Hysteresis effect, membrane

A coating bearing one enzyme (papain) is produced on the surface of a glass pH electrode by the method previously introduced (co-crosslinking). The papain reaction decreases the pH, and the pH-activity variation gives an autocatalytic effect for pH values greater than the optimum under zero-order kinetics for the substrate (benzoyl arginine ethyl ester) the pH inside the membrane is studied as a function of the pH in the bulk solution in which the electrode is immersed. A hysteresis effect is observed and the enzyme reaction rate depends not only on the metabolite concentrations, but also on the history of the system. 

Yeo and Chin have observed that the membrane hysteresis effect occurs when the change of electrolyte concentration is faster than the change of concentration in the membrane, which is controlled by the diffusion of electrolyte in the membrane. The electrolyte content in the membrane does not reach its equilibrium value under this condition. The authors have thus suggested various methods for controlling this hysteresis effect and the electrolyte content of the membrane, so that a higher cell efficiency can be obtained. 

The overvoltage of the hydrogen halogen cell and the zinc-bromine cell is mainly contributed by the membrane resistivity, and this resistivity is a strong function of the electrolyte content in the membrane. It is clear that the membrane hysteresis effect will influence the cell performance. 

BET Adsorption Data. A wealth of information about the size and shape of pores may be obtained from adsorption isotherms where the mols of nitrogen adsorbed on the membrane are measured as a function of pressure. However, the use of this techniques is not widespread due to the tedious regimen required in gas adsorption measurements. Further, the hysteresis effects make conclusions about pore-structure ambiguous. 

Sadeghi, E., Djilali, N., and Bahrami, M. 2010. Effective thermal conductivity and thermal contact resistance of gas diffusion layers in proton exchange membrane fuel cells. Part 2 Hysteresis effect under cyclic compressive load. Journal of Power Sources 195(24) 8104-8109. 

Peterson et al. (1998) also used UTDR to show that the compressive strain for integral cellulose-acetate membranes has both elastic and inelastic components, only some of which are recoverable that is, membranes display some degree of nonrecoverable compressive strain when subjected to high pressures. UTDR also revealed that the recovery of these membranes is viscoelastic or time dependent, which possibly explains the hysteresis effects observed when membranes are subjected to pressure cycling. 

They are subject to the effects of hysteresis, or, rather, the tendency of materials to remember distortions and not return to their original shapes (mechanical gauges with glass distortion membranes will not have symptoms of hysteresis). Hysteresis of vacuum gauges can be diagnosed by the following symptoms ... 

Water uptake into the electrolyte also has a relatively long time scale that depends on the temperature, partial vapor pressure, and initial membrane state but can also be on the order of minutes or even hours. Ionic conductivity, water diffusivity in the electrolyte, and electro-osmotic drag are directly related to the electrolyte water uptake, which can also contribute to the observed performance memory effect and hysteresis. 

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