Relevance of Specific Surface of Mixed Oxide Derived from Layered Double Hydroxides on the Rheological Properties and Porosity of Cement Pastes.

Cement-based products are the synthetic materials most used by humans, with consequent environmental impacts. One strategy that can assist in mitigating the adverse environmental effects of these materials involves the incorporation of multifunctional nanostructured additives. The objective of this work was to demonstrate the efficacy of incorporating mixed oxides (MO) derived from layered double hydroxides (LDH) to control the rheology and porosity of cement-based matrices. Thermal aging of LDH enabled the preparation of MO with different specific surface areas (SSA) for incorporation in different amounts in Portland cement. A low proportion of MO and low SSA increased workability by 22%. In contrast, a high proportion of MO and high SSA led to a 2.4-fold acceleration of cement consolidation and a 36.9% decrease of the porosity of the composite. These features could be attributed to additive-matrix interactions, with the LDH memory effect playing key roles in the cement crystal seed process and in competition for the absorption of free water within the cement paste. Therefore, the unprecedent results obtained suggest that the quantity and SSA of MO are key parameters to fine-tune the paste rheology and structure of hidrated cement. The MO materials showed easy adaptability and excellent potential for use as multifunctional additives in the production of eco-friendly, high-performance cement paste formulations with controllable properties according to the desired application.

Fingerprint of semi-crystalline structure memory in the thermal and ionic conduction properties of amorphous ureasil-polyether hybrid solid electrolytes.

Correlations among the structure, thermal properties, and ionic conductivity of solid polymer electrolytes (SPEs) were studied using a ureasil-polyethylene oxide (U-PEO) organic-inorganic hybrid prepared according to a simple sol-gel route, employing a low molecular weight PEO macromer (M w = 1900 g mol-1). The behavior of an amorphous sample loaded with lithium triflate (LiTFSI) at an optimum ratio between ether oxygen and lithium (EO/Li+ = 15) was compared with that of a semicrystalline sample prepared without salt loading. The temperature range investigated by differential scanning calorimetry (DSC), Raman spectroscopy, small angle X-ray scattering (SAXS), and complex impedance spectroscopy covered both the glass transition and the melting temperature of the U-PEO. The gauche to trans conformational transformation of the (O-C-C-O)Li+ sequence showed similarity between the temperature evolution of the semi-crystalline U-PEO and amorphous U-PEO:Li+ samples, providing an indication of the local structural memory of crystalline state in the amorphous SPE. The linear thermal expansion of the average correlation distance between the siloxane crosslink nodes and the long-distance period of the lamellar semi-crystalline edifice were determined by SAXS. Comparison of the expansion curves suggested that although the siloxane nodes were excluded from the PEO crystalline edifice, the sharp expansion of the amorphous region between the lamellae during melting permitted modulation of the free volume of the hybrid network. In addition, the temperature-induced Li+-EO decomplexation observed by Raman spectroscopy explained the change of the average activation energy of the conduction process revealed by the different Arrhenius regimes. These results evidence the key role of the ionic conductivity decoupling from the segmental motion of chain pair channels on the improvement of ion mobility through the free volume between chains. This concept may inspire materials chemistry researchers to design optimized structures of polymer electrolytes with minimized structural memory of crystaline building blocks and improved ionic conductivity.

Effect of Organomontmorillonite-Cloisite® 20A Incorporation on the Structural and Drug Release Properties of Ureasil-PEO Hybrid.

This paper presents the influence of the presence of a modified organoclay, Cloisite® 20A (MMTA) on the structural and drug release properties of ureasil organic-inorganic hybrid. Sol-gel process was used to prepare the hybrid nanocomposites containing sodium diclofenac (DCF) at 5% wt. The effect of the amount of MMTA incorporated into the ureasil hybrid matrix was evaluated and characterized in depth by different techniques such as X-ray diffraction (XRD), small angle X-ray scattering (SAXS), differential scanning calorimetry (DSC), and swelling properties. The influence of MMTA on ureasil nanocomposites release profile was evaluated by in situ UV-vis. The diffraction patterns of the UPEO-MMTA nanocomposites showed a synergistic contribution effect that led to an intensity increase and narrowed the diffraction peaks, evidencing a crystallite PEO growth as a function of the modified nanoclay content. The interactions between polyether chains and the hydrogenated tallow of MMTA led to an easy intercalation process, as observed in UPEO-MMTA nanocomposites containing low (1% wt) or high (20% wt) nanoclay content. The waterway (channels) created in UPEO-MMTA nanocomposites contributed to a free volume increase in the swollen network compared to UPEO without MMTA. The hypothesis of the channels created after intercalation of the PEO phase in the interlayer of MMTA containing organoammonium ions corroborates with the XRD results, swelling studies by SAXS, and release assays. Furthermore, when these clay particles were dispersed in the polymeric matrix by an intercalation process, water uptake improvement was observed, with an increased amount of DCF release. The design of ureasil-MMTA nanocomposites containing modified nanoclay endows them with tunable properties; for example, swelling degree followed by amount of controlled drug release, opening the way for more versatile biomedical applications.

Hydroxyapatite and ß-TCP modified PMMA-TiO2 and PMMA-ZrO2 coatings for bioactive corrosion protection of Ti6Al4V implants.

Organic-inorganic hybrid coatings deposited on different types of metallic alloys have shown outstanding anticorrosive performance. The incorporation of osteoconductive additives such as hydroxyapatite (HA) and ß-tricalcium phosphate (ß-TCP) into organic-inorganic hybrid coatings is promising to improve the osseointegration and corrosion resistance of Ti6Al4V alloys, which are the most widely used metallic orthopedic and dental implant materials today. Therefore, this study evaluated the capability of poly(methyl methacrylate) (PMMA)-TiO2 and PMMA-ZrO2 hybrid coatings modified with HA and ß-TCP to act as bioactive and corrosion protection coatings for Ti6Al4V alloys. In terms of cell growth and mineralization, osteoblast viability, Ca+2 deposition and alkaline phosphatase assays revealed a significant improvement for the HA and ß-TCP modified coatings, compared to the bare alloy. This can be explained by an increase in nanoscale roughness and associated higher surface free energy, which lead to enhanced protein adsorption to promote osteoblast attachment and functions on the coatings. The effect of HA and ß-TCP additives on the anticorrosive efficiency was studied by electrochemical impedance spectroscopy (EIS) in a simulated body fluid (SBF) solution. The coatings presented a low-frequency impedance modulus of up to 430 GΩ cm2, 5 decades higher than the bare Ti6Al4V alloy. These findings provide clear evidence of the beneficial role of HA and ß-TCP modified hybrid coatings, improving both the biocompatibility and corrosion resistance of the Ti6Al4V alloy.

Conjugation of superparamagnetic iron oxide nanoparticles and curcumin photosensitizer to assist in photodynamic therapy.

In this work, we describe the synthesis and characterization of the SPIONP-CUR conjugate between curcumin (CUR) and superparamagnetic iron oxide nanoparticles (SPIONPs), in addition to its application in photodynamic therapy (PDT) using a protocol free of organic solvents as a dispersant. The SPIONP-CUR conjugate was characterized by X-ray diffraction, transmission electron microscopy, zeta potential measurements, Fourier transform infrared spectroscopy, thermogravimetry, magnetometry and magnetic hyperthermia assays. The SPIONP-CUR conjugation occurred by bonding between the keto-enol moiety of CUR and the iron atoms present on the surfaces of the SPIONPs. The conjugate showed heating power under an alternating magnetic field (AMF) and photodynamic action when irradiated with blue LED light. In experiments using PDT against Staphylococcus aureus in the planktonic phase, it was demonstrated that with application of blue light at 3.12 J cm-2, the conjugate (dispersed in water) caused a total reduction of the bacterial load. In the absence of light, the reduction was insignificant, even after 24 h of contact with the bacteria.

Dual Role of Lithium on the Structure and Self-Healing Ability of PMMA-Silica Coatings on AA7075 Alloy.

In this work, structural and active corrosion inhibition effects induced by lithium ion addition in organic-inorganic coatings based on poly(methyl methacrylate) (PMMA)-silica sol-gel coatings have been investigated. The addition of increasing amounts of lithium carbonate (0, 500, 1000, and 2000 ppm), yielded homogeneous hybrid coatings with increased connectivity of nanometric silica cross-link nodes, covalently linked to the PMMA matrix, and improved adhesion to the aluminum substrate (AA7075). Electrochemical impedance spectroscopy (EIS), performed in 3.5% NaCl aqueous solution, showed that the improved structural properties of coatings with higher lithium loadings result in an increased corrosion resistance, with an impedance modulus up to 50 GΩ cm2, and revealed that the lithium induced self-healing ability significantly improves their durability. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS) suggest that the regeneration process occurs by means of lithium ions leaching from the adjacent coating toward the corrosion spot, which is restored by a protective layer of precipitated Li rich aluminum hydroxide species. An analogue mechanism has been proposed for artificially scratched coatings presenting an increase of the impedance modulus after salt spray test compared to the lithium free coating. These results evidence the active role of lithium ions in improving the passive barrier of the PMMA-silica coating and in providing through the self-restoring ability a significantly extended service life of AA7075 alloy exposed to saline environment.

Structural and Electronic Properties of Iron-Doped Sodium Montmorillonite Clays: A First-Principles DFT Study.

First-principles calculations done via density functional theory were used to study the structural and electronic properties of sodium montmorillonite clay (Mt-Na+) of general formula M x Al3Si8O24H4Na·nH2O (M x : Mg or Fe). The final position of the interlamellar sodium atom is found to be close to the oxygen atoms located on the upper surface of silica. Following Fe-Mt-Na+ system relaxation, with subsequent analysis of magnetic moment and magnetic states, the electroneutrality of the system established that both Fe2+ and Fe3+ oxidation states are possible to occur. The Mg2+-Mt-Na+ material shows a band gap energy greater than that of Fe2+-Mt-Na+ when iron is in the octahedral site. It is found that the valence-band maximum and the conduction-band minimum of iron-doped montmorillonite are both at the Γ-point, while it is at V → Γ for magnesium-doped montmorillonite. The calculated band gap from hybrid functional (HSE06) of Fe2+-Mt-Na+ is equal to 4.3 eV, exhibiting good agreement with experimental results obtained from ultraviolet-visible spectroscopy of the natural Mt-Na+ (Cloisite-Na+).

Coupling Photoluminescence and Ionic Conduction Properties Using the Different Coordination Sites of Ureasil-Polyether Hybrid Materials.

In this article, we demonstrate that each functional group of ureasil organic-inorganic hybrid (OIH) materials can act as a specific coordination site for a given active guest species, hence allowing the possibility of combining different functional properties. To illustrate this concept, the sol-gel process was used to produce diurea cross-linked siloxane-polyethylene oxide (U-PEO) and siloxane-polypropylene oxide (U-PPO) hybrid host frameworks with similar molecular weights (1900 and 2000 g mol-1 for PEO and PPO, respectively), with Li+ and Eu3+ as active guest ions providing ionic conduction and photoluminescence (PL) properties, respectively. Comparison of Fourier transform infrared spectra and small-angle X-ray scattering results for single-doped (using Li+ or Eu3+) and co-doped (using Li+ and Eu3+) U-PEO and U-PPO hosts showed that in every case, there was specific coordination of Eu3+ by the carbonyl group of the urea bridge and of Li+ by ether-type oxygen of the PEO and PPO chains. Optical analyses demonstrated that loading with Li+ did not affect the luminescence properties of the Eu3+-loaded OIH. Although loading with Eu3+ had a small effect on ionic transport, co-doping with Li+ ions ensured macroscopic ion-conduction of the transparent and luminescent hybrid material. The results suggested that the combination of both properties in a transparent elastomeric material could be useful for the development of multifunctional devices. The results suggested that the combination of both properties in a transparent elastomeric material could be useful for the development of multifunctional polyelectrolytes applied in the field of dual luminescent devices such as photoelectrochromic smart windows.

Highly Controlled Diffusion Drug Release from Ureasil-Poly(ethylene oxide)-Na+-Montmorillonite Hybrid Hydrogel Nanocomposites.

In this work, we report the effects of incorporation of variable amounts (1-20 wt %) of sodium montmorillonite (MMT) into a siloxane-poly(ethylene oxide) hybrid hydrogel prepared by the sol-gel route. The aim was to control the nanostructural features of the nanocomposite, improve the release profile of the sodium diclofenac (SDCF) drug, and optimize the swelling behavior of the hydrophilic matrix. The nanoscopic characteristics of the siloxane-cross-linked poly(ethylene oxide) network, the semicrystallinity of the hybrid, and the intercalated or exfoliated structure of the clay were investigated by X-ray diffraction, small-angle X-ray scattering, and differential scanning calorimetry. The correlation between the nanoscopic features of nanocomposites containing different amounts of MMT and the swelling behavior revealed the key role of exfoliated silicate in controlling the water uptake by means of a flow barrier effect. The release of the drug from the nanocomposite displayed a stepped pattern kinetically controlled by the diffusion of SDCF molecules through the mass transport barrier created by the exfoliated silicate. The sustained SDCF release provided by the hybrid hydrogel nanocomposite could be useful for the prolonged treatment of painful conditions, such as arthritis, sprains and strains, gout, migraine, and pain after surgical procedures.

Catalytic performance of texturally improved Al-Mg mixed oxides derived from emulsion-synthesized hydrotalcites.

Mixed oxides of aluminum and magnesium derived from hydrotalcites were prepared by means of a sol-gel method mediated by an emulsified sol as pore template. The emulsion consisted of ethanol as the continuous phase and n-dodecane droplets as the dispersed phase, which was stabilized by the presence of the surfactant Pluronic P123. The use of such an emulsion was essential for obtaining materials with a porous structure that were assessed by mercury intrusion porosimetry and nitrogen physisorption. Additional characterization by NH3 and CO2 temperature programmed desorption confirmed that despite the enhancement of their textural properties, the number of acid and base sites was reduced in comparison to a reference and conventionally prepared Al-Mg mixed oxide, as a consequence of the depletion of surface hydroxyls during condensation of the precursors around the nonpolar droplets of the emulsion. Catalytic conversion of 2-propanol under conditions of controlled mass and heat diffusion on the texturally improved Al-Mg mixed oxides evidenced the preparation of a more effective catalyst than the poorly porous reference.

Structure and properties of epoxy-siloxane-silica nanocomposite coatings for corrosion protection.

HYPOTHESIS: The fraction of the silica/siloxane phase is a crucial parameter, which determines the structure and thus the properties of epoxy-siloxane-silica hybrid coatings. A careful adjustment of the colloidal precursor formulation allows tuning the nanostructure towards a highly condensed and cross-linked hybrid nanocomposite, suitable as an efficient anticorrosive coating. EXPERIMENTS: Novel epoxy-siloxane-silica hybrids have been prepared through the curing reaction of poly(bisphenol A-co-epichlorohydrin) (DGEBA) with diethyltriamine (DETA) and (3-glycidoxypropyl)methyltriethoxysilane (GPTMS), followed by hydrolytic condensation of tetraethoxysilane (TEOS) and GPTMS. At a constant proportion of the organic phase, the effects of the varying molar proportions of siloxane (GPTMS) and silica (TEOS) on the film properties have been investigated. FINDINGS: A detailed structural analysis suggests for intermediate TEOS to GPTMS ratios a structure of highly condensed silica-siloxane domains covalently bonded to the embedding epoxy phase. The homogeneous distribution of the quasi-spherical sub-nonmetric silica-siloxane nodes is in agreement with low surface roughness (<5 nm), observed by atomic force microscopy. This dense nanostructure results in high thermal stability (>300 °C), strong adhesion to steel substrate and excellent barrier property in saline solution, with corrosion resistance in the GΩ cm2 range.

The Monoglyceride Content Affects the Self-Assembly Behavior, Rheological Properties, Syringeability, and Mucoadhesion of In Situ-Gelling Liquid Crystalline Phase.

This article reports the development of a precursor liquid crystalline system based on a mixture of monoglycerides (MO) and Cremophor(®) (CREM) that exhibits in situ gelation to a liquid crystalline phase. The effects of different MO/CREM ratios and the water content (WC) on several performance characteristics were investigated with a full factorial design. The formulations were characterized by polarized light microscopy, small-angle X-ray scattering, and water uptake assays. Rheological, syringeability, and mucoadhesion evaluation were also performed. The polarized light microscopy and small-angle X-ray scattering results for average and high MO/CREM ratios (2.1 and 4.0, respectively) indicated the coexistence of phases in transition to the liquid crystalline phase, independently of the WC. These systems became more viscous after taking up water, showing peaks characteristic of a cubic phase. Systems that had average and high MO/CREM ratios also exhibited shear-thinning behavior and high elasticity. Most systems showed suitable mucoadhesion for buccal purposes. Response surface methodology results demonstrated that the relative contribution of MO was the principal factor that affected the performance of the system. Accordingly, these precursor systems with average to high MO/CREM ratios and an average WC (10% w/w) demonstrated physicochemical and mucoadhesive properties that could enable them to be used as an in situ-gelling controlled drug delivery platform.

A Comparative Study on Graphene Oxide and Carbon Nanotube Reinforcement of PMMA-Siloxane-Silica Anticorrosive Coatings.

Carbon nanotubes (CNTs) and graphene oxide (GO) have been used to reinforce PMMA-siloxane-silica nanocomposites considered to be promising candidates for environmentally compliant anticorrosive coatings. The organic-inorganic hybrids were prepared by benzoyl peroxide (BPO)-induced polymerization of methyl methacrylate (MMA) covalently bonded through 3-(trimethoxysilyl)propyl methacrylate (MPTS) to silica domains formed by hydrolytic condensation of tetraethoxysilane (TEOS). Single-walled carbon nanotubes and graphene oxide nanosheets were dispersed by surfactant addition and in a water/ethanol solution, respectively. These were added to PMMA-siloxane-silica hybrids at a carbon (CNT or GO) to silicon (TEOS and MPTS) molar ratio of 0.05% in two different matrices, both prepared at BPO/MMA molar ratios of 0.01 and 0.05. Atomic force microscopy and scanning electron microscopy showed very smooth, homogeneous, and defect-free surfaces of approximately 3-7 µm thick coatings deposited onto A1020 carbon steel by dip coating. Mechanical testing and thermogravimetric analysis confirmed that both additives CNT and GO improved the scratch resistance, adhesion, wear resistance, and thermal stability of PMMA-siloxane-silica coatings. Results of electrochemical impedance spectroscopy in 3.5% NaCl solution, discussed in terms of equivalent circuits, showed that the reinforced hybrid coatings act as a very efficient anticorrosive barrier with an impedance modulus up to 1 GΩ cm(2), approximately 5 orders of magnitude higher than that of bare carbon steel. In the case of GO addition, the high corrosion resistance was maintained for more than 6 months in saline medium. These results suggest that both carbon nanostructures can be used as structural reinforcement agents, improving the thermal and mechanical resistance of high performance anticorrosive PMMA-siloxane-silica coatings and thus extending their application range to abrasive environments.

Lignin as immobilization matrix for HIV p17 peptide used in immunosensing.

Immunosensors based on electrical impedance spectroscopy (EIS) are increasingly being used as a fast and potentially low cost method for clinical diagnostics. In this work we fabricated immunosensors by depositing layer-by-layer (LbL) films made with an antigenic peptide (p17-1) sequence (H2N-LSGGELDRWEKIRLRPGG-OH) and lignin on interdigitated gold electrodes, which could detect anti-p17 (HIV, human immune deficiency virus) antibodies (Ab) in phosphate buffered solutions (PBS). The molecular recognition interaction between the peptide (p17-1) and the specific Ab (anti-p17) yielded substantial changes in morphology of the with LbL films, with increased roughness according to atomic force microscopy data. This interaction is behind the high sensitivity of the immunosensor. Indeed, from the EIS results, we noted that the capacitance increased significantly with the specific Ab concentration, before getting close to saturation of available peptide sites at high concentrations. Concentrations of specific antibodies as low as 0.1 ng/mL could be detected and the immunosensors had their activity preserved for two months at least. The selectivity of the immunosensor was confirmed with two types of control experiments. First, no changes in impedance were observed when the lignin/peptide LbL immunosensor was immersed into a PBS solution containing the non-specific Ab (anti-HCV for Hepatitis C) antibodies. Furthermore, for sensing units made LbL films of lignin only, the electrical response was not affected by adding specific antibodies into the PBS buffer. The successful immunosensing for HIV with antigenic peptides in a lignin matrix is also relevant for valorization of lignin, which is an important biomass component in the sugar and ethanol industry, and brings the prospect for all-organic, biocompatible sensors if implantation is ever required.

Ligand exchange inducing efficient incorporation of CisPt derivatives into Ureasil-PPO hybrid and their interactions with the multifunctional hybrid network.

Efficient incorporation of (PtCl3EtOH)(-) anion derived from CisPt moiety into ureasil-PPO (poly(propylene oxide)) network was achieved from one-pot sol-gel synthesis carried out in the presence of water, HCl, and ethanol. Reactant proportion was adequately chosen to lead the sol-gel formation of siloxane nodes at the end of short PPO chains, to prevent the CisPt hydrolysis, and to induce platinum ligand exchange. The efficient dissolution of Pt species and the formation of a homogeneous liquid-like solution on the transparent and elastomeric ureasil-PPO hybrid were evidenced by differential scanning calorimetry and small-angle X-ray scattering. The CisPt ligand exchange and the formation of a Zeise-type salt Y(+)(PtCl3R)(-) were demonstrated by Raman spectroscopy and Pt L3-edge EXAFS analysis. In light of these results and in agreement with the proportion of reactants introduced in the media for synthesis and those self-produced by hydrolysis and condensation processes, we proposed for R the ethanol moiety and for Y the ammonium cation. The Raman spectroscopy studies indicated also that the ammonium cations are coordinated by the ether-type oxygen atoms of the PPO chains backbone, whereas the amine groups of the urea linkage participate in the (PtCl3EtOH)(-) anion coordination. In situ Raman monitoring of Pt species decomplexation induced by immersion of hybrid matrix in water highlighted the specific participation of Pt ligands in interaction with the urea group and of NH4(+) cations coordinated by ether-type oxygen atoms in the formation of supramolecular interactions between the PPO chains. The electrospray mass spectrometry analysis of the Pt species released in water from the ureasil-PPO hybrid evidenced that the structure of the complex, NH4 (PtCl3 EtOH), incorporated in the matrix is totally preserved after delivery. Due to both well-known antitumoral and catalytic activities of Pt species, the results reported herein are of prime importance for further applications as drug delivery systems with optimized release pattern or as potential materials for new conceptual development of in situ catalyst delivery in homogeneous catalysis.

Controlled cisplatin delivery from Ureasil-PEO1900 hybrid matrix.

The ability of assembling inorganic, organic, and even bioactive components in a single material unfolds an exciting direction in the development of novel multifunctional hybrid materials. Recently, we have observed that the hydrophilic/hydrophobic character of the organic polymeric moieties determines the swelling/diffusion control of the drug release. In this work, the antitumor cisplatin (CisPt) molecules incorporated into the ureasil-PEO (poly(ethylene oxide)) hybrid material was used as a probe for the in situ and simultaneous UV-vis and Raman spectroscopies monitoring of the kinetics of both the water uptake as well as the CisPt release by the hybrid matrix. Drug molecules were incorporated during the hydrolysis and polycondensation steps. The monolithic xerogel were analyzed by X-ray absorption spectroscopy and differential scanning calorimetry, while the drug release properties were monitored by Raman as well as UV-vis spectroscopies. The results show that the molecular structure of the CisPt is preserved in the one pot sol-gel route used in synthesizing the CisPt-loaded PEO1900 hybrid. The in situ monitoring of water uptake clearly points out the key contribution of the osmotic flow on the stepped profile of the CisPt delivered from the PEO1900 hybrid matrix.