Structure Of Polysiloxane Research Articles

Machine‐learning interatomic potentials for pyrolysis of polysiloxanes and properties of SiCO ceramics

AbstractWe present machine‐learning interatomic potentials (MLIPs) for simulations of Si–C–O–H compounds. The MLIPs are constructed from moment tensor potentials (MTPs) and were trained to a library of configurations that included polysiloxane structures, hypothetical crystalline and amorphous SiCOH structures, and trajectories of Si–C–O–H systems obtained via ab initio molecular dynamic (aiMD) simulations at elevated temperatures. Passive, active, and hybrid learning strategies were implemented to develop the MLIPs. The MLIPs reproduce vibrational properties of polymers and SiCOH structures obtained from aiMD simulations, thus providing a tool to identify chemical units and distinct structural characteristics through their vibrational properties. Simulations of the polymer‐to‐ceramic transformation show the development of mixed tetrahedra in SiCO ceramics and align with experimental observations. Million‐atom simulations for several nanoseconds highlight the precipitation of graphitic nanosheets from a carbon‐rich SiCO precursor. Atomistic simulations with the MLIPs deliver details of chemical reaction mechanisms during the pyrolysis of polysiloxanes, including methane abstraction and Kumada‐like rearrangements that transform the siloxane backbone. While the MLIPs still leave room for systematic improvement, they deliver simulations with “density functional theory (DFT)‐like” quality at low and high temperatures.

Ultrathin polyorganosilica membranes synthesized by oxygen-plasma treatment of polysiloxanes for H2/CO2 separation

Oxygen plasma treatment of polydimethylsiloxane (PDMS) induces an ultrathin polyorganosilica (POSi) layer (<10 nm) on top of a PDMS membrane, leading to excellent H2/gas separation properties and providing a rapid and scalable way to fabricate robust silica membranes compared with conventional high-temperature and time-consuming sol-gel methods. Here, we thoroughly investigate POSi membranes derived from poly (dimethylsiloxane-co-methylhydroxidesiloxane) (poly (DMS-co-MHOS)) containing -SiOH groups that can be more easily converted to silica networks than the -SiCH3 in PDMS. The effect of the polysiloxane structure and plasma treatment conditions (including plasma generating powers, oxygen flowrate, chamber pressure, and treatment time) on the silica chemistry, structure, and H2/CO2 separation properties are systematically determined to derive structure/property relationships. An optimized membrane exhibits H2 permeance of 880 GPU and H2/CO2 selectivity of 67 at 150 °C, superior to state-of-the-art polymeric membranes. The membrane retains H2/CO2 selectivity as high as 46 when challenged with simulated syngas containing 2.8 mol% water vapor at 150 °C, demonstrating the potential of these POSi membranes for practical applications.

Toward understanding the cross‐linking from molecular chains to aggregates by engineering terminals of supramolecular hyperbranched polysiloxane

AbstractCrosslinking thermosets with hyperbranched polymers confers them superior comprehensive performance. However, it still remains a further understanding of polymer crosslinking from the molecular chains to the role of aggregates. In this study, three hyperbranched polysiloxane structures (HBPSi‐R) are synthesized as model macromolecules, each featuring distinct terminal groups (R denotes amino, epoxy, and vinyl groups) while similar molecular backbone (Si‐O‐C). These structures were subsequently copolymerized with epoxy monomers to construct interpenetrating HBPSi‐R/epoxy/anhydride co‐polymer systems. The spatial molecular configuration and flexible Si‐O‐C branches of HBPSi‐R endow them with remarkable reinforcement and toughening effects. Notably, an optimum impact strength of 28.9 kJ mol−1 is achieved with a mere 3% loading of HBPSi‐V, nearly three times that of the native epoxy (12.9 kJ mol−1). By contrasting the terminal effects, the aggregation states and crosslinking modes were proposed, thus clarifying the supramolecular‐dominant aggregation mechanism and covalent‐dominant dispersion mechanism, which influences the resulting material properties. This work underscores the significance of aggregate science in comprehending polymer crosslinking and provides theoretical insights for tailoring material properties at a refined molecular level in the field of polymer science.

Polysiloxane/Poly(vinylidene fluoride)‐co‐Hexafluoropropylene Polymer Blend‐based Lithium‐Ion Conducting Polymer Electrolytes for Room‐Temperature Lithium‐Metal Batteries

AbstractTo harness the synergistic effect of different polymer chains, poly(methyl(2‐(tris(2‐H methoxyethoxy)silyl)ethyl)siloxane)) grafted with Si‐tripodant centers (2550EO) known for their flexible structure was physically blended with poly(vinylidene fluoride‐co‐hexafluoropropylene (PVdF‐HFP). Here, 2550EO containing varying amounts of amide salts (LiF(SO2CF3)2 (LiTFSI)) was used as the main matrix. PVdF‐HFP was used in concentrations of up to 30 % to increase the film‐forming ability of 2550EO/LiTFSI, and a series of solid polymer electrolyte (SPE) membranes were prepared. After incorporating the blended SPE with a minute amount of organic carbonates (only 15 wt%), the electrochemical features, such as Li+ conductivity and transference number (tLi+), significantly increased. For example, a tLi+ of 0.42 and ionic conductivities of 0.64 and 0.3 S cm−1 at 60 °C and 25 °C, respectively, were achieved. In addition, the electrochemical stability exceeded 5 and 4.8 V at 25 °C and 60 °C, respectively. Thus, a high Li/LiFePO4 battery performance with high coulombic efficiencies exceeding 96 % and 98 % at 60 °C and 25 °C were achieved at 0.1 C, respectively. This was due to the superiority of the polysiloxane structure over its organic counterpart, attributed to its highly flexible backbone, high segmental mobility, and outstanding thermal and chemical stability.

Silicon Oxycarbide Coatings Consisting of Defined Bottom-Up-Grown Nanostructures.

Silicon oxycarbide (SiOC) materials have arisen in the past few decades as a promising new class of glasses and glass-ceramics thanks to their advantageous chemical and thermal properties. Many applications, such as ion storage, sensing, filtering, or catalysis, require materials or coatings with high surface area and might benefit from the high thermal stability of SiOC. This work reports the first facile bottom-up approach to textured high surface area SiOC coatings obtained via direct pyrolysis of polysiloxane structures of well-defined shapes, such as nanofilaments or microrods. This work further investigates the thermal behavior of these structures by means of FT-IR, SEM, and EDX up to 1400 °C. The rods shrink in volume by ≈30% while their aspect ratio remains unaffected by pyrolysis until at least 1100 °C. The nano-sized filaments show signs of viscous flow already at a comparably low temperature of 900 °C which is very probably due to the nano-size effect. This might open a way to experimentally study the size-effect on the glass transition temperature of oxide glasses, an experimentally unexplored but very relevant topic. These structures have great potential, for example, as ion storage materials and supports in high temperature catalysis and CO2 conversion.

Progress in Polymer-Ceramic Hybrid Antifouling Coatings

Simultaneous realization of superior mechanical and antifouling properties is critical for a coating. The use of stereoscopic polysiloxanes in place of linear polysiloxanes to fabricate antifouling coatings can combine properties of organic and inorganic materials, i.e., they can exhibit both high hardness and wear resistance from inorganic components as well as the flexibility and tunability from organic components. This strategy is used to prepare hard yet flexible antifouling coatings or polymer-ceramic hybrid antifouling coatings. In this mini-review, we report the recent advances in this field. Particularly, the effects of stereoscopic polysiloxane structures on their mechanical and antifouling properties are discussed in detail.

Identification of radiation degradation products of soluble fraction of silicone foams

It is important to understand the radiation degradation process of silicon foam in radiation aging. Past researches studied the irradiation induced change of mechanical properties. However, the mechanism of micro-degradation is still unclear. In this study, we took a simple pre-treatment of silicone foams with toluene immersion before irradiation. And the results showed that toluene immersion was the key to remove the non-cross-linked oligomers that would interfere with the identification of degradation products. After irradiation, the silicone foams were re-soaked in deuterated toluene solution, and the degradation products were analysed by 1H-NMR, XPS and GPC. The main degradation product of two kinds of silicone foams (methyl vinyl silicone and methyl phenyl silicone) was identified as polysiloxane structures. And the polymerization degree of polysiloxane structures decreased when the irradiation dose increased from 100 kGy to 500 kGy. Theoretical calculations suggested a gradual degradation process, which was in accordance with experiment results.

Antireflective laser coating with improved mechanical property and organic-contaminant resistance for high-power laser application

Mono-layer silica-based antireflective laser coating with modulated structure has been designed and fabricated, in which cross-linking network structure of polysiloxane was prepared as backbone and porous silica spheres (PSSs) were inserted to create interior porosity. Cured polysiloxane provided dense structure that could both prevent the invasion of volatile organic compounds (VOCs) and improve the mechanical property of this coating, while PSSs endowed this coating with proper porosity to adjust its refractive index and relax the high-power laser energy. With certain structure modulation, excellent transmission and laser-damage resistance of this coating at 355 nm (for the application in high-power laser system) and 1064 nm (for the application in laser-guided component) was both achieved. Meanwhile, the hardness of this coating increased significantly compared with that of the conventional porous silica coating. In addition, qualified VOCs endurance of this coating was also proved, which effectively extended the lifetime of such coating.

“Aerogel-like” polysiloxane-polyurethane hybrid foams with enhanced mechanical and thermal-insulating properties

New organic-inorganic polyurethane-based hybrids with enhanced mechanical properties and thermal insulation properties are reported. Polyurethane-based hybrids are characterized by the intimate interactions of their inorganic and organic co-networks and prepared by sol-gel approach, have exhibited properties exceeding those of polyurethane foams, e.g. enhanced thermal stability, durability and thermal insulating effectiveness. However, mechanical properties have previously been poor. Here, new porous organic-inorganic materials consisting of a polyurethane network modified by in-situ formation of aerogel-like polysiloxane domains, were developed. They exhibit a multiscale-porosity which enhances the insulation, mechanical and thermal properties. The synthesis was performed through a novel stepwise process consisting of: preparation of a siloxane precursor based on methyl-triethoxysilane and tetraethoxysilane; functionalization of traditional polyol for polyurethane foams with 3-(triethoxysilanepropyl)isocyanate as coupling agent; use of suitable catalysts and silicone surfactants; and foaming with methylene-di-isocyanate compound. The siloxane precursors and coupling agent led to formation of “aerogel-like” polysiloxane domains within the walls and struts of the polyurethane foams. The synthesis method enabled increased incorporation of the “aerogel-like” polysiloxane structures into the foams, compared to literature, with 20 wt% SiO2, reducing thermal conductivity of the hybrid foams 30% compared with pristine polyurethane, in addition to significant improvement in thermal stability and mechanical properties.

An efficient approach to strengthen polyvinyl alcohol physical hydrogel via in situ growing NH2-decorated polysiloxane structures

This study aims to reveal a novel approach to synthesize high strength polyvinyl alcohol (PVA) physical hydrogel through the freezing-thawing method, with γ-aminopropyl triethoxysilane agent as an auxiliary factor. It was shown that the synthesized PVA-based hydrogels had high water content, excellent mechanical properties, and good biocompatibility. The saline agent γ-aminopropyl triethoxysilane in PVA solution was hydrolyzed and polymerized into NH2-decorated polysiloxane structures, which could be anchored to the porous PVA network and acted as a very effective hydrogen bond acceptor/donor, and thereby arousing a large increase in strength and toughness of PVA hydrogels. Meanwhile, the hydrophobic polysiloxane structures also increased the crystal cross-linking of PVA network and promoted a well-distributed porous PVA network. This work provides a simple and efficient route to synthesize high strength PVA-based physical hydrogel with desirable structure and properties.

Combined use of methacrylate/epoxy functionalized silanes for tuning of hyperbranched polysiloxane structure

In this work, three hyperbranched polysiloxanes with methacrylate (HSiM), epoxy (HSiG) and methacrylate/epoxy groups (HSiMG) were prepared through the hydrolysis of γ-glycidoxypropyltrimethoxysilane (γ-GPS), γ-methacryloxypropyltrimethoxysilane (γ-MPS) and their binary blends. The results indicated that methacrylate groups could accelerate the condensation reaction, thus producing more branching sites with a branching degree of 0.67 for HSiMG. In addition, the effects of terminal groups on the microstructural and thermal properties of the post-cured hyperbranched polysiloxanes were evaluated. Consequencely, the UV-cured HSiM produced more cracks at a higher temperature due to a tighter crosslinked structure. The thermal-cured HSiG decomposed at a lower temperature. While the dual-curing PHSiMG had a more stable structure and relatively excellent thermal stability, based on sequential free-radical photopolymerization and epoxy anionic polymerization. Thus, this work provides a promising approach for structural design and optimization of the polysiloxane.

Structure of vinyl polysiloxane on properties of polyacrylates film and its pigment printing application

Polysiloxane is a promising modified material due to its good hydrophobicity and toughness, but it suffers from serious uneven distribution and migration during film formation process which gradually lead to the destruction of the hydrophobic structure. A novel silicon-modified copolymer with different molecular weight and vinyl content was synthesized to overcome this problem: an appropriate amount of double bonds between the polysiloxane backbone ensures uniform distribution. Moreover, a multicrosslinked network binder was prepared by miniemulsion polymerization of the polyacrylate copolymers and polysiloxane. Unlike the common crosslinked network of an uneven distribution and migration of silicone backbone, the polysiloxane with suitable crosslinking degree and molecular weight could be effectively distributed evenly during the film formation process. As a result, a better hydrophobicity and toughness performance (89.7° ± 0.5°, 2500% elongation at break) was achieved with this novel poly(methylvinylsiloxane) with 11,024 g/mol at 0.804 mmol/g vinyl content. The product was applied to pigment printing with better wet rubbing fastness and soft handle compared with the unmodified polyacrylates binder. The DSC, SAXS, and XPS indicated that high molecular organosilicon chain and moderate vinyl content were prone to phase separation and obviously shifted onto the surface of film, enriching a uniform organosilicon layer, which played a vital role in the surface hydrophobicity and mechanical properties.

Synthesis of a benzoxazine monomer contained hyperbranched polysiloxane and the characteristics of its polymer alloys blend with bismaleimides

A novel benzoxazine monomer contained hyperbranched polysiloxane structure (HBPSi-BOZ) was synthesized via a solvent process based on the polyformaldehyde, aniline, and a new hyperbranched polysiloxane with terminal amino groups (HBPSi-NH2). The HBPSi-BOZ was then used as modified phase to blend with bismaleimides (BMIs) resin, and a polymer alloy HBPSi-BOZ/BMI was successfully prepared. The thermal resistant properties, mechanical properties, and tribological properties of HBPSi-BOZ/BMI resins with different contents of HBPSi-BOZ prepared were researched to get an optimal ratio. The thermogravimetric analysis was also carried out to study the polymerization process and stability of HBPSi-BOZ/BMI resins. The results showed that as the thermal resistance increased, the wear resistance and mechanical properties of HBPSi-BOZ/BMI resins were also enhanced.

Pyrenyl-Functionalized Polysiloxane Based on Synergistic Effect for Highly Selective and Highly Sensitive Detection of 4-Nitrotoluene.

4-Nitrotoluene (NT) is an important intermediate for the manufacture of dyes, agricultural chemicals, medicaments, and synthetic fibers. But its wide use has resulted in a series of ecological problems and health issues due to high toxicity, mutagenicity, and carcinogenicity. However, no fluorescent probes with high selectivity and high sensitivity to NT has been reported yet, and the current probes usually prefer to detect multi-nitrosubstituted nitroaromatic compounds (NACs) including 2,4,6-trinitrotoluene and 2,4,6-trinitrophenol. Herein, we report a series of pyrene-functionalized polysiloxanes with high selectivity and high sensitivity to NT. Pyrene was introduced into polysiloxane through a carbon-carbon double bond, and the formed rigid side-chain fluorophore and flexible backbone structure of polysiloxane provide an ideal platform for the highly selective detection of NT. We further explored the possible response mechanism and speculated that the high selectivity and high sensitivity were derived from the synergistic effect between steric hindrance and dipolar interaction. In addition, paper sensors based on the obtained fluorescent materials were fabricated and change in their high sensitivity and visible fluorescence indicated that the paper sensor is a simple testing tool for portable and visual detection of NT. Furthermore, the design strategy in this work provides a novel synthetic route to synthesize other fluorescent probes with unique selectivity to NACs detection.

Enhanced mechanical properties of polyacrylamide/chitosan hydrogels by tuning the molecular structure of hyperbranched polysiloxane

Hyperbranched polysiloxane (HSi) molecules with tunable molecular structure were synthesized and served as a novel crosslinker for fabricating polyacrylamide/chitosan (PCH) hydrogels. Various characterizations demonstrated that HSi molecules with tunable bi-functional vinyl and epoxy groups were successful prepared and utilized to optimize the network architecture and interactions of polymer chains. Benefiting from the structure of bi-functional crosslinker, PCH hydrogels demonstrated remarkably improved mechanical properties, superior to that of conventional crosslinker or HSi with single vinyl or epoxy group. A tensile strength of 302 kPa, elongation at break of 2263%, and toughness of 3.85 MJ·m–3 can be achieved by optimizing the molecular structure and content of HSi with bi-functional group (e.g. ratio of vinyl/epoxy = 0.68). Additionally, such hydrogels showed outstanding antifatigue ability to withstand cyclic compressive tests. Based on the structure observation and analysis, the improved mechanical properties are likely derived from the combination of homogeneous and strong polymer network and improved interactions of polymer chains (e.g. covalent and hydrogen bonds). Approaches in this study may inspire the design and development of novel crosslinker for fabricating mechanically robust hydrogels.

Cold remote plasma modification of wood: Optimization process using experimental design

A Cold Remote (N2 + O2) Plasma (CRNOP) process was used in order to create new surface properties on various wooden samples. Two applications were studied and optimized using experimental design. The first one involved samples (fir, pine, beech and oak) treated by the CRNOP in order to increase their impregnability evaluated by dynamic wetting and water absorption measurements. In the best conditions, water absorption was increased by 1.8; 1.9; 2.0 and 5.1 for fir, pine, oak and beech, respectively. The second application involved a plasma polymerization of 1,1,3,3, tetramethyldisiloxane induced by the CRNOP in order to create a superhydrophobic coating on beech sample previously treated by the CRNOP. In optimal conditions, a contact angle equal to 160° could be reached. FTIR spectroscopy give evidence for Si-O-Si, Si-O-C and Si(CH3)n bands in a polysiloxane structure.

Effect of Polysiloxanes on Roughness and Durability of Basalt Fibres⁻Reinforced Cement Mortar.

The influence of roughness and the way it affects the adhesion properties and surface free energy (SFE) of polysiloxanes hydrophobised basalt fibres–reinforced cement mortars were determined in this article. The physical properties of mortars were investigated in the experimental part, which also explored the impact of hydrophobisation and basalt fibres (BF) addition on SFE, frost resistance, contact angle (CA), and roughness. A device capable of calculating all parameters was used to indicate the surface roughness and 3D topography. Prior to and after conducting surface and weight hydrophobisation, the contact angle of mortars was specified. Subsequently, it was used for carrying out SFE calculation by means of Neumann’s method, enabling us to characterize the adhesion properties and wettability of mortars. The research indicated that the surface roughness was substantially decreased, in turn raising the frost resistance. The corrosion resistance drops when the surface roughness, water absorption, and number of fibres in the mortar increase. The SEM images presenting the structure of polysiloxane coating and mortars were provided.

Digital light processing of ceramic components from polysiloxanes

Additive manufacturing using photocurable polymers is one method to answer the increased demand of ceramic structures with complicated morphology by fabricating ceramic parts with high resolution and good surface quality. We introduce here a new method to fabricate SiOC ceramic structures by utilizing a simple physical blend between two different preceramic polysiloxanes, one providing photosensitive acrylate groups while the other one a high ceramic yield. Different blend ratios have been realized and respectively optimized concerning the printing additives and setting times to fabricate exact replications of highly complex polysiloxane structures by Digital Light Processing. After pyrolysis, a uniform, homogenous shrinkage was observed yielding dense, pore- as well as crack-free SiOC ceramics. By adjusting the ratio between the different polysiloxanes, parameters such as the ceramic yield, shrinkage, chemical composition and resolution after pyrolysis could be tailored in a wide range of values.

Monitoring structural evolution of organosilicate species during sol–gel processes by electrospray ionization mass spectrometry

Electrospray ionization mass spectrometry (ESI-MS) has been employed to study species distribution in controlled acid-catalyzed hydrolysis and condensation of (3-chloropropyl)trimethoxysilane (CPTMS), which is frequently used in the synthesis of hybrid silica-based materials. The conditions of analysis for reaction products, i.e. organosilicate oligomers, were optimized by using various capillary temperatures and solute concentrations. The structures of organosilicate oligomers were shown to vary with reaction duration and the molar ratio of water to siloxane (r), with multiple types of oligomers attributed to linear, cyclic and hydroxylated species. The evolution of oligomeric structures was elucidated from the ESI-MS spectra. The number and intensity of cyclic oligomers increase with an increase in the r-value or reaction length, at the expense of linear species, indicating the trend to formation of cross-linked polysiloxane structures. Overall, this work demonstrates that ESI-MS is an indispensable tool for the comprehensive characterization of the correlation between properties and structure of hybrid silica-based materials.

Permeation properties of BTESE–TEOS organosilica membranes and application to O2/SO2 gas separation

In the present study, a BTESE–TEOS mixed precursor was proposed for control of the pore sizes of organosilica networks in organic–inorganic hybrid silica membranes. FT-IR spectrometry confirmed the formation of a partially cross-linked polysiloxane structure with hydrocarbon units in a BTESE–TEOS-derived silica network produced by the co-hydrolysis and condensation of BTESE with TEOS, which also showed an improved thermal stability. Single gas permeation measurements and normalized Knudsen-based permeance (NKP) established the order of the average membrane pore sizes as follows: BTESE>BTESE–TEOS>TEOS. The organosilica membranes derived from BTESE–TEOS exhibited a superior O2 permeance that was higher than 10−8molm−2s−1Pa−1 with an O2/SO2 selectivity of 7.3, which indicated that the pore size control in organosilica networks using BTESE–TEOS as a precursor was effective for selective O2/SO2 separation. Moreover, the effective molecular size of SO2 permeates through organosilica membranes was discussed.