Posts Tagged ‘How Does It Work’
Shellac Nail Polish: How Does It Work?
by azmanam on Mar 01 2012 (21847 Views)See other articles in the How Does It Work series.
Shellac nail polish, sometimes referred to as gel nail polish, is all the rage these days. They claim to give a chip-free coating to your nails and can last several weeks. It can last even longer than that, but after two or three weeks, your nails have grown out and you can start to see unpolished nail at the base of your polished nail. If you go in for a quick touch up and fill in, your shellac nail polish can I guess last indefinitely!
What is Typical Nail Polish?
To start, let’s talk about typical, boring, old nail polish. At is core, nail polish is nitrocellulose dissolved in a solvent. Nitrocellulose is known for giving a nice, shiny, hard film once the solvent evaporates. Nitrocellulose is also known for exploding. It’s what makes up magicians ‘flash paper,’ and guncotton. Fortunately, our nails don’t explode. I’m pretty sure the manufacturers worked on figuring that one out before mass producing nail polishes.
Microwave Grilling: How Does It Work?
by azmanam on Nov 17 2011 (9858 Views)Previous articles in the How Does It Work series:
If you have any topics where you'd like to know: How Does It Work, let me know in the comments 
Today: how microwave grilling works. How does my Lean Cuisine Microwave Panini grill itself in my microwave? And how come when I microwave other things they just get soggy instead of crispy and grilled? It’s like using a toaster oven or George Forman, but not! What the heck is going on?
How'd you get so crispy?! Via Lean Cuisine
Fruit Ripening: How Does It Work?
by azmanam on Oct 12 2011 (17088 Views)This is the third time I've written a How Does It Work column (homemade chloroform and Coors Light cold-activated bottles). It's a lot of fun (and a lot of work) to write these columns, and I'm really enjoying writing them. I have two more ideas for upcoming How Does It Work columns (forest fire fighting, microwave panini "grilling"), but if you've always wondered how something (chemical) works, let me know and I'll try to work it into the queue! On to Fruit Ripening: How Does It Work?!
via Westwood Banana
Have you ever wondered what causes fruit to ripen? Why do we store some fruits in the refrigerator and some on the counter? Why do we have a special fruit crisper drawer in the fridge?
The answer has to do with a plant growth hormone. One plant growth hormone is primarily responsible for the complex transition we call ‘Fruit Ripening.’ So what would you guess that growth hormone looks like? Do you think it looks more like the protein-based human growth hormone (HGH) or bovine growth hormone (BGH)? Like the synthetic hormone zearalanol, or like other plant hormones like auxins? Or none of the above? Answer below the jump.
What does the Fruit Ripening Hormone look like???
Before I tell you the answer, let’s look at the physical changes that occur when a fruit ripens. Before the fruit is ripe enough to eat, the unripe fruit is green, immature, and not as tasty. It is hard, sour, not fragrant, and is starchy. (sometimes we desire some of these characteristics… do you prefer Granny Smith apples over Red Delicious?) These unripe fruits are generally unappealing to humans and animals – the latter being important evolutionarily because animals will eat the fruit and disperse the fruit’s seeds.
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Coors Light Cold-Activated Bottles: How Does It Work?
by azmanam on Aug 02 2011 (22148 Views)If you're in the US, no doubt you've seen the commercials. Coors Light's parodies of NFL coaches during post-game interviews was brilliant, but I'm talking about the one's for their cold-activated bottles:
So how does it work? The ability of something to change color with temperature is known as thermochromism, and the Coors Light bottles are printed with a thermochromic ink called a leuco dye. A leuco dye is a coloring agent which can acquire two different forms: a colorless form and a colored form. At warm temperatures, the thermochromic ink is colorless, and at cold temperatures, the thermochromic ink is (in this case) blue. Put your beer in the fridge, when the ink cools below the color changing temperature, "the Rockies turn blue," and your beer is ready to drink.
So how do thermochromic inks work? Well, in general one aspect of a molecule that makes it colored at all is an extended conjugated pi-system. A pi-bond absorbs light. A single pi-bond absorbs light in the UV spectrum. As the pi-system extends further and further, the wavelength of light absorbed becomes longer and longer, until extended pi-systems begin to absorb light in the visible spectrum - and the molecule becomes colored (see figure). A molecule will typically absorb one wavelength of light better than others, and this wavelength of maximum absorption is designated λmax (read "lambda max"). Lycopene is red because its λmax is in the blue region. It absorbs light in the blue region and reflects light in the red region and thus appears red. If one were to disrupt an extended conjugated system in the middle of the pi-system, the extended pi-system would be severely shortened, and the molecule would (potentially) become colorless. So most widely used thermochromic inks contain an extended conjugated pi-system that is easily interrupted.
The prototypical thermochromic ink is crystal violet lactone. When the pH is high, the lactone interrupts the conjugation that would otherwise extend through all three aromatic rings. When the pH is low, the lactone becomes protonated, and the lactone opens to the carboxylic acid, leaving a tertiary, benzylic carbocation behind. This carbocation allows the conjugation to extend throughout all three aromatic rings. With the conjugation extended, λmax increases into the visible region, and the leuco dye appears, well, violet colored.
For inks, the equilibrium is controlled in a very clever way. We can't constantly be dousing our beer bottles with acid or base depending on which color we want. For thermochromic inks, the manufacturers take the lecuo dye, some weak acid, and a high molecular weight solvent and encapsulate the components into a particle usually <50 μm in diameter. The leuco dye chosen will depend on what color is desired. Weak acids typically chosen include bisphenol A (yes, that BPA), octyl or methyl p-hydroxybenzoate, 1,2,3-triazoles, or 4-hydroxycoumarin derivatives. The solvent is typically an alcohol (laurel or cetyl alcohol), an ester (butyl stearate), a ketone, or an ether. The melting point of the solvent is important. The melting point of this solvent is the temperature at which color change will take place.
The paradox: It might seem at first glance that when the solvent is liquid, increased mixing should take place, and with more acid available in solution, the carbocation should be favored at elevated temperatures. But if that were true, the thermochromic inks should be colored at high temperatures. But almost invariably, all thermochromic inks are colored at cool temperatures and colorless at elevated temperatures. It seems that in the solid state, the leuco dye and weak acid are in contact with each other and color change takes place. In the liquid state, the two components disperse and the colorless form predominates.
- via www.chromazone.co.uk
Fun Facts: Note it's not actually temperature that's changing the form of the leuco dye. The temperature changes the equilibrium point of the acid/base reaction which changes the form of the leuco dye. So the dyes are not, technically, thermochromic... rather, they're halochromic. The color actually changes with pH. But the temperature controls the acid/base equilibrium, which controls the color, so these inks are generally referred to as thermochromic inks. So when the color change occurs at the temperature of my refrigerator, I can use thermochromic inks to tell when my beer is cold (actually, it only tells me when my beer bottle is cold... not the actual liquid inside the bottle...) Phenolphthalein is another example of halochromicity.
On reading a few patents, it appears Coors Light utilizes thermochromic inks prepared by ChromaZone. The actual structure of the blue dye appears to be either proprietary or a trade secret or I can't find it by browsing Google Patents or ChromaZone's webpage. Maybe it's just crystal violet lactone! ChromaZone's website has a lot of neat information on thermochromic inks. Another popular manufacturer of thermochromic inks is Matsui. Their thermochromic ink page has several headers with a lot more neat information to read.
Other Uses: • Other common uses of thermochromic inks are temperature probes for microwaveable foods. Some maple syrup bottles have a black thermochromic ink which reveals the word HOT written in red when the syrup is warm enough to eat. The ink doesn't actually change from black to red, though. The thermochromic ink changes from black to colorless... to reveal the regular ink printed underneath which has the word HOT printed in red ink.
• The fad of on-the-battery testers utilizes thermochromic and conductive inks. A three layer system is in use here. The conductive ink is printed in a strip that gradually expands in width. On top of that is printed (in regular rink) whatever design the company desires to show the battery is good. On top of that is printed the thermochromic ink. When the battery is tested, the resistance in the conductive ink causes the ink to warm. A small current will heat the narrow parts of the testing strip, and more current is needed to heat the widest parts of the testing strip. If there is enough current to heat the ink past the color-change temperature of the thermochromic ink, the ink will turn colorless and reveal the "good" indicator. As the battery drains, less of the testing strip will turn colorless and the battery will show that it is less "good."
• A two-toned effect can be created by mixing a colored thermochromic ink with a colored regular ink. Mixing a blue thermochromic ink with a yellow regular ink will result in a layer that appears green at low temperatures and yellow at elevated temperatures.
• As we said, leuco dyes are really halochromic inks dressed up as thermochromic inks. The true thermochromic material is a thermochromic liquid crystals, with the most famous thermochromic liquid crystal being the old school mood ring. Thermochromic liquid crystals are much more sensitive to temperature change than leuco dyes, but are more expensive to manufacture. Liquid crystals appear in silly mood rings, practical LCD monitors, and more serious forehead thermometers where exact temperature is important. In a liquid crystal, the molecules are oriented in a particular direction, but that orientation direction varies periodically with depth into the crystal. The distance between repeating orientations is the pitch, and the pitch varies with temperature. The value of the pitch is typically on the order of visible light, thus as the pitch changes, the colors reflected change, and the color of the mood ring changes. See this paper for more information.
• Leaving thermochromicity for a second, transitions lenses for prescription eyeglasses also exhibit a similar effect - colorless indoors, colored (tinted) outdoors. This is photochromicity, not thermochromicity, but the concept is the same. When hit with ultraviolet light, the photochromic compound undergoes a chemical change which turns the molecule from colorless to black reversibly. This interaction with UV light, but not visible light, is important so the lenses aren't tinted indoors. The problem with many transitions lenses is they don't work well if there is UV tinted glass between the wearer and the sun... such as when driving a car. Many windshields block UV light, thus the UV light can't interact with the photochromic molecules, and the wearer could experience no sunglasses effect when driving. A product called Drivewear claims to combat this problem with a combination of UV-sensitive and visible light-sensitive molecules.
So now you know! Next time you're enjoying a Coors Light (if that's your beer of choice), you can tell all your friends about thermochromic inks. They'll either think you're real cool and buy your next beer... or they'll think you're real nerdy and buy your next beer because you need to be more drunk. Either way, make sure you get a free beer out of it!
**Most of my information came from this awesome J. Chem. Ed. paper by Mary Anne White and Monique LeBlanc (insert joke about color chemistry paper written by White & The White here).
Casey Anthony and Chloroform: How Does It Work?
by azmanam on Jul 08 2011 (24722 Views)
Much of the country was all caught up in the Casey Anthony trial over the past few weeks as the testimony concluded and the verdict was announced (full disclosure: I was not at all caught up. I didn't even read any articles about the trial until after the verdict was announced). If you want background on the trial, wikipedia's as good as any in this case.
One of the points raised during the trial was whether or not a Google search was performed on How to Make Chloroform. One way to make homemade chloroform is by reacting household bleach with acetone. Whether or not the search was performed or for what reason, and whether or not anyone involved in this case actually tried to prepare homemade chloroform is irrelevant. We're going to talk here about how the process works from a chemical and intellectual perspective (full disclosure: This will NOT be a how-to post on how to prepare and purify chloroform. That information can be found elsewhere).
Safety First: Nearly all the chemicals involved in this process are dangerous and need to be handled with caution and respect. Bleach is a solution of sodium hypochlorite in water, usually containing a small amount of sodium hydroxide (lye) and/or sodium chloride. Sodium hypochlorite is a strong oxidant and will cause severe burns when concentrated (it is generally safe for low level exposure when dilute as in household bleach, but will still discolor skin and clothes). Sodium hydroxide is a strong base and will cause severe burns (think Fight Club). Acetone is generally safe when used as indicated, and it is commonly used as nail polish remover. Careful, though, it can dry out the skin. Chloroform itself is a suspected carcinogen and can cause dizziness and fainting. Also, if this process is done incorrectly, the byproducts can be quite dangerous as well. Bleach mixed with the wrong ingredients (like vinegar - don't mix your bleach with vinegar!) can produce chlorine gas - a highly toxic gas that no one should want to be around. Chloroform will decompose on exposure to oxygen to produce phosgene - a WWI chemical warfare agent. Needless to say, do not try this at home.
General procedure: To make chloroform, acetone is mixed with either sodium hypochlorite (bleach) or calcium hypochlorite (bleaching powder). This is a highly exothermic process releasing a lot of heat. The reaction is generally cooled by submersion of the reaction vessel in ice-cold water or by directly adding ice to the reaction mixture. The acetone is oxidized by the hypochlorite to form chloroform, with sodium (or calcium) acetate as a byproduct. The chloroform needs to be purified and stored away from light by processes not discussed here. The general reaction is as follows:
- Net Reaction for Making Chloroform
Three molecules of sodium hypochlorite react with one molecule of acetone to produce one molecule of chloroform, two molecules of sodium hydroxide, and one molecule of sodium acetate.
How it works: The mechanism for this reaction generally follows the mechanism of the haloform reaction: a classical organic chemistry reaction whereby a methyl ketone (acetone is a methyl ketone) reacts with a halogen (Br2, Cl2, or I2) under basic conditions (NaOH) to produce a haloform (bromoform: HCBr3, chloroform: HCCl3, or iodoform, HCI3). Iodoform is a pale yellow solid that is insoluble in water. For this reason, organic chemists have developed what's known as the iodoform test. Aqueous solutions of unknown compounds can be treated with iodine (I2) and sodium hydroxide. If a yellow precipitate forms, this is a positive indication that your unknown has a methyl ketone. This is the general scheme for a haloform reaction involving chlorine (Cl2):
- The classical haloform reaction
The mechanism (below) for the classical haloform reaction is quite clever. We need to break one of the carbon-carbon bonds to liberate chloroform from acetone. As organic chemists, we're always so concerned about how to make carbon-carbon- bonds that we rarely think about breaking them. To begin, in step 1) the base, sodium hydroxide, deprotonates the mildly acidic proton on the CH3 group of acetone, forming a resonance-stabilized enolate intermediate. In step 2) This enolate intermediate becomes monochlorinated by reacting with one molecule of chlorine. By repeating step 1) and step 2) two more times, one side of acetone becomes trichlorinated. This is a favorable process. In step 1), the base was deprotonating a mildly acidic proton. After each addition of chlorine, the acidic proton becomes more and more acidic, making the deprotonation easier and faster each time.
In step 3), the sodium hydroxide acts as a nucleophile and attacks the central carbon atom, causing the carbon-oxygen double bond to break into a single bond resulting in a negative charge on the oxygen atom. Oxygen would rather have a carbon-oxygen double bond than a negative charge, so in step 4), the carbon-oxygen double bond reforms, and the anion Cl3C- is released from the molecule. Typically, carbon is rarely released from a molecule, as a carbon with a negative charge is very, very unstable. Because of the three, electron-withdrawing chlorine atoms attached to carbon, the negative charge is stabilized and the carbon anion can easily be released from the molecule in step 4. As a byproduct of step 4, the carboxylic acid acetic acid (vinegar) is formed.
One more step is needed to finish the mechanism for this reaction, and it is also the final step in forming chloroform. While the carbon anion is somewhat stabilized by the three, electron-withdrawing chlorine atoms, the carbon is still unhappy having a negative charge. All things considered, generally carbon would like to be neutral, not negatively charged. In step 5), the carbon anion acts as a base and deprotonates the acidic proton on acetic acid. This forms chloroform and sodium acetate.
- The Mechanism of the Classical Haloform Reaction
This is not exactly how chloroform is produced when you use bleach, but the process is very similar. There is often a small amount of sodium hydroxide in household bleach to help with the initial deprotonation, and the sodium hypochlorite is the source of chlorine. For the traditional haloform reaction, you must use chlorine gas as one of your starting reagents. Using bleach allows you to work around using the highly hazardous chlorine gas (not that the bleach process is much better). In general, the acetone and bleach react to sequentially place three chlorine atoms on the terminal carbon atom of acetone. That carbon atom then fragments from acetone as the trichlorinated carbon anion, which picks up one hydrogen atom in an acid/base step to form chloroform. I'm not sure exactly what the intermediates look like in the bleach mechanism, but they will be generally similar to the classical haloform mechanism.
