Up in the aer(ogel)

Hi everyone, welcome to the latest #MicrobeStew article!

This week i am incredibly lucky to have my first guest post written by Laurie Winkless (@Laurie_Winkless), who is a physics and material sci Science Communicator. Please check out her blog “No Lab Coat Needed“, where she writes some excellent and informative posts. If you’re wondering, “how does this fit into a microbiology blog?”, then wonder no more. Laurie has written an article on aerogels, a technology I recently investigated as a method for antibiotic delivery in orthopaedic surgery. For my previous posts on this topic see here. This will be followed soon by a post on my research. Hope you enjoy!

I remember vividly the first time I saw aerogel – I was a 15-year old space nut, watching the news one evening with my parents. There, on my TV, was what I later described in my diary as “a block of solid smoke”.

It was a year before NASA launched their Stardust mission, which had the ridiculous aim of capturing the dust from a comet’s tail by flying behind it. This aerogel, a mysterious blue-tinted material, would be used to slow down the particles from their high velocity and store them safely until the probe returned to Earth on the mission’s completion. “Surely this is science fiction?” I thought. Unconvinced as I was, I was utterly hooked by the ambitious mission, and I kept a close eye on the project for years. Eventually, I found another pet topic, but I couldn’t forget that material – aerogel was tucked firmly into my “come back to this later” pocket.

Aerogel_hand

Figure 1: Image of aerogel from Wikipedia.

Fast-forward to August 2014. Now a 31-yr old space nut who spends far too much time on Twitter, I spotted a tweet that made me sit up straight. Berkley scientists who had been examining some of the blocks of aerogel since Stardust’s successful re-entry in 2006 had made a remarkable discovery. Amongst the many particles of comet dust captured in the aerogel they confirmed that the ship had captured tiny pieces of interstellar rocks. For the first time in human history, we had our hands on dust from beyond our Solar System. While the engineering and orbital mechanics of such a mission are enough to make even a former space scientist like myself weep with joy, it was the material that was the shining star. This discovery could not have been possible without aerogel.

What we know as aerogel is more correctly called silica aerogel. There are lots of other types of aerogel out there too (e.g. nickel aerogel), but they all have one thing in common – the ‘aer’ bit is what defines them Aerogels are 99.8% air, making them the lightest solid in the world. Silica aerogel was invented by a curious chemist called Samuel Kistler who wanted to understand why gels could wobble but hold their shape. He was the first to demonstrate that this was due to their internal structure – a continuous network of solid material supported by pores full of liquid. Kistler found a way to remove the liquid while maintaining the complex network. He’d discovered aerogel. However, his discovery failed to set the world alight – no-one could pin down a real-world application for this incredibly lightweight material. This remained the case until the 1980s when NASA started to investigate them and proposed the Stardust mission.

In addition to its low density, aerogel has another remarkable property – its thermal conductivity is very, very low. The aerogel used by Stardust had a conductivity of 0.008 W/m.K, making it at least five times more insulating than the mineral wool insulation material used in lofts across the globe. This was particularly important to Stardust. In space, tiny dust and rock particles can move incredibly fast – up to six times that of a bullet leaving a rifle but aerogel’s complex structure slows them down. The material’s low thermal conductivity ensures that the heat produced in the impact is dissipated. We know that asteroid impacts can melt surrounding rocks; well, aerogel’s insulating properties stops this from happening to the precious dust particle on impact.

Since the Stardust mission, aerogel has found many applications down here on earth, including in a new generation of insulating windows. One particularly exciting application, published in late 2014, combined aerogel with material-of-the-moment, graphene, to produce a bio-inspired sponge for use in in oil spills and electrochemical sensors. 85 years on from their discovery, it seems that aerogels are more relevant than ever.

Thanks from Microbe Stew and Laurie for reading!

References

Image: http://upload.wikimedia.org/wikipedia/commons/2/2c/Aerogel_hand.jpg

Stardust mission: http://stardust.jpl.nasa.gov/tech/aerogel.html

Berkley scientists: http://www.jpl.nasa.gov/news/news.php?release=2014-278

Thermal conductivity: http://energy.lbl.gov/ecs/aerogels/sa-thermal.html

Insulating windows: https://lauriewinkless.wordpress.com/2014/07/20/aerogels-for-insulation-its-all-about-particle-size/

Bio-inpsired sponge: https://lauriewinkless.wordpress.com/2014/10/21/bioinspired-graphene-aerogel-for-oil-spills/

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