Organofunctional Groups Research Articles

A Glass-Interphase for Highly Reversible and Stable RT-Na/S Batteries

Owing to the high theoretical specific capacity (1165 mA h g-1), high natural abundance, and low redox potential (-2.71 V vs standard hydrogen electrode), sodium metal is considered as an ideal anode material for the next-generation high-energy batteries. Though, a high-temperature variant of the sodium-sulfur batteries has already been commercialized, its compromised safety (due to high-temperature operation, 250 – 300 ⁰C) has triggered the research interest in developing its room-temperature analogue. At room-temperature, the thermodynamic instability of Na metal with the liquid electrolytes often leads to develop a thick and chemically unstable interphase, often called the solid electrolyte interphase (SEI). Upon Na plating/stripping, the SEI grows and dissolves repeatedly, results in consuming both the Na anode and the electrolyte inventory. The Na dendrites, the primary unknown risk associated with Na metal-based batteries, are inclined to develop from the fractured sites of the SEI. The SEI exfoliation can be attributed to weak chemical adhesion between the SEI and the Na metal anode. Functional additives, engineered solvents, and the high concentration electrolytes have often been used to alter the mechanical and electrochemical properties of the SEI. It is apparent that, a stable and durable SEI is the key to creating a secure, dendrite-free, and long-lasting RT-Na/S batteries.More recently, the idea of glass-electrolytes to stabilize the metal anodes is disclosed by the Nobel laureate Prof. J. Goodenough. The glass-electrolyte is used to suppress the dendrite growth and ensured improved safety of the high-energy metal-sulfur batteries. However, the cell experiences a huge interfacial resistance due to metal anode/glass-electrolyte interface.The present work relates to the development of a glass-interphase for RT-Na/S batteries. The interphase is grown directly over the sodium metal anode through a simple and scalable approach. To growth the interphase, a novel organic molecule is used to facilitate the formation of the glass-interphase, and called as “glass-interphase forming additive (GIFA). In general, GIFAs contains the hydrolysable group, which is commonly an amine, acyloxy, alkoxy, or halogen on one side, and one Si atom. It contains organo-functional group, such as epoxide, on other side. The presence of oxide or hydroxide is essential in realizing interaction of GIFA with the sodium metal surface.

Enhancing adhesion strength via synergic effect of atmospheric pressure plasma and silane coupling agent

To facilitate the widespread use of carbon fiber reinforced thermoplastic polymer (CFRTP), enhancing its adhesion strength with other materials is crucial. In this study, we investigated the synergic effect and underlying mechanism of atmospheric pressure plasma and silane coupling agent on the adhesion improvement of CFRTP. The plasma/mercapto-silane-treated CFRTP demonstrated a remarkable 282% increase in adhesion strength compared to untreated CFRTP. Our post-fracture analysis revealed that the weakest CFRTP/adhesive interface was fortified, resulting in a shift in the failure mode from adhesive to substrate. Equipment analyses indicated that plasma and silane coupling agent contributed to the formation of C-O and Si-O-Si linkages, respectively. The application of both treatments led to the creation of a macro-network at the CFRTP/adhesive interface through both linkages, which resulted in a much more substantial increase in adhesion strength than either treatment alone. Lastly, we propose guidelines for enhancing the adhesion strength of CFRTP by elucidating the dependence of the synergic or antagonistic effect on the organofunctional group in silane coupling agent.

Enhanced surface insulation for SiO2/epoxy resin composites through co-modification of nanofiller with silane coupling agent and plasma

To enhance the surface insulation properties of SiO2/epoxy resin composites, the SiO2 filler is co-modified with a chemical method and dielectric barrier discharge plasma in this work. The effects on the micro-structures, electrical parameters and surface insulation properties of the materials are studied. The results show that chemical modification using the silane coupling agent (KH550) can effectively introduce organo-functional groups into SiO2 filler. On the other hand, plasma modification shows little effect on the organo-functional group but significantly increases the dispersity of the nanoparticles, therefore reducing filler conglobation in epoxy resin composite. The composite samples with SiO2 doping concentration of 1 wt.%, 2 wt.%, 3 wt.%, 5 wt.% and 7 wt.% are prepared and characterized. It is found that the synergy of chemical and plasma methods could significantly improve the surface insulation of composite samples. Through doping 2 wt.% of the co-modified SiO2 filler, the direct current flashover voltage of the composites in dry air at atmospheric pressure can be increased to 1.53 times of the pure epoxy. The enhanced surface insulation properties are explained by the trap effect and the change of electrical parameters through the co-modification process.

Effect of Water on the Rearrangement of Hydrogen-Bonded Structures of 4-Aminobenzoic Acid on Au(111) and Ag(111) Surfaces

Water plays a very important role in promoting the biological self-assembly process, while our understanding is limited about how water affects and reshapes the assembly structure. Herein, the water-induced assembly structures of 4-aminobenzoic acid (PABA) on Au(111) and Ag(111) are investigated by scanning tunneling microscopy and density functional theory calculations. Water molecules could break the weak-hydrogen-bonded Kagomé structure on Au(111) and the consequent four-leaf clover structure formed by intermediate hydrogen bonds between the functional groups of PABA molecules and spontaneous release of water molecules. Upon water exposure, the four-leaf clover structure remains intact on the Au(111) surface, while the water molecules can break selectively the weak hydrogen bonds connecting the four-leaf clovers on Ag(111) and form preferential hydrogen bonds with the functional groups of PABA molecules, resulting in the generation of the water-involved structure. The adsorption energy of this hydrated structure on Ag(111) is significantly lower than that on Au(111), which may be the reason that the water-involved structure only appears on Ag(111). The result provides the real-space evidence of the interaction between water and organofunctional groups related to the type of the metal surface.

Influence of Perfluorooctanoic Acid on Structural, Morphological, and Optical Properties of Hybrid Silica Coatings on Glass Substrates

In recent years, various coatings based on fluorinated materials, used in a commercial application, have been created through many preparation routes. However, the techniques utilized to realize these coatings required either expensive and complex equipment, imply multiple manufacturing steps, or are time- or cost-consuming. In this paper, the major target was to develop fluorinated hybrid coatings presenting sustainable hydrophobicity and good transparency simultaneously. The sol–gel method was proposed to obtain these fluorinated hybrid coatings because it does not require expensive equipment, or the existence of stabilizing agents that reduce the storage period, it consumes less energy, and it is easy to implement. The influence of perfluorooctanoic acid, utilized in the sol–gel processing of hybrid silica materials, on the structural, morphological, and optical properties of coatings deposited on glass substrates, was evaluated. Different silane precursors (tetraethyl orthosilicate (TEOS), triethoxymethylsilane (MTES), and trimethoxyhexadecylsilane (HDTMES)) were utilized to synthesize hybrid silica materials. The properties of the obtained materials were characterized by FTIR, UV–Vis, TEM, TGA, AFM, Ellipsometry, and Contact Angle analyses. FTIR spectroscopy shows the formation of a silica network tailored with organofunctional and fluoroalkyl groups. The fluorinated silica coatings presented smooth surfaces and good transparency, with a transmittance of ~90% in the visible range. It was found that the fluorinated silica materials improved the coating’s hydrophobicity (~110° in contact angle with water). These fluorinated silica materials can create multifunctional structures with antireflective and hydrophobic coatings for possible optical devices.

(Digital Presentation) Electrochemically Induced Sol-Gel Deposition

Sol-gel electrochemistry has gained great popularity in the past decades, mostly because of the ease of formation of silica and organosilica films with tailor-made properties that can be advantageously exploited for several applications when coated on a suitable electrode surface. In particular, silica-based materials displaying a regular structure at the mesoporous level have been found to be very promising electrode modifiers [1-3] because they ensure fast mass transport processes [4], which are often rate-determining in electrochemistry. In this context, an original electrochemical method has been developed to indirectly generate sol-gel-derived (organo)silica thin films, with promising applications in the field of bioelectrochemistry and sensors and beyond. After a brief introduction to the field, this lecture will present the concept the electrochemically-assisted generation of sol-gel films [5], its interest for bioencapsulation and elaboration of electrochemical bioreactors [6-9], its suitability to get nanostructured electrode surfaces with preferential pore orientation [3,10,11], including their modification with organo-functional groups [3,12,13] and their permselective properties [14-16], and will end with promising applications in electroanalysis and sensors [17-20], electrocatalysis [20,21], energy storage [22] or electrochromism [23].

Tailoring microstructures of carbon fiber reinforced carbon aerogel-like matrix composites by carbonization to modulate their mechanical properties and thermal conductivities

The microstructure evolution of carbon fiber reinforced carbon aerogel-like matrix (C/CA) composites with carbonization temperature and its influence on their properties were investigated. The removal of residual organo-functional groups of the C/CA precursors is dominant when carbonized at 600–750 °C with a large volume shrinkage difference by 17–22% as compared to that at 1200 °C, while the rearrangement of novolac structures is dominant at 900–1200 °C with a slight volume shrinkage fluctuation of 6%. Resultantly, the amount of micropore first increases and then decreases, while the particle size experiences an opposite change. The microstructure correspondingly transforms from a completely amorphous state to a partially amorphous state with graphite crystallites in low-angle misorientation, and then with graphite-like entangling ribbons. Due to the reduced residual tensile stress and increased interfacial bonding, the resulting composites with a variable bulk density of 0.58–0.64 g cm−3 have much higher compressive strengths of 45.8–96.9 MPa than other reported carbon foams or aerogels with similar bulk densities. The increase of strength and modulus with carbonization temperature is mainly due to the smaller tensile stress, higher particle packing compactness, larger microcrystallite size and less residual organo-functional groups. The composites also present a relatively low thermal conductivity of 0.12–0.59 W m−1 K−1. The increase of thermal conductivity with temperature is related to the synergistic effect of reduced phonon scattering associated with smaller specific surface area, larger microcrystallite size and less organo-functional groups and improved phonon transfer associated with increased inter-particle contact area.

Chemistry and Applications of Organosilanes – An Overview

Organofunctional silanes are hybrid materials of silanes having attracted greater attention since the last decade owing to its versatile properties and wide range of applications. In this review, we have summarized the types of organosilanes (RnSiX4-n), their reactions, and applications. Organosilanes usually have two reactive groups, organofunctional groups and hydrolyzable alkoxy groups, which undergo hydrolysis and condensation. Silanols (Si-OH) and siloxane (Si-O-Si) structures are formed by hydrolysis and condensation reactions, respectively. In general, organosilanes acts as excellent binding agent due to its bridging capacity through (Si-O-Si) bond linkage with metal surfaces. From the extensive literature survey carried out, we understand that the silanes are synthesized without comprehending the reaction kinetics mechanism. In the past few decades, significant advances were witnessed in the development of various organofunctional silanes, which were used in a wide range of research areas based on its bifunctional characteristics.

Desirable bonding interactions between organo-functional triazinedithiol groups and heavy metal ions for significantly improved adsorption or dispersion property

Effective bonding interactions between various organo-functional groups and metals can contribute to novel materials or fancy performances. In order to reveal the superiority of triazinedithiolsilanes with di-sulfydryl groups over the conventional mercapto silanes with mono-sulfydryl, and amino silanes with mono-amine, for the first time, the above three silanes have been chemically anchored onto cutting-edge dendritic mesoporous silica nanospheres (DMSNs) for performance comparison. The three composite materials have been designed to serve as not only the adsorbents to remove heavy metal cadmium Cd(II), but also the catalyst-supports to load and disperse metal (noble metal Ag, Pd, and base metal Ni) nanoparticles (NPs). The abilities of triazinedithiol-functionalized DMSNs are far superior to the other two specimens both in Cd(II) capture and metal dispersion, owing to the specific nature of triazinedithiol group. The qe values of triazinedithiol-, mercapto-, and amino-functionalized DMSNs can reach to 1280, 816, 900 mg/g, respectively. Moreover, triazinedithiol-functionalized DMSNs could disperse metal NPs more uniformly that the conventional silane-modified ones. It is expected that triazinedithiolsilane compounds could faultlessly replace conventional mercapto silanes in some practical application fields and would shine brilliantly in the future.

Probing Covalent Interactions at a Silicone Adhesive/Nylon Interface.

Covalent bonding is one of the most robust forms of intramolecular interaction between adhesives and substrates. In contrast to most noncovalent interactions, covalent bonds can significantly enhance both the interfacial strength and durability. To utilize the advantages of covalent bonding, specific chemical reactions are designed to occur at interfaces. However, interfacial reactions are difficult to probe in situ, particularly at the buried interfaces found in well-bonded adhesive joints. In this work, sum frequency generational (SFG) vibrational spectroscopy was used to directly examine and analyze the interfacial chemical reactions and related molecular changes at buried nylon/silicone elastomer interfaces. For self-priming elastomeric silicone adhesives, silane coupling agents have been extensively used as adhesion promoters. Here with SFG, the interfacial chemical reactions between nylon and two alkoxysilane adhesion promoters with varied functionalities (maleic anhydride (MAH) and epoxy) formulated into the silicone were observed and investigated. Evidence of reactions between the organofunctional group of each silane and reactive groups on the polyamide was found at the buried interface between the cured silicone elastomer and nylon. The adhesion strength at the nylon/cured silicone interfaces was substantially enhanced with both silane additives. SFG results elucidated the mechanisms of organo-silane adhesion promotion for silicone at the molecular level. The ability to probe and analyze detailed interfacial reactions at buried nylon/silicone interfaces demonstrated that SFG is a powerful analytical technique to aid the design and optimization of materials with desired interfacial properties.

Synthesis of organotrimethoxy silane modified alumino-siloxane hybrid gels: Physico-chemical properties evaluation and design of superhydrophobic smart powders and coatings

Herein, we investigated the effect of a series of mono-substituted organotrimethoxy silanes (RTMS) on the sol-gel polymerization of hydrolyzed alumina sol (AIP) into a hybrid alumino-siloxane (AIP-RTMS) gels. RTMS with different organofunctional groups (R = methyl, vinyl, phenyl, octyl, aminopropyl, and glycidoxypropyl) were used for this purpose. The study revealed that the non-hydrolysable organo-functional groups of RTMS co-precursors strongly influence the gelation behaviour of AIP-RTMS hybrid gels. Evaporative and freeze drying methods were employed to obtain AIP-RTMS xerogels and cryogels, respectively. The remarkable variation observed in textural and morphological features of AIP-RTMS cryogels enabled them to possess greater surface area and pore-volume, and very low density than their xerogel counterpart. The study revealed that, the fissured arrangement of loosely layered morphology and non-hydrolyzable functional groups of RTMS in cryogels have a considerable influence on the surface wettability. Interestingly, a shift in hydrophobicity to superhydrophobicity was observed in AIP-VTMS and AIP-MTMS cryogels when compared to their xerogel counterparts. An excellent water repelling ability is also demonstrated using a fabric coated with AIP-VTMS hybrid. Owing to these beneficial properties, alumino-siloxane hybrids developed in this study have strong potential for the preparation of smart aerogels and coatings suitable in purification/separation applications.

Synthesis and performance of moisture curable solvent free silane terminated polyurethanes for coating and sealant applications

AbstractPolyurethanes (PUs) constitute one of the most versatile class of polymers with respect to composition, properties, and applications. Having an excellent elastomeric performance, PUs has been used in a wide range of applications. Additionally, silane terminated modified polyurethanes (STPUs) combine advantageous characteristics of PUs and organosilicon. Two PUs and four STPUs modified by a silane end‐capper N‐ethyl‐3‐trimethoxysilyl‐2‐methylpropanamine and N‐cyclohexyl aminomethyltriethoxysilane were synthesized and acted as an adhesives or coatings which could be suitable for use in moisture‐curing compositions at room temperature without releasing CO2. The effect of isocyanate groups in the polyurethane backbone and organofunctional groups in the aminosilane structure (R1–NH–R2–Si[OC2H5]3), R1 (alkyl or aryl), the spacer R2 (α or γ) was examined. The chemical and physical structures of the PUs and STPUs were investigated by nuclear magnetic resonance (13C and 1H), dynamical mechanical analysis (DMA), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT‐IR) and the mechanical properties were evaluated by universal tensile tests. The results showed that STPUs were successfully synthesized as moisture curable, exhibiting low viscosity with adequate tensile strength and elongation can be prepared environmentally benign by utilizing secondary aminosilane end‐cappers and an optimal combination of the polyol molecular weight and NCO/OH ratio.

Improved adhesion of polyurethane-based nanocomposite coatings to tin surface through silane coupling agents

Conformal coatings with higher adhesion strength is crucial for mitigating the growth of whiskers from the pure tin (Sn) or Sn-rich surfaces of the Pb-free electronics. Silane coupling agents have the ability to form a durable bond between polymeric coatings and metallic materials. The main goal of this paper is to investigate the effect of silane agents on the adhesion behavior of polyurethane (PU), polyurethane acrylate (PUA) and both coatings filled with silicone rubber (SR) nanoparticles on the tin solder pads. It was found that an isocyanate-based silane provided excellent adhesion for PU and PU + SR coatings and an acrylic-based silane for PUA and PUA + SR coatings on the tin surface. This was due to the reaction bond formation between the silane coupling agent and the coating. Hence, the selection of silane coupling agents with the organofunctional group similar to the coating material is crucial to improve the adhesion properties of the coating.

Electroinduced Surfactant Self-Assembly Driven to Vertical Growth of Oriented Mesoporous Films.

Supramolecular soft-templating approaches to mesoporous materials have revolutionized the generation of regular nanoarchitectures exhibiting unique features such as uniform pore structure with tunable dimensions, large surface area, and high pore volume, variability of composition, and/or ease of functionalization with a wide range of organo-functional groups or good hosts for the in situ synthesis of nano-objects. One appealing concept in this field is the development of ordered mesoporous thin films as such a configuration has proven to be essential for various applications including separation, sensing, catalysis (electro and photo), energy conversion and storage, photonics, solar cells, photo- and electrochromism, and low-k dielectric coatings for microelectronics, bio and nanobio devices, or biomimetic surfaces. Supported or free-standing mesoporous films are mostly prepared by evaporation induced self-assembly methods, thanks to their good processing capability and flexibility to manufacture mesostructured oxides and organic-inorganic hybrids films with periodically organized porosity.One important challenge is the control of pore orientation, especially in one-dimensional nanostructures, which is not straightforward from the above evaporation induced self-assembly methods. Accessibility of the pores represents another critical issue, which can be basically ensured in the event of effective interconnections between the pores, but the vertical alignment of mesopore channels will definitely offer the best configuration to secure the most efficient transfer processes through the mesoporous membranes. The orthogonal growth of mesochannels is however not thermodynamically favored, requiring the development of methods enabling self-organization through nonequilibrium states. We found that electrochemistry afforded a real boon to tackle this problem via the electrochemically assisted self-assembly (EASA) method, which not only provides a fast and versatile way to generate highly ordered and hexagonally packed mesopore channels but also constitutes a real platform for the development of functionalized oriented films carrying a wide range of organo-functional groups of adjustable composition and properties.This Account introduces the EASA concept and discusses its development along with the significant progress made from its discovery, notably in view of recent advances on the functionalization of oriented mesoporous silica films, which expand their fields of application. EASA is based on the in situ combination of electrochemically triggered pH-induced polycondensation of silica precursors with electrochemical interfacial surfactant templating, leading to the very fast (a few seconds) growth of vertically aligned silica walls through self-assembly around surfactant hemimicelles transiently formed onto the underlying support. This method benefits from the possibility to deposit uniform thin films onto surfaces of different natures and complex morphologies including at the microscale. From this discovery, our research expanded to cover domains beyond the simple production of bare silica films, turning to the challenge of incorporation and exploitation of organo-functional groups or nanofilaments. So far, the great majority of methods developed for the functionalization of mesoporous silica is based on postsynthesis grafting or co-condensation approaches, which suffer from serious limitations with oriented films (pore blocking, lack of ordering). We demonstrated the uniqueness of EASA combined with click chemistry to afford a versatile and universal route to oriented mesoporous films bearing organo-functional groups of multiple composition. This opened perspectives for future developments and applications, some of which (sensing, permselective coatings, energy storage, electrocatalysis, electrochromism) are also considered in this Account.

Chemical structure of amino-terminated alkyl silanes influencing the strength of aluminum-polyamide joints

Organo-functional silane coupling agents are widely used to promote adhesion in between inorganic and organic materials. Amino-functional silanes can improve bonding with polyamide. Aiming on a mechanically performant aluminum-polyamide joints, the effect of six amino silanes of different chemical structure, namely number and type of amine groups and alkyl spacers lengths, on the joint strength is investigated by means of lap-shear testing. Higher shear strengths are found along with a more pronounced capability of the amine group to form hydrogen bonds with polyamide. The results show that an additional amine group within the organo-functional group can increase joint strength, whereas long alkyl spacers reduce the observed joint strength. It is shown that high lap-shear strengths, in maximum about 15 MPa for N-(2-aminoethyl)-3-aminopropyltrimethoxysilane are achieved and that the high reproducibility can be assured when using right processing routines.

Adsorption Behavior of Divalent Metal Ions onto Surface-functionalized Mesoporous Silicate MCM-41 Having Schiff Base Structure.

Surface functionalized mesoporous silicates, MCM-41s, having 3-(2-pyridylmethylideneimino)propyl group (PI-MCM-41) or 3-(2-quinolylmethylideneimino)propyl group (QI-MCM-41) were prepared via Schiff base reaction, and the adsorption behavior of metal ions onto the modified MCM-41s was investigated. The function groups on the modified MCM-41 surface were confirmed by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and elemental analysis. The metal ions examined, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, and Pb2+, were quantitatively adsorbed on the PI-MCM-41 and QI-MCM-41, except for Mn2+. In the complexation with these metal ions, it was suggested that imine-N and heterocyclic-N atoms act as donor atoms. In addition, it was considered that the hydrophobicity derived from the organo-functional groups modified on MCM-41 contributed to improving the adsorption ability.

3D printed ceramic slurries with improved solid content through optimization of alumina powder and coupling agent

Stereolithography based-3D printing technology requires ceramic slurries with high solid content and low viscosity to prevent the formation of cracks, holes, warping, and other defects in sintered ceramic parts. In this study, several approaches based on optimization of alumina powder and coupling agent were explored to improve the solid content of ceramic slurries. It was shown that slurries containing γ-Al2O3 reached solid content of only 22.5 wt% and viscosity of 15,199 mPa·s. By comparison, slurries composed of α-Al2O3 reached higher solid content of 75 wt% and viscosity of 12,780 mPa·s. Three types of coupling agents, namely (3-Aminopropyl) triethoxysilane, (Aminoethylamino) propyldimethoxymethylsilane and 3-(Trimethoxysilyl) propyl methacrylate (abbreviated as E, F and G, respectively) were used to reduce the viscosity of the slurries. The addition of 10 wt% G led to slurry solid content reaching 82 wt% and viscosity of 860 m·Pas. The significant decrease in viscosity was mainly attributed to the presence of bifunctional hydrolyzable groups in G, which could well attach to alumina. On the other hand, the presence of organo-functional groups might also well attach to the photosensitive resin. The ceramics prepared with γ-Al2O3 exhibited numerous pores in both intraparticle and intergranular while those obtained with α-Al2O3 showed pores in only intergranular. The porous structure in γ-Al2O3 occupied large space, leading to low solid content. Ceramics prepared with 75 wt% solid content possessed flexural strength of 29.3 MPa, bulk density of 2.3 g/cm3 and open porosity of 39.8 %. By comparison, ceramics prepared with 82 % solid content showed flexural strength of 45.0 MPa. In sum, these findings look promising for future preparation of high-solid content 3D printed ceramic slurries for complex ceramics, such as ceramic cores.

Investigation of anti-aging of SBS modified bitumen containing surface organic layered double hydroxide.

To improve the anti-aging ability of SBS modified bitumen (SMB), layered double hydroxide (LDH) organically modified by hexadecyltrimethoxysilane was prepared and utilized for the modification of SMB. According to X-ray photoelectron spectroscopy, hexadecyltrimethoxysilane has been grafted into LDH through chemical bonding. Compared with LDH, the hydrophilicity of organic LDH (OLDH) was obviously reduced, and OLDH possessed better dispersibility and stability in SMB, because of the decrease of hydroxyl and the introduced organo-functional groups on the surface of LDH. The addition of OLDH and LDH can ameliorate the high temperature behavior of SMB, especially OLDH. After aging, bitumen was oxidized and SBS was degraded, which resulted in the physical and rheological property deterioration of SMB. LDH can alleviate the destruction of aging on the performance and chemical structure of SMB. Furthermore, the improvement of LDH on the anti-aging ability of SMB has been further enhanced after hexadecyltrimethoxysilane organic modification.

Morphological and Structural Properties of Amino-Functionalized Fumed Nanosilica and Its Comparison with Nanoparticles Obtained by Modified Stöber Method.

In industry, silica nanoparticles (NPs) are obtained by the fuming and the precipitation method. Fumed silica NPs are commonly used in the preparation of nanocomposites because they have an extremely low bulk density (160–190 kg/m3), large surface area (50–600 m2/g), and nonporous surface, which promotes strong physical contact between the NPs and the organic phase. Fumed silica has fewer silanol groups (Si–OH) on its surface than the silica prepared by the Stöber method. However, the number of –OH groups on the fumed silica surface can be increased by pretreating them with sodium hydroxide (NaOH) before further surface modification. In this study, the effectiveness of the NaOH pretreatment was evaluated on commercial fumed silica NPs with a surface area of 200 m2/g. The number of surface –OH groups was estimated by potentiometric titration. The pretreated fumed NPs, and the precipitated NPs (prepared by the Stöber method) were modified with 3-aminopropyltriethoxysilane (APTES) to obtain A200S and nSiO2-APTES, respectively. The NPs were characterized using electron dispersive scanning (EDS), scanning electron microscopy (SEM), dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), X-ray diffraction (XRD), BET (Brunauer–Emmett–Teller) analysis, and ζ-potential. XRD confirmed the presence of the organo-functional group on the surface of both NPs. After the amino-functionalization, the ζ-potential values of the nSiO2 and A200 changed from −35.5 mV and −14.4 mV to +26.2 mV and +11.76 mV, respectively. Consequently, we have successfully synthesized functionalized NPs with interesting, specific surface area and porosity (pore volume and size), which can be attractive materials for chemical and energy industries.

The role of the filler surface chemistry on the dielectric and thermal properties of polypropylene aluminium nitride nanocomposites

In nanocomposites, different surface states of nanoparticles can potentially provide different interactions with the base polymer and in turn change the bulk properties. Aluminium nitride (AlN) nanoparticles were surface functionalised with three different silane coupling agents (SCAs) with varying organofunctional and hydrolysable groups. The effects of the filler surface chemistry on the resulting AlN/polypropylene (PP) nanocomposites were examined and compared with an unfilled reference system. It is observed that different organofunctional groups can provide different nucleating effects and the dispersion states of nanoparticles while the hydrolysable group is not the dominant factor. The dielectric spectroscopy results show the hydrolysable group of SCA will also result in a difference of the interphase since the trimethoxy silane treated systems show much higher imaginary permittivity than the triethoxy silane treated systems when the frequency is below 1 Hz. The grafted organofunctional layer on the particle surface can provide a significant improvement of the thermal conductivity of the composite materials, e.g. 15 % improvement in thermal conductivity was observed when adding 10 wt% methacrylate silanes treated nano-AlN into PP, while the untreated counterpart only has 5 % improvement.