Differential Expansion
- ethalbookmarks
- Jan 31
- 3 min read
Updated: Feb 1
There is a section in the book Patterns in Nature called Spirals, Meanders, and Explosions. It talks about the concepts and logic behind the growth patterns in nature. One such case is related to how different growth rate based on external and internal stimuli gives you beautiful patterns. A lot of these are spiral and helical patterns like the nautilus shell and antlers/horns. We use the same principles in our day-to-day lives. For example, thermostats use the same principle. When strips of brass and iron of equal length are heated separately, the brass expands more than the iron. When these strips are joined and heated, the brass curls around the iron. This bending motion enables thermostats to control the on-off cycles of a furnace.

I wanted to try this Idea in other materials. My intuition told me if I stuck two different types of paper and sprayed some water, It would showcase the curling effect. (The expansion of paper is caused by water molecules entering the cellulose fibers in the paper, disrupting their hydrogen bonds and causing the fibers to swell. )Took a piece of paper and taped the other side using masking tape. And to my surprise when I exposed it with some moisture it curled. Relatively simple principle but gave me a lot of dopamine hits.
So you don't need to stick 2 different papers all you need to do is to tape the other side. The type of tape, thickness of the paper, and type of paper play a role in the curling rate and the degree of curling. One thing to notice is the grain alignment. (Paper expands more in its width than its length because the fibers are usually aligned that way during manufacturing). I tried playing around with grain alignment in the explorations.
Moving ahead I wanted to take this further in other materials. For example, wood showcases the same property as paper and fortunately, it also has a grain direction. I can use the above technique for prototyping purposes and a larger more rigid moisture-reactive structure with wooden strips. I did some exploration with wooden strips that I hand-cut using a saw. Tried some experiments with veneer as well. Vaneer is too flimsy for this because once it absorbs the moisture it gets heavy and bends towards gravity. (The tool they use to make veneer is like a big sharpener (Rotary peeling). It peels it out and loses its rigid interlocked microstructure).

Material as Computation: Things Fall Together by Skylar Tibbits
The first chapter of the book (Computing is Physical) explores the idea that physical embodiments of computing—if we use the broadest definition of the term as transforming information from one form to another -are abundant in the material world. Computation and logic don’t have to be confined to semiconductors or traditional programming, which ranges from low-level to high-level languages. Instead, we can harness other materials and their inherent properties for creative material computing. For instance, the ability of cellulose-based materials to expand or other reversible properties triggered by stimuli could serve as building blocks for material-based computation. I’m interested in exploring whether it’s possible to create simple input-output logic or even logic gates using these properties.
A small interactive reactive material frame was made to initiate conversations around the topic.
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