Follow the experiment, step by step

Prepare and measure the sample

Cut a rectangular PDES strip about 2 mm wide with the razor blade. Handle it only with the tweezers so it isn’t stretched or damaged.

• Zero the precision scale with the razor blade on it, then lay the sample on the side of the blade so it isn’t stretched.
• Measure the unstretched length, unstretched width and sample mass (weigh the blade and sample together).
• Take the sample off the blade and measure its unstretched thickness.
• Before adding any liquid metal, clamp the sample in the copper clips and hang it from the frame with the hanging mass you plan to use. Once it reaches its fully stretched length, measure the stretched thickness and record the hanging mass.
• Remove the sample from the setup.

Prepare the electrical setup

• Fix the ruler vertically behind the sample, in the same plane it moves in, so the video calibration has no parallax. Tape on the back of the large clip works well. Place it behind the indicator LED so both are in the video.
• With power disconnected, clip the multimeter across the thin wire only (alligator clips on the wire’s end clips) and measure its resistance. The reading should change by less than 0.1 Ω when you move the wire; about 1 Ω is typical. New wire needs the coating scraped off its ends before it will conduct.
• Move the multimeter clips back to their original positions.
• Set up the function generator for a fixed-frequency or frequency-sweep test: a 0–5 V square wave with a 180° phase offset, so the output stays at 0 V when it’s disabled.
• With no sample attached, run the generator briefly and check that the indicator LED flashes. Then disable it.
• Set the supply’s current limit, then an initial voltage of 1.5–2.0 V; you’ll fine-tune it during the run to reach 0.7–1.0 A. With the sample disconnected and the generator disabled, enable the output briefly and check the current reads about zero. Then disable the output before mounting the sample.

Mount the sample

• Coat both sides of the sample completely with liquid metal.
• Clamp it at about the same spots you used for the stretched-thickness measurement.
• Lay the sample on its side, taut but not stretched, and measure the length between the clips. This is the active length.
• Hang the sample with the same hanging mass as in step 1. The weight the thin wire is attached to must be one of the hanging weights, or the circuit won’t be complete.
• Improve the electrical contact by gently dragging the back of the glass syringe tip upward across both sides of the liquid metal. With power disconnected, repeat until the multimeter reads a stable total series resistance (thin wire + liquid-metal connection) of about 1.9–2.1 Ω.
• Record the total series resistance, then calculate the liquid-metal connection resistance: total series resistance − thin-wire resistance.
• Switch the multimeter to voltage mode, or disconnect it, so it doesn’t interfere with the circuit.

Set up the camera

• Put a fresh battery in the camera.
• Mount the camera on the tripod, squarely in front of the sample.
• Zoom so the inner edges of both copper clips stay in the frame.
• Focus manually, as sharply as you can. The tracking code depends on it.
• Check that the ruler and the LED are both visible.
• Set the camera to record at 60 fps.

Run the experiment

• Do a final check that every measurement and setup step is done.
• Enable the DC supply with the function generator still disabled, and confirm the sample current stays near zero.
• Start recording, wait about 5 seconds, then enable the function generator.
• Check that the LED and the sample are cycling and that the current is within 0.7–1.0 A.
• While it runs, note the average steady-state current on the power supply. Above 1 Hz the supply display can’t be trusted, because it samples too slowly. For faster tests, run one 0.1 Hz cycle before the experiment and use that current instead.
• After the planned duration, disable the function generator.
• Keep recording for about 60 seconds to capture cooling and recovery, then stop the camera and disable the DC supply output.
• Let the sample cool, then, with power disconnected, measure the liquid-metal connection resistance again. It isn’t used in the analysis, but an increase shows the connection is degrading.

Analyze the results

• If you don’t have it yet, clone the lab’s analysis code: kstam21/WareLab-Matlab-Repo on GitHub.
• Trim the video so the first and last frames are completely still, without cutting any real movement. The clip tool in the Microsoft Photos app works well.
• Save the trimmed video in the matching folder of the repo, named with the experiment date and a short description.
• Copy all your notebook measurements into the Experiment Data Log. Copying an earlier entry and editing it saves time.
• Run init.m in MATLAB. When asked, enter the experiment parameters, choose the LED start frame, calibrate the ruler and width, and click the tracking markers.
• Record the LED start frame in the Data Log so later analyses don’t have to find it again.
• Results save automatically to the results folder. Copy the video-measured stretched width and length into the Data Log, labeled “video-measured”.