Conducting polymers creeping effects

The same techniques were used in the present work to study the effects of orientation and rubber content upon the creep behavior of rubber-toughened SAN polymers at room temperature. As in previous work, the tests were conducted at low strain rates and were terminated at longitudinal strains between 5 and 6%. 

The electrical conductivity of hydrophilic polyamides " and the photoconductivity of nylon-6,6" are reported. The time dependence of two transient photocurrents suggest the possible formation of a space charge in the polymer. Time-dependent effects in the form of creep measurements have also been used to examine the influence of moisture on the behaviour of nylon-6,6. Other low molecular weight molecules, whose effects on the properties of this polymer have been reported are surfactant and both acid and disperse dyes. Also with a textile connotation was a paper with more general application describing the determination of amino-acid N groups in nylon-6 and -6,6. ... 

In a fuel cell, the membrane is sandwiched between two bipolar plates. This structure puts it under compressive stress, which can change the membrane resistance. It has been found that the resistance of Nafion membranes increased when they were compressed, and the increase was consistent with the elastic compression of the membrane (Satterfield et al, 2006). Casciola et al. (2006) also found that membrane conductivity decay occurs only when the membrane is forced to swell anisotropically along the plane parallel to the membrane surface. In addition to the effect of compression on conductivity decay, polymer membranes in fuel cells undergo creep, which can cause membrane thinning, pinhole formation, and other failure. Stuck et al. (1998) proposed that local stress most likely triggered and/or enhanced the nonuniform thinning of the Nafion membranes in a polymer electrolyte membrane electrolyzer. 

Creep tests can be conducted in eitho- tensile or flexural modes. The time-dependent viscoelastic deformation of polymers and composites is compared and the differences in material compliance is analyzed. The constitutive relationship for creep compliance that takes into account the effect of di-latational stresses is determined. Estimation of lifetime under non-isothermal conditions is also ixe-sented. Not only are the thermal and mechanical loading of great importance to estimation of life expectancy, but also the influence of the chemical medium and immersion time. Two possible methods of obtaining this information are discussed (1) time-temperature extrapolation of the measured aging process, and (2) a functional estimation of time-temperature collectives, the latter being more precise. 

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