Tuesday, 4 November 2014

Much Ado About Slime

http://thetigerchronicle.blogspot.co.uk/search/label/Halloween

Halloween has always been associated with the darker archetypes of human consciousness.  As such, I often find that whenever I think of science activities related to Halloween, I will end up looking at something quite revolting or disgusting.

Our Halloween dinner.

We first tried out a science kit that I acquired at the charity shop for 50p, and did a few of the experiments from the attached booklet.  However, apart from the initial fun of stretching at the ready-made polmorphic slide, making our own slime ball, and playing a game of chase with the ready-made bouncy slime ball, I didn't think we have learnt much from the kit so I took it back to the charity shop.  Maybe the next person will have more joy with the kit.


We realised that we learn best by actually making the slime/gloop/oobleck ourselves, in the old-fashioned way, using the tried-and-tested cornflour and water mix:


It is one of those cheap-and-easy way to keep a child entertained for a long time, and to have a hands-on experience with the intriguing transformation of polymer chains, which certainly beats just reading about the properties of polymers from here and here.

From our little success above, we wanted to know what would happen if we scale up our experiment (from using 1 cup of cornflour to using 7 boxes of cornflour).  We filled two-thirds of our tub with oobleck, let it settle for a day and rest a glass bottle on its surface.  The glass bottle tipped to one side after a few minutes, but did not sink further into the mixture:


We then redid the test with a few marbles, one of which promptly sank into the suspension while the others took a little while longer to do so, but all eventually sank in and we had to fish them out with our fingers.

video

While the sinking of the materials was fascinating to watch, it was the fishing out part that really demonstrated the dilatant (the mixture moves slower when an external force is applied to it) quality of the suspension.

If we had a bigger container (such as a small paddling pool), we would have made a non-newtonian fluid pool that we could walk on, like the one shown below, but we understood the principle behind it from observing what happened to the marbles in the above experiment:


What other gloopy things can we make with cornflour and water?  Silly Putty, of course!  It is really a mixture of white glue, borax powder, water, and cornflour.


Borax is vital to the stiffness of the Silly Putty (as opposed to the simpler oobleck mixture) as borax facilitates the formation of cross-links among the polymers, which in turn creates longer/bigger and stronger/stiffer polymer chains.  Hence, the bounciness of the Silly Putty.

video

Finally, we turned out attention to the humble meringue, which is essentially made up of sugar and egg white.  Did you know that egg white is about 88% water?  The rest of it is almost all proteins (polymer).  The act of whipping the egg white unfolds and stretches the protein strands (the process is called denaturing), which gives rise to the network of bubbles we see.  As we further whip the egg white, the protein chains will overlap and form a long, stretchy surface, resulting in the stiff peaks that we look for when we make meringues.


We made four different batches of meringues to compare the differences in result when we made a slight variation each time:
  1. egg whites at room temperature + cream of tartar + half a cup of white sugar
  2. egg whites from the fridge + cream of tartar + half a cup of white sugar
  3. egg whites at room temperature + cream of tartar + 1.5 cups of white sugar
  4. egg whites at room temperature + half a cup of white sugar

The results are shown above:
  1. the typical meringue: crunchy, slightly brown, with some air peaks, holds its shape well
  2. similar to the results in (1) except that it has more air peaks
  3. very white in colour, extremely crumbly, no air peaks, more like cookies, does not hold its shape well.
  4. very sticky and flat, does not hold its shape at all.

Tiger writing his science report.

After such hard work (actually, our oven worked much harder than we did on that day with 4x90 minutes of non-stop baking), we relaxed by watching a documentary that explains how various materials such as ceramics, metal, and plastics work.


This post is linked up to:
  1. Science Sunday #1: Chemistry Lessons
  2. Hip Homeschool Hop - 11/4/14
  3. Finishing Strong - Homeschooling the Middle & High School Years Week 36
  4. Hearts for Home Blog Hop #90 
  5. My Week in Review #12
  6. Collage Friday - Hands On, Field Trip, and Fine Arts Learning
  7. Weekly Wrap-Up: The one that was a lot less stressful

12 comments:

  1. Interesting, especially the results of the egg white mixtures. I have never added cream of tartar to a meringue mix, only white sugar. My meringues tend to be full, crispy on inside and chewy in middle, remaining white throughout. What does the cream of tartar do? I don't even know what it is(!). I'm thinking I might attempt to replicate this or something similar for our Incr-Edible Science. Thanks for the motivation, I'm off to google Cream of Tartar!

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    1. The cream of tartar helps the proteins unwind so that they become easier to cross-link with the whipping action, thus forming stiffer peaks (compared to not using the cream of tartar). :-)

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  2. I, too, have never seen flat and brown meringue. I also never have added cornstarch (as cornflour is known in the states) to my silly putty. It certainly looks like you two had a lot of fun with polymers, and learned a lot. Thanks for linking up.

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    1. It's odd that our meringues turned out brown, isn't it? We used white sugar so I'm not sure what made them all come out brown!

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  3. Wonderful! Brilliant experimentation. Your glass bottle in the oobleck reminds me of a post I saw where they made oobleck "quicksand" for soldiers - that might be right up Tiger's street! Your meringue experimentation looks fun. We made fudge and honeycomb in the name of science last spring - we should try meringues.

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    Replies
    1. Thanks, Lucinda. Kitchen chemistry involving food is always fun to make. I don't understand why my meringues turned out brown, though, even though I used white sugar. It's puzzling....

      The quicksand for soldiers idea is a really good one! That will add much interest in Tiger's soldiers games. Thanks for the idea. I'll pass it on to him. :-)

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  4. Looks like a bunch of fun science! Our kitchen became a laboratory this week as well, my son and his lab partner made a plasticky substance from heated milk and vinegar. It was fun, and the experiment won a first place ribbon at their science fair. We used to make flubber from Borax and glue when they were little. I love that you added in meringues to your lessons, I make them every year at Christmas and had no idea of the protein polymer reaction! :)

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    1. Material science is very cool and the process of making new materials from combining different substances is fascinating. Congratulations on winning the first place ribbon for the science fair. It must have been an awesome presentation! :-)

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  5. What awesome science. We have never made meringue before. That would be fun. I always feel inspired by your blog.
    Blessings, Dawn

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    1. Many thanks for your kind words, Dawn. :-) Meringue is surprisingly easy to make - basically just egg whites and sugar! It would be a very welcomed treat for the children!

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  6. We love that kind of science...now I have to go and see if Alton Brown has an explanation of cream of tarter :)

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