 3D surfaces obtained using a stereoscopic reconstruction of SEM images. It was concluded that, depending on the conditions of the SBS process, only variations of topography were found on the EVA films, being therefore the unique cause of different adhesion capacity of E. con cells. A correlation between roughness and the number of attached E. coli cells showed that the higher the roughness at microscale level the higher the biofilm development, demonstrating that, apart from specific interactions at nanoscale surface, heterogeneity at microscale can greatly modify the antibacterial action.
Autores: González Gaitano, Gustavo; Isasi Allica, José Ramón; Vélaz Rivas, Itziar; et al.
ISSN 1381-6128  Vol. 23  Nº 3  2017  págs. 411 - 432
The pharmaceutical applications of cyclodextrins (CDs), cyclic oligosaccharides capable of including hydrophobic molecules inside their cavities, have been known for decades. Besides the solubilising and encapsulating abilities of natural and modified CDs due to the formation of inclusion complexes, there is an increasing interest in organized macrostructures based on CDs as potential drug delivery devices and gene carrier systems. The present review discusses first the case of drug carriers based on monomeric modified CDs (amphiphilic and CD core-star polymers), in which self-assembly plays a major role. Polyrotaxanes, i.e., CDs threaded onto a polymer chain, are then reviewed in relation to their pharmaceutical applications. Finally, covalently linked CDs, either by grafting or crosslinking, are analyzed, including more complex structures formed by assembling CD-containing networks or chains. We have tried along this review to cover the most recent developments on these structures for drug delivery in a "beyond the cyclodextrin" approach. The review will be helpful, both for readers who want to be introduced into the world of these remarkable structures, or for specialists who are doing research in this field.
Autores: Puig Rigall, J. ; Grillo, I. ; Dreiss, C. A. ; et al.
ISSN 0743-7463  Vol. 33  Nº 19  2017  págs. 4737 - 4747
The aggregation and structure of D-alpha-tocopheryl polyethylene glycol succinate micelles, TPGS-1000, an amphiphilic derivative of vitamin E, were characterized using scattering and spectroscopic methods, and the impact of different cyclodextrins (CDs) on the self-assembly was investigated, with the view of combining these two versatile pharmaceutical excipients in drug formulations. Combined small-angle neutron scattering (SANS), dynamic light scattering, and time-resolved and steady-state fluorescence emission experiments revealed a core-shell architecture with a high aggregation, number (N-ags approximate to 100) and a highly hydrated poly(ethylene oxide) corona (similar to 11 molecules of solvent per ethylene oxide unit). Micelles form gradually, with no sharp onset. Structural parameters and hydration of the aggregates were surprisingly stable with both temperature and concentration, which is a critical advantage for their use in pharmaceutical: formulations. CDs were shown to affect the self-assembly of TPGS in different ways. Whereas native CDs induced the precipitation of a solid complex (pseudopolyrotaxane), methylated beta-CDs led to different outcomes: constructive (micellar expansion), destructive (micellar rupture), or no effect, depending on the number of substituents and whether the substitution pattern was regular or random on the rims of the macrocycle. Time-resolved SANS studies on mixtures of TPGS with regularly dimethylated beta-CD (DIMEB), which ruptures the micelles, revealed an almost instantaneous demicellization (<100 ms) and showed that the process involved the formation of large aggregates whose size evolved over tithe. Micellar rupture is caused by the formation of a TPGS-DIMEB inclusion complex, involving the incorporation of up to three macrocycles on the tocopherol, as shown by proton nuclear magnetic resonance (NMR) and ROESY NMR. Analysis of NMR. data using Hill's equation revealed that the binding is rather cooperative, with the threading of the CD favoring the subsequent inclusion of additional CDs on the aliphatic moiety.
Autores: Serra Gómez, Rafael; Dreiss, C. A.; González-Benito, J.; et al.
ISSN 0743-7463  Vol. 32  Nº 25  2016  págs. 6398 - 6408
We report the preparation of a nanocomposite hydrogel based on a poloxamine gel matrix (Tetronic T1107) and cyclodextrin (CD)-modified barium titanate (BT) nanoparticles. The micellization and sol-gel behavior of pH-responsive block copolymer T1107 were fully characterized by small-angle neutron scattering (SANS), dynamic light scattering (DLS), and Fourier transform infrared attenuated total reflectance (FTIR-ATR) spectroscopy as a function of concentration, pH and temperature. SANS results reveal that spherical micelles in the low concentration regime present a dehydrated core and highly hydrated shell, with a small aggregation number and size, highly dependent on the degree of protonation of the central amine spacer. At high concentration, T1107 undergoes a sol-gel transition, which is inhibited at acidic pH. Nanocomposites were prepared by incorporating CD-modified BT of two different sizes (50 and 200 nm) in concentrated polymer solutions. Rheological measurements show a broadening of the gel region, as well as an improvement of the mechanical properties, as assessed by the shear elastic modulus, G' (up to 200% increase). Initial cytocompatibility studies of the nanocomposites show that the materials are nontoxic with viabilities over 70% for NIH3T3 fibroblast cell lines. Overall, the combination of Tetronics and modified BaTiO3 provides easily customizable systems with promising applications as soft piezoelectric materials
Autores: Serra Gómez, Rafael; Martínez-Tarifa, J. M.; González-Benito, J.; et al.
ISSN 1388-0764  Vol. 18  Nº 1  2016  págs. 24
Ceramic nanoparticles with piezoelectric properties, such as BaTiO3 (BT), constitute a promising approach in the fields of nanocomposite materials and biomaterials. In the latter case, to be successful in their preparation, the drawback of their fast aggregation and practically null stability in water has to be overcome. The objective of this investigation has been the surface functionalization of BaTiO3 nanoparticles with cyclodextrins (CDs) as a way to break the aggregation and improve the stability of the nanoparticles in water solution, preventing and minimizing their fast precipitation. As a secondary goal, we have achieved extra-functionality of the nanoparticles, bestowed from the hydrophobic cavity of the macrocycle, which is able to lodge guest molecules that can form inclusion complexes with the oligosaccharide. The nanoparticle functionalization has been fully tracked and characterized, and the cytotoxicity of the modified nanoparticles with fibroblasts and preosteoblasts cell lines has been assessed with excellent results in a wide range of concentrations. The modified nanoparticles were found to be suitable for the easy preparation of nanocomposite hydrogels, via dispersion in hydrophilic polymers of typical use in biomedical applications (PEG, Pluronics, and PEO), and further processed in the form of films via water casting, showing very good results in terms of homogeneity in the dispersion of the filler. Likewise, as examples of application and with the aim of exploring a different range of nanocomposites, rhodamine B was included in the macrocycles as a model molecule, and films prepared from a thermoplastic matrix (EVA) via high-energy ball milling have been tested by impedance spectroscopy to discuss their dielectric properties, which indicated that even small modifications in the surface of the nanoparticles generate a different kind of interaction with the polymeric matrix. The CD-modified nanoparticles are thus suitable for easy preparation of the waterbased nanocomposites either as hydrogels or as nanocomposites based on thermoplastic matrices.
Autores: Valero, M.; Castiglione, F.; Mele, A.; et al.
ISSN 0743-7463  Vol. 32  Nº 49  2016  págs. 13174 - 13186
Polymeric micelles, in particular PEO-PPO-based Pluronic, have emerged as promising drug carriers, while cyclodextrins (CD), cyclic oligosaccharides with an apolar cavity, have long been used for their capacity to form inclusion complexes with drugs. Dimethylated beta-cyclodextrin (DIMEB) has the capacity to fully breakup F127 Pluronic micelles, while this effect is substantially hindered if drugs are loaded within the micellar aggregates. Four drugs were studied at physiological temperature: lidocaine (LD), pentobarbital sodium salt (PB), sodium naproxen (NP), and sodium salicylate (SAL); higher temperatures shift the equilibrium toward higher drug partitioning and lower drug/CD binding compared to 25 degrees C (Valero, M.; Dreiss, C. A. Growth, Shrinking, and Breaking of Pluronic Micelles in the Presence of Drugs and/or beta-Cyclodextrin, a Study by Small-Angle Neutron Scattering and Fluorescence Spectroscopy. Langmuir 2010, 26, 10561-10571). The impact of drugs on micellar structure was characterized by small-angle neutron scattering (SANS), while their solubilization locus was revealed by 2D NOESY NMR UV and fluorescence spectroscopy, Dynamic and Static Light Scattering were employed to measure a range of micellar properties and drug:CD interactions: binding constant, drug partitioning within the micelles, critical micellar concentration of the loaded micelles, aggregation number (N-agg). Critically, time-resolved SANS (TR-SANS) reveal that micellar breakup in the presence of drugs is substantially slower (100s of seconds) than for the free micelles (<100 ms) (Valero, M.; Grillo, I.; Dreiss, C. A. Rupture of Pluronic Micelles by Di-Methylated beta-Cyclodextrin Is Not Due to Polypseudorotaxane Formation. J. Phys. Chem. B 2012, 116, 1273-1281). These results combined together give new insights into the mechanisms of protection of the drugs against CD-induced micellar breakup. The outcomes are practical guidelines to improve the design of drug delivery systems as well as a better understanding of competitive assembly mechanisms leading to shape and function modulation.
Autores: Segura González, E. A.; Olmos, D.; González Gaitano, Gustavo; et al.
ISSN 0021-8995  Vol. 132  Nº 42  2015  págs. 42676
The effect of high energy ball milling, HEBM, and the presence of kaolin on the structure, morphology, and biofilm development of polylactic acid, PLA, were studied. Biofilm development was evaluated in terms of structural and/or morphological variations so as the sole presence of kaolin. Composites based on PLA filled with kaolin were prepared by HEBM followed by hot pressing to obtain films. Structure was studied by X-ray diffraction and Fourier transformed infrared spectroscopy whereas morphology was inspected by scanning electron microscopy and atomic force microscopy. To study biofilm development on the surface of these materials, Pseudomonas fluorescens B52 were used. The shear forces from the milling process favor kaolin dispersion within the PLA. Longer milling times and cryogenic conditions improve clay dispersion. Subsequent hot pressing process enhances the most ordered structure of PLA (alpha-phase) which is also favored with previous milling at longer times and under cryogenic conditions. Changes in P. fluorescens biofilm development are mainly due to modifications of surface properties induced by structural variations, being the most ordered structures those which better support bacterial adhesion and proliferation.
Autores: Olmos, D.; González Gaitano, Gustavo; González-Benito, J.;
ISSN 2046-2069  Vol. 5  Nº 44  2015  págs. 34979 - 34984
The effect of the presence of silica nanoparticles on the structure, thermal stability and dynamics of low density polyethylene, LDPE, has been studied. Different loads of nanoparticles were dispersed within a LDPE matrix using high energy ball milling (HEBM) as a preliminary processing step to ensure a uniform dispersion of nanofiller to obtain nanocomposites in the form of films by hot pressing. The monitoring of the FTIR-ATR spectra of the samples as a function of the temperature has proven as a convenient method to study the interactions at a molecular scale between the polyethylene chains and the nanofiller. Band splitting observed in the bending and rocking modes of the ethylene groups indicated formation of crystalline phases whereas the analysis of absorbance band ratios from the stretching vibrations of PE accounted for the behavior of the polymer bulk. No evidence of strong polymer-filler interactions were found with the exception of a thermal relaxation process observed at 55 degrees C. Structural, morphological and thermal characterization of the nanocomposites did not reveal remarkable changes at low loads of filler, indicating that in the case of LDPE-silica nanocomposites, where weak interactions between the polymer and filler occur, the volume fraction of nanoparticles must be relatively high in order to produce changes in the bulk properties.
Autores: González Gaitano, Gustavo; da Silva, M. A.; Radulescu, A.; et al.
ISSN 0743-7463  Vol. 31  Nº 20  2015  págs. 5645 - 5655
Complexes formed between cyclodextrins (CDs) and polymers - pseudopolyrotaxanes (PPRs) - are the starting point of a multitude of supramolecular structures, which are proposed for a wide range of biomedical and technological applications. In this work, we investigate the complexation of a range of cyclodextrins with Tetronic T1307, a four-arm block copolymer of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) with a pH-responsive central ethylene diamine spacer, and its impact on micellization and the sol-gel transition. At low concentrations, small-angle neutron scattering (SANS) combined with dynamic light scattering (DLS) measurements show the presence of spherical micelles with a highly hydrated shell and a dehydrated core. Increasing the temperature leads to more compact micelles and larger aggregation numbers, whereas acidic conditions induce a shrinking of the micelles, with fewer unimers per micelle and a more hydrated corona. At high concentrations, T1307 undergoes a sol-gel transition, which is suppressed at pH below the pKa,1 (4.6). SANS data analysis reveals that the gels result from a random packing of the micelles, which have an increasing aggregation number and increasingly dehydrated shell and hydrated core with the temperature. Native CDs (¿, ß, ¿-CD) can complex T1307, resulting in the precipitation of a PPR. Instead, modified CDs compete with micellization to an extent that is critically dependent on the nature of the substitution. (1)H and ROESY NMR combined with SANS demonstrate that dimethylated ß-CD can thread onto the polymer, preferentially binding to the PO units, thus hindering self-aggregation by solubilizing the hydrophobic block. The various CDs are able to modulate the onset of gelation and the extent of the gel phase, and the effect correlates with the ability of the CDs to disrupt the micelles, with the exception of a sulfated sodium salt of ß-CD, which, while not affecting the CMT, is able to fully suppress the gel phase.
Autores: Iza, N.; Guerrero-Martínez, A.; Tardajos, G.; et al.
ISSN 0743-7463  Vol. 31  Nº 9  2015  págs. 2677 - 2688
The aggregation behavior of a chiral metallosurfactant, bis(2,2'-bipyridine)(4,4'-ditridecyl-2,2'-bipyridine)ruthenium(II) dichloride (Ru24C13), synthesized as a racemic mixture was characterized by small-angle neutron scattering, light scattering, NMR, and electronic spectroscopies. The analysis of the SANS data indicates that micelles are prolate ellipsoids over the range of concentrations studied, with a relatively low aggregation number, and the micellization takes place gradually with increasing concentration. The presence of cyclodextrins (beta-CD and gamma-CD) induces the breakup of the micelles and helps to establish that micellization occurs at a very slow exchange rate compared to the NMR time scale. The open structure of this metallosurfactant enables the formation of very stable complexes of 3:1 stoichiometry, in which one CD threads one of the hydrocarbon tails and two CDs the other, in close contact with the polar head. The complex formed with beta-CD, more stable than the one formed with the wider gamma-CD, is capable of resolving the Delta and Lambda enantiomers at high CD/surfactant molar ratios. The chiral recognition is possible due to the very specific interactions taking place when the beta-CD covers-via its secondary rim-part of the diimine moiety connected to the hydrophobic tails. A SANS model comprising a binary mixture of hard spheres (complex + micelles) was successfully used to study quantitatively the effect of the CDs on the aggregation of the surfactant.
Autores: González Gaitano, Gustavo; Müller, C.; Radulescu, A.; et al.
ISSN 0743-7463  Vol. 31  Nº 14  2015  págs. 4096 - 4105
Inclusion complexes between cyclodextrins and polymersso-called pseudopolyrotaxanes (PPR)are at the origin of fascinating supramolecular structures, which are finding increasing uses in biomedical and technological fields. Here we explore the impact of both native and a range of modified cyclodextrins (CD) on the self-assembly of X-shaped poly(ethylene oxide)poly(propylene oxide) block copolymers, so-called Tetronics or poloxamines, by focusing on Tetronic 904 (T904, M-w 6700). The effects are markedly dependent on the type and arrangement of the substituents on the macrocycle. While native CDs drive the formation of a solid PPR, most substituted CDs induce micellar breakup, with dimethylated beta-CD (DIMEB) having the strongest impact and randomly substituted CDs a much weaker disruptive effect. Using native alpha-CD as a molecular trap, we perform competitive binding experimentswhere two types of CDs thread together onto the polymer chainsto establish that DIMEB indeed has the highest propensity to form an inclusion complex with the polymer, while hydroxypropylated CDs do not thread. D-1 H-1 NMR and ROESY experiments confirm the formation of a soluble PPR with DIMEB in which the CD binds preferentially to the PO units, thus providing the drive for the observed demicellization. A combination of dynamic light scattering (DLS) and small-angle neutron scattering (SANS) is used to extract detailed structural parameters on the micelles. A binding model is proposed, which exploits the chemical shifts of selected protons from the CD in conjunction with the Hill equation, to prove that the formation of the PPR is a negatively cooperative process, in which threaded DIMEBs hamper the entrance of subsequent macrocycles.
Autores: Sirera Bejarano, Rafael; Álvarez Galindo, José Ignacio; Durán Benito, Adrián; et al.
ISSN 2255-453X  Vol. 2  Nº 1  2014  págs. 83 - 92
Los medios audiovisuales son herramientas adecuadas hoy en día para ilustrar el desarrollo de las clases magistrales impartidas por el profesor universitario. El alumno se desenvuelve con soltura en estos soportes, y la utilización de estos medios es un óptimo complemento para una buena comprensión del tema. Particularizando esta acción en estudios experimentales, como la Química, las ventajas que aporta el empleo de estos materiales son claras, tanto en el entendimiento de los temas como en el propio acercamiento del alumno a aspectos más prácticos y relacionados con el ejercicio profesional al que se dedicarán cuando finalicen los estudios. El presente trabajo evalúa los resultados de aplicar las nuevas tecnologías en la enseñanza de la Química a estudiantes de la Universidad de Navarra. Se pretende identificar elementos propios del ejercicio profesional del químico y relacionar los contenidos teórico-prácticos de las asignaturas con el mismo, consiguiendo además con ello un mejor conocimiento de la materia objeto de estudio. La percepción de los alumnos ha sido ciertamente positiva en términos de un incremento de interés por las materias implicadas y de una mejora en la comprensión de las mismas.
Autores: García Pérez, A.; da Silva, M.; Eriksson, J.; et al.
ISSN 0743-7463  Vol. 30  Nº 39  2014  págs. 11552 - 11562
Autores: Olmos, D.; González Gaitano, Gustavo; Kholkin, A. L.; et al.
ISSN 1563-5112  Vol. 447  Nº 1  2013  págs. 9 - 18
In this work, PVDF-BaTiO3 composites were prepared using cryogenic high-energy ball milling (HEBM) and subsequent hot pressing. PVDF-BaTiO3 mixtures with different weight fractions of submicrometric BaTiO3 particles were subjected to 1h of active milling. By applying pressure at 200 degrees C the resulting powder was molded in the form of thin discs. This processing method allowed us to obtain an extraordinary uniform dispersion of the BaTiO3 particles within the PVDF polymer matrix. A morphological and structural characterization of the materials was done using conventional techniques (DSC, FTIR, XRD, SEM). Piezoelectric characterization of the specimens was also carried out by two different tests for inducing output voltage signals in the materials: i) single impact by ball free fall; and ii) macroscopic tapping. It was found that the output voltage decreases in both cases with the amount of BaTiO3 particles. The origin of this observation does not seem to be due to changes in the crystalline structure or morphology of the PVDF induced by the presence of BaTiO3. Rather, it can be explained taking into account that the constituents of the composites under study, BaTiO3 and PVDF, have opposite piezoelectric effects.
Autores: González Gaitano, Gustavo; Calvo-Ferrer, M. A.;
ISSN 0277-3813  Vol. 33  Nº 3  2013  págs. 217 - 233
The aim of this investigation has been to define universal parameters that could be extracted in a straightforward way from FTIR-ATR spectra for the quality control (QC) of cork stoppers for paraffin and silicone; i.e., the most common components in surface treatment for lubrication and sealing. Three indicators, namely TC (total coating), SC (silicone coating), and PC (paraffin coating), are proposed, which are readily obtained from ratios of absorbances of some characteristic bands due to cork, paraffin, and silicone. These indicators are deduced with a minimum of approximations, they are solely connected with the amount of the species on the surface, and do not depend on the instrument used for the analysis. The validity of the methodology proposed has been tested with cases coming from real life, being applicable to natural cork stoppers, 1+1 and agglomerate types. Some guidelines are also provided for its application in case of colmated stoppers. Finally, other approaches that may take advantage of the readiness and non-invasive features of FTIR-ATR spectroscopy are discussed.
Autores: Olmos, D.; Montero, F.; González Gaitano, Gustavo; et al.
ISSN 0272-8397  Vol. 32  Nº 12  2013  págs. 2094 - 2104
Composites based on polyvinylidene fluoride filled with barium titanate (PVDF/BT) submicrometric particles were prepared. To uniformly disperse BT particles within PVDF, high-energy ball cryomilling was used. The effect of processing and the presence of BT particles on the structure and morphology of the composites were analyzed by Fourier transformed infrared spectroscopy, X-ray diffraction, differential scanning calorimetry, and atomic force microscopy. In terms of the structure, it can be concluded/stated that after milling the - and -PVDF crystalline phases are reduced, whereas the content in the phase is increased. On the other hand, after film formation, the phase was recovered. It was demonstrated that the milling process is the most important factor to increase the amount of phase, being favored by the presence of BT particles. In terms of the morphology, it was observed that the PVDF lamellar aspect ratio increases with the amount of BT in cryomilled samples processed as films. Besides, the crystallization kinetics is highly affected by the milling process and the presence of BT, being the relative crystallization rate slower with the presence of BT.
Autores: González-Benito, J.; Martínez-Tarifa, J.; Sepulveda-Garcia, M. E.; et al.
ISSN 0142-9418  Vol. 32  Nº 8  2013  págs. 1342 - 1349
Composites of high density polyethylene, HDPE, filled with submicrometric particles of BaTiO3, BT, have been prepared. Uniform dispersion of the particles was achieved by high energy ball milling and subsequent hot pressing. Using SEM, FTIR, TGA-DTA and stress-strain tests, studies of the structural, morphological and mechanical features of the composites have been carried out. Frequency response analysis, dielectric strength and resistivity measurements were also performed to evaluate the final electrical properties as a function of the processing and the amount of BaTiO3 particles. From the analysis of the microscopic structure, it can be deduced that any change in the properties of the materials must be solely ascribed to the presence of the BT particles. A balance between an enhancement of space charge polarization with the presence of BT and the existence of permanent dipoles associated to them might explain an initial increase in the dielectric losses with the BT content, and its later decrease at higher BT content. The observed decrease in resistivity and breakdown voltage when increasing the amount of BaTiO3 can be explained by the lower resistivity of BT particles at room temperature and the growing accumulation of space charge.
Autores: Olmos, D.; Martínez-Tarifa, J. M.; González Gaitano, Gustavo; et al.
ISSN 0142-9418  Vol. 31  Nº 8  2012  págs. 1121 - 1130
Composites based on polystyrene (PS) filled with submicrometre particles of BaTiO3 were prepared making use of high energy ball milling (HEBM) and hot pressing. The effect of processing and the amount of BaTiO3 particles on the morphology and structure of the composites was studied to finally correlate them with their dielectric behaviour. The method of processing used was proven to be efficient to uniformly disperse the particles within the polymer matrix. Neither the milling process nor the presence of BaTiO3 nanoparticles (below 40% wt) seemed to alter the structure of the PS polymer. The glass transition temperature, as well as the thermal degradation of the polymer, remains almost without any alteration, suggesting that: i) the presence of the particles does not modify the dynamics of the PS matrix and ii) there are no strong physico-chemical interactions between the PS and the BaTiO3 particles. Changes in the relative permittivity of the systems due to milling and the incorporation of the particles were studied. HEBM by itself does not significantly affect the dielectric constant whereas the presence of BaTiO3 increases it, following reported theories.
Autores: Serra Gómez, Rafael; González Gaitano, Gustavo; Gonzalez-Benito, J.;
ISSN 0272-8397  Vol. 33  Nº 9  2012  págs. 1549-1556
Ethylene vinyl acetate copolymer, a thermoplastic semicrystalline polymer, has been blended with barium titanate submicrometric particles (BaTiO3) by means of high-energy ball milling (HEBM) for obtaining composites in the form of films by hot pressing. Two different milling conditions have been considered: (i) milling at room temperature and (ii) milling under the temperature of the liquid nitrogen (cryomilling). The resulting composites have been fully characterized by spectroscopic and microscopic techniques to study the structure and morphology as a function of the processing conditions. A very good dispersion of the particles is attained under cryogenic conditions and, irrespective of the milling method, structural modifications were not observed in any of the materials used. Cross-contamination of iron from the milling tools is also reduced to acceptable values for HEBM standards, especially in the case of cryomilling, an important issue for the use of these composites in electrical applications. POLYM. COMPOS., 2012. (c) 2012 Society of Plastics Engineers
Autores: Serra Gómez, Rafael; Tardajos, G.; González-Benito, J.; et al.
ISSN 0143-7208  Vol. 94  Nº 3  2012  págs. 427 - 436
Autores: Olmos, D.; Martínez, F.; González Gaitano, Gustavo; et al.
Revista: European Polymer Journal
ISSN 0014-3057  Vol. 47  Nº 8  2011  págs. 1495 - 1502
Autores: Maeztu Arbeo, Raquel; González Gaitano, Gustavo; Tardajos, G.; et al.
Revista: Journal of Luminescence
ISSN 0022-2313  Vol. 131  Nº 4  2011  págs. 662 - 668
Autores: Maeztu Arbeo, Raquel; Tardajos, G.; González Gaitano, Gustavo
Revista: Journal of Inclusion Phenomena and Macrocyclic Chemistry
ISSN 1388-3127  Vol. 69  Nº 3-4  2011  págs. 361 - 367
Autores: Maeztu Arbeo, Raquel; González Gaitano, Gustavo; Tardajos, G.
ISSN 1520-6106  Vol. 114  Nº 32  2010  págs. 10541 - 10549
Autores: Maeztu Arbeo, Raquel; Tardajos, G.; González Gaitano, Gustavo
ISSN 1520-6106  Vol. 114  Nº 8  2010  págs. 2798 - 2806
Autores: Fuentes Ramírez, Marta; Baigorri Ekisoain, Roberto Pedro; González-Vila, F.J.; et al.
ISSN 0047-2425  Vol. 39  Nº 4  2010  págs. 1486 - 1497