Stuff Matters

“In a very real way, then, materials are a reflection of who we are, a multi-scale expression of our human need and desires.” — Mark Miodownik

It’s often easy to get caught up and forget how much material diversity exists in the world. Even common objects found in our households are made of hundreds of natural and synthesized materials, many of which did not exist a century ago. Some of these such as ceramics, plastics, and steel, were discovered and perfected over the longer arc of scientific and technological progress.

This post was inspired by a book I recently finished reading, “Stuff Matters: Exploring the Marvelous Materials That Shape Our Man-Made World”, by Mark Miodownik. I usually don’t write longer book reviews, but I should try doing this more often. While writing this post I realized that it helped me better synthesize what I’d read into a more coherent framework, which I suspect may help longer-term recall.

I’ve written this post by liberally weaving together the numerous highlights and side notes I scribbled while reading the book.¹

The book starts with a picture of the author sitting on his rooftop terrace. At first glance, it appears to be an ordinary picture of the author surrounded by potted plants, a garden chair and table, and other standard outdoor equipment. Basically, a collection of ordinary materials that we take for granted in today’s world. The next 10 chapters are a whirlwind tour through the nature, structure, and history of many materials from this picture. Where they came from, how they were discovered, weaved together by the narrative of the countless struggles and incremental discoveries that made these materials what they are today. I often thought of materials as a static substance, in that once they are invented that’s it, we use them ad infinitum. Reading this book transformed my thoughts, helping me see that materials are a living and breathing creation, the result of past (and ongoing!) breakthroughs in human progress.

Highlights

Aerogels

A couple of years ago, at NASA’s Jet Propulsion Lab, I remember coming across an incredible material.

This material, aerogel, is close to 99.8 percent air, extremely lightweight, and eerily translucent. For comparison, aerogel is 1000x lighter than glass! It’s derived from extracting the liquid component of a silica gel and replacing it with air. Though aerogel was synthesized over 90 years ago, it gained wider recognition when JPL deployed it for its Stardust mission to capture comet particles and interstellar dust. They needed a material that could capture these particles traveling at high velocities, without heating them up and causing physical alterations in the process. These high-speed particles leave a long track burning in their wake before slowing down and coming to halt. Since these are microscopic and hard to track down, JPL and the Space Sciences Lab at Berkeley, launched the Stardust @ Home project, a citizen science effort to help aid this discovery process.

Alloys

The ritual of shaving for many thousands of years began with the process of stropping, the act of sharpening the blade along a length of leather. A blade becomes blunt due to the many thousands of collisions it undergoes with hair during shaving, which forces the metal crystals to dislocate and rearrange themselves. This making and breaking of bonds create tiny dents in the smooth razor edge.

How does a material as soft as leather sharpen steel though? It turns out that it’s actually the fine ceramic powder impregnated within the leather which does the sharpening, by causing the metal to dislocate.

This property of metal crystals to dislocate, rearrange, and change shape makes them special as materials for tools, but used in their pure form renders them weak. To enhance properties such as strength, or resistance to corroding agents, we can fuse the metal with other materials. These fusions are called alloys, and they tend to be stronger than pure metals since alloy atoms have a different size and chemistry from the host metal’s atoms. When they sit inside the host crystal they cause mechanical and electrical disturbances that make it more difficult for dislocations to move. This makes the metal stronger since it’s now harder for the metal crystals to change shape.

An example of an alloy is bronze which is an alloy of copper, tin, and sometimes trace amounts of arsenic, phosphorus, or silicon.

Of course, alloys weren’t invented overnight, but are a product of many centuries of hurdles (including war) and innovations. An alloy such as stainless steel, which is impervious to water and air, has been created mostly through trial and error over the last few thousand years.

Concrete

If we had to choose one building material that has revolutionized construction, it would be concrete. This composite material, made of sand, gravel, crushed stone, and mixed in with cement and allowed to harden over time is arguably what drives the construction of the modern world. However, concrete was also a fixture in olden times, used alongside stone and marble to create ancient wonders. In fact, the word concrete derives from the Latin word concretus (to grow together), ditto for the word cement which derives from caementis *(*rocky stuff). This article provides a good overview of the history of concrete.

In general, structural materials are commonly found to be in either compression or tension². Concrete does well under compression, which is a property that the Romans used to construct the dome of the Pantheon, in which every unit is under a state of constant compression. However, concrete does quite poorly under states of tension³, and easily crumbles.

This limitation can be overcome if we reinforce concrete with another material. However, any material won’t do, since we need to take into account the rate at which concrete either expands or contracts (i.e. its’ coefficient of expansion). Almost like a minor miracle, there does exist such a material, steel. Pouring concrete inside a steel wireframe allows us to build harder, better, faster (pun intended) than ever before

One drawback of concrete, that we haven’t been able to solve in a foolproof way yet, is the emergence of cracks through which water seeps in and causes the steel to rust, thus weakening the overall structure. Ongoing research in better forms of concrete includes a form of self-healing concrete that has bacteria embedded inside it along with a form of starch, which acts as food for the bacteria. On exposure to water or air, these bacteria are activated which consume the starch and help fill these gaps due to their metabolic activity. This makes concrete a living and breathing material, quite literally. Another development is a textile version of concrete called concrete cloth. This material comes in a roll and requires only the addition of water to harden into any shape we like. You can imagine this being used to make sculptures, art, or even in disaster zones to make a temporary city within a matter of days.

Glass

I don’t intend to wax hyperbolic, but I think there are very few materials that are as invisible, beautiful, and silently functional as glass. We often imagine there to be very few places on Earth that are left yet undiscovered. This perhaps may have a grain of truth if we refer to places existing on the human scale. However, there is nothing inherently special about the scale on which we exist. Glass as a material allows us to transcend our scale and to look to the heavens and beyond, or to the quantum and below, and peer into the depths of minute microcosms.

Why are some materials transparent? Incidentally, the answer to this question also explains why we don’t get sunburned when sitting behind a window. When light passes through an atom, it provides a burst of energy, and if this energy is above a specific threshold, it will be absorbed, thus preventing it from passing through the material⁴. Visible light doesn’t contain enough energy to be absorbed by the glass and hence allows light to pass through, which renders it transparent. However, UV light, which has a much shorter wavelength, thus a higher frequency, contains enough energy to pass this threshold in a glass. Thus, it is absorbed and results in glass being opaque to UV light.

This transparency of glass also results in neat aesthetics, such as that found in churches, shrines, and temples where we can color glass with impurities to create wonderful frescoes. It also influences what we consume, since the color of a drink becomes more relevant for example. It’s hard for us to imagine otherwise, but consider drinking through an opaque metal glass. The color of a drink wouldn’t be of as much concern to us. In fact, in medieval times, beer supposedly had a muddy color to it, which of course wouldn’t matter since people never looked at it for too long. However, the invention of glass and its’ use as a drinking device, meant that we’d have to stare at this drink and I imagine it wouldn’t have been as appealing to drink any longer (except maybe with your eyes closed?). Beer underwent a transformation into a golden lager a couple of hundred years ago in Germany and has since then become something to drink with the eyes as much as with the mouth. It’s amusing then that modern-day man has reverted to consuming beer through metal cans.

Paper

Paper is a two-thousand-year-old technology. It’s remarkable if you think about how this simple invention allows us to record and transmit ideas across time. The best device we had before the invention of paper to transmit ideas was the word of mouth, which of course is easily susceptible to mutations and cumulative error⁵. The use of paper allowed us to transcend these limitations, and create stories to have been recorded and transmitted for millennia. As a side note, this reminds me of Carl Sagan’s wonderful quote about books:

“What an astonishing thing a book is. It’s a flat object made from a tree with flexible parts on which are imprinted lots of funny dark squiggles. But one glance at it and you’re inside the mind of another person, maybe somebody dead for thousands of years."

The first iterations of paper were scrolls that were inscribed on. Longer messages would be split across many different scrolls. This naturally leads to the idea of sticking together smaller pieces of paper and binding them together, which is our modern-day notion of a book.

This is a simple, but powerful invention, since it allowed us to refer to ideas by using page numbers, instead of having to search through many long scrolls⁶. It’s believed that the Bible was amongst the first books to be written in this format, which was useful to preachers since they no longer had to search across many different scrolls.

A limitation of paper, however, is that it yellows with age and must undergo careful preservation. This is due to the presence of lignin, which is leftover from the pulp used to make paper. It reacts with oxygen in the presence of light to create the chromophores, which give the old paper its’ distinctive yellow tinge.

Paper is often made of different blends and compositions depending on how long it is made to last. For more ephemeral purposes, such as newspapers, we can get away with using cheap paper, which easily turns yellow within a couple of days.

Paper such as that used in money is not made of wood cellulose, as is common for normal paper, but from cotton. This gives it greater strength, prevents disintegration in the rain and washing machines, and allows us to craft neat tricks to prevent forgery.

One thing I was fascinated by as a child was the distinctive sound that a receipt printer makes. It seemed odd that it didn’t make sounds like a normal desk printer. Also, have you ever seen a receipt printer being refilled with ink? Well, I haven’t. It turns out the reason for this is that printing on thermal paper doesn’t actually mean adding ink to it. Rather, the ink is already present in the paper, in the form of a dye and an acid. The act of printing requires only a spark to heat up the paper, which ensures that cash registers never run out of ink! However, the drawback of this is over time, the pigment reverts to its original state, which causes the ink to fade.

Of course, the best way to solve this problem is to store things digitally, which leads us to the so-called Janus particle⁷, that finds use in e-book readers. Each particle of ink is dyed to be dark on one side, and light on the other. The two sides are given opposite electric charges so that each pixel can change color conditional on the provided electric charge. However, since these particles are physical ink and need to physically rotate so change color, they have a much lower refresh rate compared to a liquid crystal display. This means that at present they’re unable to show movies for example.

Concluding Thoughts

This book opened my mind to the hidden world of materials, a part of our environment which hitherto I’d taken for granted. It’s fascinating how there’s a world of surprises just waiting for us if we’re willing to ask the right questions. Every material in our immediate surroundings has a rich history of struggle and discovery. We literally “stand on the shoulders of giants”.

If any of this perked your interests, I’d highly recommend giving the book a read! If you do, I’d love to hear your thoughts, happy to chat :)

I’ll end with a highlight from the book:

One day whole rooms, buildings, perhaps even bridges may generate their own energy, funnel it to where it is needed, detect damage, and self-heal. If this seems like science fiction, bear in mind that it is only what living materials do already.

Thanks to Hima Tammineedi for providing feedback on initial drafts of this.

Footnotes