Dispersion stabilities and rheological properties of fumed silica suspensions

Herein, we have reviewed fumed silica suspensions in dispersing fluids, polymer melts, and polymer solutions, focusing on their dispersion stability and rheological properties as a function of the surface character of fumed silica powders and the silica volume fraction, ?. Hydrophilic fumed silica powders are well dispersed at ? < 0.01 in polar dispersing fluids or polar polymer melts, and their phase states change from sol to gel with increasing ?. Such changes should also be strongly related to the rheological responses of the hydrophilic fumed silica suspensions, which change from Newtonian flow behavior to gel-like elasticity with increasing ?. On the other hand, hydrophobic fumed silica powders are stabilized in both polar and nonpolar dispersing fluids, depending on the interactions between the surface hydrophobic moieties and the dispersing fluids, in addition to those between the residual surface silanol groups and dispersing fluid, except for the particle–particle interactions. Moreover, the effects of the adsorption and desorption of polymers, as well as of non-adsorbing polymers on the dispersion stability and rheological behavior of fumed silica suspensions are discussed, by taking account of their optical microscopic observation and SANS curves.     

化学反应-顶空气相色谱法测定气相二氧化硅表面硅羟基

建立了一种基于化学反应-顶空气相色谱测定气相二氧化硅表面硅羟基含量的新方法.实验取气相二氧化硅放入顶空瓶中于105℃烘箱中加热2 h去除水分,将甲苯稀释的格氏试剂注入密闭的顶空瓶中,格氏试剂与气相二氧化硅表面硅羟基快速反应产生甲烷(CH4),甲烷量与气相二氧化硅表面硅羟基含量成正比.经过气相色谱-氢火焰离子化检测器测定...     

Formation of Hydrophobic Silica Coatings on Stones for Conservation of Historic Sculptures

The conservation of historic sculptures is receiving growing attention because of the increasing air pollution. A hydrophobic silica coating was synthesized to protect historic sculptures from weathering by starting from a solution of tetraethoxyorthosilicate (TEOS) precursor using hexadecyltrimethoxysilane (HDTMS) as hydrophobic modifier in the presence of ammonia as a catalyst. The molar ratio of ethanol, TEOS, H₂O and NH₄OH was kept constant at 8:0.045:3:2.8 and the molar ratio of HDTMS/TEOS (M) was varied from 0 to 0.458. The organic modification was confirmed by infrared spectroscopic studies, and the hydrophobicity of the coating was tested by the contact angle measurements. The stone surface morphology of sample treated with silica coating was characterized. The results showed that the nanocomposites were composed of spherical particles with grain size of about 190 nm in diameter. After the limestone's surface was modified, the contact angle of limestone increased from 20° to 100° for M0.458. The protective performance evaluated with its ability to resist acid rain reveals that the protective effects are satisfying.     

Fluoroalkyl-functionalized silica particles: synthesis, characterization, and wetting characteristics

Fluoroalkyl-functionalized silica particles for use in nonwetting surfaces were prepared by treatment of silica particles with fluoroalkyl-functional chlorosilanes. Both fumed and precipitated silica were studied, as well as the efficiency of surface coverage using mono-, di-, and trifunctional chlorosilanes. The most effective surface treatment was accomplished via the surface grafting of monofunctional chlorosilanes in the presence of preadsorbed dimethylamine under anhydrous conditions at room temperature. Confirmation of covalent attachment was accomplished via Fourier transform infrared (FT-IR) spectroscopy, while elemental analysis, thermogravimetric analysis, and nitrogen adsorption isotherms were used to determine grafting densities and additional key geometric characteristics of the grafted layer. The effect of residual silanol content on the moisture uptake properties of the modified silica particles was determined by measuring the water uptake of unbound particles, while liquid wetting properties were determined by dynamic contact angle analysis of elastomeric composites. Although residual silanol content was shown to effect wetting properties, results suggest that surface geometry dominates the performance of liquid-repellent surfaces. The potential use of fluoroalkyl-functionalized silica particles for hydrophobic and oleophobic applications is discussed.     

Preparation of durable superhydrophobic surface by sol–gel method with water glass and citric acid

Durable superhydrophobic surface on cotton fabrics has been successfully prepared by sol–gel method. Cellulose fabric was first coated with silica sol prepared with water glass and citric acid as the acidic catalyst. The silica coated fabric was then padded with hydrolyzed hexadecyltrimethoxysilane afterwards obtaining low surface energy. Water contact angle and hydrostatic pressure were used to characterize superhydrophobicity and washing durability. Scanning electron microscopy was used to characterize the surface morphology changes after certain washing times. All results showed good durable hydrophobicity on cellulose fabrics. In addition, the influence of citric acid and sodium hypophosphite (NaH₂PO₂) on the durability of hydrophobicity was also investigated. The durability of treated cotton improved with the increase of concentration of citric acid in the presence of NaH₂PO₂. It could be concluded that citric acid acted as multi-functional heterogeneous grafting chemicals to improve washing durability of hydrophobicity by forming the ester bonds between cotton fabric and silica sol and improved the durability of hydrophobicity.     

气相白炭黑表面处理率的影响因素及判定

气相白炭黑是一种二氧化硅纳米材料，气相白炭黑的最主要应用是用于硅橡胶的补强，但气相白炭黑在硅橡胶中很难分散，影响了补强效果，本文用六甲基二硅氮烷对白炭黑进行表面处理并对白炭黑表面处理率问题做一些探讨。     

Durable Lotus-effect surfaces with hierarchical structure using micro- and nanosized hydrophobic silica particles

Surfaces with a very high apparent water contact angle (CA) and low water contact angle hysteresis (CAH) exhibit many useful characteristics, among them extreme water repellency, low drag for fluid flow, and a self-cleaning effect. The leaf of the Lotus plant (Nelumbo nucifera) achieves these properties using a hierarchical structure with roughness on both the micro- and nanoscale. It is of great interest to create durable surfaces with the so-called "Lotus effect" for many important applications. In this study, hierarchically structured surfaces with Lotus-effect properties were fabricated using micro- and nanosized hydrophobic silica particles and a simple spray method. In addition, hierarchically structured surfaces were prepared by spraying a nanoparticulate coating over a micropatterned surface. To examine the similarities between surfaces using microparticles versus a uniform micropattern as the microstructure, CA and CAH were compared across a range of pitch values for the two types of microstructures. Wear experiments were performed using an atomic force microscope (AFM), a ball-on-flat tribometer, and a water jet apparatus to verify multiscale wear resistance. These surfaces have potential uses in engineering applications requiring Lotus-effect properties and high durability.     

Facile Spray-Coating for Fabrication of Superhydrophobic SiO2/PVDF Nanocomposite Coating on Paper Surface

A facile and low-cost superhydrophobic nanocomposite coating on paper surface was fabricated through one-step simply spraying dispersion, using hydrophobic silica nanoparticles as a filter (SiNPs) and polyvinylidene fluoride (PVDF) as a film-forming material. Hydrophobic SiNPs were fabricated via co-hydropholysis and condensation of TEOS and long-chain alkyl silane based on a simple sol-gel process, and the surface chemical structure of SiNPs was characterized by Fourier transform infrared (FTIR) spectra. The wettability and morphology of the coating surface were measured by contact angle (CA) measurement and scanning electron microscope, respectively. The influence of the mass ratio of hydrophobic SiNPs to PVDF (M(SiNPs:PVDF)) on the superhydrophobicity of paper surface was studied. The results showed that when M(SiNPs:PVDF) was 3:1, the water CA was 156.0 ± 1.0° for the nanocomposite coating with micro/nano-hierarchical structure on paper surface. Further, such superhydrophobic nanocomposite coatings on paper surface showed little adhesive property with water. In addition, the prepared superhydrophobic nanocomposite coating could be applied in other substrates, such as wood, aluminum sheet, stainless steel, polytetrafluoroethylene (PTFE), etc.     

Anticorrosive self-stratified PDMS-epoxy coating for marine structures

Four self-stratified coatings were prepared by dispersion of titanium dioxide (TiO₂) and hydrophobic fumed silica (SiO₂) nanoparticles in polydimethylsiloxane (PDMS)-Epoxy mix separately and in combination. Incorporating a definite ratio of nanofillers in PDMS-Epoxy incompa ible polymer blend to form a single coat paint system with anticorrosive and improved hydrophobic properties by the self-stratifying process is the chief highlight of this research work. The appropriate characterization techniques like Fourier Transform Infrared (FTIR) spectroscopy in Attenuated Total Reflection (ATR) mode of the coatings top and bottom layers emphasized the intended stratification. The Field Emission Scanning Electron Microscopy (FESEM) displayed the morphology of the coated samples top and bottom layers and the existence of the intended stratification in the coatings cross-section. The PDMS-Epoxy coating inclusive of both the nanofillers exhibited improved hydrophobic nature, appreciable surface free energy, augmented adherence to the substrate and lesser shear force in pseudo barnacle strength test in terms of shear. This innovative formulation pertains to the application on underwater substrates with improved anti-biofouling properties.     

用于油/水分离的环保无氟超疏水织物的制备与性能

针对目前用于油/水分离的超疏水材料普遍存在的原料不环保、不可降解、涂层耐久性差等缺点,采用简便的浸渍法,制备了一种环保、工艺简单且性能优良的超疏水材料。首先,使用水性聚氨酯（WPU）将聚甲基丙烯酸甲酯-甲基丙烯酸缩水甘油酯P（MMA-r-GMA）微球固定在棉织物表面,构造微纳米级粗糙结构。其次,通过水解-缩合反应,将无毒的十六烷基三甲氧基硅烷（HDTMS）与甲基三乙氧基硅烷（MTES）锚定在棉织物表面,制备得到超疏水棉织物。结果表明,改性棉织物接触角最高可达157.3（°）,滚动角为5（°）。同时具有很好的耐溶剂性,在酸碱溶液中浸泡30 min后,接触角几乎无变化。油水分离效率最高可达97.8%,即使在经过10次循环分离之后,油水分离效率仍然在95%以上。该超疏水织物具有出色的油水分离效率和优良的稳定性,可用于可持续且环保的油水分离领域。     

The surface modification of cellulose fibres to create super-hydrophobic, oleophobic and self-cleaning properties

The surface modification of cellulose fibres was performed with the use of low-pressure water vapour plasma, followed by the application of a pad-dry-cure sol–gel coating with the water- and oil-repellent organic–inorganic hybrid precursor fluoroalkyl-functional siloxane (FAS), with the aim of creating the “lotus effect” on the cotton fabric surface. The tailored “lotus effect” was confirmed by measurements of the contact angle of water (154°) and n-hexadecane (140°), as well as by measurements of the water sliding angle (7°), which were used to identify the super-hydrophobic, oleophobic and self-cleaning properties of the modified fibres. The chemical and morphological changes caused by modifications of the fibres were investigated by XPS, FTIR, AFM and SEM. The results show that the plasma pre-treatment simultaneously increased the surface polarity, average roughness, and surface area of the fabric. The application of the FAS coating after plasma pre-treatment caused only a slight increase in the surface roughness, accompanied by a decrease in the surface area, indicating that the architecture of the surface was significantly changed. This result suggests that the surface pattern affected the “lotus effect” more than the average surface roughness. The plasma pre-treatment increased the effective concentration of the FAS network on the fabric, which resulted in enhanced repellency before and after repetitive washing, compared with that of the FAS-coated fabric sample without the plasma pre-treatment. Despite the fact that the plasma pre-treatment increased the concentration of the oxygen-containing functional groups on the fabric surface, this phenomenon insignificantly contributed to the adhesion ability and, consequently, the washing fastness of the FAS coating.     

硅源对MCM-22分子筛合成及物化性质的影响

在动态水热条件下,研究了硅溶胶、白炭黑、硅酸及硅胶为硅源时对MCM-22分子筛合成及物化性质的影响。以硅溶胶、白炭黑、硅酸三种硅源均可合成出高结晶度且无杂晶的片状MCM-22分子筛,其平均粒径分别为190、220和750 nm。硅源影响分子筛的聚集形态,三种硅源分别形成晶粒分散、晶粒半分散及晶粒聚集形态。三组样品的酸强度分布基本一致,都具有较多的中强酸分布,由硅溶胶和硅酸所得MCM-22分子筛在中强酸范围具有更高的B/L酸比值,以白炭黑合成的分子筛总酸量最高。NMR结果表明,样品中的铝以骨架铝为主,不存在明显的非骨架铝。由于硅胶对合成体系中游离水的吸附作用,水热反应难以发生,不能得到MCM-22分子筛,硅胶作为分子筛合成硅源时需要选择合适的反应条件。     

Controlled silanization of silica nanoparticles to stabilize foams, climbing films, and liquid marbles

We describe a method for the synthesis of multigram amounts of silica nanoparticles which are controllably hydrophobized to different extents using a room temperature vapor phase silanization process. The extent of hydrophobization of the particles can be adjusted by changing the amount of dichlorodimethylsilane reagent used in the reaction. The method produces particles with good uniformity of surface coating; the silane coating varies from monolayer coverage at low extents of hydrophobization to approximately trilayer at high extents of hydrophobization. Acid-base titration using conductivity detection was used to characterize the extent of hydrophobization which is expressed as the percent of surface silanol groups remaining after silanization. Particles with %SiOH ranging from 100% (most hydrophilic) to 20% (most hydrophobic) were hand shaken with water/methanol mixtures and produced either a particle dispersion, foam, climbing films, or liquid marbles. The type of colloidal structure produced is discussed in terms of the liquid-air-particle contact angle and the energy of adsorption of the particles to the liquid-air surface.     

Modification of Silica by Liquid Polybutadienes Containing Alkoxysilane Groups

Summary : The present work describes a method to modify the surface of silica, reducing its polar character and making it compatible and dispersible into hydrocarbon based elastomers. A liquid low molar mass polybutadiene (PB) was grafted with mercaptopropyltrimethoxysilane (MPTS) via radical addition of the thiol group to the double bonds. The silanized PB was reacted with silica via thermal condensation with its silanol groups. ²⁹Si NMR spectra showed that the condensation reaction of the trifunctional silane involved one or two alkoxy groups, while the third alkoxy group remained unreacted, probably for steric reasons. The characterization of the functionalized silica particles was performed by contact angle measurements and TGA analysis.     

Fabrication of AgNPs/Silane coated mechanical and washing durable hydrophobic cotton textile for self-cleaning and oil-water separation application

This study deals to develop a simple and facile two-step dip-coating method using silver nanoparticles (AgNPs) and fluorine-free silane monomer, 3-(Trimethoxysilyl) propyl methacrylate (TMSPM) for the fabrication of hydrophobic coating on cotton fabric. The anti-wetting properties, surface morphology, chemical composition, and functionality of the cotton fabric before and after modification were well characterized by contact angle measurement, scanning electron microscope (SEM), and energy-dispersive X-ray spectrum (EDX) and FT-IR respectively. The fabricated cotton fabric displays strong durability against different pH solutions, different soft/hard mechanical treatments including adhesive peeling test, abrasion with tissue paper and finger wiping, home laundering, without losing the hydrophobic property. The contact angle values (water contact angle of 148.3 ?± ?2° and oil contact angle of 0°) imply that the modified cotton has considerable hydrophobic/oleophilic properties. Additionally, the modified hydrophobic/oleophilic cotton fabric exhibits self-cleaning and oil-water separation behavior for both industrial and household importance.     

Shear-Induced Changes in Rheological Reponses and Neutron Scattering Properties of Hydrophobic Silica Suspensions at Low Silica Concentrations

Rheological responses of hydrophobic fumed silica powders, whose surface silanol groups were modified by hexadecane, suspended in 1,4-dioxane at lower silica concentrations than 6.8 vol% have been investigated as a function of the silica concentration. Transient shear stress behavior before attaining the steady-state shear stress could be classified into three regimes as follows, irrespective of the silica concentration: at the lower shear rates than ca. 0.3 s^?1 a stress overshoot was observed, at the shear rate ranges from 0.3 to 30 s^?1 sustained oscillations in shear stresses were exhibited and these oscillations were first observed for the suspensions at the low particle concentrations, and beyond the shear rate of 30 s^?1 a sigmoid decrease of the shear stress with increasing time, that is, structural breakdown, was observed. At the steady state the silica suspensions showed shear thickening. Small angle neutron scattering (SANS) measurements of the silica suspension under shear flow provided that changes in the SANS intensities were well correlated with the shear thickening behavior. However, shear thinning behavior at higher shear rates did not cause any changes in the SANS intensities.     

One-pot sonochemical synthesis of superhydrophobic organic–inorganic hybrid coatings on cotton cellulose

Inspired by the surface structure of lotus leaves, different types of superhydrophobic cellulosic materials with contact angle (CA) of higher than 150° are currently provided. However, fabrication of these surfaces in a facile one-step coating process is one of the challenging issues. This paper describes a facile method to sonochemically synthesize superhydrophobic organic–inorganic hybrid coatings on cotton fabric by an alkaline-catalyzed co-hydrolysis and co-condensation of tetraethylorthosilicate and alkyltrialkoxysilanes. The influence of alkyl chain length (methyl, octyl, hexadecyl) of silane and reaction time was investigated. Surface structure of the fabrics was investigated by SEM, EDS, FTIR spectroscopies, and reflectance spectrophotometry. Wettability properties were studied by measuring water CA, shedding angle (SHA) and resistance to wetting by a series of ethanol–water mixtures of different surface tensions. The results showed that the treated fabrics were coated with a homogeneous thin nano-scaled coating of hybrid silica nano-particles. The fabrics demonstrated CA of higher than 150°, SHA in the range of 6–24° and different stickiness to water droplets. The fabrics treated by silanes with longer alkyl chain length and at higher reaction time revealed better water repellency. The coatings were nearly transparent, could not affect the color of the fabrics and had high stability against repeated washing. In addition, mechanical properties of the fabrics were not substantially affected.     

In-situ growth of silica nanoparticles on cellulose and application of hierarchical structure in biomimetic hydrophobicity

Monodispersed silica nanoparticles were prepared by a simple two-step method with hydrolysis and condensation. The materials were characterized by dynamic light scattering (DLS), SEM and TEM. Through in-situ growth of silica nanoparticles on cotton fabrics, a dual-scaled surface with nanoscaled roughness of silica and microscaled roughness of cellulose fiber was generated. After the modification of the low surface energy, the wettability of smooth silicon slide, silicon slide with nanoscaled roughness of silica particles, cotton fabric, and cotton fabric with silica particles was evaluated by the tests of the contact angle (CA) and the advancing and receding contact angle (ARCA). The cotton fabric with dual-scaled roughness exhibits a static CA of 149.8° for 4 μL water droplet and a hysteresis contact angle (HCA) of 1.8°. The results of CA and HCA show that microscaled roughness plays a more important role than nanoscaled roughness for the value of CA and HCA. The results in the hydrostatic pressure test and the rain test show the important contribution of nanoscaled roughness for hydrophobicity.     

聚苯硫醚超疏水复合涂层的制备与性能

利用工业原料聚苯硫醚微粉和疏水性二氧化硅纳米粉末,采用喷涂法在瓷砖表面制备了疏水复合涂层.研究了热处理温度、组分配比对涂层表面形貌、粗糙度和接触角的影响,发现随着热处理温度升高,涂层表面粗糙度增大,随着疏水性二氧化硅含量的增加,由于表面聚集的疏水性二氧化硅增多,涂层疏水性增强,在热处理温度为280℃、疏水性二氧化硅与聚苯硫醚质量比为1∶1时,可获得超疏水涂层,涂层的接触角大于150°,滚落角小于4°,pH值为1～14的水溶液在其表面都具有很高的接触角.超疏水涂层具有良好的自清洁效果,并且经落沙法实验测定,超疏水涂层耐刮伤性能良好.     

气相SiO2在不同pH值介质中的分散特性

以激光动态光散射法考察了气相SiO2在不同pH值的H2SO4和NaOH介质中的分散平均水化粒径与表面Zeta电位及二者间的关系。 Zeta电位数据表明，气相SiO2在水中分散的表面硅羟基的等电点(IEP)和滴定终点(TE)的pH值分别为pH(IEP)=2.09和pH(TE)=7.47，利用滴定终点pH (TE)给出了一种简单的气相SiO2表面Si-OH浓度的测定方法。 分散相粒径数据显示，在等电点和滴定终点之间，气相SiO2在水中的分散粒子的粒径能够稳定在230 nm附近；在H2SO4介质中，当pH＜pH(IEP)时，随着H2SO4浓度的增大，体系中的分散粒子发生聚结而使表观粒径增大；在NaOH介质中，当pH＞pH(TE)时，随着NaOH浓度的增大，分散相的表观水化粒径降低，表明NaOH的加入有利于气相SiO2的分散。