Twisted Threads: The history of the LCD

Learning to tell time when I grew up was a challenge. Clocks were analog - not digital. Everywhere. I can still see the little stiff pink paper clocks we were issued in first grade, with a brass brad fastening the hands to the face. We practiced setting the hands and reading off the time. Thanks to LCDs (liquid crystal displays) my sons had a quantiative sense of time much earlier, digital clocks blinked at them in every corner of their lives.

It took quite a bit to turn the initial discovery into a technology so smoothly integrated into modern life that we rarely notice it's there (how many LCD screens are in the room where you are now? Don't forget the ones in your pockets...). You can read more about the history of the LCD in this blog post by Ben Gross, a fellow at the CHF where I'm currently a short term fellow.

One of the pivotal developments was the leveraging of the twisted nematic effect...which made me wonder what worms (nematodes) and my iPad might have in common. The Greek root of threads....

Cold as Ice

This article in the Atlantic monthly caught my eye, if only because it included an experiment and less because of my refined palate. Wayne Curtis is writing about the unsung hero or villian of mixed drinks: ice.

"I went into the kitchen with another bartender, Stephen Cole, who hunted up a scale and thermometer. He placed the two kinds of ice into separate cups filled with water. We let them sit for 10 minutes. The cheater-ice water proved to be colder (34 degrees compared with 40 degrees), but the ice had lost a full quarter of its weight, compared with just a 14 percent loss in the chunk ice. A cheater-ice cocktail is thus chillier (numbing the taste buds) and more watery (making it flat)."

He describes a bar which stocks eight different types of ice - though the classification system is not quite what a physical chemist might use - or even Kurt Vonnegut. I suspect, however, a serious flaw in the experiment, and therefore in the conclusions drawn about the effect of ice type on a drink.

Take a mixture of ice and water that has been thermally isolated (put in a thermos!) and allow it to come to thermal equilibrium (let it sit until the temperature doesn't change any longer). When the contents of the thermos reach equilibrium, if there are both ice and water present, the temperature is 32 degrees (Fahrenheit). It does not matter how cold the ice was to start, how much water is present, how warm or cold the water was - it will be 32 degrees. Not 40. Not 34.

Also known to those who know how to read a phase diagram, ice at normal pressures will not start to melt until it reaches 32 degrees, and its temperature will not rise above 32 degrees until it has all melted. Curtis' experiment isn't quite as sophisticated as the thermos one I've sketched out, but assuming that the rate of heat loss to the room was small (air - or any gas - isn't a very good thermal conductor, so over the short term this is not a bad assumption), and that the ice and water used were pure, and that a very large amount of water was used relative to the ice - I find it untenable that the "cheater-ice" cocktail is different in temperature than the one made with less porous ice. More watery, yes, colder, no.

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Photography by Sue Stafford. Used under Creative Commons license.

Weird Words of Science: Hypsometer

Every time I write an exam, I think about this story, where a physics professor asks on an exam how to measure the height of a building using a barometer. A student answered that he would tie a string to the barometer, lower it down, then measure the length of the string. Given no credit, he protests, and the professor offers him a second chance to provide an answer that is both correct and demonstrates some knowledge of physics taught in the course. The student goes on to give several answers (in some versions the student is averred to be Niels Bohr - though the origin of the story is apparently in a textbook on the teaching of math and science by Alexander Calandra, and unrelated to Bohr) all demonstrating a knowledge of physics, and none the one he seems to know the professor is fishing for (which has to do with the - probably unmeasurably small - pressure differential between the ground and the top of the building).

Here is a chemistry exam question I sometimes ask - how would you measure the height of a mountain with a thermometer? This is a well-known technique,not a trick question, the apparatus is called a hypsometer, from the Greek for "height-measure". The underlying science is that the boiling point of a liquid changes in a known way with altitude. Hypsometers were used before portable aneroid barometers became widely available, and were used in high altitude balloon measurements of pressure as late as the 1960s.

Bonus question: Is it easier to drink a liquid using a straw at the top of Mt. Everest or on the beach in Florida? (Disregard temperature differences and explain your answer for full credit!)

It's Just a Phase

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Allotropes are all the rage? Or at least sending Conan O'Brien over a very funny edge! The bit was inspired by this article in the NY Times science section. I'm not nearly this riveting when I lecture about allotropes, I've got to admit.

O'Brien gets the chemistry nearly right. My only quibble would be that he calls the different forms (the diagrams are the real thing, by the way) different phases, which they aren't really. They are technically allotropes, different structural forms within the same phase or state of matter. The quintessential example is the allotropes of solid carbon, graphite and diamond and a few others. All that said, when you draw a phase diagram for an element, you show the allotropes on it, and many chemists would characterize the change from one allotrope to another as a phase change.

Oxygen has some fascinating solid allotropes, including one that is a blue solid at room temperature!

Grapes of Wrath

My youngest came home from a father-son event with a new interest in healthy foods. I put grapes on the table with dinner. "There are grapes for dinner," he exclaimed. Who are you and what have you done with son? ran through my mind.

At the end of dinner he puts two grapes on his plate and carefully cuts them nearly in half. Then he ducks into the kitchen. "Come on, Mom!" Warm grapes? He'd eaten all the chicken, there was nothing left on his plate to veronique.

He hits the start button and suddenly the grapes start arcing, and one actually bursts momentarily into flame. I'm stunned. No metal, but the arcing is clear. We try various experiments - do you have to leave the grapes connected (no), does it work with other things (carrots), can you char a grape (yes).

What's going on? Hang on, we were producing plasmas in the kitchen. Not the kind that circulates in your veins, but the kind that stars are made out of. Plasma is often called the 4th phase of matter - the iconic triad being solid, liquid and gas. (There are many other phases in which substances can exist, in fact - such as liquid crystals and supercritical fluids.)

Plasmas are gases in which a large number of electron are "free", rather than associated with a molecule or atom.

I'm still trying to come to grips with the idea that I can create a (very tiny) ball of plasma in my kitchen.

(Read more in the paper : "Microwave Mischief and Madness" by H. Hosack, N. Marler, D. MacIsaac of Northern Arizona University, The Physics Teacher 40, 14 (2002).