Siloxane Hybrid Research Articles

Highly luminescent di-ureasil hybrid doped with a Eu(III) complex including dipicolinate ligands

A short chain di-urea cross-linked poly(oxyethylene) (POE)/siloxane hybrid host (di-ureasil), designated as d-U(600), was doped with the Na 3[Eu(dipic) s]· xH 2O (where dipic 2− is the dipicolinate ion) complex. The resulting material is non-porous, semi-crystalline and thermally stable up to 145 °C. Because of the presence of the bulky dipic 2− ligands, the addition of the complex to d-U(600) leads to the partial destruction of the hydrogen-bonded POE/urea aggregates of the hybrid matrix and to the formation of extra urea/urea aggregates. The incorporation of the complex into d-U(600) accounts for an increase of both the 5D 0 lifetime and quantum efficiency values (1.950 ± 0.007 ms and 0.50, respectively) with respect to those of the isolated complex (1.7 ms and 0.46, respectively). The addition of the complex also contributes to an enhancement of the absolute emission quantum yield value, whose maximum value (0.66 excited at 280 nm) is the highest value reported for organic–inorganic hybrids modified by lanthanide complexes.

Synthesis and characterization of chemically cross-linked polyimide–siloxane hybrid films

Abstract Chemically cross-linked polyimide and silica hybrid films were prepared through the sol–gel processing. PI matrix was prepared by the reaction of pyromellitic dianhydride with a mixture of diamines e.g., oxydianiline and 2,5-diaminohydroquinon (2,5-DAHQ) to include pendant hydroxyl groups on the chain. These groups were reacted further with isocyanatopropyltriethoxysilane. An appropriate amount of tetraethoxysilane was then added and the sol–gel process was carried out to condense ethoxy groups from both types of silanes thus producing chemically bonded composite films. The films with different silica contents were evaluated by a variety of techniques including FTIR, 29Si NMR, SEM, tensile, thermal, mechanical and thermogravimetric analyses. The chemical interaction between the phases brought about an intimate dispersion of the two phases, which resulted in the formation of nano-sized co-continuous domains. The tensile modulus of such films was higher and thermal expansion coefficient was much lower than those with similar silica contents without inter-phase bonding.

A new approach to graft siloxanes to alkyds

The effect of oil length of alkyds and substitution of siloxane backbone has been studied for alkyd–siloxane hybrids. A series of nine alkyd–siloxane hybrids were synthesized by either varying the oil length of the alkyd or the siloxane backbone substitution. Three linseed oil-based alkyds with either a long, medium, or short oil length were grafted with three hydride-terminated siloxanes substituted with methyl, cyclopentyl, or cyclohexyl groups. A hydrocoupling reaction was used to couple the telechelic siloxane with the hydroxyl functionality of the alkyds using Wilkinson’s catalyst. The reaction was monitored by the disappearance of siloxane hydride signal using Fourier transform infrared. Characterization of siloxane–alkyd hybrids was performed using 1H-NMR, 13C-NMR, and gel permeation chromatography. The hybrids were formulated with a Co, Zr, and Ca drier package and auto-oxidatively cured without using any solvent. The tensile, viscoelastic, and coating properties were evaluated for the cured films. The crosslink density, flexibility, and reverse impact resistance were found to increase as a function of oil length. Tensile modulus, elongation-to-break, glass transition temperature, drying time, and fracture toughness decreased with increase in oil length. For the alkyd–siloxane hybrids, the mechanical and rheological properties were dependant on the size of the substituents. The larger-sized cyclopentyl and cyclohexyl groups resulted in better mechanical and rheological properties than the methyl-containing siloxanes.

Controlled Drug Release from Ureasil−Polyether Hybrid Materials

Flexible, transparent, and insoluble urea-cross-linked polyether−siloxane hybrids presenting a tunable drug delivery pattern were prepared using the sol−gel method from PEO (poly(ethylene oxide)) and PPO (poly(propylene oxide)) functionalized at both chain ends with triethoxysilane. Different polyether chain lengths were used to control the urea/siloxane (named ureasil) node density, flexibility, and swellability of the hybrid network. We herein demonstrate that the drug release from swellable hydrophilic ureasil−PEO hybrids can be sustained for some days, whereas that from the unswellable ureasil−PPO hybrids can be sustained for some weeks. This outstanding feature conjugated with the biomedically safe formulation of the ureasil cross-linked polyether-siloxane hybrid widens their scope of application to include the domain of soft and implantable drug delivery devices.

Phenyl‐Substituted Siloxane Hybrid Gels that Soften Below 140°C

A characteristic of so‐called melting gels is that the gels, which are rigid at room temperature, are able to soften and resoften at temperatures around 110°C. However, after consolidation at temperatures higher than 150°C, the gels no longer resoften. Two systems of melting gels were investigated: phenyltrimethoxysilane (PhTMS)–diphenyldimethoxysilane (DPhDMS) and phenyltriethoxysilane (PhTES)–diphenyldiethoxysilane (DPhDES). The influence of disubstituted versus monosubstituted alkoxide on the softening behavior and the temperature of decomposition was studied. The consolidation temperature increased as the amount of disubstituted alkoxide increased, while the decomposition temperature increased only slightly. In general, the ethoxy‐containing gels (maximum at 150°C) consolidated at lower temperatures than the methoxy‐containing gels (maximum at 180°C).

Hybrid siloxane epoxy coatings containing quaternary ammonium moieties

AbstractAn ever increasing concern over bacterial infections caused by consumer products as well as medical devices is obvious from the recent surge in literature documenting the need for novel self‐decontaminating coatings. Within, we report a hybrid ionic organic/inorganic siloxane epoxy system containing quaternary ammonium moieties. This novel low surface energy antimicrobial coating is capable of self‐decontaminating in a variety of environments. The system is designed to be used as an over‐coating, for devices that are prone to come into contact with pathogenic bacteria. These coatings have been synthesized, characterized, and analyzed for both physical and antimicrobial properties. Preliminary antimicrobial evaluation indicates a direct correlation between antimicrobial activity and hydrophobicity of the biocidal functional group within the resin matrix. These coatings have demonstrated the ability to eliminate up to 99.9% of pathogenic bacteria on the surface. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Di-ureasil xerogels containing lithium bis(trifluoromethanesulfonyl)imide for application in solid-state electrochromic devices

In this study we report the characterization of a prototype solid-state electrochromic device based on poly(ethylene oxide) (PEO)/siloxane hybrid networks doped with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The polymer networks prepared, designated as di-ureasils and represented as d-U(2000), were produced by a sol–gel procedure and are composed of a siliceous framework to which both ends of polyether chains containing about 40 CH 2CH 2O units are covalently bonded through urea linkages. Samples with compositions of 200 ≥ n ≥ 0.5 (where n is the molar ratio of CH 2CH 2O to Li +) were characterized by thermal analysis, complex impedance measurements and cyclic voltammetry at a gold microelectrode. Electrolyte samples were obtained as self-supporting, transparent, amorphous films and at room temperature the highest conductivity was observed with the d-U(2000) 35LiTFSI composition (3.2 × 10 −5 Ω −1 cm −1). We report the results of preliminary evaluation of these polymer electrolytes as multi-functional components in prototype electrochromic displays. Device performance parameters such as coloration efficiency, optical contrast and image stability were also evaluated. The electrolytes with n > 8 presented an optical density above 0.56 and display assemblies exhibited good open-circuit memory and stable electrochromic performances.

Functionalization of atomic force microscope tips by dielectrophoretic assembly ofGd2O3:Eu3+ nanorods

An atomic force microscopy (AFM) tip has been coated with photoluminescentEu3+-dopedGd2O3 nanorods using a dielectrophoresis technique, which preserves the red emission of thenanorods (quantum yield 0.47). The performance of the modified tips has been tested byusing them for regular topography imaging in tapping and contact modes. Both a regularAFM standard grid and a patterned surface (of an organic–inorganic methacrylateZr-based oxo-cluster and poly(oxyethylene)/siloxane hybrid) have been used. Similar depthvalues have been measured using a conventional silicon tip and the nanorod-modified tip.The tips before and after use exhibit similar SEM images and photoluminescence spectraand, thus, seem to be stable under working conditions. These tips should findapplications in scanning near-field optical microscopy and other scanning techniques.

Cationic copolymerization of epoxy siloxane monomer with liquid poly‐butadiene and its light emitting diode encapsulation

AbstractA novel epoxy siloxane hybrid was prepared using epoxy siloxane monomers of 1,3‐bis[2‐(3‐{7‐oxabicyclo[4.1.0]heptyl})ethyl]‐tetramethyldisiloxane (BEPDS) with hydroxyl terminated hydrogenated polybutadiene (GI‐1000), in different proportions. Apparent polymerization reactivity was decreased with increasing GI‐1000 concentration but the normalized reactivity per epoxy group was slightly increased due to reaction between hydroxyl group and epoxy group. Increasing GI‐1000 concentration showed significant flexibility improvement in epoxy siloxane hybrid. At 30 wt % of GI‐1000 addition, glass transition temperature was decreased from 116 to 21°C and shore D hardness was decreased from 75 to 46.5% weight loss temperature of these epoxy siloxane hybrid was decreased with increasing GI‐1000 concentration, whereas thermal discoloration was increased. LED encapsulation with this epoxy siloxane demonstrated no crack when GI‐1000 was 30 wt % or more. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Mechanism of Stabilization of Silicone Oil−Water Emulsions Using Hybrid Siloxane Polymers

Silicone polymers, due to their high lubricity and good spreading properties, are widely used in industrial applications. Being insoluble in water and most hydrocarbons, a common mode of delivering silicones is in the form of emulsions. To stabilize silicones in the emulsion form more efficiently, it is useful to understand the mechanism of emulsion stabilization. Two different mechanisms of emulsion stabilization have been proposed in the past: film formation and precipitation (known as the Pickering mechanism). These two mechanisms are different, and there is a need to further investigate this issue. The aim of the present work was to investigate the mechanism of stabilizing silicone emulsions and to propose a generalized behavior. Several experiments including the measurement of Langmuir isotherms, rheology experiments, phase diagram studies, and microscopy experiments were conducted. All of the above techniques indicated that the functional groups interact strongly with the water phase. The emulsions were found to be stable only if the emulsifiers were soluble in silicone oil or the water phase, and the stability decreased as the emulsifier precipitated. In most cases tested here, the emulsifiers were not observed to precipitate as reported earlier for the Pickering mechanism, and the emulsion stabilization followed film formation. These results should help to predict emulsion stabilization for unknown systems.

Bioactive microspheres produced from gelatin–siloxane hybrids for bone regeneration

In this study, we produced a novel microsphere with a hybridized composition of gelatin and siloxane which is bioactive and degradable for the applications in bone regeneration fields. A solution of gelatin organic and siloxane inorganic containing calcium chloride was formulated into microspheres in an oil bath mediated by a surfactant. Following the processes of hydration, gelation and solidification, well-shaped spherical particles were produced with sizes of a few to hundreds of micrometers (68 microm on average). The obtained microspheres were highly stable in an aqueous solution due to the in situ cross-linking of the siloxane with gelatin chains, which eliminated the additional cross-linking step generally used in pure gelatin. The hybridized microspheres exhibited rapid induction of apatite-like crystals on their surface with incubation in a simulated body fluid, suggesting an excellent bone bioactivity in vitro. It is considered that the newly developed organic-inorganic microspheres may be useful for the regeneration of skeletal defects.

Vibrational spectra and microstructure of poly( ε-caprolactone)/siloxane biohybrids doped with lithium triflate

Fourier Transform infrared (FT-IR) and Raman (FT-Raman) spectroscopies and Scanning Electron Microscopy (SEM) were used to investigate ionic association, hydrogen bonding and morphology in a family of sol–gel derived lithium triflate (LiCF 3SO 3)-doped di-urethane cross-linked poly( ε-caprolactone) (PCL(530))/siloxane hybrid electrolytes. The materials studied, with compositions ∞ > n ⩾ 0.5 (where n – composition – expresses the molar ratio of PCL(530) ester repeat units per Li + ion), are non-porous and homogeneous. The Li + ions interact with the urethane and ester carbonyl oxygen atoms within the whole range of salt concentration analyzed, promoting the formation of hydrogen-bonded aggregates. The composition dependence of the relative concentration of “free” anions and coordinated anions (weakly coordinated anions, Li + CF 3 SO 3 - ion pairs or [Li(CF 3SO 3) 2] − triplets, aggregates I ([Li 2(CF 3SO 3)] +) and aggregates II ([Li 3(CF 3SO 3)] 2+) in all the samples is in perfect agreement with the values of the room temperature ionic conductivity reported previously.

Photoluminescence and quantum yields of organic/inorganic hybrids prepared through formic acid solvolysis

Three undoped di-urea cross-linked poly(oxyethylene) (POE)/siloxane hybrid matrices, classed as di-ureasils, incorporating POE segments with different lengths were prepared through the carboxylic acid solvolysis sol–gel method using formic acid. The resulting hybrids were characterized by X-ray diffraction, Fourier transform mid-infrared spectroscopy, 29Si and cross-polarization 13C magic-angle spinning nuclear magnetic resonance and photoluminescence spectroscopy. The hybrids’ structure is essentially independent of the polymer chain length and the materials are room temperature white-light emitters with emission quantum yields of ∼10±1% and lifetime average values between 2 and 4ns. For the di-ureasil host with short polymer chains the solvolysis method favours the increase of the PL quantum yields relatively to conventional sol–gel route.

Microstructure and protonic conductivity of H3PO4‐doped polyethylenimine–siloxane chemically covalently organic–inorganic hybrids

AbstractThe chemically covalent polyethylenimine–siloxane hybrids doped with various amounts of ortho‐phosphoric acid (H3PO4) were prepared and characterized by FTIR, DSC, TGA, and solid‐state NMR spectra. The protonic conduction behavior of these materials was also investigated by means of impedance measurements. These observations indicate that the hydrogen bonding and protonic interactions exist between the dopant H3PO4 and the hybrid host, resulting in an increase in T g of polyethylenimine segments. These hybrids are thermally stable up to 200 °C from TGA analysis. Conductivity studies show an Arrhenius behavior characteristic and the Grotthus‐like proton conduction, and a high conductivity of 10−2–10−3 S cm−1 at 110 °C in dry atmosphere for the hybrid membrane with H3PO4/EI of 0.5. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2135–2144, 2006

Optically functional nanocomposites with poly(oxyethylene)-based di-ureasils and mesoporous MCM-41

Di-urea cross-linked poly(oxyethylene) (POE)/siloxane hybrid structure (di-ureasil) was incorporated into the hexagonal array of one-dimensional channels of mesoporous silica MCM-41. X-ray diffraction, nitrogen adsorption–desorption, Fourier transform mid-infrared spectroscopy, 29Si and 13C nuclear magnetic resonance, transmission electron microscopy and photoluminescence results demonstrate the interaction (covalent grafting and impregnation) between the di-ureasil structure and the silanol groups of the MCM-41 channels, preserving their integrity. The composites are photoluminescent displaying the intrinsic green emission of MCM-41 superposed to the blue and purplish-blue di-ureasil components. Time-resolved spectroscopy provides further support from energy transfer between the mesopourous silica and the di-ureasil matrix.

FT-IR and Raman spectroscopic study of di-urea cross-linked poly(oxyethylene)/siloxane ormolytes doped with Zn 2+ ions

The interactions occurring in di-urea ( NHC( O)NH ) cross-linked poly(oxyethylene) (POE)/siloxane hybrids (di-ureasils) doped with zinc triflate (Zn(CF 3SO 3) 2) were investigated by Fourier Transform infrared (FT-IR) and Raman (FT-Raman) spectroscopies. Bonding of the Zn 2+ ions to the urea carbonyl oxygen atoms occurs in the entire range of compositions studied (∞ > n ≥ 1, where n, salt content, is the molar ratio of oxyethylene moieties per Zn 2+ ion). At n > 20 the incorporation of the guest cations progressively reduces the number of free C O groups. At n = 20 the saturation of the urea cross-links is attained and the Zn 2+ ions start to coordinate to the POE chains giving rise to the formation of a crystalline POE/Zn(CF 3SO 3) 2 complex. The latter process occurs at the expense of the destruction of the hydrogen-bonded POE/urea structures of the host di-ureasil structure. New hydrogen-bonded associations, more ordered than the urea–urea aggregates present in the non-doped matrix and including Zn 2+⋯O C coordination, emerge in parallel. “Free” and weakly coordinated CF 3SO 3 − ions, present in all the xerogels studied, appear to be the main charge carriers of the conductivity maximum of this family of ormolytes located at n = 60 at 30 °C. In materials with n ≤ 20 contact ion pairs, “cross-link separated” ions pairs and higher ionic aggregates appear. The data reported demonstrate that the behaviour of the di-ureasils doped with triflate salts depends on the type of cation.

Solid polymer electrolytes. XI. Preparation, characterization and ionic conductivity of new plasticized polymer electrolytes based on chemical‐covalent polyether–siloxane hybrids

AbstractA new hybrid polymer electrolyte system based on chemical‐covalent polyether and siloxane phases is designed and prepared via the sol–gel approach and epoxide crosslinking. FT‐IR, 13C solid‐state NMR, and thermal analysis (differential scanning calorimetry (DSC) and TGA) are used to characterize the structure of these hybrids. These hybrid films are immersed into the liquid electrolyte (1M LiClO4/propylene carbonate) to form plasticized polymer electrolytes. The effects of hybrid composition, liquid electrolyte content, and temperature on the ionic conductivity of hybrid electrolytes are investigated and discussed. DSC traces demonstrate the presence of two second‐order transitions for all the samples and show a significant change in the thermal events with the amount of absorbed LiClO4/PC content. TGA results indicate these hybrid networks with excellent thermal stability. The EDS‐0.5 sample with a 75 wt % liquid electrolyte exhibits the ionic conductivity of 5.3 × 10−3 S cm−1 at 95°C and 1.4 × 10−3 S cm−1 at 15°C, in which the film shows homogenous and good mechanical strength as well as good chemical stability. In the plot of ionic conductivity and composition for these hybrids containing 45 wt % liquid electrolyte, the conductivity shows a maximum value corresponding to the sample with the weight ratio of GPTMS/PEGDE of 0.1. These obtained results are correlated and used to interpret the ion conduction behavior within the hybrid networks. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1000–1007, 2006

Implantation of a New Porous Gelatin–Siloxane Hybrid into a Brain Lesion as a Potential Scaffold for Tissue Regeneration

For brain tissue regeneration, any scaffold for migrated or transplanted stem cells with supportive angiogenesis is important once necrotic brain tissue has formed a cavity after injury such as cerebral ischemia. In this study, a new porous gelatin-siloxane hybrid derived from the integration of gelatin and 3-(glycidoxypropyl) trimethoxysilane was implanted as a three-dimensional scaffold into a defect of the cerebral cortex. The porous hybrid implanted into the lesion remained at the same site for 60 days, kept integrity of the brain shape, and attached well to the surrounding brain tissues. Marginal cavities of the scaffolds were occupied by newly formed tissue in the brain, where newly produced vascular endothelial, astroglial, and microglial cells were found with bromodeoxyuridine double positivity, and the numbers of those cells were dose-dependently increased with the addition of basic fibroblast growth factor (bFGF) and epidermal growth factor (EGF). Extension of dendrites was also found from the surrounding cerebral cortex to the newly formed tissue, especially with the addition of bFGF and EGF. The present study showed that a new porous gelatin-siloxane hybrid had biocompatibility after implantation into a lesion of the central nervous system, and thus provided a potential scaffold for cell migration, angiogenesis and dendrite elongation with dose-dependent effects of additive bFGF and EGF.

Local Structure and Near-Infrared Emission Features of Neodymium-Based Amine Functionalized Organic/Inorganic Hybrids

Nd(3+)-based organic/inorganic hybrids have potential application in the field of integrated optics. Attractive sol-gel derived di-urea and di-urethane cross-linked poly(oxyethylene) (POE)/siloxane hybrids (di-ureasils and di-urethanesils, respectively) doped with neodymium triflate (Nd(CF(3)SO(3))(3)) were examined by Fourier transform mid-infrared (FT-IR), Raman (FT-Raman), (29)Si magic-angle spinning (MAS) nuclear magnetic resonance (NMR) and photoluminescence spectroscopies, and small-angle X-ray scattering (SAXS). The goals of this work were to determine which cation coordinating site of the host matrix (ether oxygen atoms or carbonyl oxygen atoms) is active in each of the materials analyzed, its influence on the nanostructure of the samples and its relation with the photoluminescence properties. The main conclusion derived from this study is that the hydrogen-bonded associations formed throughout the materials play a major role in the hybrids nanostructure and photoluminescence properties.

Gel-melting method for preparation of organically modified siloxane low-melting glasses

Softening or melting behavior of the organically-modified siloxane hybrid gels and glasses in the system of RSiO3/2 and R2SiO2/2 (R: methyl and phenyl) has been investigated to obtain a new family of low-melting glasses. The RSiO3/2 and RSiO3/2–R2SiO2/2 gels showed softening temperatures around 50–100 °C. The softening temperature of RSiO3/2 single-component glasses, which were obtained by melting the corresponding gels at a temperature above the softening temperature, increased by heat-treatment at 200 °C, and finally showed no softening behavior. On the other hand, in the PhSiO3/2–Ph2SiO2/2 binary glasses, the softening temperatures showed a tendency to saturate after longer heat treatment over 200 h. These facts indicate that the present organically modified siloxane system will be a potential candidate for the low-melting glass.