Organosilicon Precursors Research Articles

Comparison of Different Organometallics Towards Electrophilic Aromatic 211At-Astatinations of Highly Reactive Tetrazines.

Organometallics can be used as precursors for electrophilic 211At-statinations. In this report, we compared the potential of aryl trimethylsilanes, -germanes, or -stannanes to be used as precursors to 211At-label highly reactive tetrazines. Tetrazines can be used for pretargeted radioligand therapies or be applied as synthons to radiolabel rapidly and orthogonally a broad set of precursors such as peptides, mAbs or nanomedicines. All precursors could successfully be synthesized and radiolabeled. The reactivity of organogermanium reagents ranged between those of respective organotin and organosilicon precursors. Moreover, organogermanium reagents proved promising for accessing more complex and polar tetrazine scaffolds. In contrast to organotin derivatives, the use of protecting groups could be avoided for organogermanium and -silicon precursors. The developed 211At-labeled tetrazines could be labeled in radiochemical conversions of 60-90%. Organogermanium and -silicon precursors were clearly advantaged as additional deprotection steps could avoided. Reported labeling procedures allow astatinations of highly reactive tetrazines to be used for pretargeted approaches or to applied as highly reactive synthons to label the next-generation of 211At-labeled radiopharmaceuticals.

A sustainable deposition method for diamond-like nanocomposite coatings – Insights into the evolution of atomic structure and properties

Silicon and oxygen-doped hydrogenated amorphous carbon (a-C:H:Si:O), typically termed as diamond-like nanocomposite (DLN), is amongst the most widely adapted coating materials for advanced applications. Traditionally, these coatings are deposited by plasma-enhanced chemical vapor deposition (PECVD) using organosilicon precursors, which not only restrict coating stoichiometry but also have a high environmental footprint. Here, we report the deposition of highly dense and microscopically defect-free a-C:H:Si:O coating using magnetron sputtering as a facile and sustainable deposition method that allows a fine stoichiometry control. Furthermore, we investigate the evolution of the atomic structure and the local-atomic environment when Si, O, and H atoms are successively doped into the amorphous carbon (a-C) matrix. Diffraction and spectroscopic analyses of doped coatings indicate the absence of any long-range order and an atomic-scale composite structure. The results also establish that doping of a-C leads to improved sp3 bonding, formation of Si–O-based networks, and termination of carbon dangling bonds, resulting in increased structural stability. The densification of the coating, combined with improved sp3 character, results in hardness and modulus exceeding those of PECVD-deposited coatings. These findings present a viable potential of magnetron sputtering as a straightforward and greener alternative to traditional PECVD-based methods for producing a promising coating material.

Microstructure, mechanical properties, and wettability of CrN and CrSiCN coatings with graded architectures

Protective CrN-based coatings are of interest for applications requiring a combination of corrosion resistance and toughness. Here, the processing-microstructure-properties relationships for metallic Cr, binary CrN, and quaternary CrSiCN coatings are reported. Hexamethyldisilazane (HMDS) was used as a single-source organosilicon precursor for Si and C during plasma-enhanced magnetron sputtering (PEMS). By varying the availability of reactive species during coating growth, graded coating architectures were produced. Scanning and transmission electron microscopy revealed that as Si and C content increased, the coating microstructure evolved from a coarse, columnar growth structure (0 at.% Si), to a nanocolumnar structure (3 at.% Si), and, finally, to a dense, nanoscale structure (6 at.% Si). Coating surface topography was characterized using optical microscopy and atomic force microscopy. While the CrSiCN coating deposited at the highest HMDS flow rate exhibited the lowest nanoscale surface roughness (Rq = 6.74 nm), it also had the greatest area fraction of microscopic surface defects. Evidence of the formation of secondary Cr2N phases within the graded interlayers of the coatings was acquired from selected area electron diffraction analysis. However, the practical adhesion of the coatings, as evaluated by the Rockwell C indentation test, was not adversely affected. Nanoindentation testing revealed that greater incorporation of Si and C into the CrN-based coatings increased coating hardness from 25.4 ± 1.6 GPa to 30.7 ± 1.8 GPa and decreased apparent elastic modulus from 295 ± 14 GPa to 284 ± 12 GPa. Contact angle goniometry was conducted to determine the wettability of the coatings. It was found that sessile water contact angles decreased from 86.5° ± 1.6° to 77.3° ± 2.1° as coating Si and C content increased.

Vinyl-based interlayers synthesized by variable pulsed plasma for polymer composites

The low-pressure pulsed plasma is a crucial tool for the construction of materials in the form of coatings with variable properties. The pulsed mode is characterized by many parameters such as pulse on-time, off-time, pulse period, pulse frequency, duty cycle, and using the total power, the average power during the pulse can be introduced as the effective power. Based on a pulse period ranging from 2 to 100 ms and a total power of 10–500 W, it is demonstrated that the effective power is the key parameter responsible for the properties of the synthesized coatings independent of the total power. When an organosilicon precursor with a vinyl functional group, this parameter allows the chemical and physical properties of vinyl-based coatings to be controlled over a wide range, allowing to optimize their properties as functional interlayers in polymer composites to control their performance.

A promising method for promoting interfacial adhesion of aramid/rubber composite using atmospheric pressure plasma surface modification

AbstractToday, aramid fibers are well known as a high‐performance and ideal material for reinforcement purposes in rubber product manufacturing including hoses, tires, cables, and conveyors composites. However, surface modification of aramid fiber is necessary to solve poor interfacial adhesion between aramid fibers and the rubber matrix. Accordingly, in the present study, the effect of the surface modification of aramid fibers using atmospheric pressure plasma treatment with different precursors on adhesion to the rubber matrix was investigated. For that, the plasma coating was conducted using argon as the main working gas, and toluene, acetonitrile, tetraethyl orthosilicate (TEOS), and hexamethyldisiloxane (HMDSO) as liquid precursors. The physical–chemical characterization of the layer confirmed the successful deposition of amorphous carbon, amorphous nitride‐carbon, SiO2, and Polydimethylsiloxane (PDMS)‐like coating layers on the surface of aramid fibers by using toluene, acetonitrile, TEOS, and HMDSO as precursors, respectively. Overall, the result showed that the plasma surface modifications with acetonitrile precursor leads to the increase in interfacial adhesion of aramid/rubber composite, while retaining the tensile strength, and flame resistance properties of aramid as original fibers. Notably, the results of this study confirm the potential use of atmospheric pressure plasma for surface modification of aramid yarn to produce functional aramid for use in rubber composites.Highlights The plasma‐coated aramid using HMDSO, TEOS, toluene, and acetonitrile precursors was prepared; and its effect on the tensile properties of aramid fiber as well as interfacial adhesion between aramid/rubber composite was investigated. The positive effect of atmospheric pressure plasma coating using HMDSO precursor on the tensile properties of aramid fiber was revealed. The positive effect of atmospheric pressure plasma coating using toluene and acetonitrile on the interfacial adhesion between aramid/rubber composite was revealed. The positive effect of atmospheric pressure plasma coating using TEOS precursor on the flam resistance property of aramid fiber was revealed. This study provides valuable insights into the effect of the different plasma‐coated organosilicon and hydrocarbon precursors on the interfacial adhesion between aramid/rubber composite.

Evolution of Organometallasiloxanes

The development of organometallasiloxane chemistry from first polymeric systems to individual organometallasiloxanes and functional oligomeric compounds is considered. The structural diversity of organosilicon precursors and the variability of metal-containing components are presented. Synthetic approaches are considered in detail, including those that allow targeted production of organometallasiloxanes of a certain structure. Using the example of organometallasiloxanes synthesized from trifunctional organoalkoxysilanes, methods for the synthesis of unique stereoregular functional cyclosiloxanes and their derivatives are highlighted. Considerable attention is given to the applied aspects of various structure organometallasiloxanes and their derivatives. The state of the art of the chemistry of organometallasiloxanes and their further evolution are evaluated critically.

Aerogel-Like Material Based on PEGylated Hyperbranched Polymethylethoxysiloxane.

Aerogels are a class of materials that have gained increasing attention over the past several decades due to their exceptional physical and chemical properties. These materials are highly porous, with a low density and high surface area, allowing for applications such as insulation, catalysis, and energy storage. However, traditional aerogels, such as pure silica aerogels, suffer from brittleness and fragility, which limit their usefulness in many applications. Herein, we have addressed this problem by using organosilicon compounds, namely polymethylsilsesquioxane derivatives, for the synthesis of aerogel-like materials. Specifically, we have developed a novel approach involving surfactant-free synthesis of microcapsules from partially PEGylated hyperbranched polymethylethoxysiloxane. Due to the highly diphilic nature of these compounds, they readily concentrate at the oil/water interface in aqueous emulsions encapsulating oil droplets. During the subsequent condensation, the organosilicon precursor is consumed for hexane encapsulation (yielding hollow microcapsules) followed by the formation of a continuous condensed phase. Concurrently, methyl groups ensure the hydrophobicity of the resulting materials, which eliminates the need of using additional reagents for their hydrophobization.

New insight into multiple hydrogen-bond networks of functional organosilicas system for collaborative transformation of CO2 under mild conditions

It is challenging to integrate various active species into porous materials in an organized manner to realize efficient and synchronous CO2 adsorption and chemical conversion. Here multiple Lewis base and dual hydrogen bond donor (HBD) units were integrated into an organosilicon precursor, and novel triazine and hydrazo sites co-modified periodic mesoporous organosilicas (THPMOs) were prepared via a simple hydrothermal self-assembly method. The morphological structures of THPMOs with different contents of active sites were characterized. The THPMOs displayed high BET surface areas (699–876 m2/g) and favorable low-pressure CO2 adsorption capacities at 273 K. When combined with tetrabutylammonium iodide (TBAI), they promoted the model cycloaddition of CO2 and propylene oxide (PO) effectively. By regulating the molar ratios of organosilica precursors, the obtained THPMO-25 catalyzed this reaction and produced a 96 % propylene carbonate (PC) yield under mild conditions. Moreover, the THPMO-25 was applicable using various epoxides and also exhibited satisfactory structural stability during recycling. Combined with theoretical calculations, an insight into the reaction mechanism involving multiple hydrogen-bond interactions was provided. The robust and recyclable nanomaterials offer an attractive approach for CO2 adsorption and subsequent chemical synthesis of organic carbonate.

Selection of precursors of safe silica-based fireproof coatings for textile materials

The selection of the inorganic precursor SiO2 as the main component of the simplified safe technology for obtaining flame-retardant coatings on textile materials was carried out. By thermo-graphic research of organic and inorganic SiO2 precursors, performed on an OD-102 deri-vatograph under conditions of heating at a rate of 10ºС/min in an air environment, the processes of decomposition of the coating that occur during the action of fire were investigated. Gels based on inorganic precursors produced by industry (silica sol, silica gel) and silicic acid, which was obtained by the exchange reaction of an aqueous solution of sodium silicate of liquid glass and acetic acid, were studied for the comparative characteristics of thermal destruction of coatings. As organic precursors of SiO2, gels of ethyl silicate-32 and methyltriethoxysilane were studied, which were obtained by hydrolysis of organosilicon compounds in an acidic water-alcohol medi-um with subsequent polycondensation of the hydrolysis products. The effect of temperature on the nature of thermal destruction of silica gel, silica sol, silicic acid and organosilicon gels of ethyl silicate and methylotriethoxysilane was investigated. It is shown that inorganic precursors differ favorably from organosilicon precursors in terms of the overall thermal effect during their de-composition, mass loss during heat treatment, and the rate of change of this parameter. Consider-ing that, in addition to total mass loss, the increase in mass loss during heating is less than 1 % in compositions based on inorganic precursors, it is possible to use all three types of inorganic pre-cursors, but from the point of view of acidity and safety of impregnation compositions, prefer-ence is given to silicic acid obtained by the exchange reaction of silicate sodium liquid glass with acetic acid.

Stable a-CSi:H films with a wide range of modulus of elasticity and low internal stress

Amorphous hydrogenated silicon carbide (a-CSi:H) thin films were deposited by plasma-enhanced chemical vapor deposition using tetravinylsilane as organosilicon precursor. The mechanical properties of the thin films, namely the modulus of elasticity, hardness, and elastic recovery parameter, were determined by nanoindentation, as well as the internal stresses by scanning electron microscopy and optical profilometry. It was found that the modulus of elasticity increased from 10 to 137 GPa with increasing power (2–150 W) delivered to plasma, while the hardness increased from 1.5 to 14.5 GPa. This improvement in mechanical properties with increasing energy delivered to the plasma is related to greater fragmentation of the precursor which led to an increase in the crosslinking of the material network. The compressive internal stresses in the films reached low values of −0.04 to −0.2 GPa with increasing power (2–75 W) and an acceptable −0.5 GPa for 150 W. The elastic recovery parameter decreased with increasing power from 0.86 to 0.64, i.e., the thin films behaved more plasticity with increasing power. The modulus of elasticity and hardness were investigated in terms of the aging of the films for a period of 6 years when samples were stored under ambient conditions. No significant changes in these properties were observed. However, minor changes were observed in the indentation curves obtained for the 2 W and even less for the 10 W samples. Small changes were then also observed for the elastic recovery parameter, whose value for these samples partially decreased which may be related to postdeposition oxidation. No changes in internal stress values over time were observed. The wide range of mechanical properties of stable a-CSi:H films with low internal stress increases their application potential and their wide use as materials with tailored properties from polymer-like to tough material.

Synthesis of mesoporous silica using a mineral silica source

AbstractMesoporous silica has been applied in catalysis, separations, and drug delivery. It has generally been made using organosilicon precursors such as tetraethyl orthosilicate. For sustainability, it is necessary to find readily accessible mineral sources for making mesoporous silica. In this work, we demonstrate the successful synthesis of mesoporous silica with 10 nm average pore size using the mineral forsterite (Mg2SiO4) as a silica source, providing a potentially cheaper and more Earth‐friendly route to making technologically important porous silica materials. Pure forsterite was synthesized by a solid‐state chemistry route at 1000°C and underwent dissolution–reprecipitation in aqueous hydrochloric acid containing the soft template surfactant, Pluronic P123. Variations of initial reaction pH (−0.2 to 0.6), reaction time (12–24 h), reaction temperature (50 to 90°C), and silica precursor (forsterite and fumed silica) were performed. The mesoporous silica aged at 70°C for 24 h had the highest porosity, with a surface area of 735 m2/g and a pore volume of 1.4 ml/g, comparable to mesoporous silica made using conventional starting materials. This novel geomimetic synthesis route supports the possibility of analogous formation of structured (mesoporous or zeolitic) silica in nature under abiotic or prebiotic conditions.

Kinetics driving nanocomposite thin-film deposition in low-pressure misty plasma processes

Mist-assisted methods have recently attracted much attention for plasma deposition in high-quality (multi)functional thin films. However, very little is known on plasma interactions with misted colloidal solutions and their role in plasma process kinetics. Time-resolved optical diagnostics have been carried out to study the deposition of TiO2–SiO2 nanocomposite thin films in low-pressure oxygen-argon plasmas with organosilicon precursors and TiO2 suspensions. Each pulsed injection of the dispersion was followed by a pressure rise due to solvent evaporation. This caused a significant reduction in the electron temperature and density, which mitigated matrix precursor fragmentation and SiO2 deposition as TiO2 nanoparticles were supplied to the film. Comparing injections with and without nanoparticles, misty plasma effects were dominated by plasma droplets rather than plasma-nanoparticle interactions. Successive matrix-rich and nanoparticle-rich deposition steps were confirmed by in situ spectroscopic ellipsometry.

Area selective atmospheric pressure PECVD of organosilicon precursors: Role of vinyl and ethoxy groups on silicon oxycarbide deposition patterns - A case study

An atmospheric pressure Dielectric Barrier Discharge plasma torch was used to perform selective area plasma enhanced chemical vapour deposition of four organosilicon precurors: Triethylvinylsilane (VTES), Vinyltriethoxysilane (VTEOS), Tetraethoxysilane (TEOS) and Tetraethylsilane (TES). The precursors were chosen in such a way that they differ only by the presence or absence of vinyl and/or ethoxy groups. Experimentally, major differences have been observed on the deposition speed, coating patterns and thin film composition. Precursor with vinyl group has confined deposition at the central region of plasma torch, in contrast precursor with only ethoxy groups has circular deposition in the periphery region of plasma torch, and precursors with both the vinyl and ethoxy groups has deposition at both locations. A detailed chemical analysis revealed the film composition to be silicon oxycarbide (SiOxCyH) with high content of carbon for the central region's coating whereas the peripherical coating is close to silica like (SiOx) with a minuscule carbon content. Coatings patterns and composition have been investigated in the light of gaseous flows mixing obtained from computational Fluid Dynamic (CFD) simulation. A strong correlation is evidenced for central SiOxCyH deposition of vinyl containing precursors, to the high concentration of precursor. Whereas the peripheral SiOx deposition of ethoxy containing precursors corresponds to high concentration of plasma species. Furthermore, the role of reactive plasma species on the underlying deposition mechanisms has been identified as crucial and has been purposed as the driving factor.

Superhydrophilic organosilicon plasma modification on PES membrane for organic dyes filtration

Plasma-based surface modification is perceived as environmental friendly and green method because the absence of harmful solvent and capable of introducing diverse functional groups on the surface. In this paper, we propose a surface modification by plasma polymerization using organosilicon precursor tetraethyl orthosilicate (TEOS) on PES membrane for the entrapment of water pollutants especially organic dye (Congo Red). The superhydrophilic surface was obtained by optimizing the plasma deposition process parameters with TEOS as a precursor and oxygen as the gas carrier to increase the amount of SiOSi functional groups. Subsequently, the chemical composition of the coatings was evaluated using Attenuated Total Reflectance Fourier Transform Infrared (FTIR/ATR) spectroscopy and FESEM-EDX. As a result, we observed a significant improvement in terms of hydrophilicity, pure water flux, rejection, and anti-fouling properties on the modified membrane especially for the deposition of TEOS-O2 with 20 W compared to the untreated sample. The outcome from the proposed plasma modified membrane using organosilicon precursor could be useful to further improve the performance of the commercial filtration membrane especially for the removal of organic dye without changing its fabrication process.

Facile low-temperature route toward the development of polymer-supported silica-based membranes for gas separation via atmospheric-pressure plasma-enhanced chemical vapor deposition

The use of inexpensive porous polymers instead of conventional ceramics to support silica-based membranes can potentially minimize the cost of membrane synthesis. To develop polymer-supported silica-based membranes, lowering the high synthesis temperature of the silica-based top layer is essential. In this study, we explore the application of atmospheric-pressure plasma-enhanced chemical vapor deposition (AP-PECVD) for synthesizing polymer-supported silica-based membranes. The deposition of a continuous silica-based layer on an asymmetric polysulfone ultrafiltration membrane using hexamethyldisiloxane as an organosilicon precursor was achieved at ambient temperature and pressure via AP-PECVD. The gas permeation properties of the AP-PECVD-derived polymer-supported membranes strongly depended on the deposition duration, as prolonged deposition could reduce the remaining defects by covering the entire surface of the support with the plasma-deposited layer. The membranes showed increased selectivities for H2/N2 and H2/SF6 from 2.9 to 9.5, and from 4.5 to 184, respectively, exhibiting gas permeation dominated by molecular sieving. The present study demonstrates that AP-PECVD is a promising strategy for the fabrication of polymer-supported silica-based membranes for gas separation.

Modification of Ceramic Membranes with Carbon Compounds for Pharmaceutical Substances Removal from Water in a Filtration-Adsorption System.

The aim of this work is to develop a new type of carbon-ceramic membranes for the removal of pharmaceutical substances from water. The membranes were prepared by the chemical modification method using an organosilicon precursor—octadecyltrichlorosilane (ODTS). Graphene oxide, multi-walled carbon nanotubes with carboxylic groups, and single-walled carbon nanotubes were used in the modification process. The filtration properties and adsorption properties of the developed membranes were tested. In order to characterize the membrane, the water permeability, the change of the permeate flux in time, and the adsorbed mass of the substance were determined. Additionally, the surface properties of the membranes were characterized by contact angle measurements and porosimetry. The antibiotic tetracycline was used in the adsorption tests. Based on the results, the improved adsorption properties of the modified membrane in relation to the unmodified membrane were noticed. Novel ceramic membranes modified with MWCNT are characterized by 45.4% removal of tetracycline and permeate flux of 520 L·h·m−2·bar−1. We demonstrated the ability of modified membranes to adsorb pharmaceuticals from water streams that are in contact with the membrane. Novel membranes retain their filtration properties. Therefore, such membranes can be used in an integrated filtration–adsorption process.

Obtaining of TiSiCN coatings by anodic evaporation of titanium and decomposition of hexamethyldisilazane in a low-pressure arc discharge

The method of TiSiCN-coatings deposition by anodic evaporation of Ti and decomposition of an organosilicon precursor (hexamethyldisilazane) in a low-pressure (∼1 mTorr) nitrogen-argon arc discharge with a self-heated hollow cathode is investigated. The plasma composition was analyzed by optical emission spectroscopy. TiSiCN coatings with a thickness of up to 10 microns and a hardness of up to 30 GPa were obtained in 1.5 hours at a temperature of 400°C.

Deposition of halogen-free flame retardant and water-repellent coatings on firwood surfaces using the new version of DBD

In this study, a rapid, cost-effective, and environmentally-friendly approach was developed for the production of high-performance thin films to reduce the flammability of firwood as well as controlling its wettability. In this regard, a hydrophobic and flame-resistant organic thin coating was prepared through halogen-free plasma polymerization using a novel version of dielectric barrier discharge (DBD) apparatus optimized at atmospheric pressure. The home-made device does not require expensive vacuum instruments and operates in open-air using an organosilicon precursor (hexamethyldisiloxane (HMDSO)) as a liquid monomer. The morphology, composition, and chemical structure of the deposited polydimethylsiloxane-like (PDMS-like) thin films were comprehensively evaluated through FESEM, AFM, XPS, FTIR, EDX, and DTA-TG. The samples showed remarkable cross-linking. This innovative strategy made it possible to achieve the desired characteristics within a concise treatment time. The modifications include the increase in the static contact angle of super-hydrophilic firwood surfaces to 137.73°, enhancement of the surface roughness from 573 pm to 22.5 nm, and a significant reduction in the maximum rate of wood thermal decomposition from 0.94 to 0.65 mg min−1. Applying a creative and simple approach combining the image processing method with the heater test indicated that plasma modification of the wood surfaces improved their thermal stability without altering their aspect ratio or color surface. Therefore, the plasma-synthesized PHMDSO layers prepared by this device could be a promising candidate for fire retardancy and water repellency applications.

Multi-pass deposition of organosilicon-based superhydrophobic coatings in atmospheric pressure plasma jets

Atmospheric-pressure plasma polymerization of organosilicon precursors such as hexamethyldisiloxane is a well-known process used in the development of SixOyCz thin films on various substrates in different plasma configurations. Typically, long treatments or multi-pass treatments are used to achieve a sufficient thickness. However, the effects of multiple deposition passes on surface properties are rarely considered. In this paper, the development of a superhydrophobic organosilicon-based coating on pre-treated micro-roughened Al-6061 substrates through multiple deposition passes with an atmospheric-pressure plasma jet is reported. It is shown that besides the expected effect on coating's thickness, multiple passes of plasma deposition can also alter surface morphology and surface chemistry through a mechanism similar to the activation of organosilicon substrates with oxygen-containing plasmas. While the increase in coating thickness enhances coating stability in aggressive conditions, the rise of oxygen content reduces the hydrophobic behaviour of the coating.

Thin SiNC/SiOC Coatings with a Gradient of Refractive Index Deposited from Organosilicon Precursor

In this work, optical coatings with a gradient of the refractive index are described. Its aim was to deposit, using the RF PECVD method, films of variable composition (ranging from silicon carbon-oxide to silicon carbon-nitride) for a smooth change of their optical properties enabling a production of the filter with a refractive index gradient. For that purpose, two organosilicon compounds, namely tetramethyldisilazane and hexamethyldisilazane, were selected as precursor compounds. The results reveal better optical properties of the materials obtained from the latter source. Depending on whether deposited in pure oxygen atmosphere or under conditions of pure nitrogen, the refractive index of the coatings amounted to 1.65 and to 2.22, respectively. By using a variable composition N2/O2 gas mixture, coatings of intermediate magnitudes of “n” were acquired. The optical properties were investigated using both UV-Vis absorption spectroscopy and variable angle spectroscopic ellipsometry. The chemical structure of the coatings was studied with the help of Fourier transform infrared and X-ray photoelectron spectroscopies. Finally, atomic force microscopy was applied to examine their surface topography. As the last step, a “cold mirror” type interference filter with a gradient of refractive index was designed and manufactured.