Metal/polymer nanocomposites have attracted much attention in recent years due to their exceptional properties and wide range of potential applications. A key challenge to obtain these materials is to stabilize the metal nanoparticles in the matrix, avoiding uncontrolled aggregation processes driven by the high surface free energy of nanosized particles. Here, we investigate the aggregation mechanism of primary particles in gold-epoxy nanocomposites prepared via light-assisted in situ synthesis, under different irradiation conditions. The growth and aggregation of gold nanoparticles were monitored in situ by time-resolved small-angle X-ray scattering experiments, whereas spectroscopic measurements were performed to interpret how matrix polymerization influences the aggregation process. It was found that light intensity has a greater influence on the reduction rate than on the polymerization rate. Under irradiation, gold nanostructures evolve through five time-defined stages: nuclei-mass fractals-surface fractals-spherical nanoparticles-aggregates. If the maximum in the polymerization rate is reached before the aggregation step, individual primary nanoparticles will be preserved in the polymer matrix due to diffusional constraints imposed by the reaction medium. Because the light intensity has a different influence on the reduction rate than on the polymerization rate, this parameter can be used as a versatile tool to avoid aggregation of gold nanoparticles into the polymer matrix.

The photothermal response of mercaptoundecanoic acid (MUA)-coated Ag nanoparticles (Ag@MUA NPs) in both aqueous dispersions and paper substrates was determined as a function of pH when irradiated with a green laser or a blue LED source. Aqueous dispersions of Ag@MUA NPs showed an aggregation behavior by acidification that was used for the formation of NPs clusters of variable sizes. Aggregation was induced by changing the pH across the apparent pKa of the acid, higher than the pKa of the free acid. Formation of these aggregates was completely reversible allowing the return to the well-dispersed initial state by simply increasing the pH by the addition of a base. Aggregation produced a shift of the plasmon band that changed the spectra of the dispersions and their ability to be remotely heated when irradiated with visible light. These aggregates could be transferred to paper by simple impregnation of the substrates with the dispersion. On the solid substrate, a higher photothermal response than in the liquid medium was observed. A high local increase of up to 75 °C could be recorded on paper after only 30 s of irradiation with a green laser, whereas a blue LED array was enough for inducing the melting of a solid paraffin (Tm = 36-38 °C) deposited on it. This work demonstrates that photothermal heating can be controlled by the reversible aggregation of NPs to induce different thermal responses in liquid and solid media.

Epoxy vitrimers were synthesized employing stoichiometric amounts of diglycidyl ether of bisphenol A (DGEBA), sebacic acid (20% eq.) and an n-alkylamine, either octylamine (OA), dodecylamine (DA) or hexadecylamine (HA) (80% eq.). Apart from the chemical crosslinks generated by diester groups formed in transesterification reactions, these vitrimers include physical crosslinks arising from self-association of alkyl chains. The relative fraction and strength of physical crosslinks was high for octylamine (OA), intermediate for dodecylamine (DA) and low for hexadecylamine (HA). This was reflected by rubbery moduli that increased significantly from HA to OA. The covalently bonded tertiary amine generated in the epoxy-amine addition reaction was an efficient catalyst of transesterification reactions. Relatively fast stress relaxation rates were observed driven by transesterification reactions coupled to the dynamic exchange of self-associated alkyl chains. The occurrence of this last mechanism was evidenced by the stress relaxation observed for the linear polymer synthesized with stoichiometric amounts of DGEBA and OA that forms a permanent network up to temperatures close to degradation due to the presence of a high fraction of self-associated n-octyl chains. These vitrimers might find applications in several fields such as soft robotics, electro and magnetorheological elastomers, soft tissues and in additive manufacturing.

Hybrid organic–inorganic coatings showing photothermal activity and anti-bacterial properties were easily obtained by cross-linking of glycerol in presence of silane-coated silver NPs (Ag NPs). Ag NPs functionalized with aminosilane groups were prepared by reduction of AgNO3 with 3-aminopropyl trimethoxysilane (APTMS), by following a previously published procedure (dell’Erba et al., J Mater Sci 51:3817–3823, 2016), using glycerol as both reducing agent and solvent. Thermal treatment of these dispersions induced reaction between hydroxyl from glycerol and methoxysilane groups, producing a chemically resistant, cross-linked nanostructured network with covalently bonded Ag NPs. Control on the degree of glycerol release during synthesis enabled producing, in just one step, a cross-linked material with variable concentrations of Ag NPs. Tuning the annealing temperature and composition of the reactive samples allowed controlling the final concentration of NPs in the solid samples and the physicochemical properties of the coatings. Obtained materials showed an excellent chemical stability, bactericidal effect against Escherichia coli, and a significant photothermal effect. The simplicity of the procedure, the use of glycerol as monomer and solvent, and the high versatility of the strategy that enables the inclusion of different metals in a cross-linked matrix, make the synthetic strategy very promising for the development of materials with technological applications.

The development of convenient synthetic methods and improved materials for the production of high load-capacity and biocompatible drug delivery systems is a challenging task with important implications in health sciences. In this work, acrylamide/2-hydroxyethylmethacrylate and N-isopropylacrylamide/2-hydro-xyethylmethacrylate hydrogels were synthesized by photopolymerization using energy-efficient green-LEDs. A functionalized silsesquioxane was used as both crosslinker and co-initiator for the photo-polymerization. The hybrid organic-inorganic nature of the silsesquioxane improved the resulting hydrogels' properties increasing their swelling capacity and biocompatibility. Additionally, the mild conditions used during the photo polymerization allowed the synthesis of hydrogels in the presence of antibiotics yielding high load-capacity materials in which the drug preserves its molecular structure and antimicrobial activity (as confirmed by HPLC and microbiological assays). The materials were characterized by FTIR, DSC and SEM. Additionally, the kinetics of gels' swelling and drug release were studied under physiological conditions (pH 7.4 and 37 degrees C). The results demonstrate how hydrogel composition affects the antibiotics-release kinetics. The final drug release percentage increased with increasing molar fraction of acrylamide or N-isopropylacrylamide and in most cases exceeded 85%. Finally, the antibacterial effect of loaded gels was characterized using a number of assays against Gram negative and Gram positive bacteria. The observed antibacterial effect correlated well with swelling and drug release results. Furthermore, gels are not toxic for isolated erythrocytes as demonstrated by haemolytic tests. Overall, our results indicate that the produced hydrogels are promising materials to develop controlled drug-delivery devices such as capsules, dermatological patches and others.

Fil: Cativa, Nancy Maribel. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnologia de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingenieria. Instituto de Investigaciones en Ciencia y Tecnologia de Materiales; Argentina

Mineral-coated silsesquioxane particles of approximately 600 nm diameter were synthesized from the hydrolytic co-condensation of N-[3-trimethoxysilyl]-propyl]ethylenediamine (DAS) and tetraethyl orthosilicate (TEOS). The hybrid particles involve nanocomposites with a mineral core (montmorillonite-MMT-or goethite-Gt-nanoparticles) and coated with a silsesquioxane shell containing hydroxyl and amine groups. These particles were specially designed (exposing amino groups) to be highly efficient for the removal of As(V) and to enhance the adsorption properties of the minerals employed in this work. They were characterized by infrared spectroscopy, X-ray diffraction, scanning electron microscopy, zeta potential, dynamic light scattering and thermogravimetric techniques such as dynamic scanning calorimetry and thermogravimetric analysis. The characteristics found in the composite particles compared with pure organosilane DAS/TEOS or with the unmodified minerals proved the effectiveness of the silanization process. As result, hybrid nanocomposite materials were obtained, denoting versatility in their adsorption properties of different types of pollutants. Moreover, all synthesized particles showed a high arsenic retention capacity; experimental results demonstrated that superficial modification of the minerals is the preponderant factor that determines their adsorbent properties, favoring the versatility of these materials making them suitable for the removal of pollutants of diverse charge and nature.

Synthesis of polyethylene/silica-silver nanocomposites (PE/SiAg) by in situ polymerization with supported and non-supported catalysts was achieved using the Cp2ZrCl2/MAO catalytic system. Silica-silver nanoparticles (SiAg) were synthesized via two routes (acidic and basic) and characterized to determine the silver content, morphology, and size. The basic route resulted in particles with a lower concentration of silver and with smaller diameters. The polymerizations of ethylene in the presence of the fillers produced high yields of nanocomposites. The catalyst support in SiAg was efficient, although the percentage of Zr effectively immobilized was very low. Polyethylene melting and crystallization temperatures did not change significantly with the addition of the filler. SEM images showed differences in the morphologies between the supported and non-supported catalysis, and between the acidic and basic conditions for SiAg preparation. Two different tests were performed and showed that the nanocomposites inhibited the proliferation of bacteria in contact with the films.

Alkyl chains of β-hydroxyesters synthesized by the capping of terminal epoxy groups of diglycidylether of bisphenol A (DGEBA) with palmitic (C16), stearic (C18), or behenic (C22) fatty acids self-assemble forming a crystalline phase. Above a particular concentration solutions of these esters in a variety of solvents led to supramolecular (physical) gels below the crystallization temperature of alkyl chains. A form-stable phase change material (FS-PCM) was obtained by blending the ester derived from behenic acid with eicosane. A blend containing 20 wt % ester was stable as a gel up to 53 °C and exhibited a heat storage capacity of 161 J/g, absorbed during the melting of eicosane at 37 °C. Thermally reversible light scattering (TRLS) films were obtained by visible-light photopolymerization of poly(ethylene glycol) dimethacrylate-ester blends (50 wt %) in the gel state at room temperature. The reaction was very fast and not inhibited by oxygen. TRLS films consisted of a cross-linked methacrylic network interpenetrated by the supramolecular network formed by the esters. Above the melting temperature of crystallites formed by alkyl chains, the film was transparent due to the matching between refractive indices of the methacrylic network and the amorphous ester. Below the crystallization temperature, the film was opaque because of light dispersion produced by the organic crystallites uniformly dispersed in the material. Of high significance for application was the fact that the contrast ratio did not depend on heating and cooling rates.

A detailed understanding of the processes taking place during the in situ synthesis of metal/polymer nanocomposites is crucial to manipulate the shape and size of nanoparticles (NPs) with a high level of control. In this paper, we report an in-depth time-resolved analysis of the particle formation process in silver/epoxy nanocomposites obtained through a visible-light-assisted in situ synthesis. The selected epoxy monomer was based on diglycidyl ether of bisphenol A, which undergoes relatively slow cationic ring-opening polymerization. This feature allowed us to access a full description of the formation process of silver NPs before this was arrested by the curing of the epoxy matrix. In situ time-resolved small-angle X-ray scattering investigation was carried out to follow the evolution of the number and size of the silver NPs as a function of irradiation time, whereas rheological experiments combined with near-infrared and ultraviolet-visible spectroscopies were performed to interpret how changes in the rheological properties of the matrix affect the nucleation and growth of particles. The analysis of the obtained results allowed us to propose consistent mechanisms for the formation of metal/polymer nanocomposites obtained by light-assisted one-pot synthesis. Finally, the effect of a thermal postcuring treatment of the epoxy matrix on the particle size in the nanocomposite was investigated.

Stable dispersions of silver nanoparticles (Ag NPs) were synthesized employing glycerol as both a solvent and reducing agent, and 3-aminopropyl trimethoxysilane (APTMS) as a stabilizer. Average sizes varied between 13 and 55 nm, depending on the molar ratio of APTMS/Ag. Terminal alkoxysilanes reacted with OH groups of glycerol leading to the covalent bonding of glycerol moieties to the chain ends of the stabilizer. This produced extremely stable colloidal dispersions from which NPs could not be extracted with solvents immiscible with glycerol (as THF). Ag NPs were covalently bonded to the surface of a colloidal silica by hydrolysis/condensation of terminal Si–O–C bonds of the stabilizer with superficial SiOH bonds of silica. TEM images revealed the presence of individual NPs and small clusters of NPs attached to the silica surface. These clusters were presumably generated by intermolecular reactions among chain ends of the stabilizer producing Si–O–Si bonds. The antibacterial properties of the resulting powder were confirmed by conventional tests employing a culture of Escherichia Coli.

The synthesis and characterization of silsesquioxane (SSO) films with pendant dodecyl groups and doped with goethite (Gt) or montmorillonite (MMT) nanoparticles were carried out and the new materials tested as sorbents of diverse contaminants. The synthetic method used yielded SSO films with the inorganic substrates homogeneously distributed within the polymeric matrices. The new materials were characterized by SEM, FTIR, XRD, and DSC and tested to evaluate their capability for adsorbing metallic cations, organic dyes, and phosphate, frequent contaminants of industrial effluents. All films were found suitable for removing metallic cations. Results also showed that the SSO films undoped and doped with Gt are primarily apt for anionic compounds removal. Although the SSO films doped with MMT are capable of removing cationic contaminants from aqueous samples, the stiffness of the SSO matrix hinders MMT properties as an adsorbent. The possibility of dispersing nanoparticulate systems in the stable and chemically inert SSO matrices simplifies their application for contaminant removal, particularly because it makes the separation process of the absorbed pollutant from the treated medium easier.

Diglycidyl ether of bisphenol A (DGEBA) is among the most popular and widely used epoxy monomers. This monomer is commonly used in thermal network polymerizations with amines, phenols, isocyanates or mercaptans as curing agents. However, the photoinitiated polymerization of DGEBA is very sluggish and hence finds little use in high-speed photocuring applications. In this contribution, we demonstrated that this monomer can undergo very fast visible-light photopolymerization when combined with a silsesquioxane (SSO) functionalized with reactive epoxycyclohexane groups. The SSO was synthesized via alkoxysilane hydrolysis/condensation chemistry, using DGEBA as a solvent. We found that the photopolymerization of DGEBA is markedly accelerated as the amount of SSO in the mixture is increased. The promoter effect on the reactivity of DGEBA was ascribed to a combination of both thermal and copolymerization effects. Using dynamic mechanical analysis, we demonstrated that the resulting hybrid materials present a single-phase network structure, where the SSO species function as highly multifunctional epoxy reactants.

Nanoparticles (NPs) may be homogeneously dispersed in the precursors of a polymer (reactive solvent) by an adequate selection of their stabilizing ligands. However, the dispersion can become metastable or unstable in the course of polymerization. If this happens, NP-rich domains can be segregated by a process called polymerization-induced phase separation (PIPS). This occurs mainly due to the decrease in the entropic contribution of the reactive solvent to the free energy of mixing (increase in its average size) and, for a reactive solvent generating a cross-linked polymer, the additional contribution of the elastic energy in the post-gel stage. The extent of PIPS will depend on the competition between phase separation and polymerization rates. It can be completely avoided, limited to a local scale or conveyed to generate different types of NPs' aggregates such as crystalline platelets, self-assembled structures with a hierarchical order and partitioning at the interface, and bidimensional patterns of NPs at the film surface. The use of a third component in the initial formulation such as a linear polymer or a block copolymer, provides the possibility of generating an internal template for the preferential location and self-assembly of phase-separated NPs. Some illustrative examples of morphologies generated by PIPS in solutions of NPs in reactive solvents, are analyzed in this feature article.

Hybrid organic-inorganic macrophotoinitiator bearing pendant tertiary amine groups (Ol-AH) was prepared by hydrolytic condensation of a silane containing amino groups. The macromolecular aminofunctionalized photoinitiator was used in combination with camphorquinone (CQ) for visible-light photo-polymerization. The Ol-AH was incorporated into methacrylate resins at loadings between 1 and 10 wt.%. The photodecomposition of the CQ/OI-AH in methacrylate monomers under visible light irradiation (lambda = 470 nm) was examined. The photolysis products of CQ/OI-AH were transparent at the irradiating wavelengths; consequently, the consumption of the CQ is accompanied by increased light intensity in the underlying lays. The clean and rapid photobleaching of CQ in combination with Ol-AH makes this photoinitiator system very attractive for polymerization of thick sections. The evolution of monomer conversion versus irradiation time showed that the Ol-AH is an efficient co-initiator of CQ because a fast reaction and high conversion of methacrylate groups result after 60s irradiation with a LED source of 140 mW. (C) 2014 Elsevier B.V. All rights reserved.

Hybrid systems formulated with epoxy and methacrylate monomers at mass fraction either 50:50 or 75:25 were studied. The individual monomer conversions during photopolymerization with visible light were monitored by Raman and near-infrared spectroscopies. The rate of polymerization and final degree of conversion of the methacrylate groups were raised when the epoxy monomer was present. This is attributed to enhancement of the mobility of the reactive species caused by the presence of the epoxy monomer. Conversely, the earlier vitrification of the system due to the faster polymerizing methacrylate network resulted in reduced conversion of epoxy rings.

Photoluminescence of Au(I)-dodecane thiolate (Au(I)-DDT) and its thermal reduction to metallic gold have been extensively reported in the literature. However, the incorporation of this salt to a polymeric matrix to produce photoluminescent materials or gold nanocomposites by thermal reduction is a difficult task due to the insolubility of Au(I)-DDT. In this study it is shown that a silsesquioxane with pendant dodecyl chains can be a convenient host of Au(I)-DDT. The presence of dodecyl chains in both compounds and the in situ generation of the salt in the solution of the silsesquioxane precursor enabled to obtain a uniform dispersion of Au(I)-DDT in the silsesquioxane matrix. Flexible films were generated, exhibiting characteristic photoluminescent properties before thermal treatment and a uniform dispersion of gold nanoparticles after heating at 150 °C for different periods of time.