On some aspects of the silica surface modification with hexamethylcyclotrisilazane,hexamethyldisilazane and their mixtures

Summary The paper is concerned with the structure of an organic layer bonded to the silica surface modified with silazanes. The changes of the retention volumes of hydrocarbons is studied for the silicas modified with hexamethylcyclotrisilazane, hexamethyldisilazane and their mixtures. It is shown that most of the carbon in the layer after hexamethylcyclotrisilazane modification is bonded to the surface by Si−O−Si bonds. This fact supports the assumption of a fragmentation of the cyclosilane used for modification.     

Modified silica precipitated in the medium of organic solvents — an active rubber filler

Studies were performed on application of highly dispersed silicas, specially obtained in organic solvent medium, to processing of elastomers. Particular attention was paid to silica surface modification and to estimation of an extent of the surface modification. To this aim, near infrared techniques were used and heat effects associated with surface wetting with water and benzene were estimated. Application studies were also conducted on the use of modified silicas in butadiene-styrene rubber.     

硅溶胶改性及其应用研究进展

二氧化硅在自然界中通常为晶态,而以溶胶-凝胶、水热、模板剂等方法人工合成的二氧化硅纳米颗粒(SiO₂ NPs)通常为无定形态。无定形SiO₂ NPs广泛应用于航空航天、催化剂载体、靶向送药等众多高端领域。生产SiO₂ NPs的方法有很多,但制备结构、形貌简单的SiO₂ NPs的主要方式为离子交换法、硅醇盐水解法、单质硅粉水解法,这些方法可制备粒径在10～800 nm的单分散SiO₂ NPs,同时可根据生产条件控制粒子的单分散性与粒径大小。寻找一种成本低廉且成品单分散性好、粒径可控的生产方法成为目前研究的热点。本文简介了SiO₂ NPs的结构形貌、基础性质、生产方法和最佳合成条件,总结了各方法的优缺点与适用领域。随后介绍了近年来SiO₂ NPs的改性研究与应用,最后在此基础上展望了合成硅溶胶存在的挑战与未来需解决的问题。     

Characteristics of morphology,structure and composition of titanium surface under its modification by electrochemical polarization in phosphate‐alkaline solutions

The modification of titanium surface under electrochemical polarization (EP) in the phosphate‐alkaline solutions has been studied using the methods of X‐ray diffraction, electron probe microanalysis, atomic force microscopy, X‐ray photoelectron spectroscopy (XPS), cyclic voltammetry and spectroscopic ellipsometry. It is shown that the morphological parameters of the surface, e.g. roughness and stringiness, as well as its structural‐chemical characteristics, e.g. preferred orientation, size and habit of crystallites, titanium chemical forms, thickness and phase composition of oxide film are generally dependent on the polarization potential. The characteristics of titanium surface modified at low anodic potentials 500, 750 and 1000 mV and 10‐min polarization time have been measured. The processes of Ti surface dissolution and etching along grain boundaries are found to be most intensive at 750 mV. Under 500 mV, these processes are poorly developed yet, while at 1000 mV, the surface passivating film formation limits the previous processes. Despite relatively low polarization potentials (1 V), the surficial oxide films have sufficient thickness (up to ~20 nm) and a specific multilayer structure of variable composition and oxidation state of titanium. The data obtained allow to assert that EP represents an effective tool for morphological and a structural chemical modification of a titanium surface. Copyright © 2015 John Wiley & Sons, Ltd.     

New procedure of silica gel surface modification preparation of gaseous standard mixtures for calibration purposes

The new type of silica gel surface modification with using the trimethylamine as a reagent is described. The samples of chemically modified silica gel have been used for generation of gaseous standard mixtures (methyl chloride as a measurand) using the technique of thermal decomposition of the surface compound. The main aim of the research was to check the suitability of the new type of silica gel surface modification for obtaining methyl chloride as a measurand of gaseous standard mixture. The gaseous standard mixture obtained with using this technique was used for calibration of a thermal desorber-gas chromatography-flame ionization detector (TD-GC-FID) system. The homogeneity of coverage of silica gel surface with the immobilized compound has been evaluated. The full uncertainty budget of determination of liberated amount of methyl chloride has been calculated. The average amount of methyl chloride liberated from the unit sample of chemically modified silica gel is 3.59 +/- 0.13 mg g(-1). The influence of the modification way on the amount of liberated analyte has also been determined.     

The effect of filler surface modification and processing conditions on distribution behaviour of silica nanofillers in polyesters

Dispersion and distribution of nanosized precipitated amorphous silica particles in poly(ethylene terephthalate) PET and poly(butylene terephthalate) PBT matrices have been studied. The effect of silane coupling agent as well as processing conditions has been analysed on the basis of microscopic analysis of sample morphology. N-2-(aminoethyl)-3-aminopropyltrimethoxysilane (A-1120) has been used as a silica surface modifier. The effect of the extrusion process performance with a single and a twin screw extruder has been tested. It has been found that the processing conditions are more important factors determining fine dispersion and homogenous distributions of filler particles in the matrix than the filler surface modification. The results obtained have revealed that single screw extrusion is preferred only for processing the composites comprising the silica modified with aminosilane, while the application of twin screw extrusion leads to homogenous dispersion and fully deagglomeration of filler particles without silane treatment. It has been established that when the concentration of silica filler increased from 3 up to 7% by weight, the secondary process of particle aggregation occurs.     

The modified talcs as semi-active fillers of rubbers

We present a new modification method to additonally micronize talcs to a particle diameter of 0.8 m using silane and titanate coupling agents, thus allowing an increase of acitvity against elastomers. It appears that the silane modification proceeds in greater extent when acid medium is used. After the modifications, the wettability of talcs in water and benzene was measured by the calorimetric technique. A direct correlation between heats of immersionh _i ^W andh _i ^B of silane (titanate) surface coverage has also been found.     

Investigation into the surface modification of aragonite whiskers

Aragonite whiskers (AWs) were treated with several fatty acid surfactants and silane coupling agent in order to determine the optimal modifier by using contact angle measurements. The results revealed that the AWs modified by fatty acids showed more remarkable increase in the contact angle than by silane, suggesting the former were preferentially applied in modifying AWs. While the samples coated with fatty acids exhibited hydrophobicity with contact angles ranging from 104.08° to 137.87° with increasing of carbon chain length. Therefore, the highest contact angle of AWs treated by oleic acid was discussed in detail as an example, which was characterized by field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM), thermo‐gravimetry analyses (TGA), X‐ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR). FESEM and TEM results showed a thin layer coated on the modified sample surface. Both the results of TGA and XPS confirmed organic groups existed in the sample of AWs treated by oleic acid. FTIR demonstrated that calcium dioleate was formed in the modification process. Further, modification mechanism was proposed based on the obtained results. Copyright © 2016 John Wiley & Sons, Ltd.     

Effects of the degree of surface modification on the rheological responses of precipitated silica suspensions in benzyl alcohol

Two types of precipitated silica powders modified by poly (dimethylsiloxane) (PDMS) were suspended in benzyl alcohol and their rheological properties were investigated as a function of silica volume fraction, φ. The suspensions were classified into sol, pre-gel, and gel states based on the increase in φ. An increase in the degree of surface modification by PDMS caused gelation at higher φ. Plots of apparent shear viscosity against shear rate in the sol and pre-gel states of highly modified silica suspensions showed weak shear thickening behavior, while the same plots for silica suspensions with a low modification level exhibited shear thinning behavior. The dynamic moduli of hydrophobic suspensions in the pre-gel and gel states were dependent on the surface modification: the storage modulus G′ was larger than the loss modulus G″ in the linear region and these moduli increased with increasing φ, irrespective of the silica powder. The linear region of the φ range for the precipitated silica suspensions was wider than that for the fumed silica powders modified by PDMS suspended in benzyl alcohol, while the G′ value in the linear region for the precipitated silica suspensions was less than those for the fumed silica suspensions.     

The surface chemical modification of cellulosic fibres in view of their use in composite materials

The surface modification of various cellulosic materials was studied in heterogeneous conditions using different grafting agents bearing anhydride or isocyanate reactive groups. Some of these reagents were oligomeric, others polymeric and most were chosen so as to provide a non-polar character to the surface of the fibres in view of their possible use as reinforcing agents in composites based on polymeric matrices. The success of these chemical modifications was assessed by Fourier-transform Infrared Spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy and elemental analysis. The accessibility of the superficial OH groups varied as a function of the coupling agent in terms of both molecular size and chemical nature and ranged between 1 and 3% of the total hydroxy groups borne by the initial cellulose sample. This revised version was published online in August 2006 with corrections to the Cover Date.     

Chemical modification of silica surface by immobilization of functional groups for extractive concentration of metal ions

Increased utilization of mechanically stable synthetic matrices particularly silica gel as a solid support and its surface modification either by impregnation of organic ligands directly or covalent grafting through spacer unit for extractive concentration of trace elements are highlighted in the present article. Experimental evidences for existence of surface silanol and its chemical nature have explored the idea of silica surface modification. Recent methods of development in functionalized silica synthesis by attachment of various ligands or organic reagents to the silica surface and techniques of characterization of the modified surface have been reported. Analytical applications of various modified silica surfaces, in particular, adsorption of trace elements taking separation and preconcentration into account from complex synthetic mixture as well as natural water is presented.     

Synthesis and surface modification of mesoporous mcm-41 silica materials

Surface modification offers a great opportunity to adjust both the pore diameter and surface properties of MCM-41 type organic–inorganic hybrid materials which result in materials of improved hydrothermal and mechanical stability. Therefore, MCM-41 silica, surface modified with organic ligands, are promising systems with engineered properties and attractive for advanced applications. In the present study, after optimization of the reaction conditions highly ordered MCM-41 silica spheres with uniform mesopores were prepared by the pseudomorphic transformation route. The effect of functionality and alkyl chain length of the alkyl ligands during surface modification was probed by using butyl and octylsilanes with two different functionalities. Due to steric hindrance, the longer chains are assumed to bind only on the outer silica surface and near the entrance of the pores, while the shorter chains are also able to bind to the interior mesopore walls. The resulting materials were comprehensively characterized before and after surface modification using nitrogen sorption techniques, XRD, SEM, solid-state NMR spectroscopy and FTIR spectroscopy. From chromatographic test measurements it was found that the separation power primarily depends on surface coverage and alkyl chain length. On the basis of the present data, surface modified mesoporous silica of MCM-41 type are very promising candidates for future chromatographic applications.     

Effect of surface modification of colloidal silica nanoparticles on the rigid amorphous fraction and mechanical properties of amorphous polyurethane–urea–silica nanocomposites

Colloidal silica nanoparticles (NPs) modified with eight different silane coupling agents were incorporated into an amorphous poly(tetramethylene oxide)‐based polyurethane–urea copolymer matrix at a concentration of 10 wt % (4.4 vol %) in order to investigate the effect of their surface chemistry on the structure–property behavior of the resulting nanocomposites. The rigid amorphous fraction (RAF) of the nanocomposite matrix as determined by differential scanning calorimetry and dynamic mechanical analysis was confirmed to vary significantly with the surface chemistry of the NPs and to be strongly correlated with the bulk mechanical properties in simple tension. Hence, nanocomposites with an RAF of about 30 wt % showed a 120% increase in Young's modulus, a 25% increase in tensile strength, a 15% decrease in elongation at break with respect to the neat matrix, which had no detectable RAF, whereas nanocomposites with an RAF of less than 5% showed a 60% increase in Young's modulus, a 10% increase in tensile strength and a 5% decrease in the elongation at break. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2543–2556     

Preparation of ultrathin coating layers using surface modified silica nanoparticles

Silica nanoparticles are used in various applications including catalysts, paints and coatings. To reach an optimal performance via stability and functionality, in most cases, the surface properties of the particles are altered using complex procedures. Here we describe a simple method for surface modification of silica nanoparticles (SNP) using sequential adsorption of oppositely charged components. First, the SNPs were made cationic by adsorption of a cationic polyelectrolyte. Poly(allylamine hydrochloride) (PAH) and polyethyleneimine (PEI) were chosen as polycations to investigate the difference between a linear and a branched polyelectrolyte. Next, the dispersion of cationic SNPs was combined with an anionic alkyl ketene dimer (AKD) emulsion. Using this approach cationic, hydrophobic silica particle dispersions were produced. Dynamic light scattering, contact angle measurements and atomic force microscopy (AFM) were used for analyzing the particle and coating layer properties. The chosen polyelectrolyte affected the structure of the dispersion. The layer build-up was studied in detail using a quartz crystal microbalance with dissipation monitoring (QCM-D). The adsorption and layer properties of the cationic polyelectrolytes adsorbed on silica as well as the affinity of AKD to this layer were explored. The application possibilities of the modified particle dispersions were demonstrated by preparing paper and silica surfaces with tailored properties, such as elevated surface hydrophobicity, using an ultrathin coating layer.     

Plasma surface modification of chitosan membranes: characterization and preliminary cell response studies

Surface modification of biomaterials is a way to tailor cell responses whilst retaining the bulk properties. In this work, chitosan membranes were prepared by solvent casting and treated with nitrogen or argon plasma at 20 W for 10-40 min. AFM indicated an increase in the surface roughness as a result of the ongoing etching process. XPS and contact angle measurements showed different surface elemental compositions and higher surface free energy. The MTS test and direct contact assays with an L929 fibroblast cell line indicated that the plasma treatment improved the cell adhesion and proliferation. Overall, the results demonstrated that such plasma treatments could significantly improve the biocompatibility of chitosan membranes and thus improve their potential in wound dressings and tissue engineering applications.     

Modification of silica with mixtures of hexamethylcyclotrisilazane and hexamethyldisilazane

Summary For chromatographic purposes the use of mixtures instead of individual silylating agents can produce better deactivated surface than those shown by silicas modified by hexamethylcyclotrisilazane or hexamethyldisilazane separately.     

A study on the surface free energy of modified silica fillers and poly(ethylene terephthalate) fibers by inverse gas chromatography

The surface free energy of modified silica fillers and poly(ethylene terephthalate) (PET) fibers was analyzed by inverse gas chromatography in order to investigate the relationship between their surface characteristics and the performance of the composite formed from these materials. The adsorption isotherms of n-heptane and 1-propanol were determined by the elution-peak-maximum method. The dispersive and polar components of the surface free energy were determined by use of the Young–Dupré equation and the Fowkes equation on the basis of the saturated spreading pressure derived from the Gibbs adsorption equation. The acidity and the basicity of the surface were estimated by the specific retention volume of each probe molecule with different donor number and acceptor number. It was found that the dispersive component of the surface free energy for modified silica fillers was mostly lower than that for original silica filler. The polar component of the surface free energy for ethylene glycol modified silica filler became large, while that for n-butanol modified silica filler decreased remarkably. It was also found that original silica filler exhibited high acidity, while modified silica fillers exhibited low acidity. Although these methods have been applied to PET fibers, the surface free energy could not be determined quantitatively because of the surface change during the pretreatment of PET fibers. It was observed that the polar component of the surface free energy decreased when the pretreatment was made at a temperature higher than the glass-transition temperature of PET. It became clear that the interaction between modified silica fillers and PET fibers correlated well with the basicity of the fillers, but not with their acidity. Received: 18 October 1999 Accepted: 8 February 2000     

碳纤维表面改性研究进展

碳纤维因其优异的综合性能常被用作树脂基体的增强材料.然而由于碳纤维与树脂基体之间的界面结合性能较差,其增强的复合材料的力学性能往往与理论值相差甚远,因此必须对碳纤维进行表面改性,以提高其与聚合物基体的界面粘结性能.本文作者综述了国内外关于碳纤维表面改性技术的研究进展,概述了涂层法、氧化法、高能辐射法等改性方法对碳纤维增强复合材料界面强度的改性效果.     

Model hydrophobing compounds with nitrogen or sulphur atoms in oxyethylene structures,as modifiers of silica filler

Results of studies are presented on effect of new model compounds, applied to modify precipitated silica, on reinforcing of butadiene-styrene rubber vulcanizates filled with modified silica. Precipitated silica applied for the pur pose has been obtained according to our own procedure. Estimation of heats of immersion, mainly in benzene, has documented effect of model compounds involving hydrophobization of silica surface.For comparative reasons, results of strength tests have also been presented on vulcanizates of butadiene-styrene rubber filled with silica modified with a recognized coupling agent-mercaptosilane A-189.     

Ion-beam-induced surface modification and nanostructuring of AIIIBV semiconductors

Ion-beam-induced modification of InSb (0 0 1) semiconductor surface has been studied by means of atomic force microscopy and Kelvin probe force microscopy. It was found that non-stoichiometric sputtering of the compound surface and beam enhanced surface diffusion led to unusual development of surface structures in the form of dots and wires with nanometer scale dimensions. The shape, the size and the surface density of nanostructures were investigated as a function of the beam flux and fluence, and as a function of the crystal orientation with respect to the ion-beam direction. The mechanisms involved in the surface modification were compared with results of Monte-Carlo computer simulations of anisotropic surface diffusion.