Competition between hydrolysis and condensation reactions of trialkoxysilanes, as a function of the amount of water and the nature of the organic group

Silsesquioxane Cages under Solvent Regimen: The Influence of the Solvent on the Hydrolysis and Condensation of Alkoxysilane

This study investigates the formation mechanisms of oligomeric phenyl silanols, focusing on polyhedral oligomeric silsesquioxane (POSS) and double-decker silsesquioxane (DDSQ) derivatives. Combining literature reports and crystal structures of solvated derivatives obtained in our laboratory, we show that the solvent choice significantly influences their structures. POSS-based silanols prefer aprotic solvents like THF, preserving dimerization, while double-deckers form stable architectures in protic solvents like isopropanol. This discrepancy arises from different stabilization mechanisms. Our findings enhance our understanding of hydrolytic condensation involving trimethoxyphenylsilane and suggest aprotic solvents for efficient reactions with POSS-based silanols.

The Role of APTES as a Primer for Polystyrene Coated AA2024-T3

(3-Aminopropyl)triethoxysilane (APTES) silane possesses one terminal amine group and three ethoxy groups extending from each silicon atom, acting as a crucial interface between organic and inorganic materials. In this study, after APTES was deposited on the aluminum alloy AA2024-T3 as a primer for an optional top coating with polystyrene (PS), its role with regard to stability as a protection layer and interaction with the topcoat were studied via combinatorial experimentation. The aluminum alloy samples primed with APTES under various durations of concentrated vapor deposition (20, 40, or 60 min) with an optional post heat treatment and/or PS topcoat were comparatively characterized via electrochemical impedance spectroscopy (EIS) and surface energy. The samples top-coated with PS on an APTES layer primed for 40 min with a post heat treatment revealed excellent performance regarding corrosion impedance. A primed APTES surface with higher surface energy accounted for this higher corrosion impedance. Based on the SEM images and the surface energy calculated from the measured contact angles on the APTES-primed surfaces, four mechanisms are suggested to explain that the good protection performance of the APTES/PS coating system can be attributed to the enhanced wettability of PS on the cured APTES primer with higher surface energy. The results also suggest that, in the early stages of exposure to the corrosion solution, a thinner APTES primer (deposited for 20 min) enhances protection against corrosion, which can be attributed to the hydrolytic stability and hydrolyzation/condensation of the soaked APTES and the dissolution of the naturally formed aluminum oxide pre-existing in the bare samples. An APTES primer subjected to additional heat treatment will increase the impedance of the coating system significantly. APTES, and silanes, in general, used as adherent agents or surface modifiers, have a wide range of potential applications in micro devices, as projected in the Discussion section.

High-Performance Methylsilsesquioxane Aerogels: Hydrolysis Mechanisms and Maximizing Compression Properties

Synthesis of methylsilsesquioxane aerogels by ambient pressure drying instead of supercritical drying has recently emerged as a major trend, but the issues of low mechanical strength and unstable performance still need to be resolved. This work reveals the microscopic formation mechanisms of gel skeleton based on the kinetic characteristics of methyltrimethoxysilane (MTMS) precursor hydrolysis and the associated sol-gel reactions. The effects of oxalic acid concentration (cOA) and hydrolysis time of MTMS solution (th) on the gelation time, morphologies, microstructures, chemical structure, and compression properties of the as-synthesized methylsilsesquioxane aerogels are investigated. The optimal cOA and th are 38.4 mmol/L and 120 min, respectively, endowing the methylsilsesquioxane aerogels with a compression strength of 0.170 MPa and a maximum compression strain of 61.2%. Precise control of the hydrolysis conditions ensures the formation of branched particle-to-particle networks, which is crucial for maximizing the compression properties of methylsilsesquioxane aerogels synthesized under industry-relevant conditions.

Performance and mechanisms of PropS-SH/Ce(dbp)3 coatings in the inhibition of pyrite oxidationtion for acid mine drainage control

Inhibition of tailings oxidation could availably control the generation of acid mine wastewater from its source. Organosilanes serving as a high-efficiency inhibitor of the oxidation of pyrite, bring some problems including safety hazards caused by large amounts of organic solvents, difficult high-temperature curing, poor long-term properties, and so on. In our work, the PropS-SH/Ce (dbp)₃ (PS/Ce (dbp)₃) passivator with excellent passivation performance and self-healing properties was prepared by choosing 3-mercaptopropyltrimethoxysilane (PropS-SH) and dibutyl phosphate (Ce (dbp)₃) as the main passivating agent and the repair agent, respectively. We reduced the ratio of ethanol to water by adjusting the pH of the organosilane condensation and also achieved room-temperature curing by extending the curing time. Electrochemical and chemical leaching experiments results showed that the most appropriate addition of Ce (dbp)₃ was 0.2 wt% for enhancing the passivation performance of the passivated coating. In a 6-month chemical leaching experiment, the PS/Ce (dbp)₃-0.2 passivation coating cured at room temperature showed a better passivation effect and maintained 90.55% and 78.54% of total Fe and SO₄^2- passivation efficiencies. The passivation and self-healing mechanisms were investigated by FT-IR, XPS, ²⁹Si NMR, and other characterization methods, which were as follows: silane formed a cross-linked mesh structure by Si-O-Si bonding, in which Ce (dbp)₃ was physically filled. And the Si-OH on the surface of the passivation film formed Fe-O-Si bonds with the hydroxyl groups on the surface of the pyrite, thus attaching to the surface of the pyrite and isolating the oxidation medium. When the passivation coating was locally damaged, the oxidation reaction caused a change in pH, which accelerated the dissolution of Ce (dbp)₃ in the passivation layer. Ce³⁺ underwent a valence change and formed a CeO₂ precipitate, while dbp^- could form a complex with Fe²⁺ on the pyrite surface, both of which worked together to repair the broken passivation coating and prevent the oxidation reaction.

Robust and Scalable In Vitro Surface Mineralization of Inert Polymers with a Rationally Designed Molecular Bridge

The artificial integration of inorganic materials onto polymers to create the analogues of natural biocomposites is an attractive field in materials science. However, due to significant diversity in the interfacial properties of two kinds of materials, advanced synthesis methods are quite complicated and the resultant materials are always vulnerable to external environments, which limits their application scenarios and makes them unsuitable for scalable production. Herein, we report a simple and universal approach to achieve robust and scalable surface mineralization of polymers using a rationally designed triple functional molecular bridge of fluorosilane, 3-[(perfluorohexyl sulfonyl) amino] propyltriethoxy silane (PFSS). In a two-step solution deposition, the fluoroalkyl and siloxane of the PFSS take charge of its adhesion and immobilization onto polymers by hydrophobic interaction and wrapping-like chemical cross-linking, and then the assembly and growth of inorganic nanoclusters for integration are achieved by strong chemical coordination of PFSS sulfonamide. The versatile mineralization of inorganic oxides (e.g., TiO₂, SiO₂, and Fe₂O₃) onto chemically inert polymer surfaces was realized very well. The resultant mineralized materials exhibit robust and multiple functionalities for hostile applications, such as hydrophilic membranes for removing oils in strong acidic and alkaline wastewaters, fabrics with advanced anti-bacteria for healthy wearing, and plates with strong mechanical performance for better use. Experimental results and theoretical calculations confirmed the homogenous distribution of the PFSS onto polymers via cross-linking for robust coordination with inorganic oxides. These results demonstrate a skillful enlightenment in the design of high-performance mineralized polymer materials used as membranes, fabrics, and medical devices.

Reactivities of silane coupling agents in the silica/rubber composites: Theoretical insights into the relationships between energy barriers and electronic characteristics

Si69 and Si75, typical commodities of silane coupling agents, are often employed in tire recipes to work as the bridges connecting silica and polymers, with which rolling resistance and wet traction are enhanced without loss in abrasion resistance. In this article, the reactivities of Si69 and Si75 with silica and various rubbers were theoretically investigated by using density functional theory (DFT). When the agents were coupled with silica, not only the acid+water condition but also the pure acid condition was confirmed to readily trigger the condensation reactions. The corresponding Gibbs free energy barriers were related to the charge distributions of reaction regions. As the agents suffered from the homolysis of central SS bonds, the generated single-S-tailer radicals (RS·) showed significantly higher reactivities of both the radical addition and the α-H transfer reactions with rubbers, due to the stronger radical philicities of the terminal sulfur radicals with larger condensed local softnesses [s⁰ (S)]. When the agents underwent the heterolysis of central SS bonds, the terminal sulfur anions with smaller s^- (S) indices, however, facilitated the nucleophilic addition reactions with rubbers. Several derivative indices based on the condensed local softnesses were also proposed here to shed light on the reactivities from the viewpoint of the relationship between energy barriers and electronic characteristics. The above findings pave the way for the design of new kinds of silane coupling agents using computer-aided techniques, and meanwhile, provide references for the practical application of Si69 and Si75 to the silica/rubbers systems.

Cationic Emulsion Polymerization of Octamethylcyclotetrasiloxane (D4) in Mixtures with Alkoxysilanes

The cationic emulsion polymerization of octamethylcyclotetrasiloxane (D4) in mixtures with methyltriethoxysilane (MTES) and vinyltriethoxysilane (VTES) was studied by FTIR ATR, GC, the development of a toluene insoluble fraction of the polymer and a gravimetric analysis. The polymerization of D4 alone was also conducted for comparison and, additionally, the development of molecular weight of polydimethylsiloxane (PDMS) obtained in that process was studied by GPC. Dodecylbenzenesulphonic acid (DBSA) was used as a surfactant and catalyst. The process was carried out in a “starved feed” mode by adding dropwise the monomer mixture to the aqueous solution of DBSA. FTIR ATR spectra were recorded by the sensor placed in the probe tip of a ReactIR 15^TM apparatus. It was found that the silicone polymer formation proceeded faster when D4 was polymerized in the mixture with alkoxysilanes, especially in the beginning of the process, and that already at the beginning of the process, the partly crosslinked polymer was formed. The induction period of ca. 30 min was observed and the concentration of cyclic siloxanes (D4 and decamethylcyclopentasiloxane—D5) remained at a very low level in the course of the reaction and only traces were detected in the final product. The particle size development in the course of the reaction was also studied and it was found that the particle size distribution was bimodal and was broadening as the reaction proceeded, though this phenomenon was less distinct when D4 was polymerized in the mixtures with alkoxysilanes. The structure of the reaction product was confirmed by ²⁹Si NMR.

Layered Si-Ti oxide thin films with tailored electrical and optical properties by catalytic tandem MLD-ALD

Oxides with well-controlled optical and electrical properties are key for numerous advances in nanotechnology, including energy, catalysis, sensors, and device applications. In this study we introduce layer-by-layer deposition of silicon–titanium layered oxide (Si–Ti LO) thin films using combined MLD-ALD methodology (M/ALD). The Si–Ti LO film deposition is achieved by acid–base catalysis establishing an overall catalytic tandem M/ALD super cycle (CT-M/ALD). The catalytic nature of the process allows relatively fast deposition cycles under mild conditions compared with the typical cycle time and conditions required for ALD processes with silane precursors. The Si–Ti LO thin films exhibit tuneable refractive index and electrical conductivities. The refractive index is set by the stoichiometry of Si- to Ti-oxide phases simply by selecting the MLD to ALD proportion in the CT-M/ALD super cycle, with low and high refractive index, respectively. Thermal treatment of Si–Ti LO thin films resulted in conductive thin films with both graphitic and Magnéli oxide phases. Enhanced conductivity and reduced onset temperature for Magnéli phase formation were obtained owing to the unique Si–Ti layer structure and stoichiometry attained by the CT-M/ALD process and facilitated by breaking of Si–C bonds and Red–Ox reactions between the Si sub-oxide and TiO₂ phases leading to the conductive Magnéli phase. Hence, the embedded amine silane functions not only for catalysing Si–Ti LO deposition but also to further promote subsequent transformations during thermal processing. This work demonstrates the concept of embedding a meta-stable organic motif by the MLD step to facilitate transformation of an oxide phase by taking advantage of precise layer-by-layer deposition of alternating phases enabled by M/ALD.

Layer-by-layer deposition of Si–Ti layered oxide thin films are obtained using catalytic tandem M/ALD methodology. The films exhibit optical (RI) and electrical conductivities by selecting the MLD to ALD proportion in the super cycle.

Hybrid Xerogels: Study of the Sol-Gel Process and Local Structure by Vibrational Spectroscopy

The properties of hybrid silica xerogels obtained by the sol-gel method are highly dependent on the precursor and the synthesis conditions. This study examines the influence of organic substituents of the precursor on the sol-gel process and determines the structure of the final materials in xerogels containing tetraethyl orthosilicate (TEOS) and alkyltriethoxysilane or chloroalkyltriethoxysilane at different molar percentages (RTEOS and ClRTEOS, R = methyl [M], ethyl [E], or propyl [P]). The intermolecular forces exerted by the organic moiety and the chlorine atom of the precursors were elucidated by comparing the sol-gel process between alkyl and chloroalkyl series. The microstructure of the resulting xerogels was explored in a structural theoretical study using Fourier transformed infrared spectroscopy and deconvolution methods, revealing the distribution of (SiO)₄ and (SiO)₆ rings in the silicon matrix of the hybrid xerogels. The results demonstrate that the alkyl chain and the chlorine atom of the precursor in these materials determines their inductive and steric effects on the sol-gel process and, therefore, their gelation times. Furthermore, the distribution of (SiO)₄ and (SiO)₆ rings was found to be consistent with the data from the X-ray diffraction spectra, which confirm that the local periodicity associated with four-fold rings increases with higher percentage of precursor. Both the sol-gel process and the ordered domains formed determine the final structure of these hybrid materials and, therefore, their properties and potential applications.

The effect of column history in supercritical fluid chromatography: Practical implications

Long-term stability of retention times of a wide range of analytes has been evaluated using eight different stationary phases. These were from a single manufacturer to minimize the differences in silanol activity caused by the manufacturing process. The tested stationary phases included bridge ethylene hybrid, 2-ethylpyridine bridge ethylene hybrid with direct modification of silica particles, bidentate crosslinked charged surface hybrid fluorophenyl, bidentate crosslinked high strength silica C18, and propanediol linked phases including diol (pure propanediol linker), and three phases based on diol further modified with 2-picolylamine, diethylamine, and 1-aminoanthracene group. Retention times were monitored at the first injection, after three, nine, twelve months, and after the column regeneration via washing with pure water. The analyses were carried out using three different mobile phases, including methanol, methanol with 10 mmol/L ammonium formate, and methanol with 0.1% ammonium hydroxide. No overall decreasing or increasing trends were observed after evaluating individual contributing parameters such as analyte, stationary phase, and organic modifier. Our results suggest that the silyl-ether formation is not the only factor contributing to changes in the stationary phase pore surface. Indeed, the adsorption of mobile phase additives is probably another significant factor. That was also confirmed by the regeneration procedure using water, which is likely to reverse the silyl-ether formation to achieve the original retention. However, the retention times returned to the original values for all analytes only on three columns. Retention times on other columns remained shifted within ± 15 % RSD depending on the analyte properties and the nature of organic modifier. The retention time variations observed for each analyte group, i.e., acids, bases, and neutrals, were interpreted for each stationary phase. We concluded that the sterically protected surfaces exhibited significantly smaller changes in the retention times. Although the regeneration procedure effect depended on the column type, the results suggested beneficial effect of water. However, as the adsorption of additives on the column surface is an additional factor leading to retention time variations, the recommendation of using only one additive and/or organic modifier in each column will clearly improve the long-term repeatability of the retention times.

Formation Mechanism of Monodispersed Polysilsesquioxane Spheres in One-Step Sol-Gel Method

Monodispersed polysilsesquioxane (PSQ) spheres with diameters from hundreds of nanometers to several microns have been successfully synthesized; however, the knowledge of their formation mechanism still lags behind. Herein, with methyltrimethoxysilane and 3-mercaptopropyl trimethoxysilane as model silicon sources, the formation process of PSQ spheres in the one-step sol-gel method was revealed for the first time by monitoring the time evolution of particle morphology, size, and size distribution via transmission electron microscopy and dynamic light scattering. A four-stage formation mechanism was proposed: rapid hydrolysis of organic silicon source and subsequent oligomer micelle nucleation, fast growing of nuclei particles and formation of their aggregates, followed by a further relatively fast growth of dispersed particles, and finally a slow growth to form monodispersed PSQ spheres. Due to the reversibility of hydrolysis and condensation reactions, thermodynamically unstable particles gradually transformed to hydrolytic monomers/oligomers and then regrew on the thermodynamically stable particles until the concentration of hydrolytic oligomers reached the dissolution equilibrium in the alkaline reaction solution. The variation of growth rate during the formation process and the effects of NH₄OH concentration on the yield and particle size were investigated to facilitate analyses and understanding of the formation mechanism.

Design of PEGylated Three Ligands Silica Nanoparticles for Multi-Receptor Targeting

The synthesis of silica nanoparticles (SiNPs) decorated on their surface with a range of various elements (e.g., ligands, drugs, fluorophores, vectors, etc.) in a controlled ratio remains a big challenge. We have previously developed an efficient strategy to obtain in one-step, well-defined multifunctional fluorescent SiNPs displaying fluorophores and two peptides ligands as targeting elements, allowing selective detection of cancer cells. In this paper, we demonstrate that additional level of controlled multifunctionality can be achieved, getting even closer to the original concept of “magic bullet”, using solely sol–gel chemistry to achieve conjugation of PEG chains for stealth, along with three different ligands. In addition, we have answered the recurrent question of the surface ungrafting by investigating the stability of different siloxane linkages with the ERETIC Method (Electronic Reference to Access In Vivo Concentrations) by ¹⁹F NMR quantification. We also compared the efficiency of the hybrid silylated fluorophore covalent linkage in the core of the SiNP to conventional methods. Finally, the tumor-cell-targeting efficiency of these multi-ligand NPs on human endothelial cells (HUVEC or HDMEC) and mixed spheroids of human melanoma cells and HUVEC displaying different types of receptors were evaluated in vitro.

Synthesis of size-controlled and highly monodispersed silica nanoparticles using a short alkyl-chain fluorinated surfactant

Highly monodispersed silica nanoparticles (SiNPs) were synthesised using a fluorinated surfactant, HOCH2CH(CF3)CO2H, and its efficiency was compared with efficiencies of five other surfactants. The size of the SiNPs (∼50-200 nm) was controlled by controlling the surfactant amount. The short alkyl-chain fluoro surfactant was found to be more efficient at producing monodispersed SiNPs than its long alkyl-chain fluoro or non-fluorinated surfactant counterparts.

Tailored Synthesis of PEGylated Bismuth Nanoparticles for X-ray Computed Tomography and Photothermal Therapy: One-Pot, Targeted Pyrolysis, and Self-Promotion

Complex experimental design is a common problem in the preparation of theranostic nanoparticles, resulting in poor reaction control, expensive production cost, and low experiment success rate. The present study aims to develop PEGylated bismuth (PEG-Bi) nanoparticles with a precisely controlled one-pot approach, which contains only methoxy[(poly(ethylene glycol)]trimethoxy-silane (PEG-silane) and bismuth oxide (Bi₂O₃). A targeted pyrolysis of PEG-silane was achieved to realize its roles as both the reduction and PEGylation agents. The unwanted methoxy groups of PEG-silane were selectively pyrolyzed to form reductive agents, while the useful PEG-chain was fully preserved to enhance the biocompatibility of Bi nanoparticles. Moreover, Bi₂O₃ not only acted as the raw material of the Bi source but also presented a self-promotion in the production of Bi nanoparticles via catalyzing the pyrolysis of PEG-silane. The reaction mechanism was systematically validated with different methods such as nuclear magnetic resonance spectroscopy. The PEG-Bi nanoparticles showed better compatibility and photothermal conversion than those prepared by the complex multiple step approaches in literature studies. In addition, the PEG-Bi nanoparticles possessed prominent performance in X-ray computed tomography imaging and photothermal cancer therapy in vivo. The present study highlights the art of precise reaction control in the synthesis of PEGylated nanoparticles for biomedical applications.

Crosslinked Facilitated Transport Membranes Based on Carboxymethylated NFC and Amine-Based Fixed Carriers for Carbon Capture, Utilization, and Storage Applications

Herein, we report the performances of crosslinked facilitated transport membranes based on carboxymethylated nanofibrils of cellulose (cmNFC) and polyvinylamine (PVAm) with the use of 3-(2-Aminoethylamino) propyltrimethoxysilane (AEAPTMS) as second fixed carrier for CO2 selectivity and permeability. The grafting of AEAPTMS on cmNFC was optimized by following the hydrolysis/condensation kinetics by 29Si Nuclear Magnetic Resonance (NMR) analyses and two different strategies of the process of membrane production were investigated. In optimized conditions, around 25% of the -COOH functions from cmNFC have crosslinked with PVAm. The crosslinked membranes were less sensitive to liquid water and the crystallinity of PVAm was tuned by the conditions of the membrane elaboration. In both processes, CO2 selectivity and permeability were enhanced especially at high water vapor concentration by the use of PVAm and AEAPTMS suggesting the existence of a facilitation effect due to amine-CO2 interaction, while the mechanical integrity of the swollen membranes remained intact.

Carboxybetaine functionalized nanosilicas as protein resistant surface coatings

Materials with protein resistant properties are increasingly sought after for their potential application as low-fouling surface coatings. Hydrophilic coatings with improved resistance to protein fouling have been prepared from zwitterionic carboxybetaine (CB) functionalized silica nanoparticles (SiNPs). The authors report three methods of coating preparation via direct tethering of CB to predeposited particle films, a two-step surface functionalization process, and deposition of CB functionalized particle dispersions. The pH at which aqueous CB solutions were prepared and reacted to SiNPs was found to drastically influence the mechanism of CB attachment and affect the protein resistance of the resultant coatings. Depending on the method of coating preparation, protein binding to functionalized particle coatings was reduced by up to 94% compared to unfunctionalized SiNP control surfaces. As a result, all three methods offer simple and scalable fabrication routes for the generation of hydrophilic, zwitterionic interfaces with improved inhibition to protein fouling.

Kinetics of Alkoxysilanes and Organoalkoxysilanes Polymerization: A Review

Scientists from various different fields use organo-trialkoxysilanes and tetraalkoxysilanes in a number of applications. The silica-based materials are sometimes synthesized without a good understanding of the underlying reaction kinetics. This literature review attempts to be a comprehensive and more technical article in which the kinetics of alkoxysilanes polymerization are discussed. The kinetics of polymerization are controlled by primary factors, such as catalysts, water/silane ratio, pH, and organo-functional groups, while secondary factors, such as temperature, solvent, ionic strength, leaving group, and silane concentration, also have an influence on the reaction rates. Experiments to find correlations between these factors and reaction rates are restricted to certain conditions and most of them disregard the properties of the solvent. In this review, polymerization kinetics are discussed in the first two sections, with the first section covering early stage reactions when the reaction medium is homogenous, and the second section covering when phase separation occurs and the reaction medium becomes heterogeneous. Nuclear magnetic resonance (NMR) spectroscopy and other techniques are discussed in the third section. The last section summarizes the study of reaction mechanisms by using ab initio and Density Functional Theory (DFT) methods alone, and in combination with molecular dynamics (MD) or Monte Carlo (MC) methods.

Hydrolytic Stability of 3-Aminopropylsilane Coupling Agent on Silica and Silicate Surfaces at Elevated Temperatures

3-Aminopropylsilane (APS) coupling agent is widely used in industrial, biomaterial, and medical applications to improve adhesion of polymers to inorganic materials. However, during exposure to elevated humidity and temperature, the deposited APS layers can decompose, leading to reduction in coupling efficiency, thus decreasing the product quality and the mechanical strength of the polymer-inorganic material interface. Therefore, a better understanding of the chemical state and stability of APS on inorganic surfaces is needed. In this work, we investigated APS adhesion on silica wafers and compared its properties with those on complex silicate surfaces such as those used by industry (mineral fibers and fiber melt wafers). The APS was deposited from aqueous and organic (toluene) solutions and studied with surface sensitive techniques, including X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), streaming potential, contact angle, and spectroscopic ellipsometry. APS configuration on a model silica surface at a range of coverages was simulated using density functional theory (DFT). We also studied the stability of adsorbed APS during aging at high humidity and elevated temperature. Our results demonstrated that APS layer formation depends on the choice of solvent and substrate used for deposition. On silica surfaces in toluene, APS formed unstable multilayers, while from aqueous solutions, thinner and more stable APS layers were produced. The chemical composition and substrate roughness influence the amount of deposited APS. More APS was deposited and its layers were more stable on fiber melt than on silica wafers. The changes in the amount of adsorbed APS can be successfully monitored by streaming potential. These results will aid in improving industrial- and laboratory-scale APS deposition methods and increasing adhesion and stability, thus increasing the quality and effectiveness of materials where APS is used as a coupling agent.

Preparation and characterization of a microemulsion via polycondensation of alkoxyl silane

A microemulsion was successfully prepared via polycondensation of alkoxy silanes.

Modification of Bacterial Cellulose with Organosilanes to Improve Attachment and Spreading of Human Fibroblasts

Bacterial Cellulose (BC) synthesized by Acetobacter xylinum has been a promising candidate for medical applications. Modifying BC to possess the properties needed for specific applications has been reported. In this study, BCs functionalized by organosilanes were hypothesized to improve the attachment and spreading of Normal Human Dermal Fibroblast (NHDF). The BC gels obtained from biosynthesis were dried by either ambient-air drying or freeze drying. The surfaces of those dried BCs were chemically modified by grafting methyl terminated octadecyltrichlorosilane (OTS) or amine terminated 3-aminopropyltriethoxysilane (APTES) to expectedly increase hydrophobic or electrostatic interactions with NHDF cells, respectively. NHDF cells improved their attachment and spreading on the majority of APTES-modified BCs (∼70-80% of area coverage by cells) with more rapid growth (∼2.6-2.8× after incubations from 24 to 48h) than on tissue culture polystyrene (∼2×); while the inverse results (< 5% of area coverage and stationary growth) were observed on the OTS-modified BCs. For organosilane modified BCs, the drying method had no effect on in vitro cell attachment/spreading behaviors.

Novel hybrid epoxy silicone materials as efficient anticorrosive coatings for mild steel

Novel hybrid organic–inorganic coatings were successfully prepared, coated on mild steel, and subjected to different spectral, electrochemical and morphological characterizations.

High interfacial activity of polymers "grafted through" functionalized iron oxide nanoparticle clusters

The mechanism by which polymers, when grafted to inorganic nanoparticles, lower the interfacial tension at the oil-water interface is not well understood, despite the great interest in particle stabilized emulsions and foams. A simple and highly versatile free radical "grafting through" technique was used to bond high organic fractions (by weight) of poly(oligo(ethylene oxide) monomethyl ether methacrylate) onto iron oxide clusters, without the need for catalysts. In the resulting ∼1 μm hybrid particles, the inorganic cores and grafting architecture contribute to the high local concentration of grafted polymer chains to the dodecane/water interface to produce low interfacial tensions of only 0.003 w/v % (polymer and particle core). This "critical particle concentration" (CPC) for these hybrid inorganic/polymer amphiphilic particles to lower the interfacial tension by 36 mN/m was over 30-fold lower than the critical micelle concentration of the free polymer (without inorganic cores) to produce nearly the same interfacial tension. The low CPC is favored by the high adsorption energy (∼10(6) kBT) for the large ∼1 μm hybrid particles, the high local polymer concentration on the particles surfaces, and the ability of the deformable hybrid nanocluster cores as well as the polymer chains to conform to the interface. The nanocluster cores also increased the entanglement of the polymer chains in bulk DI water or synthetic seawater, producing a viscosity up to 35,000 cP at 0.01 s(-1), in contrast with only 600 cP for the free polymer. As a consequence of these interfacial and rheological properties, the hybrid particles stabilized oil-in-water emulsions at concentrations as low as 0.01 w/v %, with average drop sizes down to 30 μm. In contrast, the bulk viscosity was low for the free polymer, and it did not stabilize the emulsions. The ability to influence the interfacial activity and rheology of polymers upon grafting them to inorganic particles, including clusters, may be expected to be broadly applicable to stabilization of emulsions and foams.

Iron oxide nanoparticles grafted with sulfonated copolymers are stable in concentrated brine at elevated temperatures and weakly adsorb on silica

Magnetic nanoparticles that can be transported in subsurface reservoirs at high salinities and temperatures are expected to have a major impact on enhanced oil recovery, carbon dioxide sequestration, and electromagnetic imaging. Herein we report a rare example of steric stabilization of iron oxide (IO) nanoparticles (NPs) grafted with poly(2-acrylamido-2-methylpropanesulfonate-co-acrylic acid) (poly(AMPS-co-AA)) that not only display colloidal stability in standard American Petroleum Institute (API) brine (8% NaCl + 2% CaCl2 by weight) at 90 °C for 1 month but also resist undesirable adsorption on silica surfaces (0.4% monolayer NPs). Because the AMPS groups interacted weakly with Ca(2+), they were sufficiently well solvated to provide steric stabilization. The PAA groups, in contrast, enabled covalent grafting of the poly(AMPS-co-AA) chains to amine-functionalized IO NPs via formation of amide bonds and prevented polymer desorption even after a 40,000-fold dilution. The aforementioned methodology may be readily adapted to stabilize a variety of other functional inorganic and organic NPs at high salinities and temperatures.

Aminoalkoxysilane reactivity in surface amine gradients prepared by controlled-rate infusion

The reactivity of a series of substituted aminoalkoxysilanes for surface amine gradient formation has been studied using a newly developed time-based exposure method termed controlled-rate infusion (CRI). The aminoalkoxysilanes used include those that contain primary, secondary, and tertiary monoamines as well as more than one amine group (diamine and triamine). X-ray photoelectron spectroscopy (XPS) was used to confirm the presence of a gradient in each case and to acquire detailed information on gradient composition from which kinetic data were obtained. The total area under the N 1s XPS spectra allows for the extent of amine modification to be quantitatively assessed along each gradient. The N 1s peaks actually appear as doublets, providing additional data on the level of protonation and, hence, amine basicity on the dry surface. The degree of protonation showed an interesting trend toward smaller values running from top to bottom along gradients incorporating the most basic amines. The gradient profiles, including initial steepness and extent of saturation, were shown to be highly dependent on the aminoalkoxysilane precursor employed. The highest levels of modification were achieved for the diamine and primary monoamine precursors while the more hindered amines produced lower levels of surface modification and took longer for saturation to be achieved. By fitting the gradient data to a simple first-order kinetic model, rate constants for the condensation reaction between each aminosilane and accessible surface silanol groups were obtained. The rate constants follow the trend: triamine ~ diamine > monoamine and primary > secondary > tertiary, indicating kinetic factors also play an important role in controlling surface modification. The presence of more than one amine group on the silane is concluded to enhance the rate of condensation to the surface silanol groups, while the more hindered secondary and tertiary amines slow condensation. Collectively, the results provide valuable new data on how the number of amine groups, degree of substitution, and steric hindrance influence silane reactivity with silica surfaces, amine surface coverage, and basicity along the gradient profile.

Mechanisms of silicon alkoxide hydrolysis-oligomerization reactions: a DFT investigation

Silica aerogels possess a variety of unique and remarkable properties, but the mechanisms of silicon alkoxide, Si(OR)(4), hydrolyses and oligomerization in the initial stage of sol-gel processes are still not well understood. On the basis of density functional theory calculations at the B3LYP/6-31G(d,p)//B3LYP/6-311++G(d,p) basis set level, the hydrolysis and oligomerization reactions of Si(OR)(4) in neutral, acidic, and alkaline solutions were systematically investigated and we found that in acidic solutions the precursor Si(OCH(3))(4) was inclined to hydrolyze rather than to condense and the hydrolysis processes were energetically more favorable than the neutral ones. In alkaline solutions, the hydrolysis products oligomerize through an S(N)1 dimerization mechanism and the condensation rates are fast to form denser colloidal aerogels. Our calculations also testify that the subsequent cyclization reactions are energetically unfavorable.

Amine-based nanofibrillated cellulose as adsorbent for CO₂ capture from air

A novel amine-based adsorbent for CO₂ capture from air was developed, which uses biogenic raw materials and an environmentally benign synthesis route without organic solvents. The adsorbent was synthesized through freeze-drying an aqueous suspension of nanofibrillated cellulose (NFC) and N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane (AEAPDMS). At a CO₂ concentration of 506 ppm in air and a relative humidity of 40% at 25 °C, 1.39 mmol CO₂/g was absorbed after 12 h. Stability was examined for over 20 consecutive 2-h-adsorption/1-h-desorption cycles, yielding a cyclic capacity of 0.695 mmol CO₂/g.