F. del Monte

Faraday rotation in magnetic γ-Fe2O3/SiO2 nanocomposites

Faraday rotation spectrum has been measured at room temperature in a magnetic nanocomposite of γ-Fe2O3/SiO2. The material consists of isolated γ-Fe2O3 nanoparticles dispersed in a silica matrix, and it was prepared through a sol-gel method. The composite contains 18% of γ-Fe2O3 in weight with an average particle size of 20 nm. It has a coercitivity of 30 Oe and an MS of 6 emu/g. The specific Faraday rotation spectrum exhibits a narrow peak centered around 765 nm, reaching a value of 110°/cm and an absorption coefficient of 64 cm−1. Faraday rotation versus applied field has also been measured, and a cycle similar to the one described by the magnetization has been found.

Photopolymerization of hydroxyethylmethacrylate in the formation of organic–inorganic hybrid sol–gel matrices

Hydroxyethylmethacrylate (HEMA) monomer in different contents was used in the preparation of transparent organic-inorganic hybrid sol-gel matrices. The matrices were studied by analytical techniques before and after irradiation. An increase in the homogeneity of the composite material after the irradiation of HEMA, and a chemical linkage of the monomer with the surface has been observed. Photopolymerization processes were studied by differential scanning calorimetry (DSC). Details of the irradiation times, polymerization rates, and DSC related parameters of HEMA in the sol-gel matrices are reported.

3D free-standing porous scaffolds made of graphene oxide as substrates for neural cell growth

The absence of efficient therapies for the treatment of lesions affecting the central nervous system encourages scientists to explore new materials in an attempt to enhance neural tissue regeneration while preventing inhibitory fibroglial scars. In recent years, the superlative properties of graphene-based materials have provided a strong incentive for their application in biomedicine. Nonetheless, a few attempts to date have envisioned the use of graphene for the fabrication of three-dimensional (3D) substrates for neural repair, but none of these involve graphene oxide (GOx) despite some attractive features such as higher hydrophilicity and versatility of functionalization. In this paper, we report novel, free-standing, porous and flexible 3D GOx-based scaffolds, produced by the biocompatible freeze-casting procedure named ISISA, with potential utility in neural tissue regeneration. The resulting materials were thoroughly characterized by Fourier-transform infrared, Raman, and X-ray photoelectron spectroscopies and scanning electron microscopy, as well as flexibility testing. Embryonic neural progenitor cells were then used to investigate adhesion, morphology, viability, and neuronal/glial differentiation. Highly viable and interconnected neural networks were formed on these 3D scaffolds, containing both neurons and glial cells and rich in dendrites, axons and synaptic connections, and the results are in agreement with those obtained in initial studies performed with two-dimensional GOx films. These results encourage further investigation in vivo on the use of these scaffolds as guide substrates to promote the repair of neural injuries.

HOLOGRAPHIC DIFFRACTION GRATINGS RECORDING IN ORGANICALLY MODIFIED SILICA GELS

The silica gel-methyl methacrylate organically modified ceramic is proposed for recording of volume holograms. Both low-spatial-frequency (54 line pairs/mm(-1)) and high-spatial-frequency (1400 line pairs/mm(-1)) holographic gratings were successfully recorded in the medium by interference of two coherent beams of 351.1-nm wavelength. High diffraction efficiencies (93%) and extremely low absorption and scattering coefficients were measured during the holographic reconstruction by a 632.8-nm He-Ne beam. The optimum UV recording exposure was ~3 J cm(-2). A grating refractive-index modulation amplitude of 1.1 x 10(-4) was achieved. Virtually no changes in diffraction efficiency were observed after thermal-heating, light-curing, and long-term-aging experiments.

Photochromic Doped Sol-Gel Materials for Fiber-Optic Devices

Photochromic-doped sol-gel materials have been prepared by adding a spiropyran photochromic dye to a solution of ethoxy silane monomers containing non-reacting ethyl radicals. After polymerization, normal photochromism (i.e., colored material upon UV irradiation) is obtained in the resulting matrix. The sol-gel matrix hinders the organic molecule rotations, thus giving two stable states, which can be reversibly switched by UV and green-blue irradiation respectively.If these materials are attached to optical fibers, the properties of the light throughput may be modified. Simple fiber-optic/photochromic devices made of two optical fibers placed in a V-groove removable connector have been prepared. Once cured, these devices behave as optically addressed variable delay generators. The same devices can be used for preparing simple optical switches and routing systems.

DES assisted synthesis of hierarchical nitrogen-doped carbon molecular sieves for selective CO2versus N2 adsorption

Deep eutectic solvents (DESs) composed of resorcinol, 3-hydroxypyridine and tetraethylammonium bromide were used for the synthesis of hierarchical nitrogen-doped carbon molecular sieves. DESs played multiple roles in the synthetic process, as the liquid medium that ensures reagent homogenization, the structure-directing agent responsible for the achievement of the hierarchical structure, and the source of carbon and nitrogen for the solid sorbent obtained after carbonization. Thus, the synthesis offers an economy of reagents that emphasizes the green nature and low cost of conventional polycondensation. Interestingly, while macropores facilitated mass transport and access to the surface area, the combination of the molecular sieve structure and nitrogen functionalization provided, respectively, excellent CO2 adsorption capacities of up to 3.7 mmol g−1, and outstanding CO2–N2 selectivities of up to 14.4 from single component gas data. Nonetheless, the CO2–N2 selectivity in the Henry law regime – representative of post-combustion flue-gas streams – of some of our carbons was particularly remarkable (e.g. 96), comparable to or even higher than those described for most recent carbons, and only surpassed by those of certain zeolites.

Optically tunable fiber optic delay generator utilizing photochromic doped sol‐gel gel‐glass delay line

A tunable fiber optic delay generator has been demonstrated utilizing a novel photochromic material embedded in a silica sol‐gel matrix. This material has been placed between two multimode commercial fibers filling up the V‐shaped groove of a removable connector. With this simple structure, the ability to control optically propagation times of optical signals is achieved. Measurements of input wavelength and optical power required for the desired delay time are presented.

Porous monoliths synthesized via polymerization of styrene and divinyl benzene in nonaqueous deep-eutectic solvent-based HIPEs

Stable nonaqueous high internal phase emulsions (HIPEs) were prepared and thermally polymerized to yield poly(HIPEs). The internal phase accounting for 80 vol% of the HIPE consisted of a deep-eutectic solvent (DES) while the continuous one comprised styrene and divinyl benzene in a 10 : 1 molar ratio. DESs with different viscosities were used as an internal phase: choline chloride combined with urea, glycerol or ethylene glycol in a 1 : 2, salt : hydrogen bond donor molar ratio, respectively. HIPEs were stabilized with different amounts of the surfactant Span 60 (10, 20 and 50 wt% with respect to the total amount of monomers). DESs viscosity and the amount of surfactant employed impact the morphology and mechanical properties of poly(HIPEs). Resulting poly(HIPEs) showed interconnected porosity and high thermal stability above 310 °C. Its worth noting that DES was recovered from 89 to nearly 95 wt% and the monomer conversion was as high as 0.96. In addition, water-in-oil HIPEs were stabilized and then polymerized under the same conditions, but the porous structure of the resulting poly(HIPEs) collapsed. This research demonstrates that DESs are a suitable internal phase for HIPEs thus expanding on the range of monomers forming polymerizable DES-based HIPEs.

Controlled formation of the anhydrous polymorph of ciprofloxacin crystals embedded within chitosan scaffolds: study of the kinetic release dependence on crystal size

This work describes a simple procedure for preparation of chitosan (CHI) scaffolds containing ciprofloxacin (CFX) anhydrous crystals. The capability of CHI scaffolds to control the CFX crystal size and to preserve the anhydrous crystal habit even after long term storage was useful for the development of drug delivery systems (e.g., CFX/CHI scaffolds) exhibiting a novel way to control the kinetic release, that is, by the solubility/hydration ratio of CFX anhydrous crystals depending on their crystal size rather than by typical mechanisms based on swelling, hydration and/or erosion of the polymer acting as carrier.

Color displays with gel-glass dispersed liquid crystals

Liquid crystal microdroplets trapped into silica gel-glasses by sol-gel processes may be used for display applications. Gel-glass dispersed liquid crystals (GDLC) are switched between opaque and transparent states by applying external AC-voltage signals; no polarizers are required. The feasibility of applying these materials to colored displays has been explored. A comparative study of different dyes for GDLC color displays, which were either embedded in the sol-gel matrix or dissolved in the liquid crystal microdroplets is presented.