Structure development in curing of poly(phenylene sulfide)

The structure development during melt curing of poly(phenylene sulfide) (PPS) is reported. The changes in the structure were monitored using various characterization techniques such as differential scanning calorimetry, thermogravimetric analysis, infrared spectroscopy, and optical microscopy. It was observed that the thermal parameters such as melting point and heat of fusion are very sensitive to the structural changes and can be effectively used to monitor the curing process. The effect of curing environment was also investigated, and it was found that the rate of change of structure is considerably higher in air than in nitrogen. The results are discussed on the basis of the different mechanisms for curing of PPS.     

Computational investigation into the mechanisms of UV ablation of poly(methyl methacrylate)

Molecular dynamics simulations with an embedded Monte Carlo based reaction scheme were used to study UV ablation of poly(methyl methacrylate) (PMMA) at 157 nm. We discuss the onset of ablation, the formation and distribution of products in the plume and stress relaxation of the polymer matrix. Laser induced heating and bond-breaks are considered as ablation pathways. We show here that depending on the nature of energy deposition the evolution of ablation plume and yield composition can be quite different. If all of photon energy is converted to heat it can set off ablation via mechanical failure of the material in the heated region. Alternatively, if the photon energy goes towards breaking bonds first, it initiates chemical reactions, polymer unzipping and formation of gaseous products inside the substrate. The ejection of these molecules has a hollowing out effect on the substrate which can lead to ejection of larger chunks. No excessive pressure buildup due to creation of gaseous molecules or entrainment of larger polymer chunks is observed in this case.     

Molecular dynamics of poly(ethylene terephthalate)/poly(phenylene sulfide) nanocomposites with barium titanate

The relaxation processes and the properties of polymer/ceramic nanocomposites have been studied by the ¹H nuclear magnetic resonance methods. Nanocomposites of poly(ethylene terephthalate) PET and poly(phenylene sulfide) PPS with 0.25, 2.5 and 5% wt. barium titanate BT were prepared using a twin screw extruder and injection moulding machine. The spin-lattice relaxation time T₁, second moment M₂ and the motional parameters as e.g. the activation energies in the nanocomposites were investigated.     

Gamma irradiation of poly(phenylene sulfide): Effects on crystallization behavior

The irradiation of polymers can bring about significant changes in the polymer structure and ultimately in their performance. Poly-(phenylene sulfide) (PPS) is an engineering polymer which is mostly used in applications where it is subjected to high-energy radiation. This paper reports the results of gamma irradiation of PPS. The technique of differential scanning calorimetry was used to monitor the changes in the melting and crystallization parameters of irradiated PPS. The heat of fusion was found to decrease upon irradiation, indicating a lower degree of crystallinity; however, a marginal increase was observed in the melting point. The nonisothermal crystallization of irradiated PPS indicated reduced crystallizability. This contention is also supported by the isothermal crystallization studies in which the crystallization rate for irradiated PPS was found to be decreased. The retardation in the crystallization of irradiated PPS has been attributed to the possible changes in the structure of the polymer.     

Fractoluminescence of poly(phenylene sulfide) and a fiber composite on its basis

The object of investigation is fractoluminescence induced by the blow of a steel striker on plates made of poly(phenylene sulfide) and carbon-iber-einfor ced poly(phenylene sulfide). It is found that fractoluminescence shows up as a series of bursts several tens of microseconds long. Simultaneously, microcracks develop on the surface. It is assumed that the bursts are caused by microcracking. The linear size of the cracks is estimated to vary from 0.2 to 10.0 fum. The crack size distribution obeys a power law. In the composite, the amount of cracks is an order of magnitude smaller than in the poly(phenylene sulfide) and the crack size distribution is somewhat broader because of a larger fraction of large cracks.     

One-pot synthesis of gold/poly(3,4-ethylendioxythiophene) nanocomposite

In this paper, we report the preparation of highly stable gold nanoparticles/poly(3,4-ethylendioxythiophene) nanocomposites by a one-pot chemical route in aqueous medium without surfactants to increase the solubility of the monomer (3,4-ethylendioxythiophene, EDOT) or to stabilize gold nanoparticles (Au NPs). The generation of the nanocomposite was followed by UV–Visible transmission spectroscopy combined with multivariate curve resolution alternating least squares analysis to deconvolute the individual spectra of the different species generated in the synthesis: oligomers, polymer and gold nanoparticles. The plasmon band observed at 530 nm during the synthesis step indicates the generation of gold nanoparticles. The influence of monomer and metal precursor concentration and their concentration ratios on Au NP size were analyzed. The electrochromic properties of the composite were investigated by UV–Visible absorption spectroelectrochemistry, being mainly related to polymer oxidation and reduction. The main difference observed is the hypsochromic shift of the polymer spectra due to the gold nanoparticles inside the polymer. Multicyclic spectroelectrochemical experiments evidence a high stability and adhesion of the nanocomposite.     

Effects of carbon fibers on the transcrystalline interphase in poly(phenylene sulfide) of different molecular weights

Composite films of different molecular weight poly(phenylene sulfide) (PPS) and three types of carbon fibers (Pitch, PAN, and Rayon-based fibers) have been studied by optical microscopy and wide-angle X-ray diffraction. Transcrystallization of growing spherulites on carbon fibers is found under all thermal conditions of growth on Rayon and Pitch-based carbon fibers for all types of matrices. For composite films with PAN carbon fibers transcrystallization of growing spherulites is not uniform and sometimes is not found at all. Existence of b axial orientation of twisted lamellae for transcrystalline zone of PPS is demonstrated by X-ray diffraction technique and compared with orientation of the stretched sample. The new induction time quantitative approach is applied to the transcrystalline growth of PPS spherulites on the surface of carbon fibers. The interfacial free energy difference for fiber/crystallite and heterogeneities/ crystallite systems in the melt that is defined from growth and nucleation studies are calculated and compared. The relative tendency for a polymer to crystallize at the fiber surface rather than in the bulk is demonstrated.     

Microwave bonding of poly(methylmethacrylate) microfluidic devices using a conductive polymer

Component binding within microfluidic devices is a problem that has long been seeking a solution. In this investigation, the use of microwave radiation to seal PMMA components has been investigated using polyaniline as an absorber that is capable of inducting interfacial bonding. Straight microchannels were machined into PMMA using a Datron CAT3DM6 CNC machine with widths and depths across a range of 100-1000 μm. Prototype fluidic devices were prepared with channel patterns utilizing varying feature sizes, bends and flow profiling to demonstrate the application of the technique to real microfluidic devices. Experimental data illustrated the successful bonding of channels in the range stated previously and bonding (tensile) strength was assessed via pull tests on bonded PMMA using an Engstrom Zwick 100 tensile testing system (Engstrom Ltd, US). Coherent, defect free seals were attained with breakage tests requiring an excess of 1 kN force.     

Studies of blends of poly(phenylene sulfide) and a liquid crystalline polymer: Time-temperature superposition

Polymer blends containing poly(phenylene sulfide) (PPS) and liquid crystalline polymer (LCP) of varying compositions were injection molded and tested. Three-point bending tests were carried out on annealed and unannealed samples at various temperatures and strain rates. The time–temperature master curves were constructed by shifting the experimental modulus data at each point of the curves. The increase in bending modulus and reduction of bending strength with increasing LCP content were attributed to the skincore morphology. The time-temperature curves revealed that the bending modulus of the blends can be superimposed over a wide range of temperatures and strain rates.     

The bonding of oxygen to Al(111)

Oxidation of the Al(111) surface is a two-stage process in which the formation of an ordered oxygen overlayer precedes the creation of a bulk-like amorphous oxide. An electronic structure calculation is reported here for the clean and oxygen-covered Al(111) surface and for bulk A1₂O₃. The calculation uses an atomic-orbital basis and the metal surface is modelled by an infinite two-dimensional crystal, containing seven layers of aluminium atoms. Oxygen atoms occupy three-fold sites, with an Al-O separation of 1.9 Å. The oxygen 2p resonance in the (1 × 1) chemisorbed overlayer is about 3 eV wide, compared to 1.9 eV for an equivalent isolated layer of oxygen atoms unhybridized with the metal. The valence band of A1₂O₃ is about 1.5 eV wider than the chemisorbed oxygen resonance, but in both cases most of the states are concentrated in the top 1.5 eV of the band. The results are related to available ultraviolet photoemission spectra, including the recent angular-resolved spectra of Martinson and Flodström.     

Theoretical insights into the formation of thiolate-protected nanoparticles from gold (III) chloride

Reaction pathways for the formation of thiolate-gold nanoparticles are investigated by density functional theory (DFT) and a new mechanism upon solvent polarity and tetraalkylammonium is obtained. In solvents with high polarities, [Au(I)SR]_n polymers can be formed as the precursor of metal ions prior to the addition of a reducing agent; while a product of [Cl…AuCl(HSR)] is identified as the precursor in solvents with low polarities, such as toluene and chloroform. In addition, tetraalkylammonium also has an obvious effect on the reactions when it is used as a phase transfer agent in the two-phase synthesis. These findings offer a systematic analysis on the pathways to thiolate-stabilized nanoparticles and give a favorable explanation by comparison with those in an experimental system.     

Role of hydrogen bonding in solubility of poly(N-isopropylacrylamide) brushes in sodium halide solutions

By employing molecular theory, we systematically investigate the shift of solubility of poly(N-isopropylacrylamide)(PNIPAM) brushes in sodium halide solutions. After considering PNIPAM–water hydrogen bonds, water–anion hydrogen bonds, and PNIPAM–anion bonds and their explicit coupling to the PNIPAM conformations, we find that increasing temperature lowers the solubility of PNIPAM, and results in a collapse of the layer at high enough temperatures. The combination of the three types of bonds would yield a decrease in the solubility of PNIPAM following the Hofmeister series: Na ClNa BrNa I. PNIPAM–water hydrogen bonds are affected by water–anion hydrogen bonds and PNIPAM–anion bonds. The coupling of polymer conformations and the competition among the three types of bonds are essential for describing correctly a decrease in the solubility of PNIPAM brushes, which is determined by the free energy associated with the formation of the three types of bonds. Our results agree well with the experimental observations, and would be very important for understanding the shift of the lower critical solution temperature of PNIPAM brushes following the Hofmeister series.     

Sorption of water vapor into polyelectrolyte complex of poly(styrenesulfonic acid)/poly(4-vinyl-N-ethylpyridinium bromide)

Successive differential and integral sorptions of water vapor into the polyelectrolyte complex of poly (sty renesulfonic acid) / poly(4-vinyl-N-ethylpyridinum bromide) have been measured; films of stoichiometric (1/1 molar ratio) and nonstoichiometric (2/1 molar ratio) complex were employed in the experiments. Sorption isotherms have been also determined by using the values obtained from integral sorption experiments. The sorption data have suggested the following. (i) The rearrangement of polymer chains plays a relatively unimportant role in sorption of water. (ii) The relaxation motion of network chains is suppressed. (iii) The change of morphological structure caused by vapor sorption is obscure. (iv) The ionic character of the 1/1 complex is higher than that of 2/1 complex. (v) A small amount of water can be dispersed on specific polymer sites, but the sorption of a large amount of water is accompanied by an expansion of network structure. Points (i)-(v) have been consistently interpreted on the basis of the network structure and ionic character of this complex.     

Monte Carlo calculation of penetration of electrons into poly(methylmethacrylate)

Monte-Carlo method is applied to the problem of penetration of 20 keV and 30 keV electrons to polymethylmethacrylate. In this paper the ranges and backscattering yields are calculated and a comparison with the results obtained by different methods is made. Depth-dose functions are depicted as well.The authors wish to thank Mr. J. Kae of the Research Institute of Mathematical Machines for a valuable help in programming.