Electrolyte Gel Model: Experimentation

1. Purpose

The developed model of the polymer gel needs to be verified through matching of the computer simulation results to the experimentation results. Our goal is to design and construct the appropriate experimental setup to test and verify the electrolyte polymer gel's lumped parameter model. In addition, the experimental setup will be employed to test simple control strategy in controlling the gel.

2. Requirements

In addition, the desired characteristics of the experimental setup are as follows.

3. Proposed Designs

3.1 Design No. 1

In this design, the strips of the polymer gel sheet are mounted on a common block which slides vertically on two rails. The whole gel/slider assembly is immersed in the bath of the surrounding solution, and the gel is activated by changing the pH of the bath solution. The contracting and expanding gel raises and lowers the weight, and the length of the gel and the force applied to the gel are measured by the optical encoder and the load cell respectively. The magnetic stirrer situated at the bottom of the bath enhances the uniformity of the bath condition. Following are the pros and the cons of this design.



3.2 Design No. 2

This design is similar to the design no. 1 (planar design) except the gel units are situated horizontally rather than vertically. As a result, the hydrodynamic disturbance force due to stirring would be significantly reduced. However, this design employees an extra pulley, and thus would increase the overall friction. Rest of the design characteristics are identical to the design no. 1.

3.3 Design No. 3

Top View

Side View

Unlike the previous designs, in this design, a single gel strip unit is situated in a relatively small enclosed chamber. The internal chamber is further divided into three chambers separated by perforated dividers. The acid/base solutions and the water flows into the first chamber where the mixing occurs, and the mixed solution would then diffuse into the middle chamber where the gel unit is situated and to the outlet chamber. The separate acid, base and water inlet flows are controlled by either servo valves or flowrate controlled pumps located at just the upstream of the inlet ports. The pH sensor continually monitors the pH level in the mixing chamber, and the appropriate amount of acid/base/water will be injected into the mixing chamber based on pH measurement and theoretical calculation.



3.4 Design No. 4: Enhancement of Design No. 3

This design attempts to address the potential difficulties the design no. 3 faces, and the enhancements are as follows.

This design is selected for the gel model verification test setup, and the detailed diagram of the design is shown below. As shown below, the terminations of the gel strip will be molded into the epoxy blocks along with the transmission cable.

Schematic of the gel model testing device.

4. Experimentation

Primary goal of the experimentation would be to test the effects of the surrounding bath pH, ion concentrations and the mechanical loading on the gel's static and dynamic swelling behavior. Especially, the change in gel's swelling in response to change in the mechanical loading is of particular interest. The PVA/PAA gel is proposed for this purpose rather than the PAN gel because the model is suitable for unipolar gel only at this point. The PAN gel exhibits severe discontinuous hysterisis, i.e. it swells at high pH and contracts at low pH due to its bipolar nature. On the other hand, the unipolar PVA/PAA exhibits continuous non-hysteric response at near the neutral pH. The mechanical strength and the response speed of the PVA/PAA gel fall much short of the PAN gel fiber. However, for our purpose, the performance is of major concern.

The experimental results will be compared to the computer simulation results based on the theoretical lumped parameter model, and the model will be further enhanced. Upon successful verification of the model, a simple control strategy will be implemented.