M. Clara Gonçalves

Rare-earth-doped transparent glass ceramics

Abstract Glass ceramics are a known class of polycrystalline ceramic materials, where, depending on the glass matrix and the particular crystalline phases, one can obtain materials with improved mechanical, thermal, electrical or optical properties. The characteristics and applications of optical glass ceramics are reviewed, with particular emphasis on rare-earth-doped transparent glass ceramics for photonics, including the search for new transparent glass ceramic compositions and the development of suitable methods to process such materials into functional devices.

Densification of hybrid silica–titania sol–gel films studied by ellipsometry and FTIR

Abstract Hybrid silica–titania films were prepared via sol–gel processing, by dip-coating on silicon wafer substrates, from organically-modified silane and titanium isopropoxide precursors. These hybrid sol–gel films were then subjected to selected heat treatments at temperatures up to 950°C and their densification was followed by ellipsometry and infrared absorption (FTIR) spectroscopy. The volume fraction of residual porosity was estimated, based on the refractive index data. A clear correlation was observed between the intensity of the infrared spectral shoulder near 1150 cm −1 and the porosity values, for the different heat treatment temperatures. For any treatment up to 950°C, the porosity of the hybrid silica–titania gel films was higher than that of the corresponding inorganic gel films, while both continuously decreased with increasing heat treatment temperature. The residual SiCH 3 groups, whose presence was identified in the hybrid silica–titania films until a temperature near 500°C, tend to be transformed into SiOH (silanol) groups as they are eliminated. Most silanol groups are eliminated at a temperature near 600°C. The hybrid silica–titania films were found to have a more porous and more compliant gel network than the corresponding inorganic films, while their structure appears to exhibit a smaller spread in the SiOSi intertetrahedral angle distribution.

XPS and NEXAFS studies of rare-earth doped amorphous sol–gel films

Abstract Information about the structural environment of rare-earth (RE) ions in different host matrices is necessary in order to select a glass composition with optimized spectral properties for integrated optic devices, such as lasers or amplifiers. The present study is aimed at determining the influence of co-dopant elements (P and Al) on the structural environment around (RE) cations (Nd 3+ and Er 3+ ) in amorphous silica–titania matrices. For this purpose, thin film samples in the SiO 2 –TiO 2 –P 2 O 5 –Nd 2 O 3 and SiO 2 –TiO 2 –Al 2 O 3 –Er 2 O 3 systems were prepared by sol–gel processing and studied by X-ray photoemission spectroscopy (XPS) and near edge X-ray absorption fine structure (NEXAFS), after being densified at 900°C. These measurements allowed the determination of the concentrations of the different types of oxygen atoms present in the Si–O–Ti, Si–O–P and Si–O–Al bonding sequences and these were found to reach maximum total values for compositions containing ∼10 mol% of the PO 2.5 or AlO 1.5 co-dopants.

Relaxivities of magnetoliposomes: the effect of cholesterol.

We present relaxivities measurements for both the longitudinal and transverse relaxations of two types of liposomes loaded with ultra small superparamagnetic iron oxide nanoparticles. The magnetoliposome systems presented are soybean phosphatidylcholine liposomes, with and without cholesterol, in the phospholipid bilayer with different molar ratios lipid:cholesterol. In fact, cholesterol is needed to obtain stable liposomes for intravenous administration. The longitudinal and transverse relaxivities were measured with a NMR spectrometer in a 7T magnetic field. For the studied concentrations, the liposomes show a negligible effect on the longitudinal relaxation time T1 of the medium, but they are very efficient on decreasing the transverse relaxation time T2, the behaviour one expects for a negative CA. We observed a lower transverse relaxivity for the magnetoliposome nanosystem with cholesterol, which strongly decreases with the cholesterol content in the liposome bilayer.

Incorporation of OH species in fluorozirconate glasses: nature and influence on physical properties

Abstract The main purpose of the present study is to correlate the presence of controlled amounts of residual OH groups with the values of several physical properties, namely, the characteristic temperatures, linear thermal expansion coefficient, density, refractive index, microhardness, ultrasonic velocities, elastic constants and infrared transmission of ZrF4-based fluoride glasses. A series of glass samples were prepared in the ZrF4BaF2LaF3AlF3NaF system, with increasing NaF contents. Batches for the reference (dry) glass samples were first dried in a vacuum oven and were then melted in Pt crucibles in a dry box filled with high purity N2. Weakly hydrated glasses were prepared according to a similar procedure, but the batches were kept in water vapor saturated atmosphere for at least 24 h before fusion. Strongly hydrated glasses were melted in a fume hood, under a water vapor saturated stream of N2. For levels of OH incorporation up to 8 × 10−4 mol l−1 for ZBLA, 1.0 × 10−3 mol l−1 for ZBLAN6.6 and 1.5 × 10−3 mol l−1 for ZBLAN17.8, the density, refractive index and glass transition temperature, Tg, decrease with increasing OH content (by 0.8%, 0.25% and 3.0%, respectively) is similar to what has been observed for v-SiO2. At OH levels greater than 8 × 10−4 mol l−1 for ZBLA, 1.0 × 10−3 mol l−1 for ZBLAN6.6 and 1.5 × 10−3 mol l−1 for ZBLAN17.8, an increase in physical properties, such as the density, refractive index and Tg with increasing OH content, was noticed (of 0.8%, 0.4% and 2.8%, respectively), similar to what has been observed in silicate glasses. This behavior strongly suggests the presence of hydrogen bonded ZrOH species. A structural model is proposed for a typical fluorozirconate ZBLAN glass, based on structural data and physico-chemical properties. The model allows a correlation between the effect of residual OH groups and the values of some of the most representative properties of these glasses.

Preparation and Chemical Characterization of Eco-friendly ORMOSIL Nanoparticles of Potential Application in DNA Gene Therapy

One focus in nanotechnology is the development and use of nonviral vectors for safe and efficient gene delivery. Inorganic and organically modified silica nanoparticles are chemical and biologically inert, optically transparent and can be doped with imaging agents and/or functionalized to promote its conjugation with different therapeutic molecules. Silica/ORMOSIL nanoparticles can be engineered to improve diagnosis, treatment and follow-up of diseases. A combination of diagnosis devices and therapeutics (theranostics) would be beneficial for patients. In this work, ORMOSIL nanoparticles as non-viral vectors for gene delivery were prepared via a modified Stober sol-gel process directly with 3-aminopropyltriethoxysilane (APTES), methyltriethoxysilane (MTES), vinyltrimethoxysilane (VTES), N 1 - (3-(trimethoxysilyl)-propyl)diethylenetriamine (DETA), and tetraethylorthosilicate (TEOS) as precursors. Dynamic light scattering, transmission electron microscopy and Fourier transformed infrared spectroscopy were used to characterize the ORMOSIL nanospheres. Synthesis has been optimized and monodisperse spherical nanoparticles with desired size have been obtained. Nanoparticle-DNA com- plexes were successfully obtained at different ratios (nanoparticle/pDNA) and confirmed by agarose gel electrophoresis and ethidium bromide exclusion test.

Greensilica® vectors for smart textiles☆

The present work aims developing a versatile Greensilica® vector/carrier, able to bind to a wide range of textile matrices of carbohydrate polymers and susceptible of being loaded with chemicals/drugs/therapeutic molecules, to create a green tailor-made (multi)functional high-tech textile. A green, eco-friendly, ammonia-free, easily scalable, time-saving sol-gel process was established for the production of those silica-based colloidal particles (SiO2, amine-SiO2, diamine-SiO2, and epoxy-SiO2). Two different textile matrices (cotton, polyester) were functionalized, through the impregnation of Greensilica® particles. The impregnation was performed with and without cure. Diamine-SiO2 colloidal particles exhibited the higher bonding efficiency in cured textile matrices (both cotton and polyester), while with no cure the best adherence to cotton and polyester textile matrices was achieved with diamine-SiO2 and amine-SiO2, respectively. Use once and throw away and continued use applications were envisaged and screened through washing tests. The efficiency of the textiles impregnation was confirmed by SEM, and quantified by ICP.

Rare earth doped fluorozirconate glass films

Abstract Zirconium fluoride based glassy films have been prepared in the ZrF4–PbF2 and ZrF4–PbF2–NdF3 systems, by physical vapor deposition, on single crystal silicon and microscope glass slide substrates. Amorphous ZrF4 films have also been prepared and doped with NdF3. The amorphous state of the films was confirmed by X-ray diffraction. The film composition was determined by X-ray photoelectron spectroscopy. The characteristic temperatures were determined for a-ZrF4 films to be Tg∼285°C and Tx∼460°C, by differential scanning calorimetry. The structure of these films was analyzed by infrared absorption spectroscopy and compared with bulk fluorozirconate glasses. The optical loss, measured for different films at λ=632.8 nm, was in the range of 2.9 to 4.9 dB/cm.

Structure of water in hybrid cellulose acetate-silica ultrafiltration membranes and permeation properties

Hybrid cellulose acetate (CA) silica (SiO2) (CA/SiO2) membranes were synthesized by promoting the in situ condensation between silanols from the SiO2 precursor and the COH or acetate groups from the CA polymer. For all the CA/SiO2 membranes, the ATR-FTIR peak assigned to (SiOC) proves the hybrid condensation reaction and confirms the synthesis of monophasic hybrid membranes. ATR-FTIR shows the presence of uncondensed highly reactive SiOH species, in membranes with silica contents higher than 20 mol%. Together with RMN studies, results show molecular water strongly hydrogen-bonded with SiOH groups, yielding a drastic decrease in the membrane hydraulic permeability, from 57 to 10 kg/h/m2/bar. The incorporation of 5 and 10 mol% of silica increased the hydraulic permeability from 32 to 82 kg/h/m2/bar when compared to the CA membrane.

Influence of the modifying cations on physical properties of fluorozirconate glasses

Abstract The structure of ZrF4-based glasses is still poorly understood. The addition of compounds such as BaF2 and NaF to ZrF4 breaks up the Zr-F-Zr network (such as it exists in β-ZrF4), creating new bonds and changing the physical properties of the material. Although both Ba2+ and Na+ cations play the role of traditional glass modifiers, they affect certain physical properties in a different way. A structural model previously proposed for a typical ZBLAN fluorozirconate glass composition is able to explain the effect of the substitution of Na+ for Ba2+ cations, in glasses with the same overall degree of modification.