Novel Rare Earth–Polyvinyl Pyridine Complex Functionalized Hybrid Silica Microspheres: Molecular Assembly and Photophysical Property

The functional silica microspheres are derived from the three different silane crosslinking reagents, and then the polyvinyl pyridine-based rare earth hybrids are synthesized through free radical copolymerization of rare earth–vinyl pyridine complex monomer with these functionalized silica microspheres (RE = Eu, Tb). The obtained hybrids are characterized by Fourier transform infrared, X-ray diffraction, Scanning electronic microscope and photoluminescence spectra. The intramolecular energy transfer process between rare earth ions and polymer polyvinyl pyrrolidone matrices took place within these polymer-based hybrids and especially the quantum efficiency of europium hybrids are determined, suggesting that the hybrid material systems derived from different functional silica microspheres present different luminescence efficiencies.     

Hybrid organic-inorganic catalytic mesoporous materials with proton sponges as building blocks

Non-ordered organic-inorganic mesoporous hybrid materials with basic sites have been synthesized following a fluoride-catalysed sol-gel process at neutral pH and low temperatures that avoids the use of structural directing agents (SDAs). Proton sponges have been used as the organic builder of the hybrids, while the inorganic part corresponds to silica tetrahedra. The proton sponges are diamines that exhibit very high basicity and, after functionalization, have been introduced as part of the walls of the mesoporous silica by one-pot synthesis. Several hybrids with different organic loadings have been synthesized and characterized by gas adsorption, thermogravimetric and elemental analysis, solid state MAS-NMR and FTIR spectroscopy. These hybrids show high activity as base catalysts and can be recycled.     

Hybrid silica-PVA nanofibers via sol-gel electrospinning

We report on the synthesis of poly(vinyl alcohol) (PVA)-silica hybrid nanofibers via sol-gel electrospinning. Silica is synthesized through acid catalysis of a silica precursor (tetraethyl orthosilicate (TEOS) in ethanol-water), and fibers are obtained by electrospinning a mixture of the silica precursor solution and aqueous PVA. A systematic investigation on how the amount of TEOS, the silica-PVA ratio, the aging time of the silica precursor mixture, and the solution rheology influence the fiber morphology is undertaken and reveals a composition window in which defect-free hybrid nanofibers with diameters as small as 150 nm are obtained. When soaked overnight in water, the hybrid fibers remain intact, essentially maintaining their morphology, even though PVA is soluble in water. We believe that mixing of the silica precursor and PVA in solution initiates the participation of the silica precursor in cross-linking of PVA so that its -OH group becomes unavailable for hydrogen bonding with water. FTIR analysis of the hybrids confirms the disappearance of the -OH peak typically shown by PVA, while formation of a bond between PVA and silica is indicated by the Si-O-C peak in the spectra of all the hybrids. The ability to form cross-linked nanofibers of PVA using thermally stable and relatively inert silica could broaden the scope of use of these materials in various technologies.     

Microstructure and properties of polyamideimide/silica hybrids compatibilized with 3-aminopropyltriethoxysilane

In this work, we prepared and characterized polyamideimide (PAI)/silica hybrids compatibilized with 3-aminopropyltriethoxysilane (APTES). PAI/silica nanohybrid thin films were prepared using an in situ sol-gel process, followed by thermal imidization. We have investigated the microstructures and properties of the PAI/silica hybrids using FT-IR spectroscopy, X-ray diffraction, small-angle X-ray scattering (SAXS), and differential scanning calorimetry (DSC). We also measured their tensile properties, thermal properties, refractive indices, and dielectric constants. In general, the properties of the PAI/silica hybrids were optimized when the silica content was 6 wt.%.     

Effect of inorganic phase on polymeric relaxation dynamics in PMMA/silica hybrids studied by dielectric analysis

Dielectric relaxation spectroscopy was used to investigate the effect of the inorganic phase on the polymeric relaxation dynamics in PMMA/silica hybrids synthesized in situ via sol-gel processes. It was found that the large-scale molecular motions of PMMA were influenced by the addition of silica, inducing longer mean relaxation times, more heterogeneous relaxing environments and the higher activation energy. Explanations based on hydrogen-bond interactions between two phases and a fraction of entrapped chain segments in silica networks were proposed to understand the influence of the silica.     

Sol–gel synthesis and enhanced properties of a novel transparent PMMA based organic–inorganic hybrid containing phosphorus,nitrogen and silicon

A novel flame-retardant silane containing phosphorus and nitrogen, tetramethyl(3-(triethoxysilyl)propylazanediyl) bis(methylene) diphosphonate (TMSAP), is firstly synthesized and then incorporated into poly(methyl methacrylate) (PMMA) matrix through sol–gel method to produce organic–inorganic hybrids. The chemical structure of TMSAP was confirmed by Fourier transform infrared spectra, ¹H nuclear magnetic resonance (NMR) and ³¹P NMR spectra. The hybrids obtained maintain relatively high transparency, and exhibit a significant improvement in thermal properties, mechanical performance and flame retardancy when compared to pure PMMA, including increased glass transition temperature (T _g ) by 11.4 °C, increased onset thermal degradation temperature (T_0.1) by 82.6 °C, increased half thermal degradation temperature (T_0.5) by 42.0 °C, increased hardness, increased limited oxygen index and decreased heat release rate. Morphological studies of hybrids by scanning electron microscopy (SEM) and ²⁹Si MAS NMR suggest that cross-linked silica network is formed in the hybrids and the inorganic silica particles are distributed well in the polymer matrix. Thermal degradation behaviors investigated by thermogravimetric analysis and char structure analysis studied by SEM and X-ray photoelectron spectroscopy demonstrate the catalytic charring function of TMSAP, and synergistic effect between phosphorus, nitrogen and silicon element. The formation of network structure, homogeneous distribution of silica and the char formation during degradation play key roles in these property enhancements. Detailed mechanisms for these enhancements are proposed.     

Bacterial cellulose–silica organic–inorganic hybrids

Bacterial cellulose (BC) hydrated membranes present nanometric reticulated structure that can be used as a template in the preparation of new organic–inorganic hybrids. BC–silica hybrids were prepared from BC membranes and tetraethoxysilane, (TEOS) at neutral pH conditions at room temperature. Macroscopically homogeneous membranes were obtained containing up to 66 wt.% of silica spheres, 20–30 nm diameter. Scanning electron micrographs clearly show the silica spheres attached to cellulose microfibrils. By removing the cellulose, the silica spheres can be easily recovered. The new hybrids are stable up to 300 °C and display a broad emission band under UV excitation assigned to oxygen-related defects at the silica particles surface. Emission color can be tuned by changing the excitation wavelength.     

Rapid and controlled deswelling of porous poly(N‐isopropylacrylamide) hydrogels prepared by the templating of interpenetrated nanoporous silica particles

Free radical polymerization of N‐isopropylacrylamide (NIPAAm) and crosslinker solutions, which were fulfilled in silica particles with an interpenetrated and nanometer‐sized porous structure (a diameter of 3 mm and mean pore sizes of 15, 30, and 50 nm), fabricated hybrids of organic hydrogels and inorganic silica. Differential scanning calorimetric analyses of the hybrids revealed that silica components affected the thermoresponsive properties of polyNIPAAm hydrogels. Porous polyNIPAAm hydrogels were prepared by the subsequent acid treatment of the hybrids to remove silica. Transmission Fourier transformed infrared spectra indicated the selective extraction of silica. Scanning electron microscopic observation of the hydrogels confirmed the porous structure. The deswelling rate of porous hydrogels was 7 times larger than that of conventional hydrogels and increased with increasing the pore size of silica used. However, the swelling was not affected by the pore formation. The thermoresponsiveness of porous polyNIPAAm hydrogels could be regulated by the pore size. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3542–3547, 2002     

Polyurethane–nanosilica hybrid nanocomposites synthesized by frontal polymerization

Polyurethane–nanosilica hybrids were synthesized with frontal polymerization. Structurally well‐dispersed and stable hybrids were obtained via a two‐step functionalization process: First, the silica was encapsulated with 3‐aminopropyltriethoxysilane (APTS). Second, poly(propylene oxide) glycol, toluene 2,4‐diisocyanate, 1,4‐butanediol, and a catalyst (stannous caprylate) were dissolved in dimethylbenzene and mixed together at room temperature along with the modified nanosilica. A constant‐velocity propagating front was initiated via the heating of the end of the tubular reactor. For the complete encapsulation of the silica with APTS, different weight ratios of APTS to silica were investigated. The polyurethane hybrids were characterized with Fourier transform infrared, differential scanning calorimetry, and transmission electron microscopy. The polyurethane hybrids produced by frontal polymerization had the same properties as those produced by batch polymerization with stirring, but the frontal polymerization method required significantly less time and lower energy input than the batch polymerization method. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1670–1680, 2005     

Positional assembly of hybrid polyurethane nanocomposites via incorporation of inorganic building blocks into organic polymer

Polyurethane (PU)/silica nanocomposites (PSNs) were synthesized using the grafting from technique by incorporation of inorganic nano-sized silica building blocks into a polyurethane matrix. Structurally well-dispersed and stable hybrids were obtained via a two-step functionalized reaction. Firstly, 3-aminopropyltriethoxysilane (APTS) was employed to encapsulate silica as the core surface. Secondly, the PU shell was tethered to the silica core surface via surface functionalization. In order to obtain complete encapsulation of silica with APTS, different ratios of APTS to silica were investigated. The mechanism of the incorporation process was also revealed. PSNs hybrids were characterized by attenuated total reflectance and Fourier transform infrared spectroscopies, differential scanning calorimetry, thermogravimetric analysis, and transmission electron microscopy.     

Silica hybrid nanocomposites

In this work we present experimental results about the formation, properties and structure of sol — gel silica based biocomposite containing Calcium alginate as an organic compound. Two different types of silicon precursors have been used in the synthesis: tetramethylortosilicate (TMOS) and ethyltrimethoxysilane (ETMS). The samples have been prepared at room temperature. The hybrids have been synthesized by replacing different quantitis of the inorganic precursor with alginate. The structure of the obtained hybrid materials has been studied by XRD, IR Spectroscopy, EDS, BET and AFM. The results proved that all samples are amorphous possessing a surface area from 70 to 290 m²/g. It has also been established by FT IR spectra that the hybrids containing TMOS display Van der Walls and Hydrogen bonding or electrostatic interactions between the organic and inorganic components. Strong chemical bonds between the inorganic and organic components in the samples with ETMS are present. A self-organized nanostructure has been observed by AFM. In the obtained hybrids the nanobuilding blocks average in size at about 8–14 nm for the particles.     

Chemical hybridization of imidized waterborne polyurethane with silica particle

Chemical hybrids of imidized waterborne polyurethane (WPU) with silica nanoparticle were synthesized by UV cure. Imide groups were introduced into the hard segment of UV curable WPU by extending the NCO-terminated prepolymers with pyromellitic dianhydride where chemical hybridization by UV cure was made between the acrylate-terminated polyurethane prepolymer and vinyltrimethoxysilane-silica oligomer. It was found that imidization of WPU and imidized WPU-silica hybrids showed remarkably high mechanical and dynamic mechanical properties at room and elevated temperatures as well as thermal stability.     

Molecular dynamics in nanostructured polyimide–silica hybrid materials and their thermal stability

Molecular motion and thermal stability in two series of nanophase‐separated polyimide–silica (PI–SiO₂) hybrid materials with chemically bound components were studied. The hybrids were synthesized from p‐aminophenyltrimethoxysilane‐terminated poly(amic acid)s as PI precursors and tetramethoxysilane as a silica precursor via a sol–gel process. The hybrids differed in their PI chemical structure and chain length (number‐average molecular weight = 5.000, 7.500, or 10.000) and in their SiO₂ content, which ranged from 0 to 50 wt %. Differential scanning calorimetry, laser‐interferometric creep rate spectroscopy, and thermally stimulated depolarization current techniques were used for studying the dynamics from 100 to 650 K and from 10^?3 to 10^?2 Hz. Comparative thermogravimetric measurements were also carried out from 300 to 900 K. Silica nano‐ or submicrodomains that formed affected PI dynamics in two opposite directions. Because of the loosening of the molecular packing of PI chains confined to nanometer‐scale spaces between silica constraints, an enhancement of small‐scale motion, mostly at temperatures below the β‐relaxation region, occurred. However, a partial or total suppression of segmental motion could be observed above the β‐relaxation temperature, drastically so for the shortest PI chains at elevated silica contents and within or close to the glass‐transition range, because of the covalent anchoring of chain ends to silica domains. Large changes in thermal stability, including a 2.5‐fold increase in the apparent activation energy of degradation, were observed in the hybrids studied. A greater than 100 °C rise in long‐term thermal stability could be predicted for some hybrids with respect to pure PI. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1056–1069, 2002     

Polysaccharide-Silica Hybrids: Design and Applications

This article discusses and reviews the current status and future perspectives of silica hybrids of polysaccharides and biosilicas derived thereof. The hybrids have been produced in various morphological shapes and utilized in water remediation, separation, enzyme immobilization, sensor, and biomedical fields. The polysaccharides show templating and structure directing influence in manipulation of sol gel silica hybrid materials which can be calcined to derive functional biosilicas. The development of energy storage devices and white light emitting solid phosphors may be the fields of future research.     

Design,Synthesis, and Evaluation of Tetraethylene Glycol‐Tethered Isatin–1,2,3‐Triazole–Coumarin Hybrids as Novel Anticancer Agents

We report herein the design and synthesis of a series of novel tetraethylene glycol‐tethered isatin–1,2,3‐triazole–coumarin hybrids and evaluate their in vitro antitumor activities against seven common human cancer cell lines including drug‐resistant cell line. Results revealed that all the synthesized hybrids showed weak to moderate activities against the tested seven cancer cell lines. The structure–activity relationship was also discussed, and the enriched structure–activity relationship may pave the way for further rationale design of this kind of hybrids.     

Polyimide-silica Hybrids: Structural and Morphological Investigations

Polyimide (PI) containing pendant hydroxyl functional groups have been employed for preparation of PI-silica hybrids through the sol-gel process. A stoichiometric amount of pyromellitic dianhydride (PMDA) was reacted with a mixture of oxydianiline (ODA) and 3,3′-diamino-4,4′-dihydroxybiphenyl (DAHP) in dimethylacetamide (DMAc) solvent to prepare the precursor poly(amic acid) (PAA) solution for the PI. Various proportions of tetraethoxysilane (TEOS) were mixed with PAA to prepare PI-silica hybrids through sol-gel process. The structure and morphology of these hybrids were investigated with field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), optical surface profilometery, and Fourier transform infrared (FTIR) spectroscopy and compared with the one in which the matrix was prepared from PMDA and ODA with no pendant hydroxyl functionalities. Formation of silica lean and silica rich phases (SLP and SRP) as a result of formation of nano-sized silica clusters with diffused boundaries, dispersed in the matrix and their agglomerates, respectively, along with totally different morphology suggest a strong influence of hydroxyl groups in controlling the morphology of PI-silica hybrids. A model namely “Retain and React” has been introduced to explain observed structure.     

Natural Phenolic Compounds as Modifiers for Epoxidized Natural Rubber/Silica Hybrids

Silica is a popular filler, but in epoxidized natural rubber, can act as a cross-linking agent. Unfortunately, a high amount of silica is necessary to obtain satisfactory tensile strength. Moreover, a high amount of silica in ENR/silica hybrids is associated with low elongation at break. In our paper, we propose natural phenolic compounds, including quercetin, tannic acid, and gallic acid as natural and safe additional crosslinkers dedicated to ENR/silica hybrids to obtain bio-elastomers with improved mechanical properties. Therefore, toxic crosslinkers, such as peroxides or harmful accelerators can be eliminated. The impact of selected natural phenolic compounds on crosslinking effect, mechanical properties, color, and chemical structure of ENR/silica composite have been analyzed. The obtained results indicated that only 3 phr of selected natural phenolic compounds is able to improve crosslinking effect as well as mechanical properties of ENR/silica hybrids. Moreover, some of the prepared materials tend to regain mechanical properties after reprocessing. Such materials containing only natural and safe ingredients have a chance of becoming novel elastomeric biomaterials dedicated to biomedical applications.     

Polymer-silica nanocomposites prepared by sol-gel technique: Nanoindentation and tapping mode AFM studies

Polymer-silica nanocomposites based on poly(2-hydroxyethyl acrylate) (PHEA) have been prepared by the simultaneous polymerization of the organic and the silica phases in a sol-gel process with the silica precursor tetraethyl orthosilicate (TEOS). The structure of this system is investigated using atomic force microscopy (AFM) in the tapping mode and in nanoindentation experiments. The structure of the PHEA/silica hybrids strongly depends on the ratio of both components in the system. For silica weight fractions lower than 0.15, the system consists of aggregated silica particles dispersed in the organic matrix; above that concentration of silica the structure is co-continuous with that of the organic matrix, similarly to two interpenetrated networks.     

Effect of the silica content on the physico-chemical and relaxation properties of hybrid polymer/silica nanocomposites of P(EMA-co-HEA)

Poly(ethyl methacrylate-co-hydroxyethyl acrylate) 70/30 %wt/silica, P(EMA-co-HEA)/SiO₂, nanocomposites, with silica contents ranging from 0 to 30 %wt, were synthesized and studied as promising candidate materials for the synthetic matrix of scaffolds for bone substitutes or dentin regeneration. The physico-chemical properties of the hybrids were studied by calorimetry and by contact angle measurements on the surfaces. The dynamic-mechanical and compression properties were analysed. Intermediate silica contents in the range from 10 to 20 %wt of silica rendered co-continuous interpenetrated structures, in which silica produced a reinforcing effect in the polymeric matrix and at the same time conferred bioactivity to the surfaces by improving surface wettability, making these hybrids appropriate for the proposed application. On the contrary, silica percentages below 10 %wt formed disconnected inorganic aggregates at the nanoscale dispersed in the copolymer matrix, which did not modify significantly the copolymer properties. Silica contents above 20 %wt formed denser inorganic networks with few terminal silanol groups available at the surfaces, much more rigid and hardly manageable samples.     

Hybrids of colloidal silica and waterborne polyurethane

Waterborne polyurethane (WPU) was synthesized and followed by adding colloidal silica to prepare WPU-silica hybrids. The silica content in the hybrid thin films was varied from 0 to 50 wt%. The experimental results revealed that the viscosity of these hybrid solutions increased with increasing silica content and resulted in the aggregation of silica particle in the hybrid films. The latter result was evidenced by SEM examination. The effect of interaction between silica particle and urethane polymer chains is more significant with increasing silica content. The prepared hybrid films show much better thermal stability and mechanical properties than pure WPU. The optical transparence did not linearly decrease with increasing the silica fraction in the hybrid thin film. At below 20% silica content, the film transparence decreased with increasing silica content; the converse is true at above 20% silica content. These results showed that the prepared hybrid films demonstrated tunable transparence with the silica fraction in the films.