Iranian Polymer Journal
Year:2010 | Volume:19 | Issue:11 (125)|Papers Count:7

The technology of opto-electronic polymer thin film deposition has advanced dramatically during the past 20 years. This advancement was driven primarily by the need for new products and devices in the electronics and optical industries. Increasingly complex tasks are performed by computers, requiring more and more memory capacity as well as faster and faster processing speeds. This leads to a constant need to develop high performance opto-electronic thin film materials, which can be used for the preparation of more highly integrated microchips. The rapid progress in solid-state electronic devices would not have been possible without the development of new thin film deposition processes and superior thin film qualities. Among the broad variety of accessible alternatives, plasma organic polymer film has been one of the most widely studied materials due to its outstanding and promising mechanical and physicochemical properties. In this review, the new opto-electronic polymer thin films deposited by glow discharge plasma technique in recent years is introduced and discussed in combination with our research results. In particular, we focus our attention on the opto-electronic properties of these polymer thin films, such as dielectric property, electric conductivity, non-linear optical property, photo(electro)luminescent property and optical band gap. The corresponding deposition methods of the opto-electronic polymer thin films including plasma polymerization deposition, plasma-enhanced chemical vapour deposition are also reviewed within their respective sections. In summarizing the review, the development, potential applications and future directions of opto-electronic polymer thin films deposited by glow discharge plasma technique are discussed, especially the film properties required for applications in opto-electronic devices.

The ionic liquid of 1-butyl-3-methyl-imidazolium bromide ([BMIM]Br) was used as a good solvent to dissolve polyacrylonitrile (PAN). In order to systematically study the rheological properties of PAN/[BMIM][Br] solutions, the shear rheology of PAN/[BMIM][Br] solutions with a concentration range of 3.0-6.0 wt% was investigated by measuring the complex and dynamic moduli at different temperatures. The effects of solution concentration and temperature on the complex viscosity of PAN/[BMIM][Br] solutions were studied. The solutions exhibited shear-thinning behaviours. The complex viscosity of solutions increased with increase in solution concentration. The heightening of solution temperature lowers the complex viscosity of the solution. Then the storage modulus, G’, and loss modulus, G”, influenced by the PAN concentration are discussed. Both G’ and G” are increased with the increasing in PAN concentration. The crossover frequency of G’ to G” is shown to decrease as the concentration is increased. Master curves are generated for complex viscosity by employing Carreau and Cross models to fit the experimental data. Both Carreau and Cross models yield good shifted curves for the complex viscosity. The activation energy for each solution concentration was calculated from the Arrhenius plots of the shift factors with respect to temperature. The activation energy for PAN/[BMIM][Br] solutions varies between 4.79 and 8.88 kJ/mol, being slightly higher for the Cross model. The activation energy is increased with the increase in PAN concentration. It can be summarized that 3-5 wt% range of PAN/[BMIM][Br] solution concentrations are considered as dilute solutions, in which PAN molecules are independent of each other without any intermolecular entanglement.

Nylon short fibres were incorporated in NR/SBR rubber matrix with and without a bonding system on a two-roll mill mixer. A dry bonding agent consisting of resorcinol, hexamethylene tetramine and hydrated silica (HRH) was chosen as the interfacial-bonding agent for this composite system. The effect of bonding agent content on the microstructure, mechanical and morphological properties of the composites was investigated. Samples were vulcanized at 150°C using a hot press after determination of the curing characteristics. The cure and scorch times of the composites decreased with increasing bonding agent concentration, while the maximum torque values showed an increasing trend. The bonding agent not only provided a shorter curing time but also enhanced the mechanical properties of the composite. The scanning electron microscopy (SEM) of the composite fracture surfaces implied that the presence of bonding agent has led to the breakage of fibres and less dark holes indicating the pull out of fibres without bonding agent. The results of anisotropic swelling studies, carried out to analyze fibre/matrix interactions and also orientation of the fibres, showed that the restriction to swelling is higher for the composites containing bonding agent. Furthermore, the preferential orientation of the fibres was observed to be in the milling direction. For composites prepared with short fibres and different loading levels of bonding agent, the dependence of the storage modulus (G') on angular frequency followed a clear non-terminal behaviour.

Using a dope comprised of polyethersulphone (PES):N,N-dimethylacetamide: diethylene glycol (DEG) 17:43:40 (wt%), micro-porous PES hollow fibre membranes were prepared by non-solvent vapour-induced phase separation (VIPS). The effects of bore fluid solution composition, coagulation bath temperature, air-gap distance and humidity on the morphologies of micro-porous PES hollow fibre membranes were investigated. Light transmission microscopy was used to determine the precipitation rate during VIPS stage as well as during non-solvent liquid-induced phase separation (LIPS) stage. The mean pore radius of PES hollow fiber UF membranes with sponge-like structures could be calculated by Image software from the SEM images. The mean pore radius of outer surface was about 0.1 mm (0.092 ~ 0.131 mm, PES3 ~ PES14) while the mean pore radius of the inner surface of PES hollow fibre membranes was 0.051-0.064 mm (PES12 and PES14). Pure water permeation fluxes and rejections were closely related to both the inner and outer skin layers. When inner and outer surfaces possessed open structure, the pure water permeation fluxes increased, whereas rejections decreased accordingly. PES hollow fibre membranes with pure water permeation flux from 387 to 1210 L.m-2.h-1.bar-1 as well as rejection of 10.1%-98.1% could be achieved by adjusting air humidity, air-gap distance and composition of bore fluid solution. Pure water permeation fluxes of PES12, PES13 and PES14 with sponge-like structures were higher than 1000 L.m-2.h-1.bar-1 and their BSA rejections were only about 10%.

A new diamine monomer containing pyridine and amide units was prepared via two step reactions. Nucleophilic chloro-displacement reaction of 2,6-diaminopyridine with 4-nitrobenzoyl chloride in the presence of propylene oxide afforded 2,6- bis(4-nitrobenzamido)pyridine and subsequent reduction of the nitro groups led to 2,6- bis(4-aminobenzamido)pyridine. The diamine was reacted with aromatic dianhydrides including pyromellitic dianhydride, benzophenone tetracarboxylic dianhydride, and hexafluoroisopropylidene diphthalic anhydride to form polyimides via two-step polycondensation method, and formation of poly(amic acid) followed by chemical imidization. All the prepared materials and polyimides were fully characterized by common spectroscopic methods and elemental analysis. Physical and thermal properties of the polymers including solubility, inherent viscosity, thermal behaviour and thermal stability were studied and structure-property relations in these polyimides were investigated. The inherent viscosity of the polyimides in NMP at a concentration of 0.5 g.dL-1 at 30°C was between 0.47-0.51 dL/g. The polymers showed high thermal stability while their solubilities were improved. The glass transition temperatures (Tg) of the polymers were about 244-283°C. The 10% weight loss of polymers as a main criterion for their thermal stability was about 420-453°C. Char yield of the polymers at 600°C was in the range of 49-71%. High thermal stability resulted from incorporation of imide backbone, phenylation of chain, symmetry of structures to avoid the weak linkages. The polymers revealed good solubility in dipolar aprotic solvents such as Nmethyl- 2-pyrrolidone, N,N-dimethylacetamide, dimethylformamide, dimethylsulphoxide and also m-cresol. Improved solubility was attributed to the presence of pyridine polar unit and amide structures in the polyimide backbones.

The reaction conditions employed for the synthesis of biodegradable polymers via coordinated anionic ring opening polymerization (CAROP) can be very different and may result in differences between the target and actual product molar masses. Influence of three parameters, monomer (e-caprolactone) concentration, initiator/catalyst molar ratio, monomer/initiator molar ratio, on real polymer molar mass has been studied. Our modelling embodied a mathematical equation through which we calculated the initiator/catalyst (alcohol/stannous 2-ethylhexanoate) ratio for all given monomer concentrations and targeted molar masses of the polymers. We have established that in order to synthesize a polymer of certain molar mass, a lower amount of catalyst would be required when higher monomer concentrations are used. The amount of catalyst required was found to decrease as the target molar mass of the polymer increases. This reduction becomes sharper with increasing monomer concentration. For example, the initiator/catalyst ratios of 33, 24 and 10 are needed to synthesize polycaprolactones with molar masses of 10,000, 20,000 and 50,000 Da accordingly at monomer concentration of 1 mol/L. The initiator/catalyst ratio of 40 is less subjected to the influence of monomer concentration and may be used to calculate the universal amount of catalyst required for the synthesis of polymers with a particular molar mass by ring opening polymerization. The proposed mathematical model was confirmed by syntheses of polymers with different molar masses and initiators.

Ethylene polymerization with MgCl2/TiCl4/TEAl, as a Ziegler-Natta catalyst, was carried out by slurry and gas phase processes. This catalyst was synthesized with a deliberate morphology by controlling the rate of recrystallization. The particle size distribution of the catalyst was very narrow which provided good stability in the reactor. The effects of temperature, monomer and hydrogen partial pressure on the catalyst activity and its deactivation coefficient were evaluated. The kinetic parameters such as deactivation rate coefficient and activation and deactivation energies were determined for both processes. It was found that deactivation rate coefficient decreased by increased temperature of maximum 70°C, while it decreased beyond this temperature. The initial rate of reaction in slurry and gas phase ethylene polymerizations increased by increasing the reaction temperature to maximum 80°C and in comparison, at longer reaction times (>20 min) it showed a drop with maximum reaction temperature of 70°C. It was also found that the deactivation rate coefficient of gas phase polymerization decreased by increasing the partial pressure (concentration) of hydrogen. The catalyst productivity for slurry phase polymerization of ethylene increased by increasing the Al/Ti molar ratio as high as 90 and beyond this ratio the catalyst productivity dropped for the same polymerization.