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Abstract: The micromechanical origin of size effects in elasticity of solid polymers is discussed in this article. It is shown that size effects related to rotational gradients can be interpreted in terms of Frank elasticity arising from the finite bending stiffness of the polymer chains and their interactions. We derive a relationship between the gradient of the nematic director field, related to the orientation of the polymer segments, and the curvature tensor associated with rotational gradients. In the resulting couple stress model, the total deformation energy of the material contains a Frank elasticity term. The energy contribution from rotational gradients is related to an effective Frank elastic constant [N]. The corresponding characteristic length for size effects is obtained as where μ is the shear modulus. Our estimations suggest that the characteristic length for size effects in polymers is larger than that obtained for small-molecules materials. Experimental data from the literature are also discussed. [Copyright &y& Elsevier]

[S0021-9606(97)00230-4] [ABSTRACT FROM AUTHOR]

Small-angle neutron scattering was used to observe the relaxation of the structure factor from a smaller to a larger fluctuation state after a temperature jump within the one-phase region of a miscible polymer blend. The blend studied is a 60/40 by weight mixture of a hydrogen bonded polymer blend which consists of hydroxy modified deuterated polystyrene and poly(butylmethacrylate). A peak clearly evolved during the transition from the initial state at Ti to the final state at Tf as predicted by linear as well as nonlinear theories. This relaxation process, which took more than 10 h, could be represented reasonably well by a simple linear approximation of the Cahn–Hilliard–Cook (CHC) theory without involving nonlinear calculations for the evolution of the dynamic structure factor. The measurement offers an alternative method for estimating the order parameter relaxation rate in the one-phase region. Also, this demonstrates experimentally the correct relaxation (to a higher fluctuation state) mechanism predicted by the linear theory of CHC type. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A wrinkling criterion for non-linear elastic membrane materials such as thin polymer, fabric or rubber structures has been determined by employing finite element analysis as an alternative to the difficult experimental counterpart. The hyperelastic constitutive equation proposed by Ogden was implemented into the commercial finite element program ABAQUS with user material subroutine VUMAT. The relation between strain energy and the principal values of the stretch tensor was obtained in order to trace the wrinkle/non-wrinkle boundaries. It was shown that the wrinkling of an elastic membrane can be regarded as being initiated at the instance of abrupt slope change of the strain energy-stretch curve, which was verified by comparing the criterion obtained by finite element analysis with the existing analytical solution. [ABSTRACT FROM AUTHOR]

In this paper, the effects of harmonic superimposed DC voltage on electrical tree growth characteristics in ethylene propylene diene monomer (EPDM) for HVDC cable accessories insulation are studied. Harmonic component with a frequency from 50 to 450 Hz is superimposed on DC voltage to analyze the mechanism of harmonic amplitude, order and voltage polarity on electrical tree growth. The results show that the electrical treeing process is promoted with an increase in harmonic amplitude and order, which brings a longer tree length and more accumulated damage to the insulation. Especially when the amplitude of harmonic component exceeds that of DC voltage, the electrical treeing processes are significantly deteriorated, resulting from the large amount of energy released by the recombination of hetero charges. The growth of electrical tree has an obvious polarity effect which tends to be branch-like tree under positive voltage and bush-like tree under negative voltage. The polarity effect may be caused by different propagation processes of electron avalanche under different voltage polarities. As harmonic order increases, the main channel of positive electrical tree is broadened, while the negative tree becomes denser with a lot of bifurcation. These results indicate that harmonic component accelerates the initiation and propagation of electrical tree by affecting the charge transport behavior under the superimposed electric field. [ABSTRACT FROM AUTHOR]

Abstract: A chemical kinetics model was proposed to describe the abrasive size effect on chemical mechanical polishing (CMP). The model is based on the consideration of a pad as a sort of catalyst and the re-adhering of abrasives due to the large size. Therefore, a general equation was deduced according the chemical kinetics methodology to give the meanings of the size effect. Finally, according a set of data related to the abrasive size effect on CMP, a possible form can be PR=αC C C T X A C WA n /[β+γX A C WA n ] where α, β, γ and n are the parameters in a CMP system. [Copyright &y& Elsevier]

Thermal annealing of a polymer light-emitting diode (PLED) is shown to result in a remarkable improvement in the long-term stability of the device. The annealing for such a PLED has to be layer-specific in that the annealing should be carried out for the layer with the lowest glass transition temperature (T[SUBg]) to harvest the benefits of annealing. Annealing of this key layer, which is usually) the emitting layer, can enhance the thermal stability of the device. The best half-life is obtained at an annealing temperature above the T[SUBg] of emitting polymer. It is shown that the annealing of the emitting polymer layer results in a more than an order of magnitude increase in the half-life, in spite of a decrease in the efficiency of the device as the annealing temperature increases. [ABSTRACT FROM AUTHOR]

Dissolution (mixing or melting) of inhomogeneities formed during spinodal decomposition in binary polymer mixtures is studied both experimentally and theoretically. The details of the dissolution experiment with time-resolved light scattering on polystyrene/poly(vinylmethylether) are presented. The theoretical approach differs from that of Langer, Bar-on, and Miller in the way the fluctuations are treated in the nonlinear theory, and in the details of the calculations arising from the chain connectivity (polymer effect). The effect of mode coupling arising from nonlinearity on the relaxation rate is discussed. It is found both experimentally and theoretically that the wave number corresponding to peak intensity decreases in time asymptotically following a t-0.5 power law. [ABSTRACT FROM AUTHOR]

A deviation from mean-field behavior is observed in the static susceptibility and correlation length measured with small angle neutron scattering as a function of temperature near the phase boundary of a relatively low molecular weight critical polymer mixture. The possibility of a fluctuation influenced crossover from mean-field to nonmean-field behavior is considered. [ABSTRACT FROM AUTHOR]

The trap level characteristics are attracting much attentions in electrical and electronic engineering, which are closely associated with electrical properties of insulating materials. This paper try to modify the trap level characteristics of Low-density Polyethylene (LDPE), by incorporating graphene nanofillers into polymer with a filler content of 0.001, 0.003, 0.005, 0.007 and 0.01 wt%. The effects of filler content and ambient temperature on the trap level distributions are investigated, based on the isothermal surface potential decay (ISPD) method under 30, 50 and 70 °C. The experimental results show that the deep trap level and density increase with the filler content from 0 to 0.005 wt%, and then decrease with the further increase to 0.01 wt%. The increases of deep trap level and density affect the detrapping processes and suppress the electron injection into polymer bulks and cause a much slower downward trend in ISPD curves, especially at ambient temperature of 70 °C. Additionally, the apparent deep trap levels increase as temperature increases, since deeper and deeper traps are involved in the charge-release mechanism. It is concluded that the graphene nanofiller loading with a content of 0.005 wt% introduces large quantities of deep charge traps in the polymer-filler interfacial regions, which reduce the detrapping rate of charges and suppress the charge injection into polymer. [ABSTRACT FROM AUTHOR]

Charged polystyrene nanoparticles are generated by matrixassisted laser desorption/ionization (MALDI) and detected by laser-induced fluorescence (LIF) in a quadrupole ion trap. Employing the LIF technique, observations of individual fluorescent nanospheres (27 nm in diameter and containing 180 fluorescein dye equivalents) have been achieved with an average signal-to-noise ratio of ∼10. With the trap operating at a frequency around 5 kHz, charge state analysis of the particles reveals that the number of charges carried by the spheres is between 1 and 10. It suggests a mass-to-charge ratio (m/z) in the range of 10[sup 5]-10[sup 6] for the MALl)I-generated particles. To effectively trap such large particles (m > 5 MDa), damping of the particles' motions by using ∼50 mTorr He buffer gas is absolutely required. Similar findings are obtained for particles with a nominal size of I µm in diameter, demonstrating that production of charged particles with a molecular mass as high as 10[sup 12] Da is possible using the MALDI technique. [ABSTRACT FROM AUTHOR]

Levan, a polysaccharide that can be produced by both plants and micro-organisms, is a sugar polymer composed of fructose, with-2,6 linkages. Here, we have attempted to assess the possible use of levan produced by Zymomonas mobilis as a cosmeceutical ingredient. In service of this goal, we assessed a host of levan's properties, including its moisturizing effects, cell cytotoxicity, cell proliferation effects and anti-inflammation effects. Levan exhibited a moisturizing effect that was almost exactly the same as that evidenced by hyaluronic acid, as well as a similar cell proliferation effect in human fibroblast and keratinocyte cell lines. Moreover, in our cell proliferation test, which was conducted using bio-artificial skin constructed via 3-dimensional (3-D) culture after the induction of primary skin inflammation with 0.05% sodium lauryl sulphate (SLS), cell viability in the presence of levan (0.01 and 0.05 mg mL–1) was determined to be higher than cell viability in the absence of levan. In our anti-inflammation test, which was also conducted using 3-D artificial skin, and which involved the measurement of a quantity of secreted interleukin-1 (IL-1), a pre-inflammatory mediator induced by SLS, we determined that the quantity of IL-1 in the 3-D artificial skin treated with 0.01 and 0.05 mg mL–1 of levan was less than that registered in a skin sample that had been treated only with SLS. In this study, we determined that levan exerted an anti-inflammatory effect against inflammatory reactions to skin irritants, and also that levan exerted a cell-proliferative effect in bio-artificial skin, thereby indicating its potential applicability as a cosmeceutical agent. [ABSTRACT FROM AUTHOR]