Thermally stable polymer composites with improved transparency by using colloidal mesoporous silica nanoparticles as inorganic fillers

The colloidal mesoporous silica nanoparticles with small particle sizes (namely, CMS) are used as inorganic fillers of polymers (i.e. epoxy and silicone). From simple calculation, almost all polymers are estimated to be confined in the mesopores. To clarify the superiority of CMS over nonporous silica particles and mesoporous silica particles with much larger size (TMPS-4) as inorganic fillers, a systematic study on mechanical strength and transparency of polymer-silica nanocomposites was conducted. Compared with nonporous silica particles, similar to TMPS-4, CMS shows a greater effect on lowering the CTE. In addition, obtained polymer-CMS nanocomposites show improved transparency than polymer-TMPS-4 nanocomposites.     

手性有序无机介孔硅用作气相色谱固定相

手性介孔材料在手性分离、不对称催化、手性传感等领域具有广泛的应用价值。手性有序无机介孔硅是一类介孔结构高度有序、不含有机成分的手性材料。该文采用D-苯丙氨酸为手性源合成手性有序无机介孔硅(COIMS),将其用聚硅氧烷(OV-1701)稀释后用作固定相制备毛细管气相色谱手性柱,并对该手性柱的分离性能进行了考察,8种手性化合物在该手性柱上得到了拆分。COIMS柱对直链烷烃、醇的分离也表现出良好的选择性。该柱还具有分析时间短、在较高温度下测定稳定等优点,其具有开发成高温手性固定相的潜力。     

Thermal investigation of silicone rubber containing imide-siloxane copolymers

Dynamic mechanical thermal analysis and isothermal thermogravimetry yield useful information on the temperature dependence of the mechanical properties and thermal stability of silicone rubbers. In the thermal mechanical relaxation spectra, only one characteristic phenomenon may be observed. Isothermal thermogravimetry reveals that the thermal degradation is a first-order reaction. The experimental results provide a possibility for the calculation of overall (apparent) reaction rate constants characteristic of the thermal decomposition process, and for the calculation of half-time values.     

Studies of molecular dynamics of carboxylated acrylonitrile-butadiene rubber composites containing in situ synthesized silica particles

The molecular dynamics of carboxylated acrylonitrile-butadiene rubber - silica hybrid materials was investigated. Silica hybrids were formed in situ rubber matrix using varied amounts of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (DAMS), serving also as a cross-linker. Filler-filler and filler-rubber interactions were present, due to the specific nature of these materials. It was found that the amounts of added aminosilane determined the cross-linking density of obtained materials and was the highest with 20 phr DAMS used. The cross-links had ionic nature. Dielectric relaxation spectroscopy (DRS) revealed β, α and α′ relaxation processes. The β relaxation, correlated with the mobility of polymer side groups, was influenced by the weak interaction between both acrylonitrile and carboxylic groups of the rubber and silanol groups of silica. The activation energy for that relaxation was similar for all materials (∼32 kJ mol⁻¹). Both DRS and dynamical mechanical analysis (DMA) demonstrated that the amount of in situ formed silica filler did not significantly influence either the temperature of the α relaxation (correlated with glass transition) or its activation energy. Therefore, that relaxation was caused by free polymer chains, not attached to the silica particles. Similar values of glass transition temperature (T_g) for all hybrids were confirmed by DSC. It appeared that the amplitude of tangent delta (DMA) within T_g was dependent on silica amount. Detected at higher temperature α′ relaxation resulted from the presence of domains, where polymer chains were affected by silica network, geometrical restrictions and morphology of the silica-rich domains.     

Synthesis of ordered mesoporous silica membrane on inorganic hollow fiber

This paper reports on a new method for the preparation of mesoporous silica membranes on alumina hollow fibers. A surfactant-silica sol is filled in the lumen of an alpha-alumina hollow fiber. The filtration technique combined with an evaporation-induced self-assembly (EISA) process results in the formation of a continuous ordered mesoporous silica layer on the outer side of alpha-alumina hollow fibers. X-ray diffraction (XRD), transmission electron microscopy (TEM), and nitrogen isothermal adsorption measurements reveal that these membranes possess hexagonal (P6mm) mesostructures with pore diameters of 4.48 nm and BET surfaces of 492.3 m(2) g(-1). Scanning electron microscopy (SEM) studies show that the layers are defect free and energy-dispersive spectroscopy (EDS) mapping images further confirm the formation of continuous mesoporous silica layer on the outer side of alpha-alumina hollow fibers. Nitrogen and hydrogen permeance tests show that the membranes are defect free.     

Synthesis of highly-ordered mesoporous silica particles using mixed cationic and anionic surfactants as templates

We applied a molecular assembly formed in an aqueous surfactant mixture of cationic cetyltrimethylammonium bromide (CTAB) and anionic sodium octylsulfate (SOS) as templates of mesoporous silica materials. The hexagonal pore size can be controlled between 3.22 and 3.66 nm with the mixed surfactant system. In addition, we could observe the lamellar structure of the mixed surfactants with precursor molecules, which strongly shows the possibility of precise control of both the pore size and the structure of pores by changing the mixing ratio of surfactants. Moreover, use of the cationic surfactant having longer hydrophobic chain like stearyltrimethylammonium bromide (STAB) caused the increase in d(100) space and shifted the point of phase transition from hexagonal phase to lamellar phase to lower concentration of SOS.     

Synthesis and characterization of colloidal fluorescent mesoporous silica particles

Mesoporous silica particles with narrow size distribution were obtained by a seeded growth process. Depending on the size of seeds and on the time of addition of reactants, the size of particles can be varied between 300 and 1000 nm. In a second step the dye fluorescein isothiocyanate can be embedded. The structure of these new silica particles with low density was investigated by SEM, XRD, BET, and confocal microscopy.     

The permeation of organophosphorus compounds in silicone rubber membranes

The permeabilities, solubilities, and diffusivities of eight organophosphorus chemicals in silicone rubber were measured at saturation concentration using two different experimental methods: permeation experiments and absorption experiments. All tests were carried out at 25°C (±3°C). The eight organophosphorus chemicals investigated are dimethyl methylphosphonate, diethyl methylphosphonate, dimethyl hydrogenphosphonate, diethyl hydrogenphosphonate, trimethylphosphate, triethylphosphate, trimethylphosphite, and triethylphosphite. These eight chemicals were selected based on their similarities to organophosphorus chemicals used as pesticides and chemical warfare agents. The experimental data were analyzed using solutions of Fick's second law of diffusion and boundary conditions representative of the experimental settings. An unsteady-state diffusion model using boundary conditions that represent uniform initial concentration in the polymer and constant but different surface concentrations was used to interpret the permeation experimental data. In this model, the effective diffusivity calculated from the steady-state permeability and equilibrium solubility of each chemical was used and was assumed to be constant.     

Ultrafast enzyme immobilization over large-pore nanoscale mesoporous silica particles

By finely tuning the TEOS/P123 molar ratio of the octane/water/P123/TEOS quadruple emulsion system and by controlling the synthesis conditions, an ultrafine emulsion system was isolated, under the confinement of which, nanoscale silica particles with ordered large mesopores (approximately 13 nm) have been successfully constructed; the obtained mesoporous silica particles have an unusual ultrafast enzyme adsorption speed and the amount of enzyme that can be immobilized is larger than that of conventional mesoporous silica, which has potential applications in the fast separation of biomolecules.     

Understanding the reinforcement and dissipation of natural rubber compounds filled with hybrid filler composed of carbon black and silica

The performance of reinforced rubber compounds depends on the filler composition while the reinforcement and dissipation mechanisms still remain unclear.Herein linear and nonlinear dynamic rheological responses of carbon black/silica hybrid filler filling nature rubber compounds are investigated.The rheological contributions of dynamically retarded bulk phase and filler network are revealed to be crucial at high and low frequencies,respectively,and the bulk phase is shown to be of vital importance for the occurrence of nonlinear Payne effect at mediate frequencies.A framework for simultaneously solving reinforcement and dissipation varying with filler composition and content is suggested,providing a new perspective in understanding the filling effect for manufacturing high-performance rubber materials.     

Homoionic inorganic montmorillonites as fillers for polyamide 6 nanocomposites

The homoionic montmorillonites Ca-MMT, Mg-MMT, Ba-MMT and Ca-MMT intercalated with ε-caprolactam - Ca-MMT·CL were prepared from commercial Na-MMT and characterized by WAXS and TGA. They were used as fillers for nanocomposites of polyamide 6 synthesized either by anionic polymerization of ε-caprolactam (monomer casting) or by melt blending. WAXS analysis showed that the intercalation of MMT by the polyamide was complete for all nanocomposites, with only a very small fraction of exfoliated platelets being detected by TEM. The decrease in the number of layers in the MMT tactoids suggests that tactoid splitting was lower for the blended nanocomposites than for the polymerized ones. Both the rate of polymerization and the polyamide yield in the nanocomposites were comparable to those of an unfilled system. The MMT fillers, the density of which was more than twice that of the ε-caprolactam in which they were suspended, sedimented during the first stage of polymerization. TGA was used to determine the degree of sedimentation at various levels of the resulting mold. In line with the coordination of polyamide chains to the surface cations of MMT particles, the sedimentation level increased in the following sequence: Mg-MMT < Ba-MMT < Ca-MMT·CL << Na-MMT. Ca-MMT was found to be the only non-sedimenting filler suitable for use in the synthesis of polyamide nanocomposites by either monomer casting or the use of reactive injection molding (RIM) technologies.     

Large-pore mesoporous SBA-15 silica particles with submicrometer size as stationary phases for high-speed CEC separation

A new mesoporous sphere-like SBA-15 silica was synthesized and evaluated in terms of its suitability as stationary phases for CEC. The unique and attractive properties of the silica particle are its submicrometer particle size of 400 nm and highly ordered cylindrical mesopores with uniform pore size of 12 nm running along the same direction. The bare silica particles with submicrometer size have been successfully employed for the normal-phase electrochromatographic separation of polar compounds with high efficiency (e.g., 210,000 for thiourea), which is matched well with its submicrometer particle size. The Van Deemeter plot showed the hindrance to mass transfer because of the existence of pore structure. The lowest plate height of 2.0 microm was obtained at the linear velocity of 1.1 mm/s. On the other hand, because of the relatively high linear velocity (e.g., 4.0 mm/s) can be generated, high-speed separation of neutral compounds, anilines, and basic pharmaceuticals in CEC with C18-modified SBA-15 silica as stationary phases was achieved within 36, 60, and 34 s, respectively.     

Effect of conductive fillers on the cyclic stress-strain and nano-scale free volume properties of silicone rubber

The effect of carbon black(CB) and graphite(G) powders on the macroscopic and nano-scale free volume properties of silicone rubber based on poly(di-methylsiloxane)(PDMS) was studied through thermal and cyclic mechanical measurements, as well as with positron annihilation lifetime spectroscopy(PALS). The melting temperature of the composites(Tm) and the endothermic enthalpy of melting(?Hm) were estimated by differential scanning calorimetry(DSC). Tm and the degree of crystallinity(χc) of PDMS composites were found to decrease with increasing the CB content. This can be explained due to the increase in physical cross-linking which results in a decrease in the crystallite thickness. Besides, χc was found to be dependent on the filler type. Cyclic stress-strain behavior of PDMS loaded with different contents of filler has been studied. Mullins ratio(RM) was found to be dependent on the filler type and content. It was found that, RM increases with increasing the filler content due to the increase in physical cross-linking which results in a decrease in the size of free volume, as observed through a decrease of the o-Ps lifetime τ3 measured by PALS. Moreover, the hysteresis in PDMS-CB composites was more pronounced than in PDMS-G composites. Furthermore, a correlation was established between the free volume Vf and the mechanical properties of PDMS composites containing different fillers. A negative correlation was observed between Vf and RM.     

Effect of electrolyte in silicone oil-in-water emulsions stabilised by fumed silica particles

Partially hydrophobised fumed silica particles are used to make silicone oil-in-water emulsions at natural pH of the aqueous phase. The stability and rheological properties of the emulsions and suspensions are studied at NaCl concentrations in the range 0-100 mM. It is found that all emulsions are very stable to coalescence irrespective of the NaCl concentration. However, a strong effect of electrolyte on the creaming and rheological properties is observed and linked to the particle interactions in aqueous suspensions. The creaming rate and extent are large at low electrolyte concentrations but both abruptly decrease at salt concentrations exceeding the critical flocculation concentration of the suspension (approximately 1 mM NaCl). The drastic improvement of the stability to creaming is attributed to the formation of a visco-elastic three-dimensional network of interconnected particles and emulsion droplets.     

A novel phase-change composites based on silicone rubber containing energy-storage microcapsules

A novel phase-change composites based on silicone rubber (MVQ) containing n-octadecane/poly (styrene-methyl methacrylate) microcapsules were successfully obtained by mixing energy-storage microcapsules into MVQ matrix using three preparation methods. The effect of microcapsules content on thermal property of the composites was investigated by thermogravimetric analysis. The mechanical properties of the composites prepared by three methods were also investigated. The morphology and thermal properties of the composites were characterized by scanning electron microscopy (SEM), differential scanning calorimetry, and thermal response. Thermal and mechanical properties of the composites were excellent when the microcapsules were added into room temperature vulcanized silicone rubber with 2 phr (per hundred rubber) content and cured at room temperature. The composites were proved to have good energy-storage performance with 67.6 J g^?1 enthalpy value.     

Spherical silica particles decorated with graphene oxide nanosheets as a new sorbent in inorganic trace analysis

Graphene oxide (GO) is a novel material with excellent adsorptive properties. However, the very small particles of GO can cause serious problems is solid-phase extraction (SPE) such as the high pressure in SPE system and the adsorbent loss through pores of frit. These problems can be overcome by covalently binding GO nanosheets to a support. In this paper, GO was covalently bonded to spherical silica by coupling the amino groups of spherical aminosilica and the carboxyl groups of GO (GO@SiO₂). The successful immobilization of GO nanosheets on the aminosilica was confirmed by scanning electron microscopy and X-ray photoelectron spectroscopy. The spherical particle covered by GO with crumpled silk wave-like carbon sheets are an ideal sorbent for SPE of metal ions. The wrinkled structure of the coating results in large surface area and a high extractive capacity. The adsorption bath experiment shows that Cu(II) and Pb(II) can be quantitatively adsorbed at pH 5.5 with maximum adsorption capacity of 6.0 and 13.6 mg g⁻¹, respectively. Such features of GO nanosheets as softness and flexibility allow achieving excellent contact with analyzed solution in flow-rate conditions. In consequence, the metal ions can be quantitatively preconcentrated from high volume of aqueous samples with excellent flow-rate. SPE column is very stable and several adsorption–elution cycles can be performed without any loss of adsorptive properties. The GO@SiO₂ was used for analysis of various water samples by flame atomic absorption spectrometry with excellent enrichment factors (200–250) and detection limits (0.084 and 0.27 ng mL⁻¹ for Cu(II) and Pb(II), respectively).     

Effects of rubber type on the curing and physical properties of silica filled rubber compounds

As environmental regulations are getting stricter, tire industries for automobiles have shown much interest in substituting silica for conventional carbon black partially or entirely. To take full advantage of silica as fillers for rubbers, it is essential to find a reasonable rubber system that shows an excellent performance with silica reinforcement. Therefore, in this study, several different rubber compounds comprising the same amount of silica were prepared with several different rubber systems, respectively. The processability, curing characteristics, and mechanical and viscoelastic properties of the rubber compounds were investigated to analyze the performance of the rubber compounds as tire tread materials. Among the rubber compounds studied, SBR1721 compound comprising natural rubber (NR) and styrene butadiene rubber (SBR) with high styrene content was considered the most appropriate for application to tire tread materials. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis and characterization of functionalized silica as fillers of polymeric systems

This study investigates the functionalization of sol-gel silica with selected organic species, and compares the materials obtained to a commercially available silica functionalized under comparable conditions. Anilines with different active groups were grafted onto the surface of the silicas, via reaction with key surface sites, to modulate the hydrophobicity of the materials. The properties of the functionalized materials, as determined by FT-IR, DTA-TGA and nitrogen adsorption (surface area, S_BET) are discussed.     

Non-surfactant synthesis of mesoporous silica with dye as template

A novel non-suffactant method was described to synthesize mesoporous silica using dye basic fuchsin as template.Chemical reactions were introduced into the formation of mesopores rather than the weak electrostatic or hydrogen-bonding interactions in the traditional surfactant routes.The reactant composition was found to be crucial to the pore structure of objective product.The formation mechanism of mesopore was also proved.