185,937 research outputs found
Glass transition and alpha-relaxation dynamics of thin films of labeled polystyrene
The glass transition temperature and relaxation dynamics of the segmental
motions of thin films of polystyrene labeled with a dye,
4-[N-ethyl-N-(hydroxyethyl)]amino-4-nitraozobenzene (Disperse Red 1, DR1) are
investigated using dielectric measurements. The dielectric relaxation strength
of the DR1-labeled polystyrene is approximately 65 times larger than that of
the unlabeled polystyrene above the glass transition, while there is almost no
difference between them below the glass transition. The glass transition
temperature of the DR1-labeled polystyrene can be determined as a crossover
temperature at which the temperature coefficient of the electric capacitance
changes from the value of the glassy state to that of the liquid state. The
glass transition temperature of the DR1-labeled polystyrene decreases with
decreasing film thickness in a reasonably similar manner to that of the
unlabeled polystyrene thin films. The dielectric relaxation spectrum of the
DR1-labeled polystyrene is also investigated. As thickness decreases, the
-relaxation time becomes smaller and the distribution of the
-relaxation times becomes broader. These results show that thin films
of DR1-labeled polystyrene are a suitable system for investigating confinement
effects of the glass transition dynamics using dielectric relaxation
spectroscopy.Comment: 10 pages, 11 figures, 2 Table
Properties of short polystyrene chains confined between two Gold surfaces through a combined Density Functional Theory and classical Molecular Dynamics approach
The properties of atactic short-chain polystyrene films confined between two parallel gold surfaces at a temperature of 503 K are investigated using a combination of density functional theory calculations and classical atomistic simulations. A classical Morse-type potential, used to describe the interaction between the polymer and the gold surface, was parameterized based on the results of density functional calculations. Several polystyrene films were studied, with thicknesses ranging from around 1-10 nm. The structural, conformational and dynamical properties of the films were analysed and compared to the properties of the bulk polystyrene systems. The dynamics of the polystyrene close to the surface was found to be significantly slower than in the bulk
Structural investigations of poly(ethylene terephthalate)- graft-polystyrene copolymer films
Structural investigations of poly(ethylene terephthalate)-graft-polystyrene (PET-g-PS) films prepared by radiation-induced grafting of styrene onto commercial poly- (ethylene terephthalate) (PET) films were carried out by FTIR, X-ray diffraction (XRD), and differential scanning calorimetry (DSC). The variation in the degree of crystallinity and the thermal characteristics of PETfilms was correlated withthe amount of polystyrene grafted therein (i.e., the degree of grafting). The heat of melting was found to be a function of PET crystalline fraction in the grafted films. The grafting is found to take place by incorporation of amorphous polystyrene grafts in the entire noncrystalline (amorphous) region of the PET films and at the surface of the crystallites. This results in a decrease in the degree of crystallinity with the increase in the degree of grafting, attributed to the dilution of PET crystalline structure with the amorphous polystyrene, without almost any disruption in the inherent crystallinity
Comparative analysis of the toxicity of gold nanoparticles in zebrafish
The use of nanoparticles - particles that range in size from 1 to 100 nanometres - has become increasingly prevalent in recent years, bringing with it a variety of potential toxic effects. Zebrafish embryos were exposed during the 3-day post-fertilisation period to gold nanospheres (GSSs), gold nanorods (GNRs), gold nanorods coated with polystyrene-sulfate (PSS-GNRs), and gold nanorods coated with both polystyrene-sulfate and polyallamine hydrochloride (PAH/PSS-GNRs). All nanorods were stabilised with cetyltrimethylammonium bromide (CTAB). GNSs were the least toxic of the nanoparticles studied, with exposure resulting in no significant changes in mortality, hatching or heart rate. Exposure to GNRs and PSS-GNRs resulted in significant increases in mortality and significant decreases in hatching and heart rate. Treatment with GNRs caused significant changes in the expression of a variety of oxidative stress genes. The toxic effects of GNRs were ameliorated by coating them with polystyrene-sulfate and, to a more marked extent, with a double coating of polystyrene-sulfate and polyallamine hydrochloride
Polystyrene Magadiite Nanocomposites
An organically modified magadiite has been prepared and used to make a mixed intercalated-exfoliated polystyrene nanocomposite by bulk polymerization. This system gives excellent improvement in mechanical properties, but the thermogravimetric analysis curves do not show any change in the onset of the degradation and the degradation pathway is not changed from that for virgin polystyrene, unlike the situation for an aluminosilicate clay, monlmorillonite. By cone calorimetry, the peak heat release rate is not changed, again unlike the results with the aluminosilicate. This suggests that not all clays exhibit the same behavior in nanocomposite formation
Insecticide-treated nets against malaria vectors and polystyrene beads against Culex larvae.
In Parasitology Today in 1985, Curtis and Lines, and Curtis and Minjas presented the ideas of insecticide-treated nets and polystyrene beads for mosquito control. The former idea has grown to be a major component of the strategy for malaria prevention, especially in Africa. However, although polystyrene beads have been demonstrated to work extremely well, they have yet to be taken up on a major scale
Flammability of styrenic polymer clay nanocomposites based on a methyl methacrylate oligomerically-modified clay
Nanocomposites of polystyrene, high impact polystyrene, acrylonitrile–butadiene–styrene terpolymer, polypropylene, and polyethylene were prepared using a methyl methacrylate oligomerically-modified clay by melt blending and the thermal stability and fire retardancy were studied. These nanocomposites were characterized by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis and cone calorimetry. The results show a mixed morphology, depending on the polymer
Preparation of Nanocomposites from Styrene and Modified Graphite Oxides
Graphite oxide was prepared and modified with several ammonium salts and these modified graphite oxides were used to prepare nanocomposites with polystyrene by in situ polymerization of styrene monomer and by melt blending with polystyrene. Nanocomposites were characterized by X-ray diffraction, cone calorimetry, thermogravimetric analysis and the evaluation of mechanical properties. Nanocomposites are formed by in situ polymerization but not by melt blending; the graphite oxide undergoes thermal degradation at the temperature of melt blending so nanocomposite formation would be unlikely. Mechanical properties of the melt blended nanocomposites are improved relative to the virgin polystyrene while those prepared by in situ polymerization are decreased, except in the case of Young\u27s Modulus, where melt blended and in situ polymerized materials show similar results
Styrenic Nanocomposites Prepared using a Novel Biphenyl-Containing Clay
Montmorillonite was organically modified using an ammonium salt containing 4-acetylbiphenyl. This clay (BPNC16 clay) was used to prepare polystyrene (PS), acrylonitrile butadiene styrene (ABS) and high impact polystyrene (HIPS) nanocomposites. Polystyrene nanocomposites were prepared both by in situ bulk polymerisation and melt blending processes, while the ABS and HIPS nanocomposites were prepared only by melt blending. X-ray diffraction and transmission electron microscopy were used to confirm nanocomposite formation. Thermogravimetric analysis was used to evaluate thermal stability and the flammability properties were evaluated using cone calorimetry. By thermogravimetry, BPNC16 clay was found to show high thermal stability, and by cone calorimetry, a decrease in both the peak heat release rate and the mass loss rate was observed for the nanocomposites
Fourier Transform Infrared Spectroscopy and Scanning Electron Microscopy Characterization of Adhesive Produced From Polystyrene Waste
In this study, the optimized adhesive formulated from polystyrene waste was characterized for Fourier transform infrared (FTIR) spectra, Scanning Electron Microscopy (SEM) / Energy Dispersive X-ray (EDX) spectroscopy, solubility, density and water absorption for identification of existing functional group(s), morphology, elemental compositions, etc. The results revealed that polystyrene, unsaturated hydrocarbon has been degraded to form a new product containing aromatic compounds. SEM morphology showed well mixed blended adhesive with silver-like appearance due to additives and EDX revealed 12 existing elemental compositions with their corresponding percentage atomic weights as follows; carbon 93.14 %, hafnium 1.44 %, vanadium 1.66 %, chromium 1.40 %, bromine 0.47 %, palladium 0.26 %, copper 0.43 %, nickel 0.31 %, cobalt 0.29 %, potassium 0.38 %, iron 0.15 % and manganese 0.08 %. The produced polystyrene adhesive was sparsely soluble in water after 30 minutes; it has a density of 1041 kg/m3 and does not absorb moisture. Because of these results, the adhesive from polystyrene waste could serve as green adhesive, since there are no threats of toxic substance emission from the spectral analysis since most of the elements are used as a supplement in pharmaceuticals and catalyst in process industries
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