In a previous post, I learned that a Scrub Daddy sponge is mainly comprised of a polymer called polycaprolactone.1 I have continued to gather information on polycaprolactone and also to experiment with Scrub Daddy sponges. For example, I learned that the glass transition temperature of polycaprolactone is 213 K (-60oC or -76oF).2 The glass transition temperature,Tg, is the temperature above which a polymer transforms from a brittle, glassy state to a flexible, elastic state. Thus, it would make sense if a Scrub Daddy sponge could be cooled below its Tg when immersed in liquid nitrogen, which is at 77 K (-196oC or -321oF) – well below Tg for polycaprolactone. I decided to cool a Scrub Daddy in liquid nitrogen and subsequently hit it with a hammer to find out:
The Scrub Daddy certainly displayed brittle, glassy characteristics when cooled to 77K! After doing this experiment, I noticed that the temperature of dry ice, 196 K (-78.5oC or -109oF), is below Tg for polycaprolactone. This made me wonder if a Scrub Daddy would shatter when struck with a hammer after being cooled using dry ice. If this experiment worked, I figured it might give experimenters who have access to dry ice a cool way (pun intended) to shatter items without requiring the use of liquid nitrogen, which is often difficult to obtain. In the video below, you can see what I found out:
As you can see, the Scrub Daddy did shatter when struck with a hammer after being cooled in dry ice! So if you don’t have access to liquid nitrogen, you can still demonstrate the shattering of a cooled item using a Scrub Daddy, dry ice, and a hammer.3
Let me know if you and your students try some experiments with the Scrub Daddy sponge. Also, I would be interested to hear if anyone learns of any other materials that can easily be shattered by striking with a hammer after cooling in dry ice.
References and notes:
2. Progress in Polymer Science, 2010, 35, 1217-1256.
3. Notice that the Scrub Daddy was cooled in dry ice only, and not a mixture of dry ice and alcohol (or acetone). Striking the Scrub Daddy after cooling in such mixtures would likely cause organic solvents to be splattered about, causing an unnecessary hazard.