Surface Of SiO2 Particles Research Articles

Features of doxorubicin adsorption on Fe3O4 magnetic nanoparticles coated with SiO2 or SiO2/aminopropylsilane

New nanocomposites based on Fe3O4 magnetic nanoparticles coated with SiO2 or SiO2/aminopropylsilane (APS), including those using N-(phosphonomethyl)iminodiacetic acid (PMIDA), were obtained, and the immobilization of the antitumor agent doxorubicin (Dox) on nanocomposites was examined. It has been shown that the binding of Dox to the negatively charged surface of SiO2 particles occurs more efficiently than that to the APS-modified surface with positively charged amino groups; the presence of PMIDA molecules on the surface significantly increased the loading content. Based on DFT calculations, a mechanism for Dox binding to the surface of the synthesized nanocomposites was proposed.

Fabrication of acanthosphere-like SiO2@Ag with designed angular tip silver shape for construction of superhydrophobic-electromagnetic shielding surface by imitating lotus leaf structure

Superhydrophobic electromagnetic interference (EMI) shielding coating is of great significance to the safety and long-term service of all-weather outdoor equipment. However, it is still challenging to achieve long-term durability or other harsh service conditions. This work is based on the design of silver-based micro-nano structures, simulating the lotus leaf papilla structure, and then combining with nano-silver wires to obtain a superhydrophobic-electromagnetic shielding composite surface. SiO2@Ag particles with dual-scale structure are synthesized. The size of the SiO2 particles is about 1.5 μm, and the size of silver particles, growing on the surface of SiO2 particles in the shape of papilla, is about 50 nm, which means that the SiO2@Ag particles have a micro-nano dual-scale structure. Then SiO2@Ag particles were mixed with PDMS and uniformly sprayed onto substrates that have been pre-sprayed with Ag NWs/PDMS. A variety of instrument characterization methods were used to characterize its phase composition, composition, morphology, structure, water contact angle (WCA) and electromagnetic interference shielding effectiveness (EMI SE). The prepared Ag NWs/PDMS-SiO2@Ag/PDMS (AP-SP), imitating lotus leaf superhydrophobic-electromagnetic shielding composite surface, has a high WCA (168.3°) and superior EMI SE (51.7 dB). The product can withstand the erosion of acid and alkali while maintaining outstanding superhydrophobic performance, and the electromagnetic shielding performance can still reach 34 dB. The product also can withstand high temperatures 400 °C without deterioration of super-hydrophobic- electromagnetic shielding performance.

Experimental Investigation of Rheological Properties and Thermal Conductivity of SiO2-TiO2 Composite Nanofluids Prepared by Atomic Layer Deposition.

In the current research, surface-modified SiO2 nanoparticles were used upon immersion in an applied base fluid (ethylene glycol:water = 1:1). The atomic layer deposition method (ALD) was introduced to obtain a thin layer of TiO2 to cover the surface of SiO2 particles. After the ALD modification, the TiO2 content was monitored by energy dispersive X-ray spectroscopy (EDS). Transmission electron microscopy (TEM) and FT-IR spectroscopy were applied for the particle characterization. The nanofluids contained 0.5, 1.0, and 1.5 volume% solid particles and zeta potential measurements were examined in terms of colloid stability. A rotation viscosimeter and thermal conductivity analyzer were used to study the nanofluids’ rheological properties and thermal conductivity. These two parameters were investigated in the temperature range of 20 °C and 60 °C. Based on the results, the thin TiO2 coating significant impacted these parameters.

In-situ growth of CNTs in silica powder by polymer pyrolysis chemical vapor deposition and their separation resistances

ABSTRACT This study investigated the in-situ growth of carbon nanotubes (CNTs) in silica (SiO2) powder by polymer pyrolysis chemical vapor deposition with a polyethylene glycol (PEG) carbon source and cobalt nitrate catalyst. The mass ratio of PEG:citric acid:cobalt nitrate was determined to control the microstructures of the in-situ CNTs. Results indicated that with an increase in the mass ratio of PEG:citric acid:cobalt nitrate, the in-situ generated CNTs content in the SiO2 powder increased, the CNTs diameters (approximately 40 nm) did not significantly change, and the CNTs lengths decreased from 400–800 nm to 200–400 nm. Additionally, the in-situ CNTs that were anchored on the surfaces of SiO2 particles presented fewer defects and a high degree of graphitization. However, when the mass ratio of PEG:citric acid:cobalt nitrate exceeded the critical value, excessive amounts of amorphous carbon grown in situ on SiO2 particles were obtained. The suspension experiments showed that unlike the CNTs/SiO2 powders prepared by a combination of surfactant and ultrasonic methods with commercial CNTs, in-situ CNTs grown in SiO2 powders exhibited improved separation resistance in water. This would favor the uniform dispersion of CNTs within the matrix, improving the performance of nanocarbon-modified cement-based composites.

Asymmetric Colloidal Particles Fabricated by Polymerization-Induced Surface Self-Assembly Approach

In the past decades, the synthesis of asymmetric colloidal particles has been of wide concern in material science because of their anisotropic morphologies and unique properties. However, the synthesis of the asymmetric particles with controllable anisotropy still remains a big challenge because of the lack of effective methods. In this research, polymerization-induced surface self-assembly (PISSA) approach was demonstrated to be an effective method in the synthesis of colloidal particles with tunable asymmetric core–shell structures. Reversible addition–fragmentation chain transfer agents were covalently anchored onto the surfaces of silica particles and coupled onto the ends of methoxy polyethylene glycol (PEG) chains, leading to the synthesis of CTA-modified silica particles (SiO2-CTA) and PEG macro-CTA agents (PEG-CTA), respectively. PISSA process was conducted by using SiO2-CTA and PEG-CTA as co-RAFT agents in RAFT dispersion polymerization of styrene. In the RAFT polymerizations, polymer layers with PS nodules were formed on the surfaces of SiO2 particles. It was demonstrated that the formation of the nodules was related to the production of the PS homopolymer in the PISSA process. In order to control the asymmetric surface structures, RAFT dispersion polymerizations of styrene with added “free” RAFT agents were performed, and it turned out that the eccentrically positioned core–shell structures with silica cores and polymer layers were prepared. The colloidal particles experience morphology changes from surface nodules to snowman-like structures and finally to asymmetric spherical structures, depending on the monomer conversion and the feeding ratio of the co-RAFT agents. Kinetics studies were performed to investigate the mechanism of the formation of the asymmetric particles. After etching the silica cores with HF solution, asymmetric hollow capsules were fabricated.

Hydrophobic Modification on the Surface of SiO2 Nanoparticle: Wettability Control.

Good control of the morphology, particle size, and wettability of silica nanoparticles is of increasing importance to their use in a variety of fields. Here, we propose a strategy to tune the surface wettability of nanosilica by changing the dosage of a chemical modifier. A series of measurements, including scanning electron microscopy (SEM), laser scatting technique, Fourier transform infrared (FTIR) spectroscopy, thermogravimetry, and surface hydroxyl number and water contact angle measurement, were conducted to verify the surface chemistry and wettability of these nanoparticles. Through controlled chemical modification, the contact angle of the treated nanoparticles increases from 34.7 to 155° with increasing amount of dichlorodimethylsilane (DCDMS) within a molar ratio (MR) between DCDMS and nanoparticles of 5.17. The number of hydroxyl groups covered on the particle surface decreases gradually from 1.79 to 0.47, and the surface grafting rate could reach 73.7%. As the addition of dichlorodimethylsilane equals MR 5.17, the contact angle reaches the maximum value of 155°, which displays excellent superhydrophobicity. After surpassing the point of MR 5.17, the contact angle does not increase but starts to decrease, ultimately remaining stable at 135°. It can be concluded that the surface wettability of nano-SiO2 particles can be precisely modulated by varying the amounts of the modifier. Furthermore, the modulating mechanism of the process occurring on the surface of SiO2 particles has been investigated at the molecular level.

Enhancement of water barrier properties of cassava starch-based biodegradable films using silica particles

Biodegradable films are used in a variety of applications, including packaging. However, their use is limited due to their high moisture and water sensitivity. In this work, cassava starch (CS) was blended with poly(vinyl alcohol) (PVA). Silica particles (SiO2) were incorporated to increase the hydrophobicity of the blend by intermolecular interaction through hydrogen bonding between the three components. Instead of a plasticizer or crosslinker, a small amount of triethylamine was added to eliminate residual acetate groups in PVA. The miscibility of CS and PVA phases was confirmed by smooth fracture surfaces and a single glass transition temperature. When SiO2 content was below 5% (wt), the particles were well dispersed in a continuous phase of polymer matrix. At this loading of SiO2, the increase in tensile strength was as high as 170% and in elongation-at-break, 250%. All loadings of SiO2 increased thermal stability of the blend films because silanol groups on the surface of SiO2 particles formed effective interfacial interactions with hydroxyl groups of the polymers. These interactions also prevented the ingress of water molecules, significantly increasing the hydrophobicity of the films. The water contact angle increased as high as 113° and moisture absorbency and water solubility were low. These highly hydrophobic, photodegradable, biodegradable CS/PVA/SiO2 films show great potential as a low-cost, eco-friendly material.

A comprehensive study of the resistance to biofouling of different polymers for optical oxygen sensors. The advantage of the novel fluorinated composite based on core-dye-shell structure

The control of the biotechnological reactors for the wastewater processing and for multiple biotechnological syntheses often requires the in situ monitoring of the current concentration of dissolved molecular oxygen (DO) within the reactor. The method of determining of DO based on the quenching of the indicator dye phosphorescence is becoming readily used due to be unaffected by sulfur-containing compounds and relatively insensitive to hydrodynamic conditions as compared with the traditional electrochemical sensors (the Clark electrodes).Any types of sensors inserted into the biotechnological reactor however are objected to biofouling, that is the adsorption of the alive and dead cells of the microorganisms and also the formation of the attached polysaccharide matrix (the biofilm) on the surface of the sensor. Thus any DO sensor inserted into the bioreactor is subjected to two effects, that is 1) the actual change of the bulk DO concentration and 2) the deviation of the sensor readings due to the hindering of the oxygen diffusion to the indicator dye caused by the biofouling. In order to distinguish of these two phenomena we made two series of experiments in the present study. In the first series we subjected optical DO sensors with the sensitive layers manufactured of three different polymers that are polystyrene (PS), polybuthylmetacrylate (PBMA) and fluoroplast 42 (F42) to biofouling and tested the change of their response time in the pure model solutions with the known concentration of DO (in vitro experiments). In the second series we subjected optical DO sensors made of the same materials to the biofouling in the model biotechnological reactors and imitated the technological process of the aeration by purging for a while air throw the biological media (in situ experiments). The comparison of the sensors response in the first and in the second series can account for the contribution of the biofouling and the one of the bulk DO consumption processes.In order to facilitate the dispersion of the indicator dye (Pt(II) 5,10,15,20-tetrakis(2,3,4,5,6-pentafluorophenyl)-porphyrin, PtTFPP) in the fluorinated matrix and to improve the quality of the sensor we applied an original core-dye-shell technology, where the indicator dye is first absorbed onto the surface of SiO2 particles and then covered by the shell made of the salt of two fluorinated surfactants, that is trimethyl-1-propanaminium iodide (FC-135) and tetraethylammonium perfluorooctanesulfonate (FT-248).For the both in vitro and in situ experiments we used separately Saccharomyces cerevisiae yeast and Pseudomonas putida k12 bacteria.All polymeric sensor films were observed to be vulnerable to the cell absorption and biofilm formation. The sensor with the membrane made of the F42 filled with core-dye-shell particles, was the only to provide the possibility to determine the actual concentration of DO after two weeks of the incubation in the bioreactor, the damage of the film due to biofouling being not critical.

Sol-gel preparation of fluorine-containing hydrophobic SiO2 coating by using trifluoroethanol as dispersant and modifier simultaneously

A facile sol-gel method was proposed to prepare fluorine-containing hydrophobic SiO2 coating using trifluoroethanol (TFE) as the dispersant and hydrophobic modifier simultaneously. FTIR and XPS analysis indicated that CF3 groups were incorporated onto the surface of SiO2 particles. The resultant SiO2 coating possessed excellent hydrophobicity with a water contact angle (WCA) of 145°. This provides a new method for the preparation of fluorine-containing sol-gel SiO2 coating without the expensive long-chain alkyl fluorosilane.

Adsorption Properties and Mechanism of Cd2+ in Water by Zr-containing Silica Residue Purification.

Zirconium (Zr)-containing silica residue purification (ZSR-P) discharged from industrial production of ZrOCl2 was used as an adsorbent, and CdCl2 solution was used as the simulated wastewater containing cadmium ions (Cd2+). The properties and mechanisms of ZSR-P absorbing Cd2+ were studied. The results showed that ZSR-P had a good effect on the adsorption and removal of Cd2+ in water. The adsorption time, initial concentration of Cd2+, and pH of the solution had a significant effect on the adsorption behavior, whilst the pH value had the greatest effect amongst them. Under optimal conditions, the amount of Cd2+ adsorbed by ZSR-P was 43.1 mg/g. The isothermal adsorption conformed to the Langmuir adsorption model, and the adsorption kinetics conformed to the secondary adsorption rate model. In ZSR-P-Cd, Cd2+ was uniformly distributed on the surface of SiO2 particles and in the pores formed by the accumulation of particles. Adsorption of Cd2+ by ZSR-P was achieved through the reaction between Si-OH on the surface of SiO2 and Cd2+ hydroxyl compounds.

Direct growth of carbon microfibres on SiO 2 particles by chemical vapour deposition from ethanol

Carbon microfibres (CMFs) were synthesised on SiO2 particles by catalytic chemical vapour deposition at 1200°C using ethanol as carbon precursor, iron nitrate as the catalyst precursor, and nitrogen as a carrier gas. The structure and morphology of the products were characterised by X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy and Raman spectroscopy. CMFs obtained after a deposition time of 5 h have a diameter of 5–10 μm and a length of a few hundred micrometres. In the deposition process, Fe–Si–O–C droplets were first formed on the surface of SiO2 particles, and then carbon fibres grew as a result of the catalysis of the droplets. Carbon fibres have the higher graphitic structures when the deposition process is conducted at 1200°C.

Readily dispersible antimicrobial Ag–SiO2 Janus particles and their application on cellulosic fabric

Silver–silica (Ag–SiO2) Janus particles with varying functionalities i.e. amine, thiol and epoxy on the exposed surface of SiO2 particles were synthesized and explored for their antimicrobial activity. Due to their easy dispersibility, Janus particles with silver nanoparticles (AgNPs) of diameter ∼3 nm showed much lower minimum bactericidal concentration (MBC) as compared to conventional isotropic AgNPs powder having AgNPs of almost similar diameter. The isotropic AgNPs and functionalized Ag–SiO2 Janus particles were attached on cotton fabric using exhaustion method followed by curing. The treated fabrics were tested for their antimicrobial activity and wash durability. Ag–SiO2 Janus particles, due to the presence of various functionalities on one–half of their surface, could be attached to cellulosic substrates for imparting durable antimicrobial property.

Surface molecularly imprinted material for enantiomeric resolution of ibuprofen: Preparation and study on chiral recognition and resolution property

ABSTRACTThe surface imprinted material of one single enantiomer of ibuprofen ((S)-ibuprofen) was successfully prepared using the novel surface imprinting technique of synchronously graft/crosslinking-polymerizing and molecule imprinting. Micron sized-silica gel particles as matrix were first modified with coupling agent γ-mercaptopropyl trimethoxysilane (MPMS), obtaining MPMS-SiO2 particles, on which there was a great deal of mercapto group (‒SH). Hydroxyethyl methylacrylate (HEMA) as functional monomer and dibenzoyl peroxide (BPO) as initiator were dissolved into 1,2-dichloroethane (DCE), and HEMA molecules are automatically combined around (S)-ibuprofen molecules by right of multi-site hydrogen bonds, forming self-assembly complex. A surface-initiating system of ‒SH/BPO was constituted at the interface between MPMS-SiO2 particles and DCE solution. The free radicals produced on the surfaces of MPMS-SiO2 particles initiated HEMA molecules around (S)-ibuprofen molecules to produce graft/crosslinking-polymerization on the surfaces of SiO2 particles. At the same time, (S)-ibuprofen molecules were wrapped in the cross-linked networks so that the surface-imprinting of (S)-ibuprofen was realized, forming (S)-ibuprofen surface imprinted particles ((S)-IBU-SIP). The enantiomeric recognition and resolution properties of (S)-IBU-SIP particles were investigated. The experimental results show that (S)-IBU-SIP particles have excellent enantiodiscrimination property and enantioseparation ability. The binding capacity of (S)-IBU-SIP particles for (S)-ibuprofen gets up to 177 mg g−1, and the selectivity coefficient of (S)-IBU-SIP particles for (S)-ibuprofen relative to (R)-ibuprofen is 5.03. For the ibuprofen raceme solution, after solid phase extraction by (S)-IBU-SIP particles, the optical purity (ee value of (S)-ibuprofen) of the eluent reaches up to 82.5%, whereas the optical purity (ee value of (R)-ibuprofen) of the supernatant is 44.2%.

Synthesis of High Surface Area Magneli-Phase Ti5O9 from SiO2 Supported TiO2 Nanosheets

Magnéli phases are substoichiometric titanium oxides with oxygen-deficiency (Ti n O2n-1 n = 4~10), and shows good electronic conductivity and stability in acidic solution. Synthesis of Ti n O2n-1 is typically conducted by reduction of TiO2 with H2 at high temperature, thus making it difficult to prepare in nanoscale and high surface area reduction. In this study, TiO2 nanosheets were deposited on SiO2 particles in order to prevent sintering and aggregation during the reduction process at high temperature. TiO2 nanosheet colloid was prepared by exfoliation of layered H2Ti4O9∙nH2O.2 The preparation process of the nano-sized Ti n O2n-1 is schematically shown in Fig. 1. TiO2 nanosheet lamellar structures were fabricated on spherical SiO2 by layer-by-layer (LbL) deposition using poly(diallyldimethylammonium chloride) (PDDA) as the polycation. Alternately-layered structures (TiO2ns/PDDA)10 were obtained on spherical SiO2 by repeating the process 10 times. (TiO2ns/PDDA)10 was treated under hydrogen flow at 950˚C for 7 hours. After hydrogen treatment, the color of the (TiO2ns/PDDA)10 changed from white to black, indicating reduction. XPS measurement revealed that the average Ti valence was 3.6+, suggesting that the n = 5 phase Ti5O9 was synthesized. TEM images of (TiO2ns/PDDA)10 and Ti5O9 on SiO2 particles are shown in Fig. 2. (TiO2ns/PDDA)10 lamellar structures are observed on the surface of SiO2 particles (Fig. 2a). After reduction, Ti5O9 with particle size of ca. 30 nm was observed on spherical SiO2 (Fig. 2b). The particle size of the obtained Ti5O9 on SiO2 was smaller than other process such as UV-irradiation1 and H2 reduction3. Thus, sintering of Ti5O9 particles was effectively suppressed during the reduction process by using SiO2 particles. Cyclic voltammogram of Ti5O9 on spherical SiO2 in 1.0 M H2SO4 is shown in Fig. 3. Assuming a double layer capacitance of 10 ~ 20 mF cm- 2 for Ti5O9, the surface area is estimated as 50~100 m2 g-1 which is in good agreement with the particle size. The good conductivity, high oxidation resistance, and high surface area of nano-size Ti5O9 may allow its use as a fuel cell catalyst support. 1) T. Ioroi, H. Kageyama, T. Akita, K. Yasuda, Phys. Chem. Chem. Phys., 12, 7529 (2010). 2) W. Sugimoto, O. Terabayashi, Y. Murakami, Y. Takasu, J. Mater. Chem., 12, 3814 (2002). 3) T. Ioroi, Z. Siroma, N. Fujiwara, S. Yamazaki, K. Yasuda, Electrochem. Commun., 7, 183 (2005). Figure 1

Applying Mesoporous Silica SBA‐15 in Electrochemical Detection of DNA Hybridization

AbstractMesoporous silica SBA‐15 powder was used as the separation surface for hybridization purposes and it has proved appropriate and effective. By help of a simple procedure any oligodeoxynucleotide (ODN) modified by NH2‐group can be covalently bound at the surface of SiO2 particles, what significantly extends the capabilities of the experimenter. Use of cathodic stripping voltammetry for electrochemical detection of ODN/DNA hybridization ensures high sensitivity of the analyses. Only ordinary laboratory equipment is needed for the implementation of these experiments. Due to the very small consumption of SBA‐15, commonly sold quantity (5 g) may be sufficient for many years of work.

Preparation of surface imprinted material of single enantiomer of mandelic acid with a new surface imprinting technique and study on its chiral recognition and resolution properties

A surface imprinted material of the single enantiomer of mandelic acid with high performance was successfully prepared with a new surface imprinting technique of synchronously graft-polymerizing and molecule imprinting, and its enantiomeric recognition and resolution properties were investigated. Micro-sized silica gel particles were first modified with coupling agent γ-mercaptopropyl trimethoxysilane (MPMS), obtaining the modified particles MPMS-SiO2 on which mercapto groups were introduced. A surface initiating system of −SH/BPO was constituted with the mercapto group (-SH) on MPMS-SiO2 particles and dibenzoyl peroxide (BPO) in N,N-dimethyl formamide (DMF) solution. In DMF solution, (R)-mandelic acid molecule was used as the template and the functional monomer hydroxyethyl methylacrylate (HEMA) were combined together by right of multi-site hydrogen bonds. The free radicals produced on MPMS-SiO2 particles initiate HEMA molecules around (R)-mandelic acid molecules and the crosslinking agent N,N'-Methylenebisacrylamide (MBA) to produce graft/crosslinking-polymerization. At the same time, the template (R)-mandelic acid molecules were enveloped within the thin grafted polymer layer on the surfaces of SiO2 particles, obtaining (R)-mandelic acid surface imprinted material MIP-PHEMA/SiO2. The experimental results show that MIP-PHEMA/SiO2 particles have excellent enantiomeric recognition and resolution ability. The binding capacity of MIP-PHEMA/SiO2 particles for (R)-mandelic acid reaches up to 278mg/g. As the resolution experiment of a racemic mixture was carried out with MIP-PHEMA/SiO2 particles as solid adsorbent, relative another enantiomer, (S)-mandelic acid, the selectivity coefficient of the imprinted particles for (R)-mandelic acid is 5.02. As a consequence, the two enantiomers were well separated, and the optical purities (ee values) of the supernatant and eluant get up to 44% (corresponding to (S)-mandelic acid excess) and 85% (corresponding to (R)-mandelic acid excess), respectively.

Comparative study on two synthesis methods of core–shell structured SiO2@Y2O3:Eu3+ particles and their luminescence properties

SiO2@Y2O3:Eu3+ spherical particles with core–shell structure have been synthesized successfully by a hydrothermal method, followed heat treatment, leading to the formation of monodisperse SiO2@Y2O3:Eu3+ core–shell particles. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectra (EDS), transmission electron microscopy (TEM), Fourier Transform infrared spectroscopy (FT-IR) and photoluminescence spectra (PL) were used to characterize the as-obtained samples. The SEM indicates that the as-obtained core–shell particles show good spherical shape and non-agglomeration with a narrow size distribution (average size of 420nm). Further studies about some experimental conditions show that the PL intensity is the highest when Y2O3:Eu3+ layers are coated on the surface of SiO2 particles with average size of about 150nm annealed at 800°C. For comparison, the core–shell particles are also synthesized by a simple precipitation method. The PL shows that under the excitation at 240nm, the samples present strong red emission corresponding to the 5D0→7F2 transition of the Eu3+ ions at 613nm. Moreover, the emission spectra intensity by hydrothermal method is much higher than that of sample by precipitation method, because the former present the better dispersion, less percentage of the interface, and more thickness shells than that of the latter.

Fabrication of core–shell structural SiO2@DNA–LDH nanocomposite with low infrared emissivity

Core–shell structural SiO2@DNA–LDH nanocomposite was prepared via Layer-by-Layer assembly of exfoliated LDH nanosheets with DNA bio-molecules over the surface of SiO2 particles. Structural characterization data show that the obtained SiO2@DNA–LDH nanocomposite presented well-defined hierarchical core–shell construction with monodispersed SiO2 core covered with functional layered structural DNA intercalated LDH shell. The infrared emissivity value (8–14μm) of the SiO2@DNA–LDH nanocomposite is 0.458, which is much lower than the composites with DNA or LDH directly assembled on SiO2. The decrease of infrared emissivity values may be attributed to the synergistic effect and the interfacial interaction strengthened by the construction of the DNA intercalated LDH functional shell.

Wear and friction performance of PTFE filled epoxy composites with a high concentration of SiO2 particles

In this work, the tribological performance of PTFE filled SiO2 particles–epoxy composites is investigated. Under a load of 60N (~140MPa contact pressure), the optimum content of PTFE lies between 10 and 15wt%, which yields an ultralow coefficient of friction (CoF) in conjunction with a low wear rate of the composite when dry sliding against bearing steel balls within 1000m. With 12.5wt% PTFE in the composite, a CoF around 0.095 and a wear rate as low as 8.4×10−7mm3/Nm were measured up to a sliding distance of around 2000m. After 2000m, eventually the gradual accumulation of the fractured SiO2 particles and back-transferred steel on the worn composite surface leads to a significant increase of CoF. In the steady-state of sliding, smearing of the PTFE particles along the worn surface was observed together with fracturing of the SiO2 particles and cracking of the epoxy matrix. Successive EDS mapping shows the formation and evolution of a PTFE-containing third-body tribolayer on the worn surface of the composite. The thickness of the tribolayer was measured about 20–30nm on the surface of SiO2 particles after sliding for more than 700m.

Effect of Al2O3-coated SiO2 on properties of Al2O3-coated SiO2/PI composite films

In this pa per, Al2O3-coated SiO2 particles were prepared using nano-SiO2 and Al2O3 sol. Al2O3 particles were also prepared by Al2O3 sol, and the obtained powders have been studied by transmission electron microscopy (TEM), X-ray diffraction (XRD), and infrared spectroscopy (FTIR). The results indicated that the average diameters of Al2O3-coated SiO2 particles and Al2O3 particles were about 30 nm and 10 nm, respectively. For Al2O3-coated SiO2 particles, Al2O3 was successfully coated on the surface of SiO2 particles, and it has been demonstrated that the ingredient of Al2O3 particles is α-monohydrate Al2O3(AlOOH). Polyimide (PI)/SiO2 composite films, Al2O3-coated SiO2/PI composite films, and PI/Al2O3 composite films with the inorganic content of 16 % (by wt) were prepared by in situ polymerization. The mechanical properties, breakdown field strength, thermal properties, and corona-resistance time of the composite films were tested and analyzed. The test results showed that the mechanical properties of the Al2O3-coated SiO2/PI composite films were optimal. The tensile strength and elongation-at-break of the Al2O3-coated SiO2/PI composite films were found to be 123.73 MPa and 12.49 %, respectively, and increase by 6.1 and 34.4 % compared with the PI/SiO2 composite films. The breakdown field strength, initial decomposition temperature, and corona-resistance time of the Al2O3-coated SiO2/PI films were measured as 224.3 kV/mm, 594.72 °C, and 168 min, respectively. The thermal performance of the Al2O3-coated SiO2/PI films is superior to that of the PI/SiO2 films and PI/Al2O3 films. The breakdown field strength and corona-resistance time of the Al2O3-coated SiO2/PI films were similar to those of the PI/SiO2 films and superior to those of the PI/Al2O3 films.