Tuesday, December 31, 2013

The "Rheology" of Fire Ants

The New York Times had a fun video a couple of weeks ago showing that groups of fire ants can show viscoelastic behavior. By clinging to each other, they show solid-like behavior, but by releasing that grip, they can flow like a liquid. While viscoelastic behavior is much more common than most people realize, this is the first time it has been observed in groups of living things. (Note that the article states that it is a first for "living things" which is clearly incorrect. As far as I know, all living things show viscoelastic behavior within at least some parts of themselves, whether it is the viscoelastic behavior of cells, mucosal fluids, blood, etc.) Being that ants are macroscopic beings, their flow would show characteristics of a granular flow rather than fluid flow, a subtle but sometimes important difference.

What is left undiscussed in the video is how the ants are able to communicate what behavior is desired at any given moment. Each ant can't be deciding on its own whether to grip or release; there has to be a rapid, universal signaling mechanism or else it would be chaos. I find this, along with the similar phenomena of flocking behavior and quorum sensing to be some of the most fascinating aspects of biology.

Monday, December 30, 2013

A Chemical Mystery - Can You Solve It?

My wife and I were able to use our chemical knowledge this past week to solve a perplexing problem. I'll post first what we observed and then let you try and figure it out.

We have a gas cooktop in our house here in Minnesota. A couple of weeks ago, the flames on it started burning more orange-like so we called in a repair guy. Non-blue flames are indicative of a rich fuel/oxygen mixture, one that can potentially put out CO, although it is less of a danger for cooktops than furnaces as the former are used for shorter periods of time often with the vent fan running too. But in any case, the regulator was failing and instead of feeding 3-4 inches water column of gas, it was feeding 6-8. A new regulator was installed and the pressure of the gas was reduced to the normal levels, but the orange flames persisted.

We tried adjusting the Venturi openings that let the air into the burners, but that didn't do anything. Besides, it would be freaky odd for all four burners to suddenly have their Venturi openings block at the same time. And then my wife (a Ph. D. in chemistry) found the solution, one which we have been able to positively confirm: by making an adjustment elsewhere in the house, we can on demand change the flames from blue to orange and back again. Neat, huh? And we also know now not to worry about the color of the flame.

Here's some other information that may or may not be helpful to finding the solution. The house is in Minnesota and is sealed up tight for the winter (it was -16 oF this morning!). Since the air is so dry, we run ultrasonic humidifiers in a couple of rooms in the house. About the same time as the problem occurred, we brought a real Christmas tree into the house. We have a dog (a Welsh Terrier), and had house guests staying on and off over the past few weeks. To make meals easier on the cook, we have been using a crockpot (electric slow cooker) a lot the last few weeks. We have hard water and soften it. Speaking of water, we have a gas water heater. Speaking of gas, we have a gas furnace and we also have a gas fireplace on both levels of the house.

With your knowledge of undergraduate chemistry, you now have enough information to solve the "Mystery of the Orange Flame". I will also tell you that the answer has nothing to do with polymers science so to make up for that, I've included a picture of a cute kitten playing with a random polymer coil. (If we had cats at our house (we never will), they would play with random polymer coils and not balls of yarn.)
Why are the flames on the cooktop burner orange and not blue? Start with the water softener. It replaces the calcium and magnesium in the hard water with sodium. That water then goes into the ultrasonic humidifiers. (Distilled water would be a better option, but since these things go through gallons of water a day, it isn't too practical of an option to be trucking in that much distilled.) The humidifier then tosses the sodium into the air where it spreads through the house. Some of it ends up in the feed air to the burner where it burns it's characteristic yellow. Combine that small amount of yellow with a rich blue flame and you get an orange flame.

To further convince ourselves of this, we shut of the humidifiers and after 4 hours, the flames went blue. Turned on the humidifiers and the flames went back to orange. Mystery solved. We were running a good old-fashioned flame test.

My wife then found a video that shows these changes in a most dramatic fashion:
Ignore the audio in the video, as it gives a wrong rationale for the color change. Just look at the pictures. Just that tiny bit of sodium is enough to significantly color the flames.

Friday, December 20, 2013

The Rheology of Santa Claus

Many scientific investigations have been performed regarding Santa Claus [1], but never before has a rheological analysis of St. Nick been undertaken. Let me change that.

The need for Santa to exhibit non-Newtonian rheology is obvious on several fronts. All chimneys by design have a narrower opening at the top than at the bottom and in cases of interest, the opening at the top of the chimney is smaller than Father Frost himself. In order to transverse such geometric disparities, it is necessary that Santa's body be of a soft, gel-like material (more on this below), that can be greatly deformed without mechanical failure. While it may be further desired that full elastic recovery is achieved, it appears that this is in fact beyond the capabilities of Kris Kringle. For support of this conclusion, examine the three representative illustrations below of Pere Noel. They are similar, indicating a goodly amount of elastic recovery has been obtained, but the differences clearly indicate that full recovery was not recovered and furthermore that viscous flow has occurred.
In short, the appearance of Father Christmas will very greatly depending on whose chimney he has recently passed through (subject to an appropriate memory function integral with more recent chimneys having stronger influence over his current appearance than chimneys from the past). Further evidence comes from the "mouths of babes" who for decades have noticed that the Santas appearing in stores, parades and elsewhere all look slightly different. Parents at a loss of words for explaining these differences now have a scientifically supported explanation to quiet the constant questions coming without end.

Rheological understanding is also needed to clarify the events occurring while Babbo Natale is flowing through the chimney. Going up and down the chimney leads to conditions of both shear and, depending on the flow direction, either extensional or expansive flow. It is desired that the Jolly Old Elf be able to flow freely in order to rapidly accomplish his worldwide sojourn. As a rheopectic St. Nick would be highly undesirable in achieving this (his rate of flow would decrease the faster that he tried to move), we can conclude that Sinter Klaas's viscosity decreases both in shear and extension, strongly indicative of pseudoplasticity. (The discussion here has focused on steady-state dynamics; flow under transient conditions (start-up and cessation of flow) are left as an exercise for the interested student.)

In summary, I have unequivocally demonstrated that Santa Claus 1) is made of a non-Newtonian gel that shows both viscous and elastic behavior, and 2) exhibits pseudoplastic flow characteristics.

Before concluding, the author is compelled to state his shock that the rheology of Santa Claus has never been discussed to any serious extent, let alone this thoroughly. The link between Santa and rheology was first noticed 190 years ago, back in 1823(!) when the eminent American rheologist Clement Moore [2] published his famous poem, "A Visit from Saint Nicholas", perhaps better know as "Twas The Night Before Christmas". In that, he described Saint Nicholas as having "...a little round belly, That shook when he laugh'd, like a bowl full of jelly". Jelly! Probably the oldest known gel of all and a classic material with intriguing rheological characteristics. How many times has that line been read and heard and spoken, and yet never once has the connection been made to the larger aspects of Santa's rheological nature!? For shame. There are many professional rheologists this year that are going to be receiving a lump of coal in their stockings and it won't be high grade anthracite, but a well-deserved stinky, sulfur-laden lump of lignite instead.

[1] These certainly could be called pseudo-scientific or tongue-in-cheek-scientific as well, such as this perspective from North Carolina State. Or what you are reading here today.

[2] Ok, so he was just some guy that noticed a little rheological behavior and now he's going to cash in big on it. It's no different than what happened with Deborah Deborah or Heraclitus.

Wednesday, December 18, 2013

Nitrile Gloves Are Not The Universal Glove!

Looks like it's time to review the choices for rubber gloves in the lab again. Just a few minutes ago on twitter, there was this conversation:
This is endlessly maddening to me:"...nitrile. So they are good except in contact with strong oxidizers (nitric acid!)..."

Not that is absolutely incorrect. As I've written in the past, "Any given rubber glove will be attacked by some solvents and not others. Is that so surprising?".

That same post has links to glove manufacturer's sites where they have recommendations for what you can and cannot expose their gloves to. The Ansell site for instance, recommends against using nitrile gloves for exposure to
  • acetaldehyde
  • acetone
  • analine
  • benzaldehyde
  • benzene
  • γ-butyrolactone
  • chlorobenzene
  • chloroform
  • chloronapthlanene
  • chlorotoluene
  • ethylene dichloride
  • dimethylacetamide
  • dimethylformamide
  • 1,4-dioxane
  • epichlorohydrin
  • ethyl acetate
  • furfural
  • methyl bromide
  • methyl chloride
  • methylene bis(4-phenylisocyanate)
  • methyl ethyl ketone
  • methyl iodide
  • methyl methacrylate
  • N-methyl-2-pyrrolidone
  • morpholoine
  • nitorbenzene
  • nitropropane (both isomers
  • phenol
  • propylene oxide
  • pyridine
  • silicon etch
  • Skydrol 500B-4
  • styrene
  • sulfuric acid
  • sulfur dichloride
  • trichloroethylene
  • Vetrel SMT
  • and as noted in the Tweet, nitric acid.
That list is quite a bit longer than just the nitric acid that was noted.

Please, please, please, don't just assume that nitrile gloves are the glove of choice. These charts have been put together for a reason - to protect you, but they are useless if not referred to. The links are freely available, so find whatever charts you need, print them out and refer to them often.

Nitrile gloves are not the universal glove. To pass on as reliable information that they are safe is to risk the health of anyone reading or hearing that. We can do better than that.

Monday, December 16, 2013

What does EPDM stand for?

While the abbreviations used to describe the make-up of polymers and rubbers is reasonably straightforward (PVA being probably the worst offender - is that polyvinyl acetate or polyvinyl alcohol?), the rubber EPDM is another nasty one. The first three letters are reasonable: "E" for ethylene, "P" for propylene and "D" for diene, which in theory could be any diene, but in practice is usually one of a few options. The "M" is the mystery however. People either have no idea or they think that it stands for "monomer". Huh?

The truth is well removed from that as it actually isn't part of an abbreviation at all. It is drawn from an ASTM standard, which is quite appropriate as the name ASTM isn't an abbreviation for anything either. (It used to stand for American Society for Testing and Materials, but it doesn't anymore). The standard D1418 is used to classify rubbers and the M-class is for rubbers that have saturated backbones. Why M? Heaven only knows. Other letters used to classify rubbers are N, for nitrogen-containing backbones and O for oxygen-containing backbones. So far so good. But then there is R for unsaturated backbones, Q for silicon- and oxygen-containing backbones (siloxane polymers have their own naming scheme, in which Q fits in quite nicely, but that is another story for another day), T for sulfur-containing backbones, U for carbon-, oxygen- and nitrogen-containing backbones and finally Z for phosphorus and nitrogen-containing backbones.

Given all of that, M isn't that bad of a choice, but since the letter S is available (since sulfur was bumped to T), why not go with S?

This all came about from a recent discussion with a friend over Superballs, the big black ones made by Wham-O. I had always thought that they were made from EPDM (with a pinch or two of carbon black), but it turns out that they are actually made from butadiene. You learn something new everyday.

Thursday, December 12, 2013

Some Goofy Thoughts on Plastic Bags Being Seized

While plastic bag bans have been proliferating of late, I only read yesterday of action being taken against a shop: "The team seized around 45 kgs of polythene bags below 40 micron thickness...". The story did get my mind wandering. For instance,
  • Do the police have calipers (calibrated ones, at that) to measure the film thickness? I've worked with films for most of my 20+ career and with my fingers can easily tell the difference between a 25 micron (1 mil) and a 50 micron (2 mil) film, and maybe on a good day, even a 37.5 micron film (1.5 mil), but my fingers are not capable of higher resolution. So do the police now have to carry around calipers on their gun belt?
  • The seized bags are now evidence, and we all have seen enough cop shows to know what happens to evidence: it is put inside a PLASTIC BAG. Hopefully the evidence bags are greater than 40 microns thick or there could be some high drama in the courtroom.
  • I wonder if all the evidence will make it back to the police station, or are cops going to start having a reputation for being the people with the best plastic bags?
  • After the bag is brought back to the crime lab, I wonder how the analysis goes. Is it like CSI? (For those of you unfamiliar with the US TV show, imagine any old analytical lab but with good-looking geeks and dramatic lighting). "Hey I got something. I ran a tensile test according to ASTM D638 and got some really strong peaks, so I dissolved the bag in hot xylene and ran a high-temp GPC and sure enough, there is a lot of metallocene-catalyzed polymer in this material. This is not some local product; this is an import and it is loaded. I mean this stuff is so strong, it could get an elephant high...err, that didn't come out right. I mean, these bags are so strong that they could lift an elephant up high...I wish I could've done more analysis, but I've only had the samples for 5 minutes. Anyway, we gotta do something before more of this stuff hits the streets."
  • I wonder how far the bag limits extend. Say for instance a drug dealer is caught and the weed is in thin-film bags. Do dealers get extra time in jail for that?
Just some thoughts. While this particular story happened in Indore, a city in central India, I would have the same thought regardless of where the seizures occurred.

Wednesday, December 11, 2013

Greenwashing Blue Jeans into Plastic

It's funny how much greenwashing can occur from good intentions and how it worsens with time. Take for instance, this attempt (a Kickstarter effort) to make plastic using recycled blue jean fibers as a reinforcing agent.
The resulting material is named Denimite (catchy enough) and has that classic indigo blue color. The composite is made by mixing an epoxy in with the fibers and then heating and compressing the material in a mold until the epoxy has reacted. The low viscosity resins undoubtedly soak into the cotton fibers before they react, thereby ensuring a good strong interface between the resin and the fibers, an essential feature to make the fibers/matrix a composite and not just a filled system.

The environmental angle is that the jeans are otherwise destined for the landfill and the epoxy is somewhat sustainably produced [1]. The Kickstarter is looking for $10,000 for a larger press (a 30" x 120" - that's 10 feet long!). In my mind, that is only a small part of what they need. Molds would be a bigger concern as they cost far more and each one needs to be custom made. Customers typically pay for them (so that they can take them and run off to a cheaper competitor when they find one!), but finding customers is a chicken-and-egg thing. Compression molding is not a fast process and that hurts the economics further. Also, the entrepreneurs are looking to get into countertops, an area that seems to have few demands but is deceptively challenging. [2] I wish them luck in their venture; they are going to need it.

Once the media got wind of this kickstarter, the greenwashing took off. The Kickstarter was originally entitled: "Denimite: Where good jeans go when they die". That's fine and dandy. But then Gizmag.com picked it up and it became "Denimite repurposes blue jeans into a "green" material". At least there are quotation marks around the word "green". But then cleantechnia.com called it "Recycled Jeans Become Green Plastics in New Process" and we're off to the races. The denim has never become plastic - it is merely encased in another plastic that is only somewhat green (and compression molding is hardly a new process). This greenwashing was then repeated verbatim in the echochamber by beforeitsnews.com.

And that's how things get hyped. A simple project with good intentions and a green-ish story of compression molding a denim/epoxy material becomes a transformation of blue jeans, via a new process, into a green plastic.

[1] It would be ironic if the epoxy was based on bisphenol A, and many of them are. But further, why use an epoxy? A totally bio-based (meth)acrylate would be greener option, would possibly cure faster and show many/all of the same mechanical properties.

[2] In my last job, I worked on a project for a client who made countertops that were loaded with minerals. They had a number of issues that were a failure of the resin that I would not have expected. It was an eye opening experience.

Tuesday, December 10, 2013

Describing Polymers with Everyday Items

I used to have 2 simple models (or maybe 3, you decide) that used everyday items to explain what polymers are like to people with formal education in the subject. I picked up a third one yesterday that I really liked. Let me list them all:
  1. /2. The most common image that people use to describe a polymer is a spaghetti noodle, which is fine for starters, but it falls short fairly quickly, even if you expand the length of the noodle to 20 feet or so. A bowl of spaghetti is somewhat better in that the noodles are coiled up somewhat with short segments going here and there randomly (until twirled by the diner's fork). But the analogy fails when it comes to describing entanglements and getting a chain to move past its neighbors since the noodles (when properly cooked and oiled) slip past each other pretty easily. Much like playing pick-up-sticks, you can pull slowly on the end of one noodle and remove it from the bowl without disturbing any other noodle and that is not realistic of polymer dynamics. Polymers are either all moving (molten state) or not (glassy state) [*].
  2. Moving polymers have a fading memory of what they shape there were previously in. The cooperation of their neighbors that I just noted often comes too slowly which leaves this lasting (but fading) impact on the molecule. Dragging a garden hose around is a (poor) example of polymer memory. If I'm watering the flower beds on the east side of the house and want to move the hose to the south side, it's not just a matter of dragging the spray nozzle around to where I want it - the entire hose has to go with it and it remembers where it was previously lying. I may have a free path to the new location for the nozzle but the remainder of the hose may have to cross trees, lawn chairs, toys... and so sometimes you have to do a lot of maneuvering to remove the memory that the hose has. Like polymers, garden hoses have a fading memory of where they previously were. Move them enough and they have no recall at all, although they keep picking up new memories along the way.
  3. The new idea is one of those so obvious ideas that makes you wonder why you didn't think of it earlier, particularly since it fits in so well with the current holiday season: A big hat tip to the redditor thewizardofosmium for this idea: "Does anyone else look at XMas lights and think of polymer chains with a high friction factor due to rigid side chains?" As I noted earlier, it is possible to pull a single spaghetti noodle free from a pile, but try pulling a strand of Christmas lights out of a jumbled pile. It would be easiest (relatively speaking of course) if the lights were little miniatures or LED bulbs. Doing it with C9 bulbs would give you dreams of something quite distinct from "visions of sugar-plums", and icicle lights would be a pleasure that only the Grinch could deliver.
    The larger/bulkier the side chain, the higher the glass transition temperature will be since mobility is already restricted and it is easy to freeze the molecules in their current position with no hope of any further movement relative to each other.
Our lights are already up for this year, but I'm sure to be thinking of this imagery when I take them down. And put them up next year. And take them down...

[*] Let's make life simple and ignore semi-crystalline polymers for now, shall we?

Monday, December 09, 2013

Real vs. Plastic Christmas Trees

It's that time of year to repeat the great debate over real and artificial Christmas trees. Each side has it advocates (real trees vs. plastic) and as it truly is with most environmental matters, it is difficult to get to the truth. A report from a few year back that did a life cycle analysis (LCA) concluded that real trees are better option, but I'm not so sure that the LCA was done well.

For starters, the LCA was generous about how little work is actually done on a Christmas tree farm. (One of my best friend's growing up would help his dad on their Christmas tree farm so I got the skinny from him.) Trees need to be sheared annually in order to achieve that Christmas tree shape and also to have proper branching to allow for hanging of the ornaments. This means multiple trips into the farm field each year. But the dirty little secret is that trees are often painted. Both of these steps reduce the "greeness" of real trees.

The most significant finding of the LCA however, is transportation plays the largest role in the comparison:
"...it is now clear from this LCA study that, regardless of the chosen type of tree, the impacts on the environment are negligible compared to other activities, such as car use."
But the kicker is that on page 7, the report assumes that people only travel 5 km to get their tree. This is a very short distance for anyone and a very dubious assumption.

I'm not trying to suggest that artificial trees are a greener option, but only that the issues involved in this (or any other) LCA can be quite complicated. Creating a proper LCA is very challenging. The best ones lay open the assumptions and calculation methods so that other scenarios can be examined and also so that the sensitivity of the various factors can be studied.

So is the Spevacek household a Palace of Plastic with Architectural Artifacts of Artificial trees paying homage to hydrocarbons holed from the Holocene [*] are as you might expect? In fact no, it is not. My wife and I have it both ways. The main tree is real and has always been real. (My parents had an artificial tree when I was growing up and I couldn't stand the thing. I will never get an artificial tree.) We bought a Siberian fir this year - What an incredible aroma! - What an incredible layer of sap on your hands! We also have a few small artificial trees scattered around the house that we have "inherited" over the years. (And by the way, the artificial trees are far older than 6 years, the assumed lifespan in the LCA. We have no plans to retire them anytime soon either.)

So make your own decision and go with what makes you feel happy. Christmas trees choices do not have a major impact on the environment either way, not compared to other choices that we live with for more than just 3 -5 weeks a year.

[*] I know that petroleum is removed from rocks older than the Holocene - I just needed something geologic for the alliteration.

Tuesday, December 03, 2013

Dow Chemical to Drop the Chemical, in both Word and Deed

The Urethane Blog is reporting that Dow Chemical is thinking about dropping the "chemical" from it's name. Much as very few people refer to E. I. du Pont de Nemours and Company by it's full name and instead go with "Dupont", very few people also refer to the company as "Dow Chemical". I don't remember the last time that the company's logo even had "chemical" in it. However, it is a handy name to have for Google searches, since if you search just "Dow", you get a mix of sites about the company and also the Dow Jones Industrial Average, which not surprisingly, is also seldom referred to by its full name but simply as "the Dow".

While we can all ask "what's in a name" [*], the bigger picture is that Dow is moving out of the commodity chemical business and has identified a$5 billion slice of their chlorine business that can be carved out of the company. It's not clear if a ready buyer for this exists, if one has to be found or it the business will be spun off on its own.

While it is not surprising that after a merger/acquisition, there are layoffs as a result of duplication of employees, it has also been my experience that spin-offs seem to also result in layoffs. In some cases it is because the CEO of the spin-off company looks at the books differently than the CEO of the spinning-off company, and in other cases it is because the spinning-off company stuck with spin off with excess employees that it want to cut anyway, but didn't want the blood on their hands. But with over 2000 employees being identified as part of this $5 billion carve-out, we can be sure that sadly some people will be cut sooner or later.

[*] To misquote the Bard, "What's in a name? That which we call a chemical plant By any other name would smell as malodorous".