The Comparison of the Samples…

The testing results are listed in the table shown below. These six samples were made by different methods, including three different kinds of membrane fabricating methods and two different electrode fabricating methods. The dendrogram is shown in figure 6.32.

Figure 6.32 the dendrogram of the classification of the samples

The main goal in this project is to make a very thick IPMC strip by using same quantity of Nafion^®, so the very thick IPMC is also very narrow, the idea has been shown in chapter 4. The other samples made in other form were used to establish the fundamental concept of the performance of typical IPMC samples. After the fabrication and experiments of the typical IPMC sample, the very narrow and very thick IPMC strips were also made and tested.

The samples have different dimensions, and the voltage used to actuate the samples was also different. All the samples were tested under wet condition except the No. 6 sample.

The test of No. 6 sample is an additional experiment beyond the original plan. But the test result of No. 6 sample may have some value of comparison. So the test result is also listed in the table, as shown in table 6.1.

Table 6.1 Experimental results of the IPMC samples

The No. 1 sample is a most common type IPMC, the test result is used to be a reference to the other test results. The No. 2 and No. 3 samples are thicker IPMC strips, and they are the same form to the No. 1 sample. The max displacement of No. 2 sample is larger than No. 3 sample. Although the displacement of No. 1 sample is smaller than No. 2 sample, but the applied voltage of No. 2 sample is larger than No. 1 sample. And the total movement time of No. 2 sample is 40 seconds, ten times of the No. 1 sample. So, a little larger displacement of No. 2 sample is reasonable. Via the above comparison, a simple and obvious trend emerges. The trend is: The thicker the IPMC strip the smaller the max displacement. And the No. 4 sample was also show the trend. Although the No. 4 sample was designed to be an approximate linear IPMC. But the test result shows the assumption in the chapter 4 is wrong. Because the small displacement means a small change in

curvature. A key point of the assumption is the change of the curvature is big for a thick IPMC. Then the approximate linear actuator would be accomplished. But the actual experiment result improve the assumption is wrong. Furthermore, compare the figure 7.26 and 7.27, the same conclusion would also be established.

The No. 5 did not be observed any displacement, and the reason is not obvious. But a probability is the electrode on the edge was too thin to control the membrane. The electrode coated by electro-less method is about 2 ~ 3 μm. It is really thin contrast to the vertical casting electrodes. The electrode can only control the nearby ions and water molecules. So the thin electrode can only control the nearby section. The nearby section is also very thin contrast to the whole membrane. So the membrane can not be actuated by the electrode.

The No. 6 sample performed a significant displacement under high voltage. And the electrode broke immediately; the durability of a sample under the dry operation is a problem.

VII. CONCLUSIONS

7.1 Several Defects in the Project

Although, the IPMC strips were made, the actuation ability is not good. The main reasons of the problems are listed below.

1. The heating treatment of membrane:

The membrane made by casting method needs the heating treatment. And the heating process is a very important factor to influence the characteristic of the membrane.

Different heating treatment temperature and time cause the different mechanical strength, dissolution ability in water and organic solutions, color of the membrane and most of all, the absorbency of water and ionic solution. The absorbency of water and ions is very critical to the actuation ability of IPMC.

2. The coating technique

Although the coating technique has the benefits said above. And to the best of our knowledge, this coating technique is really fast, cheap, low surface resistance and good in adhesion ability. And, another important benefit is the stability of the chemical reaction. If the reaction was very fragile, the coating process of electrode would be difficult to repeat.

But, the durability is not good; the electrodes on the membrane are easy to be broken. No matter the electrolysis of water or the high voltage are easy to break the electrodes.

7.2 Future works

1. To the heating treatment:

The apparatus used in the heating treatment is the simple vacuum oven system as shown in figure 5.39, 5.40. The temperature control of the oven is not precise. The tolerance of the temperature is usually about 10 centigrade. But, most of all, the temperature and time of the heating process should be lower and shorter. The membrane should be more

flexible and the absorbency of water should be better.

2. To the coating technique:

To improve the coating technique, a better heater should be used. The temperature distribution of the heater used in the experiment is not uniform. The temperature of the heater in the center is about 85 centigrade, and the temperature at the edge is about 50 centigrade as shown in figure 7.1, 7.2.

Figure 7.1 the central temperature of the heating plate

Figure 7.2 the side temperature of the heating plate

So the difference in temperature is big. Another important caution is the concentration of the Ag(NH3)2OH solution, if the concentration of the Ag(NH3)2OH solution is very high (about 10 times to the concentration listed in the chapter 6). The solution may explode when the solution is almost dried.

3. To the very thick and very narrow IPMC strip

Although the idea of approximate linear actuator failed, but the idea of the very thick and very narrow IPMC strip was accomplished. Use the vertical casting method can really make a thick IPMC with a small quantity of material.

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