Search Results

You are looking at 101 - 110 of 1,725 items for :

  • All content x
Clear All

Abstract  

In order to enhance the thermal conductivity of MWCNT filled poly(dimethyl siloxane) (PDMS) composites, the MWCNT was coated with silica layer by three step reactions. The composites filled with raw and silica-coated MWCNTs were prepared and the properties were investigated in terms of the curing characteristics, mechanical properties, and thermal conductivity. Due to the poor compatibility between raw MWCNT and PDMS, raw MWCNT showed poor dispersion uniformity and wettability in PDMS. On the other hand, due to the chemical affinity between silica/MWCNT and PDMS throughout the hydrogen bonding, the silica-coated MWCNT filled PDMS showed improved mechanical properties in terms of tensile strength and 100% modulus, and good interfacial compatibility than raw MWCNT incorporated PDMS. Finally, the good wettability of silica/MWCNT in PDMS resulted in higher thermal conductivity caused from the facile phonon movement at the interface even with the smaller MWCNT contents.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: Gordana Marković, Suzana Samaržija-Jovanović, Vojislav Jovanović, and Milena Marinović-Cincović

Abstract  

The properties of filled polymers depend on the properties of the matrix and the filler, the concentration of the components and their interactions. In this research we investigated the rheological and mechanical properties and thermal stability of polychloroprene/chlorosulfonated polyethylene (CR/CSM) rubber blends filled with nano- and micro-silica particles. The density of the nano-silica filled CR/CSM rubber blends was lower than that of the micro-silica filled samples but the tensile strength and elongation at break were much higher. The nano-silica filled CR/CSM rubber blend has higher V r0/V rf values than micro-silica composites and show better polymer–filler interaction according to Kraus equation. The nano-silica filled CR/CSM rubber blends were transparent at all filler concentration, and have higher glass transition values than micro-silica filled compounds. The higher values of the glass transition temperatures for the nano- than the micro-filled cross-linked systems are indicated by DMA analysis. The nano-filled cross-linked systems have a larger number of SiO–C links than micro-filled cross-linked systems and hence increased stability.

Restricted access

Abstract  

A method was developed to estimate the density of the silanol groups attached to silica gel surfaces from thermogravimetric data. Depending on the mechanism of condensation of silanol groups during heating, after removing physically adsorbed water, the results obtained ranged from 4.3 to 6.7 OH nm-2 for a series of silicas. The data are in good agreement with those obtained by other techniques. Thermogravimetry proved to be a reliable tool for this kind of study, with the great advantage of being a simple, quick and inexpensive method requiring only a few mg of the silica sample.

Restricted access

Abstract  

Human serum albumin (HSA) adsorbed onto silica nanoparticles modified by 3-aminopropyltriethoxysilane (APTES) and polyethyleneimine (PEI) was investigated by differential scanning calorimetry, IR spectroscopy, and photon correlation spectroscopy. The structural alterations of the protein molecules induced from adsorption process were estimated on the basis of temperatures of denaturation transition (T d) of the protein in free (native) and adsorbed form. It was found that adsorption of the protein onto the APTES-modified silica nanoparticles results in an increase in the temperature of denaturation transition from 42 to 47.4 °C. HSA adsorbed onto the PEI-modified silica nanoparticles unfolds extensively.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: Stéphanie Etienne, C. Becker, D. Ruch, B. Grignard, G. Cartigny, C. Detrembleur, C. Calberg, and R. Jerome

Abstract  

Silica nanoparticles of various sizes have been incorporated by melt compounding in a poly(methyl methacrylate) (PMMA) matrix to enhance its thermal and mechanical properties. In order to improve nanoparticles dispersion, PMMA grafted particles have been prepared by atom transfer radical polymerization (ATRP) from well-defined silica nanoparticles. This strategy was expected to ensure compatibility between both components of the PMMA nanocomposites. TEM analysis have been performed to evaluate the nanosilica dispersion whereas modified and non-modified silica/PMMA nanocomposites thermal stability and mechanical properties have been investigated by both thermogravimetric and dynamical mechanical analysis.

Restricted access

Abstract  

The source of contaminating high purity silica during grinding process and analytical sensitivity of alpha-emitting impurities have been investigated. To improve the analytical sensitivity for alpha-emitting impurities in grinding high purity silica, a new procedure was studied by employing an irradiation facility in the hydraulic transfer system (HTS) and the nitrogen flushing system. The source of silica contamination was found to be attributed mostly to alumina balls. The detection limit of U and Th in 3N-grade silica samples by neutron activity analysis (NAA) could be improved to a sub-ng/g level. The contamination rates of Th, U, Cl, Fe and Na from the alumina balls were calculated to be 95%, 15%, 15% and 3.5%, respectively.

Restricted access

Abstract  

The effects of pH, ionic strength and concentration on the sorption of Th(IV) on alumina and silica were investigated and the sorption isotherms of Th(IV) on alumina and silica at different pH values were determined. It was found for both sorbents that the absorbability of silica is less than that of alumina. The relative sorption rate of silica is similar to that of alumina. The sorption edges are similar to each other, that the insensitivity of sorption to ionic strength is about the same. These similarities between the sorbents suggest that the speciation of Th(IV) in aqueous solutions plays a significant, but subtle role, in controlling the sorption process, because the charges of both sorbents are distinctly different. The mechanism of Th(IV) sorption on alumina is distinctly different from that of the sorptions of Cs+, Eu3+ and Yb3+ on alumina, and similar to that of the sorption of Co(II) on alumina.

Restricted access

Separation of the fluoroquinolone antibiotics has been examined using numerous mobile phases and commercially available TLC plates precoated with silica gel, cellulose, and chemically bonded silica gel (RP-C18). The best separation of the antibiotic standards was achieved on silica gel with methanol-acetone-1 mol L −1 citric acid-triethylamine, 2.8 + 2 + 0.2 + 0.5 ( v / v ) as mobile phase, on cellulose with dichloromethane-isopropanol-THF-25% ammonia, 4 + 6 + 3 + 3 ( v / v ), as mobile phase, and on silanized silica gel RP-C18 with methanol-0.07 mol L −1 phosphate buffer, pH 6–10 mmol L −1 benzyldimethyltetradecylammonium chloride, 6 + 3 + 1 ( v / v ), as mobile phase. The separated compounds were detected under UV irradiation at λ = 254 nm or by treatment of the plate surface with different dyeing agents.

Restricted access

Abstract  

The60Co hot atom reactions were studied in tris/acetylacetonato/cobalt/III/ adsorbed on silica-gel surface.57Fe Mössbauer spectra of tris/acetylacetonato/iron/III/ in the corresponding system were also measured in order to examine the state of dispersion of complex molecules on silica-gel. The retention formation processes were discussed in terms of the dependence of60Co retention on the adsorbed amount /concentration/ of cobalt/III/ complexes.

Restricted access

An overview of the adsorption characteristics of 3-cyanopropylsiloxane-bonded silica gel as a specific, moderately polar sorbent which can be used for separation of different classes of organic and inorganic substances in both normal- and reversed-phase chromatography is presented. The most important separation mechanisms that govern the retention on this sorbent are underlined. In addition, some recently published applications of 3-cyanopropylsiloxane-bonded silica gel as a sorbent in thin-layer chromatography are listed.

Restricted access