Siloxane Type Research Articles

Covalently crosslinked poly(biphenyl dimethylamino benzene) membranes for high temperature proton exchange membrane fuel cells

The electrolyte membrane plays a pivotal role in high temperature proton exchange membrane fuel cells (HT-PEMFCs). Herein, we develops a new triarylmethane-backboned polymer, poly (biphenyl dimethylamino benzene) (PBDAB), synthesized through a facile one-step Friedel-Crafts reaction using biphenyl and 4-(dimethylamino) benzaldehyde as monomers. The presence of tertiary amine groups in PBDAB facilitates strong interactions with phosphoric acid (PA) molecules. To enhance the membrane's dimensional and mechanical stabilities, covalent crosslinking is performed via the Menshutkin reaction between the tertiary amine groups in PBDAB and chloromethyl groups in various crosslinkers. In order to study the influence of crosslinker chemical structure on the properties of PBDAB-based membranes, five different crosslinkers are employed, including small-molecule types such as 1,2-bis(2-chloroethoxy) ethane (BCE) and 1,4-bis(chloromethyl) benzene (BCB), siloxane type 3-chloropropyl (trimethoxy) silane (CTS), polymer types such as poly (vinylbenzyl chloride) (PVBC) and polyepichlorohydrin (PECH). Results reveal that the flexible and ether containing polymer crosslinker of PECH crosslinked membrane, denoted as CL-y%PECH, exhibits superior overall performance. When doped in an 85 wt% PA solution, the CL-5%PECH membrane achieves a PA uptake of 201%, resulting in an anhydrous proton conductivity of 0.064 S cm−1 at 180 °C and a mechanical strength of 7.2 MPa at room temperature. Using H2 and O2 as fed gases without humidification and backpressure, a single cell with abovementioned membrane attains a peak power density of 302 mW cm−2 at 160 °C. This work offers a kind of promising PBDAB based membranes for HT-PEMFC applications.

Investigation on the Synergistic Effect of Surfactants for Silylation of Montmorillonite

Silylation, also known as silane grafting, is frequently used to organically modify montmorillonite (organo-Mt), which of properties were depended on the type of siloxane and intercalated interlayer structure of Mt, for construction of functional materials utilizing in a variety application of industry. We have synthesized organo-Mt using different siloxanes after Mt was firstly modified at three different surfactants of cationic cetyltrimethylammonium bromide (CTAB), anionic sodium oleate (So) and nonionic sorbitan monostearate (Span60) to identifying the effect of surfactants for silylation of Mt. The spectral and structural characters of the obtained products were characterized by a combination of X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), thermogravimetry (TG), and contact angle analysis. The basal spacing of the organo-Mt increased with surfactants loading. We found that CTAB can significantly increase the spacing between layers of Mt from 1.55nm to 1.90nm, load more siloxane on Mt. The average contact angles of CTAB-Mt-APTES and CTAB-Mt-PTES were 69.9±0.3° and 80.7±0.3°, which could be more prone to the interlayer locking effect. Our study showed that the charge of surfactants has significant influence for silylation of Mt, resulting in the loading amount of silane, interlayer structure, and the surface wetting properties.

Adsorption of linear and cyclic siloxanes on activated carbons for biogas purification: Sorbents regenerability

Two commercial activated carbons, namely STIX and AP4, were selected to investigate their ability for siloxane adsorption and further thermal regeneration in relation with their different physico-chemical properties. In the frame of biogas purification, the studied siloxanes were L2, L3, L4 (linear molecules) and D4, D5 (cyclic molecules). The maximum capacity of adsorption was estimated by gas chromatography and gravimetric methods. AP4 presents better adsorptive properties comparing with STIX irrespective of the type of siloxane. Thermal regeneration after siloxanes adsorption was followed up to 400 °C by both gas chromatography and in situ DRIFTS. Except L2, the siloxane polymerization proceeds on the AC containing alkali metals (K, Na) as revealed by the observed release of their decomposition products during the thermodesorption treatment. The same sites are responsible for the cleavage of SiO bonds in linear molecules and formation of L2 as primary product above 100 °C. The presence of such sites, possibly strong basic sites, is detrimental to the regenerability of the spent adsorbent and to the adsorption which could be limited by partial blockage of the AC porosity. Interestingly the regenerability of the alkali-free AC depends only on the volatility of the siloxane.

Hydrophobicity Test of Silicone Rubber Based on Thermogravimetric Analysis

To study the hydrophobicity and the transfer of hydrophobicity of silicone rubber, experiments were conducted under three conditions (low-temperature ashing, room-temperature ashing, and low-temperature salting) on new silicone rubber products. Then the surface hydrophobicity of the material after cleaning the contaminants was measured using the classification of water spray, and the change laws of low molecular-weight substances in the core layer and the surface of silicone rubber samples were studied using the thermogravimetric analysis. The results showed that the low molecular-weight substances, namely the hydrophobic substances, were a typical type of siloxane. After pollutants accumulated on the surface of the silicone rubber, the surface hydrophobicity of the material declined continuously, and the contents of hydrophobic substances in the surface and the core layers reduced with fluctuations at a rate being directly proportional to the ambient temperature. The content and the decrease rate of hydrophobic substances in the surface were slightly higher than those in the core layer. The ashes in the contaminants propelled the transfer of the hydrophobic substances while salts inhibited the transfer. However, the presence of salts accelerated the hydrolysis of silicone rubber molecules in the material surface. The experimental results provide reference for the daily maintenance of composite insulators of electric power enterprises.

H2S and Siloxane D5 Removal from Anaerobic Digestion Gas by Adsorption

Global warming and depletion of fossil fuel enhances people to obtain alternative clean sources of energy. The key objective of this study was to develop adsorbent systems for sulphur (from H2S) and siloxanes removal from the anaerobic digestion gas (ADG) by commercially available adsorbents for a solid oxide fuel cell (SOFC) application. The target limits for removal of sulphur and siloxane compounds were less than 1 ppmv and 100ppbv respectively for the SOFC application. Based on the results of this work (this work is a part of a European Union project named SOFcom) and some other projects of SOFcom, a pilot plant of SOFC (capacity 100 kW fuel energy) will attempt to operate using the ADG produced from the Torino Sewage Plant, Italy. Different types of siloxanes were available in the ADG, among them D5 was chosen as representative for their higher concentrations (1200ppbv) in Torino, Italy. However, all types of siloxanes are also possible to remove from ADG by the same adsorbent. Commercially available adsorbents such as Activated Carbon (sigma), Zeolite 5A, FCDS GS-1(ZnO) and FCDS GS6, Active carbon (Norit RST3) and Soxsia were explored in the fixed bed reactor in laboratory. Artificially simulated ADG was tested in the laboratory (for simplicity) to determine the adsorption capacities of adsorbents. FCDS GS-1 (48 mg/g) and Norit RST3 (55.7 mg/g) were performed as best adsorbents for sulphur and siloxane D5 removal respectively.Journal of Chemical Engineering, Vol. 29, No. 1, 2017: 40-43

Bridging a Knowledge Gap from Siloxanes to Germoxanes and Stannoxanes. A Theoretical Natural Bond Orbital Study.

Explaining the nature of the E-O chemical bond (E = Si, Ge, Sn) has been a great challenge for theoretical chemists during the last decades. Among the large number of models used for this purpose, the one based on hyperconjugative interactions sheds more light on the nature of chemical bonding in siloxanes. Starting from this concept, this study aimed to evaluate the impact of siloxane type hyperconjugative effects on the structural features of germoxanic and stannoxanic species and in addition to assess if p-d-like back-bonding interactions can also play important roles in determining the particular structures of these heavier analogues of ethers. Natural bond orbital deletion (NBO DEL) optimizations, carried out at the DFT level of theory, revealed that hyperconjugative effects dictate to a large extent the structural behavior of these species. Furthermore, this study points out that p-d back-bonding interactions also influence the equilibrium geometry of these species, although acting as a secondary electronic effect within the E-O-E moieties (E = Si, Ge, Sn).

An unprecedented gas-phase condensation reaction mediated by a bissilylated chloronium ion intermediate

Gas phase Cl2Si(OH)+ ions undergo an unusual condensation reaction with SiCl4 to yield Cl3SiOSiCl2+ ions that by progressive hydrolysis or solvolysis give rise to a large variety of siloxane type moieties.

Epoxidized pine oil‐siloxane: Crosslinking kinetic study and thermomechanical properties

ABSTRACTIn this study, a novel approach to toughen biobased epoxy polymer with different types of siloxanes was explored. Three different modified siloxanes, e.g., amine‐terminated polydimethyl siloxane (PDMS‐amine), glycidyl‐terminated polydimethyl siloxane (PDMS‐glycidyl), and glycidyl‐terminated polyhedral oligomeric silsesquioxane (POSS‐glycidyl) were used as toughening agents. The curing and kinetics of bioepoxy was investigated by differential scanning calorimetry and Fourier transform infrared spectroscopy. The mechanical, thermal, and morphological properties of the cured materials were investigated. Rheological characterization revealed that the inclusion of POSS‐glycidyl slightly increased the complex viscosity compared to the neat resin. The morphology of the cured bioresin was characterized by transmission electron microscopy and scanning electron microscopy. The inclusion of POSS‐glycidyl to bioepoxy resin resulted in a good homogeneity within the blends. The inclusion of PDMS‐amine or PDMS‐glycidyl was shown to have no effect on tensile and flexural properties of the bioresins, but led to a deterioration in the impact strength. However, the inclusion of POSS‐glycidyl enhanced the impact strength and elongation at break of the bioresins. Dynamic mechanical analysis showed that the siloxane modified epoxy decreased the storage modulus of the bioresins. The thermal properties, such as decomposition temperature, coefficient of linear thermal expansion, and heat deflection temperature were improved by inclusion of POSS‐glycidyl. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42451.

Exploring the potential of siloxane surface modified nano-SiO2 to improve the Portland cement pastes hydration properties

This paper investigates the potential of siloxane surface modified nano-SiO2 as an admixture capable of modifying heat development and microstructure densification of Portland cement pastes. Two different types of siloxanes were grafted on nano-SiO2 (nS) particles. Calorimetric measurements of Portland cement pastes with 0.3 w/b ratio show that the siloxane functional group clearly interferes on the early age reactions of cement pastes with 0.1 or 0.5 by weight of functionalized nS. In situ soft X-ray transmission microscope images of nS/Ca(OH)2 solutions demonstrate that siloxane cover the nS surface and that the treatment allowed nS particles to last longer on a calcium hydroxide saturated solution before forming C–S–H. The possible reasons of this behavior are discussed, including the matrix densification and C–S–H nano-structure filling. The results indicate a potential use of this hybrid to improve the nanostructure of the cement paste matrix.

Synthesis of Siloxanes Containing Vinyl and Epoxy Group and its Enhancement for Adhesion of Addition-Cure Silicone Encapsulant

Three types of siloxanes containing vinyl and epoxy group, (3-glycidoxypropyl) allyloxydimethoxysilane (GAMS), [2, 2-bis (allyloxymethyl) butoxy] (3-glycidoxypropyl) dimethoxysilane (AGMS) and [3-allyloxy-2, 2-bis (allyloxymethyl) propoxy] (3-glycidoxypropyl) dimethoxysilane (AAGMS) were prepared by the transetherification of 3-glycidoxypropyltrimethoxysilane with allyl alcohol, trimethylolpropane diallyl ether and pentaerythritol allyl ether, respectively. The chemical structures were characterized by Fourier transform infrared (FTIR) spectroscopy and 1H nuclear magnetic resonance (1H-NMR) spectroscopy. GAMS, AGMS and AAGMS were used as adhesion promoter for addition-cure silicone encapsulant (ASE) with a large amount of alumina (Al2O3) as thermally conductive fillers. It was found that the adhesion promoters not only greatly improved the adhesion strength of ASE but also significantly enhanced the mechanical strength of ASE. Among them, AAGMS gave the best adhesion strength and mechanical strength of ASE. The shear strength and tensile strength of ASE were increased from 0.34 and 2.23 MPa to 1.14 and 3.27 MPa with addition of 1.5 phr AAGMS, which was about 335% and 147% higher than that of ASE without adhesion promoter, respectively. The scanning electron microscopy (SEM) results showed that the adhesion promoters could improve the compatibility between Al2O3 particles and ASE matrix. Additionally, the viscosity of ASE with less than 3.5 phr AAGMS did not exceed 5000 mPa•s, which could meet the requirements of electronic encapsulation.

Functional Properties of Novel Metallic Hard Masks

Hard masks play an important role in pattern transfer to the desired substrate in the semiconductor lithography processes. Organic and inorganic type hard masks are used. While most organic hard masks such as carbon and siloxane type are solution spin coated, inorganic type hard masks such as SiON and SiN are either chemical vapor deposited (CVD) or atomic layer deposited (ALD). Future generation of lithography processes require hard masks with higher resistance to fluorinated plasma and materials that can be easily wet stripped after pattern transfer process to prevent dry etch damage to the substrate underneath.The present paper describes formation and functional properties of novel metal oxide hard masks by simple solution spin coating process. These novel metal oxide hard masks offer good etch selectivity and can easily be partially or fully wet strippable using commonly used chemicals in the FABs. The spin coatable composition has good long-term shelf life and pot life stability based on solution LPC analysis and wafer defect studies. The hard mask material absorbs DUV wavelengths and can be used as a spin-on inorganic or hybrid antireflective coating to control substrate reflectivity under DUV exposure of photoresist. At the same time they are transparent at 500-700nm for alignment mark identification and can be spin coatable up to 450nm thickness with good film quality. Some of these metal-containing materials can be used as an underlayer in EUV lithography to significantly enhance sensitivity of the photoresist. Specific metal hard masks are also developed for via or trench filling applications in IRT processes. The materials have shown good coating and lithography performance with a film thicknesses as low as 10 nm under ArF dry or immersion conditions.

Bi-phase ceramic composite using an interpenetrating network

A secondary phase has been reinforced into a porous alumina (Al2O3) matrix using an interpenetrating network (IPN) method to enhance the mechanical properties of the porous matrix. To increase the addition effect of the secondary phase into the Al2O3 matrix, two types of SiO2 precursor were used: tetraethylorthosilicate (TEOS) of the silicate type and polydimethylsiloxane (PDMS) of the siloxane type. The PDMS does not undergo a sol–gel reaction, whereas the TEOS is converted into glass-phase SiO2 by a sol–gel reaction. This means that the siloxane type has a higher conversion ratio of precursor into the glass phase of SiO2 than does the silicate type. The mechanical properties of the composites prepared using TEOS and PDMS without sodium methoxide (NaOMe) have been improved, showing 12.9±5.9 and 9.9±6.4MPa in fracture strength, respectively, and 17.2±4.6 and 15.5±6.9GPa in elastic modulus, respectively, while the mechanical properties of the porous Al2O3 matrix were 6.0±1.2MPa and 8.0±4.0GPa in fracture strength and elastic modulus, respectively. However, the mechanical properties of the composite prepared using PDMS with NaOMe were higher than those of the composite prepared using TEOS with NaOMe, showing 25.3±7.3MPa and 26.3±5.5GPa in fracture strength and elastic modulus, respectively. The increase in mechanical properties was caused by the enhancement of glassification owing to the high conversion ratio of the SiO2 precursor, in the absence of a sol–gel reaction. Consequently, bi-phase composites with reasonable properties have been successfully prepared through the IPN method using inorganic precursors.

Composite binders for precision casting shell molds

The convert mold process has been investigated, focusing on preparation of shell molds using different composite binder systems. The glassification efficiency of binder systems with different SiO 2 precursor structures were investigated in terms of the Si content and dipping time, and the subsequent effects on fracture strength. Two types of the SiO 2 precursor were used: tetraethyl orthosilicate of the silicate type; and hexamethyl disiloxane (HMDS), octamethyl trisiloxane, and polydimethyl siloxane of the siloxane type. Use of the siloxane type precursor does not produce a hydrolysis reaction, whereas the silicate type precursor is converted into SiO 2 by a hydrolysis and condensation reactions during the drying process. The samples based on the siloxane type (except HMDS) have a much higher fracture strength, nominal value of 8 MPa, than that of samples based on the silicate type. This is a result of the enhancement of glassification. When the siloxane is added to the silicate the fracture strength is as high as about 6 MPa, independent of the Si content and dipping time. Results indicate the importance of the reaction mechanism in achieving fracture strength with related to glassification efficiency.

Hybrid Catalysts Based on Carbon Nanotubes and Nanofibres

Hybrid catalysts have been prepared by the immobilization of a Rh complex on carbon nanotubes and nanofibres. To tether the complex, a siloxane type bond has been created by reaction of a trimetoxisilane end of a ligand and -OH phenol type groups on the supports surface. The hybrid catalysts have been tested in the hydrogenation of three different substrates: cyclohexene (as a test for activity), carvone (to analyze the chemoselectivity) and 2-metyhl acetamidoacrylate (to evaluate enantioselectivity, using BINAP as chiral ligand). The obtained results show that the hybrid catalysts are more active than the homogeneous complex. The enhanced activity has been related to a confinement effect, produced as a consequence of the metal complex location inside the tubular structures of the supports. The enantioselectivity is opposite for the heterogenized and the homogeneous complex. Some differences have been found between the properties of catalysts prepared with nanotubes and nanofibres, which have been related to differences in the tube inner diameter.

Properties of iron-based soft magnetic composite with iron phosphate–silane insulation coating

This paper investigates the magnetic and structural properties of iron phosphate-aminosilane soft magnetic composites. FTIR spectra, EDX analysis and distribution maps show that the particle surface layer contains a thin layer of iron-phosphate with high coverage of powder surface. The phosphate layer decreases the loss factor and the imaginary part of permeability, as well as increasing the electrical resistivity and the operating frequencies. This layer, which lowers the electrical resistivity and the loss factor, is decomposed by the annealing treatment. The double-layer insulator increases the electrical resistivity and the operating frequency. The siloxane with high thermal stability does not decompose during the annealing treatment. This type of siloxane increases saturation magnetization, electrical resistivity and permeability but decreases microstrain and coercivity.

Influence of surface treatment of elastomers on their frictional behaviour in sliding contact

To reduce friction of elastomer parts moving against a metal counter body in dry conditions, two different surface treatment techniques were applied on elastomer parts: laser cladding and plasma treatment at atmospheric pressure. Polyamide 11 (PA 11) based coatings were produced on thermoplastic polyurethane (TPU) substrates by laser cladding. During ball-on-disc tribotesting the effect of a PA 11 coating was identical to that of a PA 11 + 9% MoS 2 coating: friction of the TPU substrate was reduced with 40%. The incorporation of 15 wt% PTFE in the PA 11 coating resulted in a further decrease of the frictional force. A reduction of 80% of the frictional force of the TPU substrate was measured. The surface of the coatings before and after tribotesting was analysed. The plasma treatment of HNBR was done using a Plasmaspot ® to form a plasma polymerised coating based on two different types of siloxanes. A reduction of 74–80% of the initial friction coefficient was measured in two different tribotest rig configurations: ball-on-disc and disc-on-disc. The resulting wear tracks were analyzed by SEM and EDX.

Molecularly imprinted polymer grafted on polysaccharide microsphere surface by the sol–gel process for protein recognition

An interfacial organic–inorganic hybridization concept was applied to the preparation of a new spherical imprinted material for protein recognition. The functional biopolymer chitosan (CS), shaped as microsphere and high-density cross-linked, constituted of the polysaccharide core for surface imprinting. After the model template protein, bovine serum albumin, was covalently immobilized by forming imine bonds with the functional amine groups of CS, two kinds of organic siloxane (3-aminopropyltrimethoxysiloxane: APTMS, and tetraethoxysiloxane: TEOS) assembled and polymerized on the polysaccharide–protein surface via sol–gel process in aqueous solution at room temperature. After template removal, the protein-imprinted sol–gel surface exhibited a prevalent preference for the template protein in adsorption experiments, as compared with four contrastive proteins. Bioinformatics methods were also employed to investigate the imprinting process and the recognition effect. The influence of siloxane type, pH, siloxane/water ratio on template removal and recognition selectivity was assessed. Under optimized imprinting conditions, a large quantity of well-distributed pores was observed on the immobilized-template imprinted surface. The surface-imprinted adsorbent offered a fast kinetics for template re-adsorption and could be reused. Compared with the imprinted material prepared with free-template, material prepared with immobilized-template possessed higher adsorption capacity towards template protein. Easy preparation of the described imprinted material, high affinity and good reusability make this approach attractive and broadly applicable in biotechnology for down-stream processing and biosensor.

Comparative study of silanisation reactions for the biofunctionalisation of Ti-surfaces

In the present work, we report on the biofunctionalisation of silanised Ti-surfaces with gelatin. In recent years, a large number of papers have been published about the silanisation of different substrates including Ti-surfaces for biomedical applications. However, a comparative study evaluating the effects of different pre-treatment methods (cleaning and/or oxidation) and the efficiency of different silanisation reactions has to our information not yet been published. Since a clean and reproducible surface is required for studying structure–property relations, all Ti-surfaces were subjected to a three step procedure including a cleaning step, an oxidation step and a silanisation step. XPS analysis and contact angle measurements revealed that the pre-treatment of the Ti samples (cleaning + oxidation) had a drastic effect both on the surface composition and its wettability. A detailed study on the effect of different silanisation parameters indicated that the siloxane concentration, the siloxane type, the solvent and a catalyst affect the coupling efficiency of siloxanes to Ti-surfaces. Stability studies revealed a dependency between the siloxane type and the stability of the siloxane coating against hydrolytic cleavage from a Ti-surface. Since Ti-surfaces modified with a methacrylate containing silane possessed the highest hydrolytic stability, these surfaces were selected for the subsequent immobilisation of methacrylamide-modified gelatin via high energy irradiation induced cross-linking. The present work clearly demonstrates the need of a proper reaction strategy for immobilising ligands on Ti-surfaces.

Synthesis, characterization and surface analysis using dynamic contact angle measurements of graft copolymers: poly(methyl methacrylate)-g-poly(dimethylsiloxane) and poly(methyl methacrylate)-g-poly(trifluoropropylmethylsiloxane)

A series of poly(methyl methacrylate)-g-poly(dimethylsiloxane) and poly(methyl methacrylate)-g-poly(trifluoropropylmethylsiloxane) copolymers have been synthesized via the ‘macromonomer’ method by which monofunctional polysiloxane macromonomers are copolymerized with methyl methacrylate. The graft copolymers have been characterized by gel permeation chromatography, 1H n.m.r. spectroscopy and differential scanning calorimetry. Dynamic contact angle (DCA) analysis afforded advancing and receding water contact angles over 15 days immersion in water. The initially hydrophobic polymer surfaces rapidly rearrange in the presence of water to more hydrophilic surfaces. The effects of varying the amount and type of siloxane in the copolymer on DCA results are discussed. The fouling and fouling release behaviour of coatings formulated from the graft copolymers have been evaluated in Chesapeake Bay. Fouling and fouling release behaviour are discussed in the light of DCA results

Bulk-like Siloxane Links on Silica Surface

A progressive increase in the intensity of the SiOSi bending band at 470 cm -1 in the DRIFT spectrum of silica gel is recorded upon heating in the temperature range 100-400°C. This increase in intensity is attributed to surface siloxanes formed due to condensation of surface hydroxyls which were necessarily too near to each other. Since the newly formed siloxanes showed their bending mode at the same frequency as that of the siloxanes in the bulk, both types of siloxanes are considered similar.