Tuesday, September 06, 2016

Curses! Environmental Stress Cracking

We've had a lot of aphids attacking plants in our garden this year. My usual approach is to use an insecticidal soap that I make by diluting down from a concentrate. "Normal" soap is the sodium salt of a fatty acid, while an insecticidal soap is just the potassium salt, which means the soap is relatively safe. It also works pretty well against the critters, and clean-up is easy. But they have gotten so out of hand that instead of making it up as needed, I made up a larger amount in a spray bottle and kept it in a cabinet.

Over the weekend, I knocked the bottle to the garage floor. No biggie; I picked it up and put it back in its place. But yesterday, I noticed that the soap had leaked out of the container. I picked up the bottle and saw this:
Environmental Stress Cracking of Polyethylene due to Soap
What an idiot I was. It was a polyethylene bottle with dilute soap in it and it had been stressed by the fall to the cement - a situation just begging for environmental stress cracking and that was what I got.

Environmental stress cracking (ESC) is where polyethylene and other plastics, when exposed to non-solvents and stress, break down unexpectedly. Soap and polyethylene. How can there by any interactions, especially at room temperature, especially when PE can withstand strong acids and bases, concentrated soaps and surfactants, bleach, hydrogen peroxide and more? And if you think you have an idea, then be prepared to explain why polypropylene doesn't experience ESC.

As you can imagine, I'll be on the lookout for a PP-based spray bottle for next year.

Previous Years

September 6, 2013 - A response to the ChemBark post (partially) about me

September 6, 2012 - Somewhere in a movie balcony...

September 6, 2011 - Polymorph Determination through Nanoindentation

September 6, 2007 - A resurgence of French?

Friday, September 02, 2016

A cool new fabric

The tale of The Emperor's New Clothes is as much about marketing hype as it is about keeping up pretenses in a social setting. The hype over "smart clothing" is just that, but a new report (open access!) from Stanford researchers about a radiative-transparent fabric appears to offer some real potential in comfortable clothing.

As humans, we feel either warm, cold or just-right depending on the heat balance that our bodies keep with the environment. Conduction, convection and radiation all play a part, with radiation dominating at over 50% according to the researchers [*]. The radiation is in the mid-IR with a peak at 9.5 μm. Unfortunately, most of the fabrics that we wear absorb rather strongly in that region, preventing that heat loss. As a result, we feel hot and need to kick down the A/C a few degrees to compensate. Polyethylene (PE) does not absorb in that region however, and so the researchers used it as the basis for a fabric that is transparent in the mid-IR.

The researchers found that a nano-porous polyethylene (normally used in the construction of lithium ion batteries) was opaque in the visible range due to the pores scattering visible light, but still transparent in the mid-IR. The PE fabric by itself was rather weak, so they ended up creating a laminate with a coarse cotton mesh to provide a stronger fabric. Tensile testing showed the laminate to be rather brittle (only about 15% elongation before break, vs. 70% for cotton), but that can be easily addressed in the future with other constructions.

Two comments: First, the use of polyethylene as an IR-transparent clothing choice is not a new idea. It was proposed (and modeled as effective) over a year ago (and earlier research may well exist too). Second, the biggest challenge I foresee is coloring the fabric. Pigments are an option for monotonic colors (no, black is not an option since it will absorb the mid-IR), but for people that want flashy prints, it could be a real challenge.

Nonetheless, it will be interesting to see what happens to this concept. PE is plenty cheap, and so a fabric based on this could be quite affordable and all that much more valuable to people in hot areas where cooling cost can be budget busters. And the use of it in athletic wear, especially for endurance events, could prove significant as well.

[*] The researchers cite articles from 1937 and 1939 (!) for this datum. (References 18 and 19). Maybe someone should look into updating it, as I wonder how valid it truly is.

Previous Years

September 2, 2010 - How To Have A Brainstorming Session

Thursday, September 01, 2016

You can't get there from here

Being on a new campus this fall means getting lost. Finding the right building is the easy part. Finding a staircase in the building is also fairly simple. But the real challenge is deciding if it is the correct staircase.

The building that I my office is in and that I teach in is over 100 years old and was concocted in bits and pieces over time. And the result that the floor plans are pretty complicated. There are floors between floors. There are floors made of unconnected sections where you need to go to a different floor to get to the other section. Worse yet, not all staircases access all floors. It's so bad they long ago gave up on numbering the floors and named them by colors instead. And of course, the colors are NOT arranged according to the rainbow. (I think the order from bottom to top is green, yellow, black, silver, blue, red, yellow and brown, but I may be mistaken.)

But all that pales compared to this:
Two sets of stairs in a double helix arrangement! We're probably all use to that with escalators, but stairs? Worse, the two sets of stairs don't stop at all the floors, so you will often see students hop the handrails when they realize that the stairs they are in won't got to the floor they want, but that the other one will.

As for me, I know how to get from my office to my classrooms and back. I'll explore more in the future when I have a lunch packed, a huge bag of bread crumbs and plenty of energy.

Previous Years

September 1, 2011 - My Version of the Triple Witching Hour

September 1, 2010 - A New Basis for Measuring the Significance of Research

Tuesday, August 30, 2016

Slide Rule Giggles

I've always loved slide rules. As soon as I learned in 8th grade about logarithms and how they formed the basis for a slide rule, I was hooked. Just like 2 rulers can be used to do addition and subtraction, so can 2 rulers, logarithmically scaled, be used for multiplication and division. That you have to keep your wits about you for locating the decimal is what separates the experts from the wannabes. 13 x 5.4 looks the same as 135,000 * 54. The significant figures were somewhat limited to 2-and-a-half or so, particularly as the value of the leading digit increased from 1 to 9. (The span between 1 and 2 takes up about 30% of the slide rule, while the distance between 8 and 9 is just 5%.)
Even with this, they were (and still can be) powerful calculation devices. Keep in mind that the atomic bomb was developed using just slide rules and that Apollo astronauts had slide rules in their capsule during their flights to the moon. No worries about power outages or dead batteries, they were consistent and reliable.

My wife and I both have slide rules that were passed on to us (mine from my grandfather, hers from her father) and they will never be tossed in the trash until you pry them from our cold, dead hands. They are not super fancy or collector's grade, but they are a way to still be in touch with these people, knowing that their fingers handled (and their brains engaged) the same instruments in the same way.

A recent alumni newsletter from Minnesota had a article on slide rules and it included anecdotes from various engineers who used them to get through engineering classes and even the early years of their jobs until electronic calculators came along. My favorite was this from a Hungarian emigrant:
"During his time in graduate school, [Erwin] Kelen served as a teaching assistant and decided he would have a little slide rule fun with his class.

'I was at the blackboard in front of my class, solving a problem, and I was reading the results off my slide rule. Four decimals first, then squinting, two more' he said. 'Imagine, six digit accuracy from a pocket slide rule!'

After class, all the students crowded around him, wanting to know how he could read this from a tool that basically had two decimal capability. At first, he was coy in telling them that it was a special secret that enabled him to calculate with such accuracy. Surprised, they insisted he tell them his secret.

'I 'fessed up that the last four decimals of the six were purely invention on my part and we all had a good laugh' Kelen said"
The fun of this is that the students themselves would have been limited to calculating just 2 or maybe 3 significant digits, and would have no way to prove that the last 3 (or 4) digits were wrong. I imagine having a Hungarian accent helped to give a further illusion of authority.

Here's the rest of the comments.

Previous Years

August 30, 2013 - The Week that Snowballed Away from Me

August 30, 2012 - Viscoelasticity: It's Not Just for Polymers Anymore

Wednesday, August 24, 2016

Theology, Rheology and some freaky strange search results

Dan Lowry (@DrFriction) tweeted last night "Whenever life seems devoid of meaning or humor, just do a web search on 'theological properties'" (referring to the fact that spellcheckers typically attempt to change "rheological" into "theological"). So I did just that.

Wow. Wow. Wow. Look at this screenshot:
The spellcheckers are winning far more often than I would have ever imagined.

But a little bit of digging suggests that there may be a far more sinister plot, one of revisionist history. I clicked on the first link and found this:
while at the bottom of the page there was this:
So what gives? Was the title later fixed? (That doesn't seem possible as it looks like an image capture, but I'm no expert in these areas.)

But weirder yet is what I found at the fourth hit:
Clearly an image of an original document, with a correct title. But that is not the weird part. It's when I searched the rest of the document for "theol" with the crtl-F key. Every single return (31 total) pointed to a word correctly spelled as rheol...For instance:

What is going on? I know and expect that Google would return a search for most people "rheology" (no quotes) as "theology", but for a word finder in a .pdf document to do that?

Again, I am swimming in the deep end. Any insight that someone could offer would be most helpful as there things here that are disturbing. I know my google search results are not neutral and haven't been for years, but for the text search in a pdf to be like that is not good.

Previous Years

August 24, 2011 - Review: "Social Marketing to the Business Customer"

August 24, 2010 - The Deborah and Weissenberg Numbers

August 24, 2009 - BASF as a hostile takeover target?

Tuesday, August 23, 2016


The number of elements that are capable of forming a polymer just by themselves and without the assistance of other elements is very small. A large part of this is due to most of the periodic table being made of metals, elements that not capable of forming polymers (at least as far as we currently understand). Throw out the noble gases and you only have a very tiny wedge of the table for consideration, consisting of the metalloids, the nonmetals and the halogens - a total of 16 out of the 92 naturally occurring elements.

Boron, carbon, silicon and germanium are all known to form covalent network solids, which I would consider to be polymers (although others certainly would be entitled to disagree). Sulfur can polymerize under high pressure, but that is it. 5 elements.

Now a new report (Open Access) has found that iodine can polymerize. Not as polyiodine, but as polyiodide (the anion). Oligomeric forms of iodide are already known. I mentioned I3- (triiodide) many times in my general chemistry class last year (it's a good one for drawing a Lewis structure) and higher iodides such as I5- and I7- are known to exist, but now comes proof of In-.

The unusual aspect of the polymer is that it doesn't exist by itself, but instead is supported by a pyrroloperylene crystal structure, with the entire iodide-pyrroloperylene complex being crystalline as well. That crystallinity is what made it possible to clearly identify the polymeric nature of the iodide. (Ferreting out the structure of an amorphous polymer is a whole new level of hurt.)

While the iodide-pyrroloperylene complex is of interest to the researchers because of its electrical conductivity, they also realize that polyiodide may finally crack a chemical mystery that is nearly 200 years old: the nature of iodine in the blue solution that form when iodine is added to starch (an elementary school favorite). Polyiodide has been suggested as a possible form, but without any proof (the iodine-starch complex is amorphous...), it was just a suggestion. This new research doesn't prove that the of iodine in a starch complex is polyiodide, but it does provide support for what could only be previously considered as just a hypothesis.

And it gives us a 6th polymeric element.

Previous Years

August 23, 2013 - Analysis of Silly Putty Swallowing a Magnet

August 23, 2011 - Plastics are Forever Jewelry

August 23, 2011 - How the Indian Supreme Court Indirectly Impacted PET Film Makers