YVO4:Eu3+ is a red emitter phosphor commercially available as micrometric powder due to its high luminescence efficiency under electron-beam excitation. Although some published results have ...demonstrated the potential of using this micrometer material in Fiber Optic Dosimetry systems, there is no information regarding its use on a nanometric scale. In order to obtain a nanometric material with high luminescent efficiency, a simple synthetic combustion method was developed and the results were compared with both, those of a commercial material and those obtained by a typical coprecipitation synthesis. A single crystalline phase was obtained when the combustion route was employed for the preparation meanwhile two crystalline phases were obtained via coprecipitation synthesis. The particle size of YVO4:Eu3+ obtained by combustion route ranges from 55 up to 200 nm. Fourier Transform Infrared Spectroscopy and Thermogravimetric Analysis indicated that annealing at 600 °C promote the degradation of the impurities that remained adsorbed onto nanoparticles surface after the synthesis. However, to improve the Radioluminescence intensity, an annealing process at 1000 °C was required. The method allows obtaining a nanometric material with a scintillation intensity almost twice higher than that of the commercial powder.
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•Combustion route is a simple synthesis method to obtain YVO4:Eu3+ nanoparticles.•Radioluminescence intensity is twice higher than that of microcrystalline sample.•YVO4:Eu3+ synthesized are suitable scintillators for Fiber Optic Dosimetry.
Conventional drug delivery systems often have several pharmacodynamic and pharmacokinetic limitations related to their low efficacy and bad safety. It is because these traditional systems cannot ...always be selectively addressed to their therapeutic target sites. Currently, target-specific and controlled drug delivery is one of the foremost challenges in the biomedical field. In this context, stimuli-responsive polymeric nanomaterials have been recognized as a topic of intense research. They have gained immense attention in therapeutics - particularly in the drug delivery area - due to the ease of tailorable behavior in response to the surroundings. Light irradiation is of particular interest among externally triggered stimuli because it may be specifically localized in a contact-free manner. Light-human body interactions may sometimes be harmful due to photothermal and photomechanical reactions that lead to cell death by photo-toxicity and/or photosensitization. However, these limitations may also be overcome by the use of photo-responsive polymeric nanostructures. This review summarizes recent developments in photo-responsive polymeric nanocarriers used in the field of drug delivery systems, including nanoparticles, nanogels, micelles, nanofibers, dendrimers, and polymersomes, as well as their classification and mechanisms of drug release.
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•The incorporation of azobenzene moieties into a bridged silsesquioxane led a material with light-induced healing ability.•The photoisomerization of the azobenzene increases the ...mobility and allows the material to flow in the damaged area.•A complete recovery of the damage was observed after only 30 s of UV irradiation.
Intrinsic healable polymers are materials capable of repairing itself through its chemical nature, in order to improve stability and durability and to restore the lost functionalities or properties.
In this study, azobenzene (AZO) moieties were incorporated into a previously reported bridged silsesquioxane based on the reaction of isocyanatepropyltriethoxysilane (IPTS) with bisphenol A (BPA), by replacing a small fraction of BPA by a bisazophenol (4,4′-dihydroxyazobenzene, AZOH). The incorporation of these AZO moieties led to a material with UV light-induced healing abilities. The underlying healing mechanism is attributed to the intra-molecular conformational changes of the azo-chromophores that are induced by the trans to cis photoisomerization of the azobenzene. These changes temporary increased its mobility and allowed the material to flow in the damaged area, followed by a process of restoring the physical hydrogen bonds. This process was monitored following the viscoelastic properties during successive cycles of turning ON and OFF the UV irradiation. Remarkably, the resultant healed material has not significant observed mechanical differences with the original one.
It has been well documented that self-assembly of block copolymers (BCP) in selective solvents, where the core-forming block is a crystallizable polymer, results in micelle structures with ...exceptional aggregation morphologies determined mainly by the crystallization energy from the core. In this contribution, we apply this concept to create ribbon-like nanostructures dispersed in an epoxy network. The selected system was a polyethylene-b-poly(ethylene oxide) (PE-b-PEO) diblock copolymer in an epoxy monomer based on diglycidyl ether of bisphenol A (DGEBA). This system was selected on the bases that PEO is an epoxy-philic block which is completely miscible with DGEBA before and after curing reaction whereas PE is a crystallizable epoxy-phobic block. Under these conditions, we access to self-assembled nanostructures with semicrystalline core before curing reaction. With the aim of preserving the structural features of these micelles, the epoxy monomers were cured at room temperature (i.e., below the melting transition of the core-forming PE block) by photoinitiated cationic ring-opening polymerization. Long nanoribbons dispersed in the cured epoxy matrix were obtained, as characterized by SAXS patterns and TEM images. These ribbon-like micelles present a tendency to aggregate resulting in the formation of face-to-face stacking of parallel micelles. We demonstrated that while the stacking number decreases with decreasing BCP concentration, the arrangement of the nanoribbons within one stack becomes less organized.
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•Nanoribbons with semicrystalline core dispersed in an epoxy matrix were prepared.•This was achieved by self-assembling a PE-b-PEO block copolymer in a DGEBA resin.•Nanostructures are formed by a crystallization-driven self-assembly mechanism.•The nanoribbons present a tendency to aggregate forming face-to-face stacking.•DGEBA was photocured at room temperature to preserve these nanostructures.
Epoxies are an important family of shape memory polymers (SMP) due to their excellent stability and thermo-mechanical endurance and the high values of shape fixity and shape recovery. Actuators based ...on these materials can be designed for large tensile elongations (e.g., 75% or higher) or large recovered stresses (e.g., 3MPa or higher). However, meeting these requirements simultaneously is a difficult task because changes in the crosslink density affect both variables in opposite ways. We show that an SMP based on an epoxy network with both chemical and physical crosslinks could be strained up to 75% in four repeated shape memory cycles with tensile stresses close to 3MPa. Shape fixity and shape recovery values were close to 98% and 96%, respectively, for everyone of the cycles, without any significant change between the first and subsequent cycles.
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•Locally aligned wormlike micelles were generated in a PS-b-PEO/epoxy network.•The strategy was to increase the molar mass of a PS-b-PEO generating HPC domains.•The large molar mass ...frustrated the generation of the HPC phase.•Instead, locally aligned cylindrical micelles were generated.
A dispersion of wormlike micelles, empirically found in some block copolymer (BCP)/epoxy blends, has been reported to produce a significant toughening of epoxy networks. In this study, a rationale procedure to generate and trap large and locally aligned wormlike micelles in an epoxy matrix is reported. A BCP/epoxy/hardener blend was selected that was homogeneous at the polymerization temperature but became nanostructured in the course of polymerization leading to hexagonally packed cylinders (HPC) domains. When a similar BCP with a molar mass about three times larger than the first one and with the same ratio between blocks was used, the nanostructuration into HPC domains was frustrated by diffusional limitations of the large cylindrical micelles generated. A morphology consisting of a dispersion of large and locally aligned wormlike micelles was trapped in the cross-linked epoxy. The selected BCP was polystyrene (PS)-b-poly(ethylene oxide) (PEO), with molar masses M=43kDa or 136kDa and a mass fraction of PEO close to 25wt%. The network precursors were based on diglycidylether of bisphenol A (DGEBA) and 4,4′-methylenebis(2,6-diethylaniline) (MDEA). Low- and high-molar-mass BCP generated, respectively, HPC domains and wormlike micelles, as supported by TEM images and SAXS spectra.
Polymerization-induced nanostructuration combined with crystallization-driven self-assembly was used to generate complex nanostructures in an epoxy network. A PE-
b
-PEO block copolymer (
M
n
= 1400; ...50 wt% PEO), was dispersed in diglycidylether of bisphenol A (DGEBA) and homopolymerization initiated by a tertiary amine was carried out at 120 °C (above the melting temperature of PE). The plasticization produced by the miscible PEO blocks decreased the
T
g
of the cured matrix to values located below the crystallization temperature of PE. Therefore, crystallization-driven self-assembly of PE blocks took place during the cooling step through the rubbery region of the epoxy network. Depending on the initial amount of PE-
b
-PEO dispersed in DGEBA, a variety of nanostructures could be generated, such as a dispersion of disk-like micelles (6.7 nm in thickness), a concentrated dispersion of short nanoribbons (50-200 nm in length and 6.7 nm in thickness), partially stacked and oriented in space, and complex spherulitic structures composed of large stacked nanoribbons. The thickness of micellar objects was close to the theoretical value of fully extended PE chains of the block copolymer. IR spectroscopy confirmed the
all-trans
conformation of PE chains. Therefore, crystals were formed by interdigitated PE chains, with PEO blocks tethered at both planar interfaces in an alternating way. The way in which these complex nanostructures affect the fracture resistance or functional properties (such as shape memory) of the resulting epoxy networks has yet to be analyzed.
This work reports how to generate complex nanostructures in an epoxy network by combining polymerization-induced nanostructuration with crystallization-driven self-assembly of a semicrystalline block copolymer.
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•A partition of reactive solvent takes place in the nanostructuration of BCP/epoxy blends.•Coils of the immiscible block are collapsed in the presence of epoxy species.•Epoxy species ...increase in size by polymerization and become insoluble.•Coils of the immiscible block gradually expand as epoxy species diffuse out of this phase.•This generates an unexpected L to HPC order-order transition.
A conventional SAXS study of ordered phases produced in cured block copolymer (BCP)/epoxy blends with different concentrations, led to the unexpected observation of an HPC (hexagonally-packed cylinders) phase for a blend containing a 55:45 volume ratio of both domains. The BCP was polystyrene (PS, Mn=28kDa)-b-poly(ethylene oxide) (PEO, Mn=11kDa), where PS is the “epoxy-phobic” block and PEO is the “epoxy-philic” block. The epoxy formulation was based on diglycidylether of bisphenol A (DGEBA) and 4,4′-methylenebis(2,6-diethylaniline) (MDEA). A fully cured blend containing 60wt% BCP, equivalent to 45% volume fraction of PS in the blend, exhibited an unexpected HPC morphology as supported by TEM images and SAXS spectra. The same techniques showed that a lamellar (L) phase was generated at low conversions in the same blend. The L to HPC transition was explained by the diffusion of epoxy–amine species out of the PS-rich phase with the increase in conversion. Order-order transitions in BCP/epoxy blends previously reported were explained by the partial phase separation of the miscible block from the epoxy solvent. These transitions go always in the sense of decreasing the interface curvature (e.g., from HPC to L). The transition reported in this study goes in the opposite sense (from L to HPC) and was generated by the change in environment of the immiscible block during polymerization.
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