Back relaxation phenomenon

The experimental setup was as follows. An IPMC sample was placed in a 10 M solution of EtBr for one hour and then into a transparent cube which also contained an EtBr solution. The treated cube was then placed in an analysis system so that the cross section of the actuator could be observed. The system was exposed to a light source and an image was captured with 

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Chapter 2 is focused on physical principles of IPMCs. It starts with an introduction to the fundamentals of IPMCs, including the fabrication techniques, and then takes a careful look at the effect of electrodes on material behavior and actuation performance. Several novel approaches, including a fluorescence spectroscopic visualization method, are then used to yield unique insight into IPMC actuation behaviors, such as the back-relaxation phenomenon. More sophisticated configurations than a singlelayer bender are also discussed in this chapter. 

Fig. 2.53 shows experimental blocking force compared to the calculated one. The model is in close agreement with the actual experimental data at the beginning however, after 14 s a discrepancy starts to occur. This is due to the fact that the model is not capable of calculating the inherent back relaxation phenomenon of IPMC. 

A comparison with Burchard s first cumulant calculations shows qualitative agreement, in particular with respect to the position of the minimum. Quantitatively, however, important differences are obvious. Both the sharpness as well as the amplitude of the phenomenon are underestimated. These deviations may originate from an overestimation of the hydrodynamic interaction between segments. Since a star of high f internally compromises a semi-dilute solution, the back-flow field of solvent molecules will be partly screened [40,117]. Thus, the effects of hydrodynamic interaction, which in general eases the renormalization effects owing to S(Q) [152], are expected to be weaker than assumed in the cumulant calculations and thus the minimum should be more pronounced than calculated. Furthermore, since for Gaussian chains the relaxation rate decreases... 

In a subsequent communication, Elliott and coworkers found that uniaxially oriented membranes swollen with ethanol/water mixtures could relax back to an almost isotropic state. In contrast, morphological relaxation was not observed for membranes swollen in water alone. While this relaxation behavior was attributed to the plasticization effect of ethanol on the fluorocarbon matrix of Nafion, no evidence of interaction between ethanol and the fluorocarbon backbone is presented. In light of the previous thermal relaxation studies of Moore and co-workers, an alternative explanation for this solvent induced relaxation may be that ethanol is more effective than water in weakening the electrostatic interactions and mobilizing the side chain elements. Clearly, a more detailed analysis of this phenomenon involving a dynamic mechanical and/ or spectroscopic analysis is needed to gain a detailed molecular level understanding of this relaxation process. 

Mobility is also reduced slightly by another phenomenon termed the relaxation effect. Here the charged species, as it is displaced by the electric field from the center of the double layer, is acted on by the opposite charge of the double layer to pull it back [38]. 

We intend to come back on the phenomenon of volume relaxation in Chap. 13, where it will be discussed and also in context of physical ageing and creep. 

The first question to ask about the phenomenon of relaxation is why it occurs at all. Both the Newton and the Schrodinger equations are symmetrical under time reversal The Newton equation, dx/dt = v,dvldt = —9K/9x, implies that particles obeying this law of motion will retrace their trajectory back in time after changing the sign of both the time t and the particle velocities v. The Schrodinger equation, 9Vr/9t = implies that if (V (Z) is a solution then t) is... 

Since the cis-isomers can only be present as a single species, this phenomenon has to be attributed to two different relaxation mechanisms. This is evident from the reduced Arrhenius plot of the rate constant k of the thermal cis-trans back reaction in terms of (Fig. 3) a is the ratio of the thermal cis-trans relaxation time T (Vk) at temperature T to its value at Tg. 

The photoinduced reduction of TCNQ by the porphyrin heterodimer ZnTPPS-ZnTMPyP provides a good illustration of these concepts [56,109]. Figure 12(a) displays photocurrent transients at the water DCE junction in the presence and absence of an equimolar ratio of Fe(CN)g /Fe(CN)g. The photocurrent relaxation in the absence of the aqueous redox couples is associated with the back electron transfer from TCNQ to the oxidized porphyrin complex. The substantial decrease in back electron transfer on addition of Fe(CN)g /Fe(CN)g is associated with the supersensitization phenomenon schematically depicted in Fig. 12(b). The back electron transfer from the radical TCNQ to the oxidized porphyrin complex is in competition with the regeneration of the dye by ferrocyanide. In the absence of back electron transfer, the overall reaction involves electron transfer from the redox species in the aqueous phase to TCNQ. In this case, the energetic balance is determined by the Galvani potential difference across the interface. 

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