4D Printing is Here

By Anupum Pant

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We had just started getting comfortable with printing objects in 3D, and 4D printing is already here. Early this year, in the month of April, Skylar Tibbits, an architect, designer and computer scientist at MIT, gave a revolutionary demonstration explaining their advances in the field of 4D printing at a TED conference. This was an initial proposal and it got things moving at a rapid pace.

Side note: In the world of 3D printing:

What is 4D printing?

At first 4D printing sounds like a catch phrase, it isn’t really just that. 4D printing is actually 1D better than 3D printing and it aims at making objects out of a 3D printer, that can reconfigure themselves into useful shapes, on their own. For instance, think of a non-living stick changing itself into a 3D cube as time passes. In short, 4D printing will enable us to create living objects without any living cells, micro-processors, chips or batteries involved. Sounds simple enough, but the promises are nothing less than extraordinary.

In the TED talk attached below, Skylar explains how a string of plastic placed in water can turn itself into the letters MIT. But, this was something that happened back in April. Things have moved further.

A few days back, Researchers at the University of Colorado Boulder revealed a successful test of their 4D printing technology. They were able to print out flat objects using normal plastic combined with a smart material which was able to turn into a cube on its own. Cubes are just the start.

According to scientists, in the future, 4D printing will probably churn out smart car bodies that would heal automatically, smart soldier uniforms and advanced building materials. Imagine a camouflage material that changes to match the surroundings, that could be the future. Or a pipe that contracts and expands to move water without pumps. Or a building material that builds itself into a structure. 4D printing could probably best suited for building in an extremely hostile environment like space. The possibilities are endless.

But, let us not get ahead of ourselves. It is almost impossible to predict what we’ll actually see in the future. Things have just started to happen in the field of 4D printing. But, it sure looks amazing. What will you build?

Why is a Metal Plate “Colder” Than a Plastic Plate?

by Anupum Pant

No, it isn’t!

What is Cold?

According to the dictionary, a body at a relatively lower temperature, especially when it is compared to the temperature of a human body is described as a colder one. So, any object below the normal human body temperature – about 37 degrees Celsius – is a cold thing. But wait a minute!

When you touch an object, what does it tell you about the temperature of the object? Can you really judge if it is a cold one or a hot one? Unfortunately, our bodies aren’t thermometers, we are not so smart when it comes to judging the temperature. Consider the following case.

A book and a steel plate kept in the same environment for a long time attain the same temperature eventually (it is called thermal equilibrium). This can be checked by using a thermometer on both the objects. But, when people are asked to touch a metal plate and a book, they find the former to be much cooler. You can try this out yourself by touching different materials around you. You’ll see how some things ‘feel colder’ while the others feel warmer. A YouTube channel Vertasium conducted a social experiment to record this on camera. See the video below:

There is no cold – only heat

So, in the video, ice melts faster, if kept on steel plate than on a plastic plate, even when the steel plate ‘feels colder’. Common sense dictates that the colder thing is supposed to sustain the ice block for a longer time, just like your refrigerator does. So why does the opposite happen?

A better way to understand this ‘contradiction’ (not really a contradiction) can be this:

According to thermodynamics, simply put, everything has heat in it. So, even a cold ice block has some amount of heat stored in it (say, around 273.15 Kelvin or 0 degree Celsius). When one object comes in contact with other object, it loses or gains heat till their temperatures get equal or till they attain ‘thermal equilibrium’. Which object loses heat and which one gains it, is decided by their relative temperatures. In case of ice and steel, ice has a lower temperature than steel (assuming it isn’t already freezing out there). Therefore, here, ice gains heat from steel till they attain the same temperature and ice melts.

Side note: The ice is also in contact with a relatively ‘hotter’ atmosphere. Hence, it gains heat from there also. In this case, we are only concerned about the steel and ice interaction.

Why does it melt faster on steel?

There is a particular property which depends on the kind of material and is called thermal conductivity. This is the parameter which decides which objects lose heat quicker and which ones do it slower.

Here, for instance, steel has a higher thermal conductivity than plastic. Hence, the steel plate gives away heat to the ice block faster than a plastic block does. As a result, ice melts faster on a steel plate than on a plastic one.

Incidentally, this effect can also be used to explain why one plate feels colder than the other, in our hands. Think of it like this, the ice is replaced by our hand. So, a steel plate, due to its better thermal conductivity, draws heat faster from our hand than a plastic plate. This makes us feel that the steel plate is colder than the plastic one.

As checked by a thermometer, both the plates have the same temperature, our bodies are only fooled into believing that the thing we feel is temperature; it isn’t. None of the plates is actually colder than the other (according to the dictionary – see first paragraph). We don’t feel the temperature. What we feel is actually the rate of heat being drawn away from our hand. Faster an object draws heat, the colder it feels.

Bricks Which Are Lighter Than Air

by Anupum Pant

What would smoke look and feel like, if you could solidify it?


Although, first made in 1931, Aerogels are relatively newer materials and a tremendous amount of research is being done on them everyday. Lightest solids ever, Aerogels weighing about seven times lesser than air have been made. Their extreme properties have given a fascinating field of interest to students and scientists. [Read the last paragraph]

How are they made?
Aerogels, also known as solid smoke or frozen smoke are extremely light materials. They are made by a process called sol-gel process which involves removing all the moisture from a specially made gel (Hypercritical Drying). Although the procedure may sound simple, there is a lot of technology involved in making them. Moreover, practically usable Aerogels which can endure moist conditions and high stress conditions are much more challenging to make. Also, it is very expensive to make them. [They can be made at home – with costly equipment of course]

Why is it so light? 
The whole lot of porosity left inside due to drying of the gel is what makes it so light. You can think of them as a sponge which is hard like pumice. But, when you think of a sponge, remember that mostly Aerogels aren’t very resilient. That means, unlike sponge they won’t get back into the previous shape after they’ve been pressed a lot. They are much sturdier/tighter than sponges. A small (not very small; due to very low density they occupy large space) piece of Aerogel weighing just 2 grams has been shown to hold a 2.5 kg brick without deforming. Poorly made Aerogels, on the other hand can also not be very sturdy. They would deform with a hard press of a finger and stay deformed.

How light are they?
Agreed, they can be lighter than air, but the practical mass varies greatly. And they don’t float in air because, with air present inside them, they are slightly heavier than air (weight of air inside + solid material), but can be made to float in air by replacing the air inside it with Hydrogen or Helium. Their lightness and density is completely dependent on the amount of porosity included during the fabrication – which can be controlled. Also, the kind of gel used to make it, affects the weight of the final block. So a block with 3 feet in length, breath and height can weigh anything from 1 kg to just 160 gm.

Aerographite, a carbon Aerogel made by German material scientists from Kiel University and the Hamburg University of Technology, was said to have weighed only 0.2 mg per cubic centimeter. It was 5000 times less dense than water and 6 times lighter than air (counting only the solid material’s weight of course). [Published Paper]

Graphene Aerogel: As if that wasn’t enough, recently, Chinese material scientists developed a lighter material than Aerographite. It was based on Graphene. A Graphene Aerogel; seven times lighter than air. This one, unlike other silica Aerogels, can recover like a sponge after getting deformed. [Published Paper]

Other Properties

Aerogels exhibit various other desirable properties which make them useful for a myriad of applications [See the Wikipedia Article]. For instance, they are very good insulators of heat. A nicely made Aerogel block which is just under a centimeter thick can protect things from a direct flame. Other desirable properties are high surface area, high thermal and acoustic resistivity, low dielectric constant, and low refractive index.

Aerogels absorb water or moisture from the air and even from human skin easily. Handling them with bare hands can cause blisters. But, the ones which repel water have been made successfully by altering fabrication parameters. Also, if particles of it are inhaled, it can cause problems. Hence, hand gloves and respiratory masks are used to handle them.

I want to study interesting materials like these

If you think Aerogels and Wolverine’s claws are interesting things. You can make a career in researching materials like these by making a foray into Materials Science and Engineering. Most good universities offer a course in it. It is a budding field, growing at a rapid pace with loads of opportunities waiting for you.