general chemistry

What links self-heating drinks and the D-day landings?


The imposing cliffs of Pointe de Hoc overlook the Normandy beaches where Allied troops landed on June 6 1944. The assaults marked the beginning of the liberation of German-occupied Europe. And the cliff tops were the perfect spot for artillery pieces capable of devastating any troops who tried to attack the Omaha and Utah beachheads.

The Allied command knew this and so, to shore up the attack, the navy bombarded Pointe de Hoc. Afraid this might not be enough, they also had a backup plan. A team of US Rangers scaled the 30-metre cliffs and, after locating the weaponry, deployed grenades, destroying the guns. The key to success was the choice of thermite-based charges. Yup, just good old iron oxide and aluminium.

 

 

Ok, so what this got to do with self-heating cans?

Link number 1:  Some of the same troops who were landing on the Normandy beaches that day had self-heating soap cans.

These were essentially a stove and can rolled into one, with a tube of cordite (more typically used as the propellant in small arms ammunition) running through the centre of the can to act as fuel. The cans were quick and easy to use and could be lit with a cigarette, allowing troops to prepare a hot meal in under five minutes. Unfortunately, they also had a tendency to explode, showering the assembled squaddies with piping hot soup.

Self-heating cocoa. University of Cambridge

Since then, there have been numerous attempts to make self-heating cans into a mainstream product. Most relied on a rather less volatile reaction to provide the heat, although some have still struggled with explosive issues.  Calcium oxide heats up rapidly when mixed with water. But it’s not particularly efficient, producing about 60 calories of energy per gram of reactant.

The upshot is that, to heat the drink by 40℃, you need a heating element that takes up nearly half the packaging. That’s just about OK if you want a small drink on a warm day, but in the depths of winter, when you might really want a hot drink, you only end up with a tepid coffee.

More powerful cans

What’s needed is a much more efficient reaction. Something, like thermite perhaps? As crazy as packing a can with a reaction capable of disabling an artillery gun may seem, that’s just what HeatGenie is planning. Over the last ten years, the firm has filed numerous patents describing the use of thermite within self-heating cans. It turns out the reaction used by the US Rangers is still too hot to handle, so they’ve dialled things back a bit by replacing the rust with a less reactive but no less familiar material, silicon dioxide. So the latest generation of heated cans is fuelled on aluminium and ground-up glass.

When this reaction is triggered it still kicks out a whopping 200 calories per gram of reactant and can achieve 1,600℃. Given the troubled history of self-heating packaging, releasing this much energy from the can in your hand might be a bit of a concern, so several of HeatGenie’s patents cover safety issues.

These include a complex arrangement of “firewalls” that can block the so-called “flamefront” should things get too hot, and energy-absorbing “heatsinks” to ensure the heat is efficiently transmitted around the drink, as well as vents to let off any steam. With all that is place, the company claims just 10% of the packaging is taken up by the heating elements, which can still produce a warm coffee in two minutes (although the exact temperature hasn’t been revealed).

A US technology firm is hoping to make a very old idea finally work by launching self-heating drinks cans. HeatGenie recently received US$6m to bring its can design to market in 2018, . Yet the principles behind the technology go back much further – to 1897, when invented the first self-heating can. So how do these cans work, why has no one has managed to make them a success, and what’s HeatGenie’s new approach? To answer that, we have to go back to World War II.

The ConversationSo, well over a century on fromRussian engineer Yevgeny Fedorov first attempts to make self-heating cans and more than 15 years after Nestle abandoned a similar idea, has HeatGenie final cracked it? Judging from the patents and investments, the firm might have sorted out the technical side, but whether it really has a hot product on its hands is another thing entirely.

This article was originally published on The Conversation. Read the original article.

By June 22, 2018 4 comments general chemistry, science news

The Chemistry of Hair Relaxers

I run a science communication module for undergraduate students. One of the assessments involves writing a blog or news style article. This year’s students did a cracking job so I’d like to share some of them with you. So enough from me and over to Ola Odu, a 3rd Year biochemistry student at the University of Hull.

Twitter: @olaodu_
Instagram: @olaodu_

 

Untangling the mystery of how relaxers work and delving into the chemistry behind the process to reveal how kinks, curls and coils are smoothed into a sleek style

The use of hair relaxers is something that is very common among women of colour all over the world and despite its name, the process is far from relaxing. The desire for silky, straight hair stems from the way the media present these flowing locks to be the epitome of beauty, but this comes at a price. From a young age, many girls, myself included, are unfamiliar with their natural hair texture as a result of their attempts to conform to this standard to beauty that they are constantly surrounded by. Despite the widespread use of relaxers, many of us would never consider how they work on a scientific level. Now that I have embraced my natural hair, I look back on the relaxers that I depended on for so long to find out what they really did to my hair.

 

Picture1

My relaxed hair 5 years ago compared to my natural hair now


My relaxed hair 5 years ago compared to my natural hair now

Relaxers come in a range of brands, strengths and consistencies, but how do they work? Essentially, it’s a straight perm, usually used by people with thick and tightly coiled hair so that it is easier to manage. Instead of using heat to straighten the hair, chemicals are used to loosen the tightly set curls. Hair fibres are made up of proteins, mainly keratin, that contain different types of bonds which are responsible for each individual’s distinctive hair texture. Hydrogen and disulphide bonds are a main factor in determining the curl pattern of the hair. Hydrogen bonds are bonds that form between water molecules, and are responsible for hair curling as it dries. When hair is wet, the hydrogen bonds are broken. As it dries, the bonds reform, as do the curls. This is why hair can be manipulated by using rollers as a temporary alternative to relaxers. As the hair dries around the rollers, it
holds its new shape once they are removed.

How hydrogen bonds in hair are broken and reformed

Disulfide bonds are much stronger than hydrogen bonds. These bonds form between sulfur atoms in hair fibres in order to provide strength in addition to the formation of curls. These bonds cannot be broken by water like hydrogen bonds, so hair relaxers are used. The chemicals present in hair relaxers break the disulfide bonds. This permanently straightens the hair. However, breaking these bonds makes the hair more susceptible to breakage and split ends.

Illustration of disulphide bonds in hair fibres breaking due to the use of hair relaxer

The relaxers are strong enough to break the disulfide bonds in hair fibres and consequently alter the structure of the curl pattern. This because of their typically high pH. In chemistry, pH is a numeric scale used to state how acidic or basic a substance is. If it has a low pH, it is more acidic and if the pH is high, it is more basic. Hair relaxers are basic, with their pH ranging from 9 to 14 to ensure that they are strong enough to change the hair structure.

 

There are different types of hair relaxers available of varying strengths and made up of different chemicals. Thio (short for ammonium thioglycolate) relaxers are much thicker in consistency than other relaxers, which makes them easier to apply. They have a pH value of at least 10 to ensure that enough of the disulfide bonds have broken. The relaxer is then rinsed out and a neutraliser used to bring the hair back to its original pH value of 4.5 – 5.5. Thio relaxers slowly break down the bonds in the hair’s proteins in order to straighten it.

However, lye relaxers work in a slightly different way. In this process, lye is the active ingredient. Lye is a mixture of sodium hydroxide, water, petroleum jelly, mineral oil and emulsifiers. This relaxer is absorbed by the hair’s proteins and weakens the bonds rather than breaking them. The curls are then loosened as the hair fibre swells open. However, the amount of lye in the relaxer can vary, so weaker products can minimise the extent of damage to the scalp. Lye relaxers typically have a pH between 12 and 14 and do not require a special neutralising step, unlike thiol relaxers.

Increasing awareness of the potentially harmful effects of sodium hydroxide led to the development of no-lye relaxers. They work in the same way as lye relaxers, but the sodium hydroxide was replaced with potassium, lithium or guanidine hydroxides. This means no-lye relaxers are gentler on the scalp.

Once the hair is relaxed, it is permanently straightened. But as the hair continues to grow, the roots will be natural. This means the relaxing process should be repeated regularly to achieve a consistent look, but excessive use of relaxers can cause damage over time, leading to chemical burns and hair loss. Relaxers contain strong chemicals to ensure that all the bonds holding the curls are altered. These chemicals can be harmful if overused or applied incorrectly.

Overall, hair relaxers are useful in managing thick, tightly coiled hair when used moderately. But, it is a permanent alteration to the hair’s curl pattern, so it is something that should be well considered before undertaking. Personally, my hair is much healthier without the use of relaxers, but this is not the case for everyone. What you do with your hair is your choice and should come from you, and you alone. Ultimately, all hair textures are wonderful and beautiful in their own way and should be celebrated!

By January 31, 2018 2 comments general chemistry

My Extra Credit Assignment: Turn a General Chemistry Topic into a Science Museum Exhibit

When traveling, I always make a point to explore local science museums. I look for engaging exhibits that explain scientific concepts in informative and fun ways. One such exhibit at the Science Museum of Minnesota asks participants to create carbon nanotubes using foam connectors. A few friends and I used our advanced degrees to produce the example shown below (sorry for the potato quality).

The exhibit engaged people of all ages in different ways. Just behind the exhibit you can see the little guy who, moments after the picture was taken, learned all about tearing carbon nanotubes apart while deploying a rather impressive Godzilla impression.

Nanotube

Since becoming a teacher I have a new appreciation for science museum exhibits. They are a literal manifestation of Einstein’s philosophy: “If you can’t explain it to a six year old, you don’t understand it yourself.” The best exhibits make the explanation entertaining too.

So, towards the end of this spring semester when my general chemistry students requested an extra credit assignment, I knew exactly what to assign. I asked them to take one of the concepts they learned in general chemistry and create a science museum exhibit to explain it.

The assignment allowed unlimited space and budget. I was less concerned about reality and much more interested in seeing their knowledge and creativity. In the end I was blown away by their creations and would like to share a few.

Dipole-dipole Board

Dipole-dipole

The above exhibit, created by Taylor Trammell, showcases intermolecular dipole-dipole interactions. Her display contains many magnets–representing molecules–with two opposing sides, one positively charged (north pole) and one negatively charged (south pole). All of the magnets/molecules are free to rotate, except for one. Museum visitors can press a button and control the orientation of that one ‘molecule’. As it’s orientation changes, the other ‘molecules’ will reorientation to maximize dipole-dipole interactions and minimize the energy within the solvent.

A visitor could also walk up to the board with a strong bar magnet and introduce only it’s north or south pole to the magnet-filled board. That would represent the solvation of cations or anions through ion-dipole interactions. Taylor may not know it, but she found a fun way to introduce the solvent reorganization associated with Marcus Electron Transfer Theory.

Collision Theory Booth

According to the Collision Theory of Reactivity, for a chemical reaction to occur the molecules must: 1) collide, 2) have enough energy to make and break bonds, and 3) have the correct orientation when they collide. Emily Nabong demonstrates these rules of engagement through a museum exhibit that repurposes an amusement park throwing booth. Instead of milk jugs or balloons, the target is a Velcro-covered molecule. And instead of baseballs or darts, visitors throw ‘molecules’ with different geometries and Velcro coverage at the target.

If the molecule is thrown with too little momentum or too little accuracy it will not hit the board (collide). Also, if the molecule hits the board with the wrong Velcro alignment it won’t ‘stick’ (correct orientation). The ‘reaction’ will only occur if the molecule is thrown hard enough and with the right orientation.

Collision

Amorphous vs Crystalline Solids

Miranda Ave introduced an interactive “build your own solid” exhibit that demonstrates the difference between amorphous and crystalline solids. It’s comprised of two building stations. The first station offers Magnetix (below left), which have curved connectors representing bonds and metal spheres representing atoms. The second station offers Tinker Toys (below right) with only one rod length (bonds) and wood circles that connect at 90° positions (atoms).

Solids

Any structure built with the Magnetix will lack long-range order like in an amorphous solid. In contrast, a structure built with the restricted connectivity of the Tinker Toys will have a continuous, repeating pattern like those observed in crystalline solids.

Tearing apart these structures will also help demonstrate differences between amorphous and crystalline solids. Tinker Toys break apart in a ridged manner along cleavage lines while Magnetix structures break in random places.

The building stations will also be accompanied by a display with both crystalline and amorphous solids as well as an atomic picture of their structures.

Viscosity Race

Both Gabby Vega (below left) and Erum Kidwai (below right) proposed races between liquids to demonstrate differences in viscosity. They envisioned racetracks with several lanes, each labeled with a molecular structure. Museum goers would pick their ‘horse’ or lane and then watch as liquids ‘race’ down the track. Afterwards, each solution would be unveiled and the intermolecular forces dictating the viscosity and flow rates of the liquids would be explained.

Viscosity

Boyle, Lussac and Avogadro

Jessica Metzger’s museum exhibit set out to teach people about the relationship between temperature, volume, number of moles of a gas, and pressure. She proposed three different interactive stations. The first (left) contains a cylinder connected to a pressure gauge with a plunger that can be pushed or pulled. When the plunger is pushed (or pulled) and the pressure increases (or decreases), the reading on the pressure gauge will increase (or decrease) just as predicted by Boyle’s law.

The second cylinder (middle) is completely enclosed and placed on top of a heating element. When the visitors press the button a red light will turn on indicating that the chamber is being heated. As the temperature increases, the pressure will increase in accordance with Lussac’s law.

The third cylinder (right) will be taller than the other two with a lid that can move up or down without allowing gas molecules to escape. The station will be equipped with a button that, when pushed, releases compressed air into the cylinder. So, when the button is pressed, the metal lid will move up and increase the cylinder’s volume to accommodate the newly introduced gas molecules (Avogadro’s Law).

PV = nRT

Electronegativity and polarity

Carolin Hoeflich proposed an exhibit to introduce the concept of electronegativity and polarity. The exhibit includes a table with a soft foam cover and blocks representing the elements. The blocks are weighted so that electronegative elements are heavier. Museum-goers can arrange the blocks into molecular structures before dumping marbles–representing electrons–onto the table’s surface. The heavier elements will sink deeper into the foam and therefore ‘attract’ a larger number of marbles. When stepping back and looking at the structure as a whole, museum-goers will see that more marbles = more electronegativity. It’s also a fun way to visualize the dipole moment of a structure.

Electronegativity

Osmosis touch screen

Hunter Hamilton introduced a touch screen exhibit to demonstrate the principles of osmosis and osmotic pressure. Visitors will use the screen to create an environment with more or less ions (red spheres) and one of three possible ‘membrane’ options: 1) no membrane, 2) permeable to water but not ions, and 3) permeable to water and ions. Once all selections are made, the visitors presses GO and observes which direction water and ions move in their environment.

Osmosis

Le Châtelier’s Principle

Another touch screen exhibit, by Kelly Wyland, covers Le Châtelier’s Principle. Her screen displays an equilibrium with colors assigned to the reactants and products. It then asks users to predict the color change upon perturbation. After a prediction is made, the screen will show an animation that adds or removes reagents from the reaction mixture’s beaker. The color change of the solution will coincide with the concentration shifts to reach equilibrium.

LCP

Reaction Coordinate Slide

I’ve saved the largest and most interactive exhibit for last. Nathan Horvat designed an exhibit with two slides that represent an exothermic and endothermic reaction coordinate diagrams. Children (maybe adults?) would start on the platform in the middle (as reactants) and climb one of two ladders representing the activation energy to the transition state before sliding down to the landing pads (products).

The ladder/slide to the left (or right) is for an endothermic (or exothermic) reaction because the end point is higher (or lower) in energy than the starting point. One thing that I found fun about this exhibit is that, while viewing it in action, you’d likely notice more children choosing the exothermic slide because the endothermic one requires more work for less return. In a statistical fashion, the children would find the product that’s more thermodynamically favorable.

rxn coordIn closing, I want thank my students for a great semester and to share my appreciation for the students who designed these exhibits. It was a pleasure to teach them and to see them come up with such creative ideas. I hope one day, during a random science museum visit, I find one of these exhibits in action.