Self-assembly of human plasma fibrinogens on binary organosilane monolayers with micro domains

The adsorption behavior and self-assembly of human plasma fibrinogen (HPF) on binary methyl- and amino-terminated self-assembled monolayers (SAMs) were investigated by atomic force microscopy (AFM). The binary SAMs were fabricated through self-assembly mechanism of organosilane molecules. The height of domains is the domain height is 0.8 ± 0.2 nm from the AFM topographic image. It corresponds to the domain height is 0.8 ± 0.2 nm from the AFM topographic image. It corresponds to the difference between the length of the alkyl chain of octadecyltrichlorosilane (OTS) and that of n-(6-aminohexyl)aminopropyltrimethoxysilane (AHAPS). The fibrinogen solution used ultrapure water as the solvent and its pH was adjusted at 3 and 10. From the AFM results at pH 3, HPF only formed network structures on the OTS domains of the binary SAM at early immersion times, and then the network structures expanded and connected between OTS domains through the AHAPS surface at long immersion times. In this case, a few HPFs are discretely adsorbed on the AHAPS surface. However, HPF is uniformly adsorbed on the binary SAM under the other conditions of pH.     

Effect of montmorillonite on abrasion resistance of SiO2-filled polybutadiene

The effect of organically modified montmorillonite (OMMT) and silane coupling agent on the abrasion resistance of SiO₂-filled butadiene rubber (BR) vulcanizates has been investigated. Various amounts of OMMT are added into SiO₂-filled BR vulcanizates. A silane coupling agent, bis-(3-triethoxysilyl propyl) tetrasulfide (Si69), is used to modify OMMT during the masterbatch preparation for evaluating the influence of surface treatment on the abrasion resistance. Incorporation of OMMT into BR results in deterioration of the abrasion resistance as compared to unfilled BR vulcanizate due to poor dispersion of OMMT and insufficient interfacial adhesion between OMMT and BR matrix. The use of Si69 improves dispersion of OMMT particles and rubber/OMMT adhesion, resulting in abrasion resistance enhancement of BR/OMMT vulcanizates. By using similar compounding conditions as those for BR/OMMT vulcanizate, nanodispersion of OMMT in BR/SiO₂/OMMT vulcanizate has been achieved as judged by the high viscosity of the SiO₂-filled BR compound. This improved dispersion leads to better abrasion resistance of the BR/SiO₂/OMMT than that of the BR/SiO₂ composite. Utilization of Si69 slightly affects the DIN volume loss of BR/SiO₂/OMMT vulcanizates and the abrasion pattern.     

Differential friction force spectroscopy of micropatterned organosilane self-assembled monolayers

Frictional properties of organosilane self-assembled monolayers (SAMs) and hydrated silicon oxide (SiOH) surfaces on a single sample substrate were studied; the frictional force difference between the surfaces was measured by employing one as a standard. Using a lateral force microscope (LFM), differential frictional force microscopic data were obtained by measuring the difference in the friction forces of the two surfaces with respect to the vertical load force applied to the LFM probe. The SAMs were prepared from n-octadecyltrimethoxysilane [ODS, H₃C(CH₂)₁₇Si(OCH₃)₃], n-(6-aminohexyl) aminopropyltrimethoxysilane [AHAPS, H₂N(CH₂)₆NH(CH₂)₃Si(OCH₃)₃], 3,3,3-trifluoropropyltrimethoxysilane [FAS3, F₃C(CH₂)₂Si(OCH₃)₃] and heptadecafluoro-1,1,2,2-tetrahydro-decyl-1-trimethoxysilane [FAS17, F₃C(CF₂)₇(CH₂)₂Si(OCH₃)₃] by chemical vapor deposition. In the vertical force range of 0 to 600 nN, the SAMs showed no damage at all, and frictional force on the SAM surfaces increased linearly with the vertical force. The order of the frictional force magnitudes determined with the SiOH-terminated probe was SiOH > AHAPS > FAS3 > FAS17 > ODS. In addition, the frictional force difference did not become zero even at a vertical force of 0 nN, that is, the frictional differences could even be imaged by LFM through probe-sample adhesion.     

Thermal and Tensile Properties of Epoxy Nanocomposites Reinforced by Silane-functionalized Multiwalled Carbon Nanotubes

Epoxy nanocomposites with unmodified multiwalled carbon nanotubes (u-MWCNTs) and silanized multiwalled carbon nanotubes (si-MWCNTs) were prepared by a cast molding method. The effects of 3-aminopropyltriethoxysilane functionalization of MWCNTs on thermal, tensile, and morphological properties of the nanocomposites were examined. The nanocomposites were characterized by thermogravimetric analysis, dynamic mechanical thermal analysis, and tensile testing. The results showed that epoxy composites based on si-MWCNTs showed better thermal stability, glass transition temperature, and tensile properties than the composites based on u-MWCNTs. These results prove the effect of silane functionalization on the interfacial adhesion between epoxy and MWCNTs. This was further confirmed by morphology study of fractured surfaces of nanocomposites by field emission scanning electron microscopy.     

Silanation and stability of 3-aminopropyl triethoxy silane on nanosized superparamagnetic particles: I. Direct silanation

The direct silanation of nanosized superparamagnetic particles (γ-Fe₂O₃) using 3-aminopropyl triethoxy silane is described. The silanized films are characterized using X-ray photoelectron spectroscopy, diffuse-reflectance Fourier transform infrared spectroscopy and electrokinetics. The silanation is conducted in both organic (toluene) and water solutions to examine the solvent effect on the molecular orientation and packing density of the silanized films. Depending on the solvent, about 74 to 83% of amine groups are found to be un-protonated and remain reactive on the particles. In acidic environment, the films silanized in toluene are more stable than that in water, but both are unstable in basic environment.     

Fabrication of superhydrophobic polyurethane/organoclay nano-structured composites from cyclomethicone-in-water emulsions

Nano-structured polyurethane/organoclay composite films were fabricated by dispersing moisture-curable polyurethanes and fatty amine/amino-silane surface modified montmorillonite clay (organoclay) in cyclomethicone-in-water emulsions. Cyclomethicone Pickering emulsions were made by emulsifying decamethylcyclopentasiloxane (D₅), dodecamethylcyclohexasiloxane (D₆) and aminofunctional siloxane polymers with water using montmorillonite particles as emulsion stabilizers. Polyurethane and organoclay dispersed emulsions were spray coated on aluminum surfaces. Upon thermosetting, water repellent self-cleaning coatings were obtained with measured static water contact angles exceeding 155° and low contact angle hysteresis (<8°). Electron microscopy images of the coating surfaces revealed formation of self-similar hierarchical micro- and nano-scale surface structures. The surface morphology and the coating adhesion strength to aluminum substrates were found to be sensitive to the relative amounts of dispersed polyurethane and organoclay in the emulsions. The degree of superhydrophobicity was analyzed using static water contact angles as well as contact angle hysteresis measurements. Due to biocompatibility of cyclomethicones and polyurethane, developed coatings can be considered for specific bio-medical applications.     

Organosilane grafted acid-activated beidellite clay for the removal of non-ionic alachlor and anionic imazaquin

Clay adsorbents were prepared via two-step method to remove nonionic alachlor and anionic imazaquin herbicides from water. Firstly, layered beidellite clay, a member of smectite family, was treated with acid in hydrothermal process; secondly, common silane coupling agents, 3-chloro-propyl trimethoxysilane or triethoxy silane, were grafted on the acid treated samples to prepare adsorbent materials. The organically modified clay samples were characterized by powder X-ray diffraction, N₂ gas adsorption, and FTIR spectroscopy. It was found that the selective modification of clay samples displayed higher adsorption capacity for herbicides compared with acid activated clay. And the amount of adsorption is increased with increasing the grafting amount of silane groups. Clay grafted with 3-chloro-propyl trimethoxysilane is an excellent adsorbent for both alachlor and imazaquin but triethoxy (octyl) silane grafted clay is more efficient only for alachlor removal.     

Mechanical Properties and Morphology of Polypropylene/Polypropylene-g-Maleic Anhydride/Long Glass Fiber Composites

Long glass fiber (LGF)-reinforced polypropylene (PP) was prepared using a self-designed impregnation device. The effect of dicumyl peroxide (DCP) and maleic anhydride (MA) content on the compatibilizer, PP grafted with maleic anhydride (PP-g-MA), was investigated by means of scanning electron microscopy (SEM) and mechanical properties. The experimental results demonstrated that the increase of DCP and MA could effectively improve the interfacial interaction between PP and GF. Good interfacial adhesion between PP and GF in PP/ PP-g-MA /LGF composites was observed from SEM studies for the higher contents of MA. The best mechanical properties of PP/ PP-g-MA /LGF(30%) composites were obtained when the content of DCP and MA were 0.4 and 0.8 wt%, respectively. The storage modulus of the PP/PP-g-MA/LGF composites increased and then decreased with the content of MA. When the content of MA was 0.8 wt%, tan δ had the lowest value, indicating that the corresponding composites had the best compatibility.     

Improved interactions in chemically modified pineapple leaf fiber reinforced polyethylene composites

Mechanical properties of pineapple leaf fiber reinforced low density polyethylene composites have been studied with special reference to the effects of interface modifications. Various chemical treatments using reagents such as NaOH, PMPPIC, silane and peroxide were carried out to improve the interfacial bonding. Both infrared spectroscopy and SEM were used to characterize the interface and the modified fiber surface. It has been found that the treatments improved the mechanical properties significantly. However, the effect varied according to the nature of the treatments. SEM studies on the fracture surfaces revealed the extent of fiber-matrix adhesion. It has been observed that the PMPPIC treatment reduced the hydrophilicity of the fiber and thereby enhanced the mechanical properties of the composites. The addition of a small quantity of peroxide and silane increased the mechanical properties considerably. The action of peroxide is associated with the peroxide-induced grafting of polyethylene on the fiber surface. Among the various treatments, PMPPIC treatment of fiber exhibits maximum interfacial interactions. Attempts have been made to illustrate the interfacial bonding with the help of schematic models.     

Investigation of Cell Structure and Expansion Ratio of Microcellular Polypropylene Nanohomocomposites Prepared by a Solid-State Process

Microcellular poly(propylene-ethylene) random copolymer (r-PP-PE)/nanoclay (nanocomposite) and r-PP-PE/nanoclay/polypropylene fibers (nanohomocomposite) were autoclave-foamed via a solid-state microcellular foaming process using supercritical N₂ as a foaming agent. Polypropylene grafted with maleic anhydride (PP-g-MA) was used as a compatibilizer. Amount of PP-g-MA to nanoclay was 3:1. This study investigated the effects of clay content and the presence of polypropylene fiber on the expansion ratio and cell morphology of the samples. The results indicated that nanoclay increased the expansion ratio of the samples, but the expansion ratio for nanohomocomposites was slightly lower than the nanocomposites. In addition, scanning electron microscopy (SEM) observation showed that the nanoclay decreased the cell size and increased the cell density, except for the nanocomposite with the highest nanoclay content, 3 wt%, which had larger cell size compared to the samples with 1.5 wt% nanoclay and less. On the other hand, the simultaneous presence of nanoclay and polypropylene fibers synergistically increased the cell nucleation effect; thus there was a dramatic increase in cell density. The Differential scanning calorimetry (DSC) analysis showed that the microcellular foaming process decreased the crystallinity of both types of samples.     

Friction,adhesion and wear durability of an ultra-thin perfluoropolyether-coated 3-glycidoxypropyltrimethoxy silane self-assembled monolayer on a Si surface

The tribological properties, such as coefficient of friction, adhesion and wear durability of an ultra-thin (<10?nm) dual-layer film on a silicon surface were investigated. The dual-layer film was prepared by dip-coating perfluoropolyether (PFPE), a liquid polymer lubricant, as the top layer onto a 3-glycidoxypropyltrimethoxy silane self-assembled monolayer (epoxy SAM)-coated Si substrate. PFPE contains hydroxyl groups at both ends of its backbone chain, while the SAM surface contains epoxy groups, which terminate at the surface. A combination of tests involving contact angle measurements, ellipsometry, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) was used to study the physical and chemical properties of the film. The coefficient of friction and wear durability of the film were investigated using a ball-on-disk tribometer (4?mm diameter Si₃N₄ ball as the counterface at a nominal contact pressure of ～330?MPa). AFM was used to investigate the adhesion forces between a sharp Si₃N₄ tip and the film. This dual-layer film had a very low coefficient of friction, adhesion and wear when compared to epoxy SAM-coated Si only or bare Si surface. The reasons for the improved tribological performance are explained in terms of the lubrication characteristics of PFPE molecules, low surface energy of PFPE, covalent bonding between PFPE and epoxy SAM coupled with reduced mobile PFPE. The low adhesion forces coupled with high wear durability show that the film has applications as a wear resistant and anti-stiction film for microcomponents made from Si.     

Thermal and Mechanical Properties of Ultra High Molecular Weight Polyethylene Fiber Reinforced High-Density Polyethylene Homocomposites: Effect of Processing Condition and Nanoclay Addition

A new method to prepare single-polymer high-density (HDPE)-ultra high molecular weight polyethylene (UHMWPE) fiber (PE-PE homocomposites) composed and also PE-PE homocomposites containing HDPE organo montmorillonite clay (OMMT) nanocomposites as a matrix (PE nanohomocomposites) was used. Owing to the major importance of fiber impregnation by the matrix and its effect on the adhesion of matrix/fiber and, consequently, the mechanical properties of the composite, a combination of powder impregnation and film stacking methods, utilizing compression molding, were used for manufacturing the PE-PE homocomposites and PE nanohomocomposites. In addition, PE nanohomocomposites with the matrix containing different amounts of nanoclay were prepared to investigate the effect of the clay on the interfacial and mechanical properties of the PE-PE nanohomocomposites. Several different processing conditions were examined to determine the best conditions for manufacturing of the PE-PE homocomposite and PE nanohomocomposites and it was concluded that 40 bar and 10 min of compression molding resulted in the highest overall mechanical properties. The PE-PE homocomposites and PE-PE nanohomocomposites showed identical trends for the relationship between the effects of processing conditions and mechanical properties. Mechanical results demonstrated that clay platelets could increase the interfacial strength by improving physical entanglements between fiber and matrix through better cocrystallization.     

Enhancement of adhesion between copper and vinyl ester in glass fiber–vinyl ester composites

The paper describes surface treatment methods to improve adhesion between copper and vinyl ester in glass fiber–vinyl ester composites. Surface treatment methods were developed for commercially available copper that was optimized for epoxies and adhesion performance was compared based on 90° peel strength measurements. Four surface treatments for copper were tested: (i) co-cured Epon/vinyl ester; (ii) fully cured Epon; (iii) epoxy film adhesive; and (iv) γ-MPS silane along with two baseline systems: copper/vinyl ester and copper/epoxy. Measured average peel strengths for the surface treatments were 21%, 101%, 110% and 91% of the baseline copper/vinyl ester system, respectively. Compared to the copper/epoxy system, fully cured Epon, epoxy film adhesive and the silane treatment generated comparable adhesion between copper and vinyl ester. For all samples tested, mixed cohesive/adhesive failure modes were observed. Overall, the surface treatment with the silane coupling agent is the most appropriate method for obtaining comparable and uniform performance compared to copper/glass fiber/epoxy system (FR4 materials).     

Effect of surface treatment of nanoclay on the mechanical properties of epoxy/glass fiber/clay nanocomposites

A new method of silane treatment of nanoclays is reported where in the clay is nanodispersed in hydrolyzed silanes. The surface functionalization of Cloisite^® 15A nanoclay has been carried out using two different silane coupling agents: 3-aminopropyltriethoxy silane and 3-glycidyloxypropyltrimethoxy silane using varied amounts of silane coupling agents, e.g. 10, 50, 200, and 400 wt% of clay. The surface modification of Cloisite^® 15A has been confirmed by Fourier transform infrared spectroscopy. The modified clays were then dispersed in epoxy resin, and glass fiber-reinforced epoxy clay laminates were manufactured using vacuum bagging technique. The fiber-reinforced epoxy clay nanocomposites containing silane modified clays have been characterized using small angle X-ray scattering, transmission electron spectroscopy and differential scanning calorimetry. The results indicate that the silane treatment of nanoclay aided the exfoliation of nanoclay and also led to an increase in mechanical properties. The optimized amount of silane coupling agents was 200 wt%. The nanocomposites containing clay modified in 200 wt% of silanes exhibited an exfoliated morphology, improved tensile strength, flexural modulus, and flexural strength. The improved interfacial bonding between silane modified nanoclays and epoxy matrix was also evident from significant increase in elongation at break.     

Three-dimensional structure of a polymer/clay nanocomposite characterized by transmission electron microtomography

Three-dimensional (3D) morphology of a polymer/clay nanocomposite, an organophilic montmorillonite (MMT) dispersed in poly(ethylene-co-vinylacetate) (EVA), was examined by transmission electron microtomography (TEMT). Using this technique, individual clay layers dispersed in the EVA matrix were clearly visualized. A volume fraction of the clay layers evaluated from the 3D reconstructed image agreed well with that calculated from the weight of the MMT component in the MMT/EVA system. The individual clay layers were digitally extracted by a newly developed 3D particle algorithm. A size distribution of the clay layers was directly obtained from the 3D reconstruction. Anisotropy of each clay layer was characterized by the determination of three semi-axes of an approximating ellipsoid with the same volume. One of the representative semi-axis of the ellipsoid was used to estimate average orientation of the MMT layers in the ultra-thin section used in the TEMT experiment. Thus, the combination of quantitative TEMT and 3D structural analysis is shown to be a powerful tool to investigate a relationship between the MMT distribution and a variety of physical properties of the nanocomposites.     

片层硅酸盐用于热固性PU/PLS复合可能性探讨

高岭土(Kaolinite)和蒙脱土(Montromollite)等粘土,被广泛用作添加剂来改善聚合物的耐热性能。文章用各种先进技术对高岭土与蒙脱土的形态、组成和结构进行表征比较。电子透射电镜及电子探针(TEM/EDX)结果显示高岭土较蒙脱土有较大的粒径和较小的硅铝比,TEM还显示出这些粘土是由片层粒子堆积而成。热重分析(TGA)的结果表明蒙脱土由于失去吸附水从60 ℃升温至90 ℃失重明显(约7%),而高岭土在此温度下几乎不失水。高岭土脱除结构羟基官能团脱水失重的温度大约在510 ℃,低于蒙脱土的670 ℃。室温下光声傅里叶变换(PAS-FTIR)红外光谱显示蒙脱土在羟基吸收区有较强的吸附水的吸收,1 650 cm-1处孤立的弱吸收谱带可给予左证。变温红外和TGA的结果显示,片层硅酸盐表面的结构羟基从100～500 ℃非常稳定,它可以和异氰酸酯基团(NCO)封端的预聚物反应形成热固性PU/PLS复合聚合物。     

Anti-fouling poly(2-hydoxyethyl methacrylate) surface coatings with specific bacteria recognition capabilities

Poly(2-hydroxyethyl methacrylate), PHEMA, brushes were prepared by surface-initiated atom transfer radical polymerization (SI-ATRP) on silanized glass slides bearing grafted initiators. High resolution X-ray photoelectron spectroscopy (XPS) highlighted the surface chemical changes of the glass slides upon silanization and surface-confined ATRP of HEMA. Particularly, the initiator sites from the silane were detected by their bromine Br3d core electron peak whilst the O/C atomic ratios and the high resolution C1s region of the glass–PHEMA hybrids are comparable to those of pure PHEMA, thus confirming that the PHEMA chains have indeed attached to the surface. The glass–PHEMA hybrids were found to behave as anti-fouling ultrathin coatings as they resisted non-specific Salmonella typhimurium bacterial adhesion. This behaviour is driven by the hydrophilic properties of the glass–PHEMA hybrids which were assessed by contact angle measurements. In contrast, after activation of PHEMA brushes by S. typhimurium antibodies through the trichlorotriazine coupling procedure, the bacteria specifically and strongly attached to the PHEMA-coated glass slides as judged from optical microscope observation.     

Theoretical and experimental investigations on the structures of purified clay and acid-activated clay

The purified and acidified montmorillonite clay were characterized by XRD, BET and TPD. These results show that acidified clay is provided with more surface area and acid sites. For NH₃-TPD, molecular NH₃ desorption on purified clay and acidified clay occurs at temperatures with 873 and 1000 K, respectively. It is shown for the existence for strong acid sites. By two reactions of the tetrahydropyranylation of n-propanol and the esterification of cyclo-2-pentene with acetic acid, it is shown that the acidified clay displays better catalytic activity for above two organic reactions. By density-functional theory (DFT) method, we have analyzed the structures of different substituted montmorillonite and the effect sorption behavior of Na⁺ in different montmorillonite models. The result shows that the process of substitution will occur apart from octahedral aluminums. The adsorption of NH₃ on clay surfaces have been investigated using TPD and DFT. This is shown that acid sites locate at round the octahedral aluminums, and substitution of Al³⁺ for tetrahedral Si will be favorable to NH₃ adsorption.     

Interfacial enhancement of flexible PVC-silica composites by silane coupling agents

Enhancement of a flexible poly(vinyl chloride) (PVC)-silica composite interface was studied by the application of γ-aminopropyltrimethoxysilane on silica. Composites containing silica and silanized silica up to 25.6 phr (per hundred resin) and prepared by sol-gel technology were subjected to water and water vapor attacks similar to that in their daily use. Silane application resulted in diminishing liquid water and water vapor sorption by about 24.0% and 11.9%, respectively. Equilibrium weight gain values of the composites having different amounts of silica correlated well with a peak at 3400 cm^-1 in the IR spectra which was attributed to the stretching vibration of the O-H group of water. Liquid water and water vapor diffusivities in composites determined by the evaluation of weight gain against time data were about 0.4 x 10^-13 and 0.4 x 10^-12 m² s^-1, respectively. Inhibition of dioctyl phthalate (DOP) migration from composites by silane application was also determined as 24% using UV measurements. The most impressive merit of silane enhancement was observed as the retention of ultimate tensile strength (UTS) under wet conditions. While the untreated silica composite reduced its UTS by about 21.2%, silanized silica composite reduced its UTS by only about 13.6%, on wetting.     

Enhancing indium tin oxide (ITO) thin film adhesiveness using the coupling agent silane

The coupling agent γ-mercapto propyl trimethoxy silane (WD-80) was used to enhance the adhesiveness of the indium tin oxide (ITO) thin film, which was prepared on a glass substrate using the sol-gel method. The nano-scratching test, XRD, TEM, SEM, and UV-vis spectrophotometer were employed to examine film adhesion, crystal structure, surface morphology, and transmittance. The results indicated that silane coupling agent, used in low concentration, did not change the film structure but increased the critical load of the film by 49%, from 4.16 mN to 6.20 mN, when the film was peeled off from the substrate. The principle by which the coupling agent works is discussed. In addition to increasing with the light wavelength, the average transmittance of the film in the visible range varied from 78.9% to 83.6%. Moreover, as a function of the WD-80 silane coupling agent, the film exhibited a high smoothness and density due to the orderly arrangement of particles.