Influence of molecular weight of polydimethylsiloxane precursors and crosslinking content on degree of ethanol swelling of crosslinked networks

Using PDMS (polydimethylsiloxane) as a basic polymeric matrix to the preparation of ethanol-permselective pervaporation membranes is a vibrant field of research. In this paper, a detailed study of the effects of the molecular weight of PDMS precursors and the content of the TEOS (tetraethyl orthosilicate) crosslinker on the degree of swelling in ethanol and ethanol contact angle is reported. Five PDMS precursors with molecular weights of 26.6 K, 35.5 K, 50.2 K, 71.7 K, and 110.4 K, and five crosslinking contents (1 wt%, 2 wt%, 5 wt%, 10 wt%, and 15 wt%) were chosen to prepare twenty-five PDMS networks. Considering only the maximum tensile strength of the networks, the optimum molecular weight of the precursor was found to be 35.5 K and the optimum crosslinker content was 5 wt%. The average Young’s modulus of the PDMS network prepared under these conditions reached 0.63 MPa after using toluene to extract the network. Some uncrosslinked precursors always occur in the networks, and have some influence on the molecular weight of the precursors and the crosslinker content that is used. It was found that the content of the uncrosslinked precursors has direct effect on the contact angle of ethanol sessile drops at the surface of the extracted PDMS networks, and higher extraction corresponded to a smaller ethanol contact angle. A combined parameter (S), defined as the quotient of the extraction amount (A_E) and the tensile elastic modulus (E_Y), gives a good linear relationship with the increase in weight of networks swelled in ethanol. This means that the degree of equilibrium swelling of the networks is simultaneously strongly influenced by the tensile modulus and the content of the uncrosslinked precursors.     

Advanced combustion,cooling and refrigeration,waste gas treatment,heat integrated separation and case studies

This is an overview of a Special Issue that has been dedicated to the 8th conference on Process Integration, Modelling and Optimisation for Energy Saving and Pollution Reduction – PRES’05. Twelve papers from the conference have been selected and peer-reviewed and cover various subjects of advanced combustion, cooling and refrigeration and waste gas treatment. These have been supplemented with heat integrated separation and case studies.     

Friction control with a graft layer of a thermo-sensing polymer

The lubricating mechanism of surfaces grafted with poly-N-isopropylacrylamide (PNIPAAM) was investigated with a thrust collar apparatus. The coefficient of friction increases with temperature rise, because PNIPAAM changes its surface property from hydrophilic to hydrophobic. Conversely the friction coefficient decreases with temperature fall. The role of water in lubrication is discussed based on the experimental result that the thickness of the graft layer decreases with temperature rise. A new technology is presented to control friction in water environments.     

Evaluation of mechanical properties of aluminium alloy–alumina–boron carbide metal matrix composites

This paper deals with the fabrication and mechanical investigation of aluminium alloy, alumina (Al₂O₃) and boron carbide metal matrix composites. Aluminium is the matrix metal having properties like light weight, high strength and ease of machinability. Alumina which has better wear resistance, high strength, hardness and boron carbide which has excellent hardness and fracture toughness are added as reinforcements. Here, the fabrication is done by stir casting which involves mixing the required quantities of additives into stirred molten aluminium. After solidification, the samples are prepared and tested to find the various mechanical properties like tensile, flexural, impact and hardness. The internal structure of the composite is observed using Scanning Electron Microscope (SEM).     

Eco-friendly phosphonic acid piperazine salt toward high-efficiency smoke suppression and flame retardancy for epoxy resins

Journal of Materials Science - In the field of electronic and electrical applications, it has always been a challenge to synchronously improve the flame-retardant and smoke-suppression properties...     

Characterization of Methylolated Lignin by H-Nmr and 13C-Nmr

The hydroxymethylation of an ammonium based lignosulfonate (ALS) was done in the presence of alkali. In terms of their chemical structures, lignin and lignin derivatives were characterized and quantified by H-NMR and ¹³C-NMR spectroscopy. Results indicate that two kinds of hydroxymethyl groups can be formed in the process of lignin methylolation. One kind is adjacent to the aromatic ring, the other is adjacent to the side chain. The amount of hydroxymethyl groups increases and of aromatic protons decreases with increasing methylolation time and levels off after 3 hours.     

Photocatalytic behavior of a new composite ternary system: WO3/SiC-TiO2. Effect of the coupling of semiconductors and oxides in photocatalytic oxidation of methylethylketone in the gas phase

It has been found that the photocatalytic activity of classical TiO₂ for the purification of polluted effluents containing volatile organic compounds (VOCs) can be greatly improved using the effect of the coupling of semiconductors and oxides. Thus, a new mixed photocatalyst has been prepared leading to a composite ternary system, WO₃/SiC–TiO₂. The results indicate that this combination can result in an enhancement in the photocatalytic activity toward methylethylketone (MEK) oxidation at room temperature by a factor greater than four with a total mineralization into CO₂ and H₂O, without creating toxic by-products. The efficiency of the composite system strongly depends on the relative amounts of WO₃ and SiC in the various samples because an optimum in photo-activity is observed when the weight ratios WO₃ and SiC are about 3.5 and 20%, respectively. The increase and synergy in photo-oxidation activity, in comparison to TiO₂ and to the binary TiO₂-based systems, WO₃/TiO₂ and SiC–TiO₂, are obtained as the simultaneous effect of WO₃ and SiC. Addition of WO₃ mainly results in the retarding of electron-hole recombination process by an electron trapping effect and in the modification of surface acidity compared to the case of pure TiO₂. On the other hand, the coupled system of the two illuminated semiconductors, TiO₂ and SiC, leads to a simultaneous electron transfer from SiC to TiO₂ and hole transfer from TiO₂ to SiC, increasing spatial charge separation and thus preventing charge recombinations, detrimental to photocatalytic efficiency.     

Influence of molecular structure on the properties of dendrimer light-emitting diodes

Iridium-based phosphorescent dendrimers have shown much promise as highly efficient light emitting materials for organic light emitting diodes (OLEDs). Here we report the effects of modifying the chemical structure on the emissive and charge transport properties of Ir(ppy)₃ based electrophosphorescent dendrimers. We investigate a novel para linked first generation (G1) iridium dendrimer. This material is compared to G1 and G2 meta linked dendrimers. We show that by blending these dendrimers into a CBP host, high external quantum efficiencies of over 10% and luminous efficiencies of 27 lm/W can be achieved.     

Conductive Polyaniline/Cellulose/Graphite Composite Films with High Thermal Stability and Antibacterial Activity

Functional composite films were successfully prepared from cellulose, graphite (GP), and polyaniline (PANI) using a combination of physical and chemical processes. Cellulose was dissolved in N-methylmorpholine-N-oxide monohydrate (NMMO) and regenerated in water to form the matrix. GP was dispersed in the NMMO solvent prior to the dissolution of the cellulose, and PANI was deposited on the surfaces of the cellulose/GP films by in situ chemical polymerization. The structures of the PANI/cellusose/GP composite films were investigated using X-ray diffraction analysis, Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), and SEM/energy-dispersive X-ray spectroscopy. The mechanical strengths, thermal stabilities, conductivities, and antibacterial activities of the films were studied in detail. The results showed that GP formed a multilayered structure in the cellulose matrix and that the PANI nanoparticles were tightly wrapped on the film surface. The film thickness increased from 40 m to 100 m after the addition of GP and PANI. The tensile strength of the composite films was 80~107 MPa, with the elongation at break being 3%~10%. The final residual weight of the composite films was as high as 65%, and the conductivity of the composite films reached 14.36 S/m. The cellulose matrix ensured that the films were flexible and exhibited desirable mechanical properties, while the GP filler significantly improved the thermal stability of the films. The PANI coating acted as a protective layer during burning and provided good electrical conductivity and antibacterial activity against Escherichia coli; both of these characteristics were slightly enhanced by the incorporation of GP. These PANI/cellulose/GP composite films should be suitable for use in electronics, antistatic packing, and numerous other applications.