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  • 1
    Electronic Resource
    Electronic Resource
    Elastic and elasto-optic properties of thin films of poly(styrene) spin coated onto Si(001) (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 7482-7488 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Brillouin light scattering (BLS) has been used to study a series of three thin films of poly(styrene) spin coated onto Si(001) wafers. Poly(styrene) molecular weights M¯w of 30 000 and 600 000 were used, and the film thicknesses h were in the range 1730 A(ring)〈h〈3750 A(ring). It was found that the poly(styrene) films have isotropic elastic symmetry and that all of the films can be described by the same set of two independent elastic constants c11=5.7±0.15 GPa and c44=1.39±0.03 GPa. Both c11 and c44 were determined unambiguously using a least-squares-fitting procedure by observation of the longitudinal guided and Rayleigh modes of the poly(styrene) films. Calculations have been performed of the BLS spectra which include both surface ripple and elasto-optic light scattering mechanisms. From comparisons of the relative mode intensities in the measured and calculated BLS spectra, it is found that the values of the elasto-optic coefficients for poly(styrene) are k11=−1.4±0.4 and k12=−1.6±0.4.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356619
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  • 2
    Electronic Resource
    Electronic Resource
    Detection of gaps in sinusoids by frog auditory nerve fibers: importance in AM coding (1994)
    Springer
    Journal of comparative physiology 175 (1994), S. 531-546 
    Details
    ISSN: 1432-1351
    Keywords: Eighth nerve ; Gap detection ; Amplitude-modulation ; Modulation transfer function ; Time-locking ; Synchronization coefficient ; Leopard frogs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Physiological studies were carried out in the frog (Rana pipiens pipiens) eighth nerve to determine: (i) whether the modulation rate or the silent gap was the salient feature that set the upper limit of time-locking to pulsed amplitude-modulated (PAM) stimuli, (ii) the gap detection capacity of individual eighth nerve fibers. Time-locked responses of 79 eighth nerve fibers to PAM stimuli (at the fiber's characteristic frequency) showed that the synchronization coefficient was a low-pass function of the modulation rate. In response to PAM stimuli having different pulse durations, a fiber gave rise to non-overlapping modulation transfer functions. The upper cut-off frequency of time locking was higher when tonepulses in PAM stimuli had shorter duration. The fact that the cut-off frequency was different for the different PAM series suggested that the AM rate was neither the sole, nor the main, determinant for the decay in time-locking at high AM rates. Gap detection capacity was determined for 69 eighth nerve fibers by assessing fiber's spiking activities to paired tone-pulses during an OFF-window and an ON-window. It was found that the minimum detectable gap of eighth nerve fibers ranged from 0.5 to 10 ms with an average of 1.23–2.16 ms depending on the duration of paired tone pulses. For each fiber, the minimum detectable gap was longer when the duration of tone pulses comprising the twin-pulse stimuli was more than four times longer. When the synchronization coefficient was plotted against the silent gap between tones pulses in the PAM stimuli, the gap response functions of a fiber as derived from multiple PAM series were equivalent to gap response functions deriving from twin-pulse series suggesting that it was the silent gap which primarily determined the upper limit of time-locking to PAM stimuli.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00199475
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  • 3
    Electronic Resource
    Electronic Resource
    Model-Filled polymers. III: Rheological behavior of polystyrene containing cross-linked polystyrene beads (1990)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990), S. 1158-1164 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The steady shear viscosity and dynamic moduli, at 180 and 200°C, of polystyrene composites, containing cross-linked monodisperse polystyrene beads varying in diameter from 0.2 to 0.8 μm, are independent of bead size and cross-link density, but increase with the volume fraction of beads. Steady shear viscosities exhibit power-law regions up to 40% concentration of beads, but no yield stress. Storage and loss moduli are initially linear with frequency, on double logarithmic plots, with limiting slopes of 1.3 and 0.9, respectively. Uncross-linked beads and beads cross-linked with 0.1% divinylbenzene are destroyed by thermomechanical dispersion in the melt.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760301808
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  • 4
    Electronic Resource
    Electronic Resource
    Model filled polymers. V. Synthesis of crosslinked monodisperse polymethacrylate beads (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 137-144 
    Details
    ISSN: 0887-624X
    Keywords: fillers ; emulsifier free emulsion polymerization ; monodisperse beads ; polymethacrylates ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Monodisperse polymethacrylate beads of varied size and crosslink density are prepared by emulsion copolymerization of methacrylate and divinyl monomers in the absence of emulsifiers. The sizes of polybutyl and polyethyl methacrylate beads decreased with increasing polymerization temperature, while polymethyl methacrylate beads were largely unchanged in size. The molar mass of polymer in polymethyl metnacrylate beads markedly exceeded that in polystyrene beads. The rate of polymerization increased, and bead size decreased, with increasing initiator concentration or decreasing monomer concentration. The polymethacrylate beads are used as filler particles in polymer composites.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300118
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  • 5
    Electronic Resource
    Electronic Resource
    Polymer-supported Ziegler-Natta catalysts. II. Ethylene homo- and copolymerization with TiCl4/MgR2/poly(ethylene-co-acrylic acid) catalyst (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 2135-2145 
    Details
    ISSN: 0887-624X
    Keywords: polymer support ; Ziegler-Natta catalyst ; ethylene ; polymerization ; copolymerization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A novel polymer-supported titanium-based catalyst shows high activity and nondecaying kinetic profiles for ethylene polymerization. The presence of 1-hexene comonomer drastically increases the catalyst activity, exhibiting a similarity to the MgCl2-supported catalysts. However, the nondecaying kinetic profiles of copolymerization distinguish this catalyst from the latter. Infrared analysis indicates that the transition metals were immobilized on the polymer support via functional groups. The effects of polymerization conditions on catalyst activity have been assessed. Characterization of the resulting polymer product by means of 13C-NMR, DSC, and SEM demonstrates a branch-free structure with high melting point, high crystallinity, and high molecular weight for the ethylene homopolymer. The reactivity ratios of ethylene-1-hexene copolymerization are evaluated from 13C-NMR analysis data. © 1994 John Wiley & Sons, Inc.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080321116
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  • 6
    Electronic Resource
    Electronic Resource
    Model filled polymers. I. Synthesis of crosslinked monodisperse polystyrene beads (1990)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 28 (1990), S. 1909-1921 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Monodisperse crosslinked polystyrene beads of varied size and crosslink density are prepared by emulsion copolymerization of styrene and divinylbenzene in the absence of emulsifier. Tumbling and internally stirred reactors were used for synthesis, with minimal agglomeration at at least 0.22 wt % potassium persulfate and up to 10% by weight of styrene in aqueous emulsion in the absence of oxygen. Particle sizes decreased from 800 to 200 nm on raising the polymerization temperature from 60 to 95°C. The glass transition temperature of the beads increased from 104.4 to 133°C by the inclusion of up to 10% by weight of divinylbenzene. The thermal stability of the beads was higher for peroxide than for persulfate initiation. The crosslink density estimated from the degree of swelling was about one third that expected from stoichiometry. The polystyrene beads are used as filler particles in polymer composites.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1990.080280722
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  • 7
    Electronic Resource
    Electronic Resource
    Polymer-supported Ziegler-Natta catalysts. I. A preliminary study of catalyst synthesis (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 2127-2134 
    Details
    ISSN: 0887-624X
    Keywords: Ziegler-Natta catalyst ; polymer support ; ethylene ; polymerization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Polymer-supported Ziegler-Natta catalysts based on various polymer carriers were synthesized by different methods, including (1) loading TiCl4 directly onto the polymer supports; (2) loading TiCl4 onto the polymer supports modified by magnesium chloride (MgCl2); (3) loading TiCl4 onto the polymer supports modified by Grignard reagent (RMgCl); and (4) loading TiCl4 onto the polymer supports modified by magnesium alkyls (MgR2). The activity and kinetic features of the catalysts for ethylene polymerization were examined. Among the combinations tested, the best was found to be TiCl4/n-Bu2Mg.Et3Al/poly(ethylene-co-acrylic acid) (92:8), which produced a catalyst of very high activity for ethylene polymerization. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080321115
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  • 8
    Electronic Resource
    Electronic Resource
    An improved finite difference method for fixed-bed multicomponent sorption (1991)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 37 (1991), S. 244-254 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A new computational procedure based on the finite difference methods is developed to solve the coupled partial differential equations describing nonisothermal and nonequilibrium sorption of multiple adsorbate systems on a fixed bed that contains bidispersed pellets. In this numerical method, a solution-adaptive gridding technique (SAG) is applied in combination with a four-point quadratic upstream differencing scheme to satisfactorily resolve very sharp concentration and temperature variations occurring in the case of small dispersing effects. Furthermore, the method resorts to a noniterative implicit procedure for solving the coupling between the column transport equations and the adsorption kinetics inside the pellets, which may be particularly efficient when the particle kinetics equations are highly stiff.The numerical model will be tested for one-, two- and three-transition systems. The results are compared to available analytical and equilibrium theory solutions.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690370210
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  • 9
    Electronic Resource
    Electronic Resource
    Model filled polymers. XIII: Mixing and time-dependent rheological behavior of polymer melts containing crosslinked polymeric particles (1992)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1418-1425 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The rheological properties of polystyrene (PS) and poly(methyl methacrylate) (PMMA) composites filled with monodisperse sized crosslinked polymeric particles are sensitive to processing history and chemical composition. Particles compatible with the matrix, such as PMMA or copolystyrene-vinylphenol in a PMMA matrix, are randomly dispersed on mixing, yielding (almost) Newtonian fluids. Particles incompatible with the matrix, such as PS or copolystyrene-acetoxystyrene in PMMA, produce composites whose steady shear viscosities depend on shear rate and whose dynamic moduli are elevated at low frequency. Particles in incompatible composites tend to cluster, producing a structure that is destroyed at high shear rates and that reforms on aging at elevated temperatures.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760321904
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  • 10
    Electronic Resource
    Electronic Resource
    Model-filled polymers. II. Stability of polystyrene beads in a polystyrene matrix (1990)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 28 (1990), S. 2707-2714 
    Details
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Thermomechanical degradation, as a result of mixing at 175°C during the preparation of polystyrene composites containing monodisperse (0.45μm) crosslinked polystyrene beads, often leads to a uniform decrease in rheological properties on increasing the concentration or on reducing the crosslink density of the beads. The extent of such degradation depends on the molecular weight of polystyrene and on the crosslink density of the polystyrene beads. Scission fragments from decomposed beads may induce free radical degradation of the polystyrene matrix. Degradation during mixing of the beads and the matrix is suppressed by mixing crosslinked beads in a polystyrene solution, and removing the solvent, or by melt mixing after adding 0.2% BHT. Polystyrene beads and composites show thermally induced weight loss on heating above 330°C in nitrogen or above 250°C in air. Networks of increased crosslink density are of enhanced thermal stability on heating in the absence of shear.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1990.090281316
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