Tutela Jurisdiccional como derecho fundamental

As the polarity o f the applied potential was reversed for the second time, the sample quickly bent towards the new anode as a result o f the expansion o f the polymer along the new cathode and its shrinkage near the new anode. As was mentioned before, 30 min after the second reversal o f the polarity, the signal obtained from the sample was dramatically weakened and very poor PD and T2 images were obtained from the sample. This can be

assigned to the intensive dehydration o f the sample during previous regimes as was discussed above.

As shown in the previous sections, the changes occurring in T2 and PD at the cathode and

anode regions in the T2 and PD images mostly conform to the Nemat-Nasser and Li m odef

However, according to their model, under application o f the electric field, thin boundary layers are formed at the anode and cathode which shield the remaining part o f the IPMC from the influence o f the applied electric field and all the processes which lead to the bending deformation of the IPMC occur at these two layers. The formation o f boundary

layers may have been observed as changes in T2 near the cathode and anode as the potential

was applied. These changes, however, were not limited to thin cathode and anode regions

since T2 changed over the whole sample.

6.5. Sum m ary

The physical structure and the bending deformation o f an AuPtjCast IPMC sample were investigated using the MRI scanner. Images o f the sample during application o f four different electrical regimes were collected in two forms o f T2 and PD images to study the

changes that took place in the physical structure o f the sample and also the distribution of absorbed water molecules over the whole sample. It was revealed that water molecules at the centre o f the IPMC sample have longer T2 than those molecules in the electrode regions,

implying different physical environments in these regions. From the uniform distribution of protons seen in the corresponding PD image o f the sample and also the T2 image of the

non-electroded cast Nafion membrane, it was deduced that this difference arises from the presence o f platinum particles in the electrode regions. It was shown that T2 o f protons was

platinum lead to shorter T2. This revealed that the rotational motion o f water molecules is

more restricted in the region containing more platinum. Application o f the potential across the thickness o f the IPMC sample resulted in the observation o f contraction o f the polymer along the anode and its expansion along the cathode in T2 and PD images. This was

associated with an increase in T2 near the cathode and a decrease near the anode. Over time,

as the region o f high T^s became more concentrated near the cathode, the bending deformation o f the IPMC sample towards the anode developed. As the IPMC sample initially had longer T^s at the centre compared to the electroded surfaces, on application of the potential the difference between high T2S, corresponding to mobile water molecules,

and short T2S, corresponding to unaffected water molecules, was less clear in the

corresponding T2 images. The changes in the T2 images o f the IPMC sample during

application o f the potential were associated with similar changes in the intensity o f the corresponding PZ) images: higher proton density was always seen near the cathode. This revealed that the region o f high T^s observed near the cathode in the T? images was related to the accumulation o f mobile water in this region, during application o f the potential. Reversing the polarity o f the applied potential resulted in the reversal o f the direction o f the bending deformation o f the IPMC sample and the distribution o f high T^s - related to protons in mobile water - was reversed. The slow back-diffusion o f water molecules towards the cathode was observed approximately 90 min after application o f the potential in regimes (b) and (c). This suggested that this process occurs when the potential is applied long enough to create a considerable difference in osmotic pressure and elastic energy between cathode and anode regions. Comparison o f the PD maps obtained during the four electrical regimes revealed that the sample was dehydrating throughout the experiment.

6.6. References

[1] . K. J. Kim, M. Shahinpoor, Smart Mater. Struct., 2000, 9(4), 543. [2] . M. Shahinpoor, K. J. Kim, Smart Mater. Struct., 2001, 10, 819. [3] . W. Kuhn, Angewandte Chemie, Int. Ed. Engl. 1990, 29, 1.

[4] . Y. Bar-Cohen, “Electroactive Polymers Actuators and Artificial Muscles - Reality,

Potential and Challenges”, SPIE Press, Bellingham WA, 2001.

[5] . S. Tadokoro, S. Yamagami, T. Takamori, K. Oguro, Smart Structure & Materials, Proc.SPIE, 3987,92.

[6] . S. Tadokoro, S. Yamagami, T. Takamori, K. Oguro, Robotics and Automation, Proc.

/ C M 2000, 2, 1340.

[7] . S. Nemat-Nasser, J. Y. Li, J. Appl. Phys., 2000, 87, 3321. [8] . S. Nemat-Nasser, Y. Wu, J. Appl. Phys., 2003, 93(9), 5255.

[9] . P. T. Callaghan, “Principles o f Nuclear Magnetic Resonance Microscopy”, Clarendon