HandsOn 13 - Growing a Pattern in the Laboratory

III. Doing the Experiment

Doing the Experiment

Divide the tasks among your partner(s). You will need to measure and record the following during the experiment on a copy of Table :

Figure 4.3: Filling the electrodeposition cell with electrolytic solution (as described in the section "Doing the Experiment.''

1. The time at intervals of 20 seconds (longer or shorter depending on the way you assemble the cell; start with 20 seconds and after you have run the experiment once, reason whether you should use longer or shorter intervals).

2. The radius of the pattern at each recorded time.

3. The current at each recorded time.

Table 4.1: Data Table for Electrodeposition experiment. Units are as follows: t and t in seconds; I in Amperes; N and Nt in atoms. To calculate N, use this algorithm: N = It/q. For Cu2 + and ZN2 + ions, q = 3.2 .10-19 Coulombs/ion.

 t t I r N Nt 20 20 20 40 20 60 20 80 20 100 20 120 20 140 20 160 20 180 20 200 20 220 20 240 20 260 20 280 20 300

With respect to the radius, the growth may not be symmetric, and some branches may stop growing during the experiment. The investigator recording the "radius'' may choose to measure the overall radius of the entire pattern or the length of an "average'' branch.

A typical procedure might be that the timekeeper watches the clock and announces the time every 20 seconds. The second person reads the current on the ammeter, and the third measures the radius of the deposit. The timekeeper records these two numbers.

Hook up the circuit shown in Figure 4.2. Depending on the time available, you may want to try several experiments using different voltages. As a guide, 1 and 20 volts are probably the low and high values. Try a value between 10 and 15 volts to begin with.

Now it is time to grow your aggregate. The current will start at a low value, 10 milliamps or so, and rise to between 100 and 250 milliamps as the aggregate grows outward. Take care not to let the aggregate grow so large that it reaches the positive terminal. What might happen if it does?

 Q4.8: Can you explain: asymmetries? branches, if your aggregate has them? size of the branches? color?

Digitize your electrodeposition aggregates by using a digital camera or a scanner. Since your aggregate is fragile, make sure you digitize the experiment immediately after you finish the experiment. You will need this digitized image for the section on measuring the fractal dimension.

Figure 4.4: Sample copper electrodeposition aggregate in the early stages of growth.

Figure 4.5: Zoom of the copper electrodeposition aggregate. Notice that the rough branches appear at both scales (e.g., at full scale and at the zoomed in scale).

Figure 4.6: Sample zinc electrodeposition aggregate. Notice the differences in structure from the Copper experiment.

Figure 4.7: Zoom of the zinc electrodeposition aggregate. Do you notice any differences between the copper and zinc experiments?
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Next: IV. Data Analysis