Silicate Condensation Research Articles

High-performance polymer electrolyte membranes incorporated with 2D silica nanosheets in high-temperature proton exchange membrane fuel cells

Silica nanosheets (SN) derived from natural vermiculite (Verm) were successfully incorporated into polyethersulfone–polyvinylpyrrolidone (PES–PVP) polymer to fabricate high–temperature proton exchange membranes (HT–PEMs). The content of SN filler was varied (0.1–0.75 wt%) to study its influence on proton conductivity, power density and durability. Benefiting from the hydroxyl groups of SN that enable the formation of additional proton–transferring pathways, the inorganic–organic membrane displayed enhanced proton conductivity of 48.2 mS/cm and power density of 495 mW/cm2 at 150 °C without humidification when the content of SN is 0.25 wt%. Furthermore, exfoliated SN (E–SN) and sulfonated SN (S–SN), which were fabricated by a liquid–phase exfoliation method and silane condensation, respectively, were embedded in PES–PVP polymer matrix by a simple blending method. Due to the significant contribution from sulfonic groups in S–SN, the membrane with 0.25 wt% S–SN reached the highest proton conductivity of 51.5 mS/cm and peak power density of 546 mW/cm2 at 150 °C, 48% higher than the pristine PES–PVP membranes. Compared to unaltered PES–PVP membrane, SN added hybrid composite membrane demonstrated excellent durability for the fuel cell at 150 °C. Using a facile method to prepare 2D SN from natural clay minerals, the strategy of exfoliation and functionalization of SN can be potentially used in the production of HT–PEMs.

Biomimetic spherical silica production using phosphatidylcholine and soy lecithin

Spherical silica particles are traditionally made via Stöber and modified-Stöber processes, which commonly use environmental toxins as reagents. Here we report a process to synthesise spherical silica particles using environmentally friendly biomolecules (phosphatidylcholine and soy lecithin) and employing water and soybean oil as solvents, rather than potentially harmful organic solvents. This scalable method represents an important step towards sustainable industrial silica syntheses. Under mildly acidic conditions phosphatidylcholine and soy lecithin can control the condensation of sodium silicate to form discrete, spherical silica particles. Silica particles with diameters ranging between 329 and 2232 nm were readily produced using phosphatidylcholine as the templating agent and soybean oil as the solvent in the presence of sodium silicate. Narrower size distributions (262–1272 nm) were achieved using soy lecithin as the templating agent in an aqueous acetate buffer solution containing sodium silicate. Silica particles grown using low concentrations of phosphatidylcholine and soy lecithin as templating agents formed by a combination of coalescence and Ostwald ripening, whilst particles grown at high concentrations predominantly formed through Ostwald ripening behaviour. The possibility of sustainably producing spherical silica particles in a simple biomolecule-templated synthesis is shown.

Elucidating the Role of Tetraethylammonium in the Silicate Condensation Reaction from Ab Initio Molecular Dynamics Simulations.

The understanding of the formation of silicate oligomers in the initial stage of zeolite synthesis is important. The use of organic structure-directing agents (OSDAs) is known to be a key factor in the formation of different silicate species and the final zeolite structure. For example, tetraethylammonium ion (TEA+) is a commonly used organic template for zeolite synthesis. In this study, ab initio molecular dynamics (AIMD) simulation is used to provide an understanding of the role of TEA+ in the formation of various silicate oligomers, ranging from dimer to 4-ring. Calculated free-energy profiles of the reaction pathways show that the formation of a 4-ring structure has the highest energy barrier (97 kJ/mol). The formation of smaller oligomers such as dimer, trimer, and 3-ring has lower activation barriers. The TEA+ ion plays an important role in regulating the predominant species in solution via its coordination with silicate structures during the condensation process. The kinetics and thermodynamics of the oligomerization reaction indicate a more favorable formation of the 3-ring over the 4-ring structure. The results from AIMD simulations are in line with the experimental observation that TEA+ favors the 3-ring and double 3-ring in solution. The results of this study imply that the role of OSDAs is not only important for the host–guest interaction but also crucial for controlling the reactivity of different silicate oligomers during the initial stage of zeolite formation.

Synthesis and Characterization of Trimethylchlorosilane-Modified Silica Xerogel

Modification of silica xerogel with TMCS (trimethylchlorosilane) reagent has been carried out to improve the hydrophobicity of silica xerogel. Silica xerogel was synthesized based on the sol-gel method using sodium silicate as a precursor, and citric acid as a catalyst, with a mole ratio of sodium silicate and citric acid, was 0.172: 0.004. The sol-gel process was carried out through several stages, i.e., hydrolysis and condensation of sodium silicate to form sol, gelation (sol transition to gel), aging, and drying. Surface modification was performed by studying the effect of TMCS: methanol: petroleum benzine volume ratio of 0.5:1:1, 1:1:1, 1.5:1:1, 2:1:1, and 2.5:1:1 on the characteristics of silica xerogel synthesized. FTIR, SEM, and GSA characterized the synthesized results. The results of FTIR characterization on silica xerogel with volume ratios of 2:1:1 and 2.5:1:1 indicate the presence of the Si‑C group absorption at a wavenumber of 848.68 cm-1 which shows that the formation of silyl groups on the modified silica xerogel surfaces occurs at a TMCS: methanol: petroleum benzine ratio of 2:1:1 and 2.5:1:1. SEM results indicate that the silica xerogels produced are porous. Meanwhile, the GSA analysis results show that the pore size distributions are in the mesoporous region with an average pore radius of 8-13 nm. The greater the volume of TMCS used, the higher the surface area, and the resulting xerogel’s hydrophobicity. Based on the contact angle and seeped time test, the highest hydrophobicity is produced by the material synthesized at a TMCS: methanol: PB volume ratio of 2.5:1:1 with a contact angle of 116.346°.

Polycondensation of Water Glass Sodium Silicates in the Presence of [BnXn]2– (n = 10, 12; X = H, Cl) Boron Cluster Anions

It has been shown that two competing processes occur in a system of water glass (WG) silicates and [BnXn]2– (n = 10, 12; X = H, Cl) boron cluster anions (WG/[An]) in the range 100–200°C: the formation of a supramolecular structure due to cation–anion contacts of the silanol groups of the silicate with [An]'s at t ≤ 100°C and the condensation of the silanol groups of the silicate, resulting in the formation of polysiloxane chains (t ≥ 180°C). The difference in temperature conditions between these processes leads to inhibition of the silicate condensation process. The detailed structure of the silicate component of the WG/[An] systems has been studied as a function of [An] content.

Durable superamphiphobic coatings with high static and dynamic repellency towards liquids with low surface tension and high viscosity

Superamphiphobic coatings have attracted great attention in academia and industry. However, the fabrication of durable superamphiphobic coatings with high repellency towards liquids with low surface tension and high viscosity is still very challenging. Here, we report a simple method for the fabrication of durable superamphiphobic coatings with high static and dynamic repellency to such liquids. First, a homogeneous suspension was fabricated by hydrolytic condensation of silanes in the presence of the chain-like aggregates of SiO2 nanoparticles. Subsequently, the superamphiphobic coatings were fabricated by spray-coating the polyurethane adhesive onto the substrates followed by spray-coating the as-prepared suspension onto the polyurethane adhesive layer. The coatings show high repellency to liquids with low surface tension and high viscosity, e.g., high apparent contact angles, low sliding angles, high impact resistance, low horizontal deformation and fast rolling velocity. Furthermore, the coatings show excellent mechanical durability against intensive sandpaper abrasion (60 m of abrasion under 10.5 kPa), water impact (60 min under 100 kPa) and tape peeling (200 cycles). The coatings also exhibit good aging stability. Based on these merits, the superamphiphobic coatings may have great potentials in various applications, e.g., handling with natural and synthetic polymer solutions.

Mechanically Robust and Flame-Retardant Silicon Aerogel Elastomers for Thermal Insulation and Efficient Solar Steam Generation.

In this work, we report the synthesis of silicon aerogel elastomers (SAEs) by one-pot hydrolytic condensation of silanes, followed by drying at room temperature. The as-synthesized SAE features excellent flexibility and mechanical robustness, for example, a high compressive strength of up to 40 kPa at 75% strain was achieved. Combined with their thermal insulation properties (a low thermal conductivity of ca. 0.02 W m –1 K –1 in air), for the first time, such SAEs were used as a porous platform for both flame-retardant measurement and solar steam generation. By coating with Mg(OH)2 via a facile coprecipitation method, the treated SAEs show excellent flame retardancy with a peak heat release rate of 25.61 kW m–2, in addition to high fire resistance and excellent smoke suppression. When used as a solar steam generator, their evaporation efficiency was measured to be 82.7% (1 kW m–2), which could compete with that of other high-performance bilayered photothermal materials reported so far. Taking advantage of their simple and cost-efficient manufacture and superior mechanical robustness and flexibility, such SAEs with multifunctionalities may have great potential for a wide variety of energy-saving applications, for example, especially for thermal insulation coatings with better flame retardancy and efficient solar steam generation for desalination or freshwater production.

Effect of the Organic Functional Group on the Grafting Ability of Trialkoxysilanes onto Graphene Oxide: A Combined NMR, XRD, and ESR Study.

The functional properties displayed by graphene oxide (GO)-polymer nanocomposites are strongly affected by the dispersion ability of GO sheets in the polymeric matrix, which can be largely improved by functionalization with organosilanes. The grafting to GO of organosilanes with the general formula RSi(OCH3)3 is generally explained by the condensation reactions of silanols with GO reactive groups. In this study, the influence of the organic group on the RSi(OCH3)3 grafting ability was analyzed in depth, taking into account the interactions of the R end chain group with GO oxidized groups. Model systems composed of commercial graphene oxide reacted with 3-aminopropyltrimethoxysilane (APTMS), 3-mercaptopropyltrimethoxysilane (MPTMS), and 3-methacryloxypropyltrimethoxysilane, (MaPTMS), respectively, were characterized by natural abundance 13C, 15N and 29Si solid state nuclear magnetic resonance (NMR), x-ray diffraction (XRD), and electron spin resonance (ESR). The silane organic tail significantly impacts the grafting, both in terms of the degree of functionalization and direct interaction with GO reactive sites. Both the NMR and XRD proved that this is particularly relevant for APTMS and to a lower extent for MPTMS. Moreover, the epoxy functional groups on the GO sheets appeared to be the preferential anchoring sites for the silane condensation reaction. The characterization approach was applied to the GO samples prepared by the nitric acid etching of graphene and functionalized with the same organosilanes, which were used as a filler in acrylic coatings obtained by cataphoresis, making it possible to correlate the structural properties and the corrosion protection ability of the layers.

Bent-core liquid crystal-functionalised flexible polymer substrates for liquid crystal alignment

ABSTRACTA transparent flexible polymer film is chemically functionalised with a bent-core liquid crystal (BCLC) compound for effective alignment of the bulk BCLC sample at the substrate–LC interface. The surface attachment was achieved via a simple procedure which involved pre-treatment of the polymer film (commercial name: over head projector film) using piranha solution followed by chemically attaching the BCLC compound through silane condensation reaction. Surface characterisation of the unmodified and BC-modified flexible films was carried out through X-ray photoelectron spectroscopy (XPS), attenuated total reflectance fourier transform infrared (ATR-FTIR) spectroscopy, contact angle (CA) and atomic force microscopy (AFM) techniques. The BC-modified flexible substrates are analysed for their efficiency to orient the bulk LC sample. Remarkably, the chemically modified polymer substrates are highly efficient in vertically aligning both the BC and rod-like LC samples at the substrate–LC interface, in comparison to their unmodified counterparts. The described method is simple, reproducible, surface modified substrates are highly stable and more importantly reusable. The demonstrated method for the alignment of BCLCs advances a step forward towards the realisation of applications proposed for these fascinating compounds.

Post-peak decelerating reaction of Portland cement: Monitoring by heat flow calorimetry, modelling by Elovich-Landsberg model and reaction-order model

The reaction kinetic of Portland cement was characterized by heat flow calorimetry, with the experiments conducted at different, constant curing temperatures. For the post-peak reaction, two distinct regimes, termed “immediate post-peak” regime and “final tail” regime, respectively, were identified from experimental data. We suggest rate equations and associated mechanisms for the two tail regimes. The immediate post-peak regime was modelled by the Elovich-Landsberg model, usually associated with chemisorption, the final tail regime with a reaction-order model. The immediate post-peak regime may be interpreted as densification of C-S-H (following space-filling dendritic growth with a low-density product during the main hydration peak). On the other hand, reaction-order modelling of the final tail regime may be associated with silicate condensation/ polymerization reaction in C-S-H.

Totally Waterborne and Highly Durable Superamphiphobic Coatings for Anti‐Icing and Anticorrosion

AbstractBioinspired superamphiphobic coatings have garnered significant interests and great achievements are achieved; however, it is still difficult to move them to practical applications because of their pollutive preparation methods and poor stability. Here, preparation of totally waterborne and highly durable superamphiphobic coatings is reported by spray‐coating adhesive layers and a homogeneous suspension formed by hydrolytic condensation of silanes with SiO2 nanoparticles in water. The surface structure and chemical composition, superamphiphobicity, mechanical and chemical stability, anti‐icing and anticorrosion performances are studied by various analytical techniques and methods. The coatings feature i) a unique three‐tier macro/micro/nanostructure, ii) high contact angles and low sliding angles for not only various room temperature liquids but also hot liquids up to 92 °C, iii) high mechanical stability against intensive sandpaper abrasion, tape‐peeling, and water jetting, and iv) exceptional long‐term chemical stability even in aqua regia, saturated NaOH and boiling water. Furthermore, the coatings on Mg alloy show excellent anti‐icing performance in actual outdoor environment and excellent anticorrosion performance in salt spray test. The waterborne and highly durable superamphiphobic coatings may be used in various fields, as the coatings with high repellency even to hot liquids can be applied onto various substrates.

Monitoring Silane Sol-Gel Kinetics with In-Situ Optical Turbidity Scanning and Dynamic Light Scattering.

Organosilanes (e.g., R’-SiOR3) provide hydrophobic functionality in thin-film coatings, porous gels, and particles. Compared with tetraalkoxysilanes (SiOR4), organosilanes exhibit distinct reaction kinetics and assembly mechanisms arising from steric and electronic properties of the R’ group on the silicon atom. Here, the hydrolysis and condensation pathways of n-propyltrimethoxy silane (nPM) and a tri-fluorinated analog of nPM, 3,3,3-trifluoropropyl trimethoxy silane (3F), were investigated under aqueous conditions at pH 1.7, 2.0, 3.0, and 4.0. Prior to hydrolysis, 3F and nPM are insoluble in water and form a lens at the bottom (3F) or top (nPM) of the solutions. This phase separation was employed to follow reaction kinetics using a Turbiscan instrument to monitor hydrolysis through solubilization of the neat silane lens while simultaneously tracking condensation-induced turbidity throughout the bulk solution. Dynamic light scattering confirmed the silane condensation and particle aggregation processes reported by the turbidity scanning. Employing macroscopic phase separation of the starting reactants from the solvent further allows for control over the reaction kinetics, as the interfacial area can be readily controlled by reaction vessel geometry, namely by controlling the surface area to volume. In-situ turbidity scanning and dynamic light scattering revealed distinct reaction kinetics for nPM and 3F, attributable to the electron withdrawing and donating nature of the fluoro- and organo-side chains of 3F and nPM, respectively.

The Impact of Accretion Heating and Thermal Conduction on the Dead Zone of Protoplanetary Disks

Abstract The paper investigates the influence of accretion heating and turbulent heat conduction on the equilibrium of protoplanetary disks, extending the 2D axisymmetric passive disk model of Flock. The model includes dust sublimation and radiative transfer with the flux-limited diffusion approximation, and predicts the density and temperature profiles as well as the dust-to-gas ratio of the disk. It is shown that the accretion heating can have a large impact: for accretion rates above 5 · 10−8 M ⊙ yr−1 a zone forms behind the silicate condensation front with sufficiently high temperature to sublimate the dust and form a gaseous cavity. Assuming a Prandtl number ∼0.7, it is furthermore shown that the turbulent heat conduction cannot be neglected in the evaluation of the temperature profile. While the inner rim position is not affected by viscous heating, the dead zone edge shifts radially outward for higher accretion rates.

Enhanced Uv shielding properties of DAS based nanocomposites

In this article, we first report the synthesis of Titanium oxide (TiO2)-Dialdehyde starch (DAS) nanocomposite which was then successfully embedded in silica (SiO2) matrix obtained by the hydrolytic poly condensation of tetra ethyl ortho silicate (TEOS). FESEM images of TiO2-DAS-SiO2 nanocomposites indicate rod-like structures with spherical DAS particles well embedded in it. Both the composites exhibited wide pore size distribution as evident from Brunauer- Emmett- Teller (BET) analysis and the significant effect of pore size on the transmission properties has also been elucidated in detail. Uv irradiation experiments confirm the enhanced Uv screening activity but reduced photocatalytic property of the TiO2-DAS-SiO2 nanocomposites in comparison to its counterpart TiO2-DAS composites which is desirable for long- term applications. Nitrogen adsorption/desorption measurements reveal a lower surface area of TiO2-DAS-SiO2 nanocomposites (2.49 m2/g) well consistent with its poor photocatalytic performance in comparison to TiO2-DAS composites. The band gap tunability and ability of the synthesized nanocomposites to absorb Uv as well as visible light makes them suitable for optoelectronic applications and as packaging materials for light sensitive food products.

Scalable Preparation of Superamphiphobic Coatings with Ultralow Sliding Angles and High Liquid Impact Resistance.

In spite of great progress, preparation of superamphiphobic coatings with excellent static and dynamic superamphiphobicity remains challenging. Here, we report superamphiphobic coatings with ultralow sliding angles and high liquid impact resistance. The coatings were prepared by spray-coating the polysiloxane/silica stock suspensions, synthesized by hydrolytic condensation of silanes with silica nanoparticles. The superamphiphobicity relies on microstructure of the coatings, controllable by the diameter of silica nanoparticles. The coatings feature excellent static and dynamic superamphiphobicity for various liquids with surface tension as low as 23.8 mN m-1. Furthermore, we achieved large-scale preparation of the coatings, which paved the way for their applications.

Biomimetic Super Anti-Wetting Coatings from Natural Materials: Superamphiphobic Coatings Based on Nanoclays

Superamphiphobic coatings (SAPCs) that resist wetting of water and low-surface-tension liquids have generated widespread attention in academia, but are very challenging to invent. Liquid adhesion, low stability, complicated and expensive preparation methods are the typical characteristics of SAPCs, which seriously hinder real-world applications of SAPCs. Here, we report a comprehensive study about preparation of SAPCs from abundant nanoclays with fibrous, plate-like and porous microstructures. The SAPCs are prepared simply by hydrolytic condensation of silanes in the presence of nanoclays, followed by spray-coating the as-formed suspensions onto substrates. The SAPCs feature high superamphiphobicity for various liquids down to a surface tension of 23.8 mN m−1 (n-decane), and high mechanical, chemical and thermal stability. The superamphiphobicity and stability depend on microscale and nanoscale surface morphology of the coatings, which are controllable by the microstructures of nanoclays and their acid activation. The fibrous nanoclays with moderate aspect ratio like palygorskite are the most suitable building blocks for the preparation of SAPCs by effectively forming the reentrant surface morphology. We believe that the findings will promote the progress of SAPCs, and pave the way for the development of clay-based super anti-wetting coatings.

Green Synthesis of Ant Nest-Inspired Superelastic Silicone Aerogels

Green synthesis of aerogels with high mechanical properties has long remained a big challenge ever since Kistler’s report in 1931. Inspired by ant nests, we report a green method to synthesize strong, superelastic and flexible silicone aerogels. The aerogels are prepared by hydrolytic condensation of silanes with trace amounts of catalyst and surfactant (0.094 mmol mol–1) followed by drying the hydrogels at ambient pressure. The aerogels can quickly recover their original shape after repeated compression and bending. The aerogels can be functionalized via their Si–OH or vinyl groups for specific purposes. We also extend the method for forming aerogel coatings on diverse types of materials. Our study demonstrates that green synthesis of superelastic aerogels is feasible and bioinspiration is an efficient strategy.

A comparative study about superamphiphobicity and stability of superamphiphobic coatings based on Palygorskite

Abstract Naturally rich clay minerals are receiving increasing attention recently in preparation of super anti-wetting coatings, superhydrophobic and superamphiphobic ones. Clay minerals are a class of very promising natural building blocks for constructing microstructures of the coatings. Clay minerals such as Palygorskite (Pal), kaolinite, halloysite nanotubes and montmorillonite have been used. However, the comparative study about the effects of source of clay minerals on properties of the coatings remains a gap to be filled. Here, the first comparative study about superamphiphobicity and stability of superamphiphobic coatings based on Pal from different sources was reported. The superamphiphobic coatings were fabricated by hydrolytic condensation of silanes in the presence of Pal followed by spray-coating the as-prepared dispersions onto substrates. Five Pal samples from Anhui, Jiangsu and Gansu Provinces of China were chosen, and their effects on superamphiphobicity and stability of the coatings were studied using various analytical techniques including scanning electron microscopy and X-ray photoelectron spectroscopy. The superamphiphobicity and stability depend on micro/nanostructures of the coatings, originating from the microstructures of Pal. The Pal sample from Anhui is more suitable for preparing superamphiphobic coatings than the others because of the higher Mg content and the higher aspect ratio of the Pal nanorods. The finding will shed light on the progress of the clay-based super anti-wetting coatings.

Preparation and characterization of modified SiO2 nanospheres with dichlorodimethylsilane and phenyltrimethoxysilane

In this study we synthesized spherical nanosilica by the Sol-Gel method using tetraethyl orthosilicate (TEOS), and the average particle diameter was measured by scanning electron microscopy (SEM). The surface of silica nanoparticles was modified with two kinds of silane coupling agents: dichlorodimethylsilane (DCDMS) and phenyltrimethoxysilane (PhTMS). We investigated the effect of the type of silane coupling agent with different functional groups (alkoxy or chloro) on the surface properties of modified silica by various analytical methods, i.e., FT-IR spectroscopy, CHN analysis, UV-visible spectra and thermogravimetric analysis (TGA) measurements. The particles modified with DCDMS showed larger grafting density from CHN analysis and higher weight loss from TGA measurement indicating the higher content of silane grafted on the surface of SiO2 nanoparticles. We suggest that the variations in grafting were dependent on the silane condensation which indicating the greater ability of condensation reaction of DCDMS with OH groups of silica rather than PhTMS.

Theoretical calculation of equilibrium Mg isotope fractionation between silicate melt and its vapor

Isotope fractionation during the evaporation of silicate melt and condensation of vapor has been widely used to explain various isotope signals observed in lunar soils, cosmic spherules, calcium–aluminum-rich inclusions, and bulk compositions of planetary materials. During evaporation and condensation, the equilibrium isotope fractionation factor (α) between high-temperature silicate melt and vapor is a fundamental parameter that can constrain the melt’s isotopic compositions. However, equilibrium α is difficult to calibrate experimentally. Here we used Mg as an example and calculated equilibrium Mg isotope fractionation in MgSiO3 and Mg2SiO4 melt–vapor systems based on first-principles molecular dynamics and the high-temperature approximation of the Bigeleisen–Mayer equation. We found that, at 2500 K, δ25Mg values in the MgSiO3 and Mg2SiO4 melts were 0.141 ± 0.004 and 0.143 ± 0.003‰ more positive than in their respective vapors. The corresponding δ26Mg values were 0.270 ± 0.008 and 0.274 ± 0.006‰ more positive than in vapors, respectively. The general $$\alpha - T$$ equations describing the equilibrium Mg α in MgSiO3 and Mg2SiO4 melt–vapor systems were: $$\alpha_{{{\text{Mg}}\left( {\text{l}} \right) - {\text{Mg}}\left( {\text{g}} \right)}} = 1 + \frac{{5.264 \times 10^{5} }}{{T^{2} }}\left( {\frac{1}{m} - \frac{1}{{m^{\prime}}}} \right)$$ and $$\alpha_{{{\text{Mg}}\left( {\text{l}} \right) - {\text{Mg}}\left( {\text{g}} \right)}} = 1 + \frac{{5.340 \times 10^{5} }}{{T^{2} }}\left( {\frac{1}{m} - \frac{1}{{m^{\prime}}}} \right)$$ , respectively, where m is the mass of light isotope 24Mg and m′ is the mass of the heavier isotope, 25Mg or 26Mg. These results offer a necessary parameter for mechanistic understanding of Mg isotope fractionation during evaporation and condensation that commonly occurs during the early stages of planetary formation and evolution.