Two-Dimensional Polymer Is A New Ultra-Strong Material

Plastics, by and large, are well-understood materials. Not as strong as most metals, but often much lighter, these man-made polymers have found innumerable applications that have revolutionized the way we live. The properties of plastics have been improved in many ways over the years, with composite materials like fiberglass and carbon fiber proving to have strength and lightness far beyond the simple properties of basic polymers alone.

However, a group of engineers at MIT have been working on a revolutionary type of polymer that promises greater strength then ever before while remaining remarkably light weight. It’s all down to the material’s two-dimensional molecular structure, something once thought to be prohibitively difficult in the world of polymer science.

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Grocery Store Rocket Fuel: Don’t Try This At Home!

It seems like whenever the topic of rocket science comes up, the conversation quickly shifts to that of rocket fuels. As discussed in the excellent [Scott Manley] video below the break, there are many rocket fuels that can be found in some way, state, or form at your local grocery or liquor store. The video itself is a reaction to some college students in Utah who caused an evacuation when the rocket fuel they were cooking up exploded.

[Scott] himself theorizes that the fuel they were cooking was Rocket Candy, a volatile mix of sugar and potassium nitrate that is known to go Kaboom on occasion. And as it turns out, the combination might not even be legal in your area because as much as it can be used as rocket fuel, it can also be used for other things that go boom.

So, what else at your local megamart can be used to get to orbit? [Scott] talks about different kinds of alcohols, gasses, cleaners- all things that can be used as rocket fuel. He also talks about all of the solid reasons you don’t want to do this at home.

If this type of things gets your molecules excited, you might enjoy a bit we posted recently about using another grocery store staple to save Martian colonists from being held back by gravity.

Big Chemistry: From Gasoline To Wintergreen

Most of us probably have some vivid memories of high school or college chemistry lab, where the principles of the science were demonstrated, and where we all got at least a little practice in experimental methods. Measuring, diluting, precipitating, titrating, all generally conducted under safe conditions using stuff that wasn’t likely to blow up or burn.

But dropwise additions and reaction volumes measured in milliliters are not the stuff upon which to build a global economy that feeds, clothes, and provides for eight billion people. For chemistry to go beyond the lab, it needs to be scaled up, often to a point that’s hard to conceptualize. Big chemistry and big engineering go hand in hand, delivering processes that transform the simplest, most abundant substances into the things that, for better or worse, make life possible.

To get a better idea of how big chemistry does that, we’re going to take a look at one simple molecule that we’ve probably all used at one time or another: the common artificial flavoring wintergreen. It’s an innocuous ingredient in a wide range of foods and medicines, but the infrastructure required to make it and all its precursors is a snapshot of just how important big chemistry really is.

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As Light As Plastic; As Strong As Steel

Chemical engineers at MIT have pulled off something that was once thought impossible. By polymerizing material in two different directions at once, they have created a polymer that is very strong. You can read a pre-print version of the paper over on Arxiv.

Polymers owe many of their useful properties to the fact that they make long chains. Molecules known as monomers join together in strings held together by covalent bonds. Polymer chains may be cross-linked which changes its properties, but it has long been thought that material that had chains going through the X and Y axis would have desirable properties, but making these reliably is a challenge.

Part of the problem is that it is hard to line up molecules, even large monomers. If one monomer in the chain rotates a bit, it will create a defect in the 2D structure and that defect will grow rapidly as you add more monomers. The new technique is relatively easy to do and is irreversible which is good because reversible chains tend to have undesirable characteristics like low chemical stability. Synthesis does require a few chemicals like melamine, calcium chloride, pyridine, and trimesic acid. Along with N-Methyl-2-pyrrolidone, the mixture eventually forms a gel. The team took pieces of gel and soaked it in ethanol. With some filtering, ultrasonics, centrifuging, and washing with water and acetone, the material was ready for vacuum drying and was made into a powder.

The powder is dissolved in acid and placed on a spinning silicon wafer to form a polymerized nanofilm. Other 2D films have been produced, of course, such as graphene, but polymer films may have a number of applications. In particular, in contrast to conventional polymers, sheets of this material are impermeable to gas and liquid, which could make it very useful as a coating.

According to the MIT press release, the film’s elastic modulus is about four and six times greater than that of bulletproof glass. The amount of force required to break the material is about twice that of steel. It doesn’t sound like this material will be oozing out of our 3D printers anytime soon. But maybe one day you’ll be able to get 2D super-strong resin.

For all their faults, conventional polymers changed the world as we know it. Some polymers occur naturally, and some use natural ingredients, too.

Screenshot from the video in question, showing 12:54 of the video, demonstrating how the electrons are being exchanged when circuit is completed

Li-ion Battery Low-Level Intricacies Explained Excellently

There’s a lot of magic in Lithium-ion batteries that we typically take for granted and don’t dig deeper into. Why is the typical full charge voltage 4.2 V and not the more convenient 5 V, why is CC/CV charging needed, and what’s up with all the fires? [The Limiting Factor] released a video that explains the low-level workings of Lithium-ion batteries in a very accessible way – specifically going into ion and electron ion exchange happening between the anode and the cathode, during both the charge and the discharge cycle. The video’s great illustrative power comes from an impressively sized investment of animation, script-writing and narration work – [The Limiting Factor] describes the effort as “16 months of animation design”, and this is no typical “whiteboard sketch” explainer video.

This is 16 minutes of pay-full-attention learning material that will have you glued to your screen, and the only reason it doesn’t explain every single thing about Lithium-ion batteries is because it’s that extensive of a topic, it would require a video series when done in a professional format like this. Instead, this is an excellent intro to help you build a core of solid understanding when it comes to Li-ion battery internals, elaborating on everything that’s relevant to the level being explored – be it the SEI layer and the organic additives, or the nitty-gritty of the ion and electron exchange specifics. We can’t help but hope that more videos like this one are coming soon (or as soon as they realistically can), expanding our understanding of all the other levels of a Li-ion battery cell.

Last video from [The Limiting Factor] was an 1-hour banger breaking down all the decisions made in a Tesla Battery Day presentation in similarly impressive level of detail, and we appreciate them making a general-purpose insight video – lately, it’s become clear we need to go more in-depth on such topics. This year, we’ve covered a great comparison between supercapacitors and batteries and suitable applications for each one of those, as well as explained the automakers’ reluctance to make their own battery cells. In 2020, we did a breakdown of alternate battery chemistries that aim to replace Li-ion in some of its important applications, so if this topic catches your attention, check those articles out, too!

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Plastics: Photopolymers For 3D Printing And Beyond

Chances are good that if you’ve done any 3D printing, it was of the standard fused deposition modeling variety. FDM is pretty simple stuff — get a bit of plastic filament hot enough, squeeze the molten goo out of a fine nozzle, control the position of the nozzle more or less precisely in three dimensions, and repeat for hours on end until your print is done. To the outsider it looks like magic, but to us it’s just another Saturday afternoon.

Resin printing is another thing altogether, and a lot closer to magic for most of us. The current crop of stereolithography printers just have a high-resolution LCD display between a UV light source and a build tank with a transparent bottom. Prints are built up layer by layer by flashing UV light patterns into the tank as a build plate slowly lifts it up from the resin, like some creature emerging from the primordial goo.

Of course it’s all just science, but if there is any magic in SLA printing, surely it’s in the resins used for it. Their nondescript brown plastic bottles and information-poor labels give little clue as to their ingredients, although their hydrocarbon reek and viscous, sticky texture are pretty good clues. Let’s take a look inside the resin bottle and find out what it is that makes the magic of SLA happen.

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Water beading up on a feather

PFAS: The Organofluorines Your Biochemist Warned You About

Sometimes it begins to feel like a tradition that a certain substance or group of substances become highly popular due to certain highly desirable chemical or physical properties, only for these chemicals then to go on to turn out to form a hazard to the biosphere, human life, or both. In the case of per- and polyfluoroalkyl substances (PFAS) it’s no different. Upon the discovery that a subgroup of these – the fluorosurfactants – have the ability to reduce water surface tension significantly more than other surfactants, they began to be used everywhere.

Today, fluorosurfactants are being used in everything from stain repellents to paint, make-up, and foam used by firefighters. In a recent study of 231 cosmetic products bought in the US and Canada (Whitehead et al., 2021), it was found that all of them contained PFAS, even when not listed on the packaging. The problematic part here is that PFASs are very stable, do not decay after disposal, and bioaccumulate in the body where they may have endocrine-disrupting effects.

Some areas have now at least partially banned PFAS, but the evidence for this is so far mixed. Let’s review what we do know at this point, and which alternatives we have to continuing to use these substances. Continue reading “PFAS: The Organofluorines Your Biochemist Warned You About”