The Mysteries of Ice Skating

That the physics of ice skating are still is not fully understood is not surprising. Making measurements on a small area that has dynamic pressure conditions wedged between the ice and the steel blade is extremely challenging. We know that ice is inherently not slippery, and that only because of the pressure of the blades somehow "melting" the ice or otherwise creating a liquid-like surface that skating happens at all. Long ago as an undergrad, I was taught that the pressure of the blade alone is enough to alter the melting point of the ice. This change can be calculated via the Clausius-Clapyeron equation but a quick back-of-the-envelope estimation shows that an enormous amount of pressure is needed. This was handwaved away by the instructor stating that skates are hollow ground (i.e., they are concave down as you look to the length of them) to increase the pressure.

Imagine my shock a few years later when I took up speedskating and found out those blades are flat ground. That right, the skates that are the fastest are the ones with the largest contact area. So much for Misters Clausius and Clapyeron (and my instructor).

New research offers a potential new explanation of ice skating. It's currently pay-per-view so I haven't read it (it will likely become downloadable in the near future as are most of the PI's papers, but I wonder if the article will really get at the dilemma that I mentioned above: the role of contact area.

Hollow ground skates are used for sports where turning tight corners is necessary, so have a "biting" edge is essential. In speedskating, having a friction free glide is essential to maintaining speed. But are there points where either approach becomes too extreme? Can skates with an extremely small contact area (an atomically thin edge?) have any value or would the performance degrade? And for speedskates, would a larger surface area aid or hinder performance? Is there a limit on either end?

I've puzzled on these questions over the years, but the greatest mystery to me is this: is there any value in creating a hybrid skate? One that is hollow ground on one or more portions and flat ground elsewhere. Maybe hollow on the front and back for turning on the toes or heels, but flat ground in the middle for maintaining speed. Even without understanding the physics of ice skating, I would love to see someone try such hybrids as I think it could provide in some very unusual results.

Previous Years

January 12, 1015 - Kinetics, Thermodynamics and Polymer Phase Transitions

January 13, 2014 - Still Proposing Changes to the Resin Identification Codes

January 13, 2010 - Race Horses and Rheology

January 13, 2009 - Walking Polymers

The IUPAC ranges for atomic masses are NOT useful

While there is considerable excitement about the 7th period of the Periodic Table being completed, I've been thinking about more mundane matters about the table.

I was recently reminded that for many of the elements on the periodic table, IUPAC has assigned ranges and not specific values to the atomic masses. I wrote about this 5 years ago and haven't done anything with it since, so I took some time over break to look into the matter further. Being an organic polymer guy, I started with carbon, since on an atomic mass fraction that element makes up the largest component of most commercial polymers. The range for this element is between 12.0096 and 12.0116 amu, which is pretty tight, about 0.017% if my math is correct. This is beyond the accuracy with which we can measure molecular weights of polymers, so even worrying about the impact on the molecular weight of ultrahigh molecular weight polyethylene (UHMWPE) is not a concern.

But I was also struck by the plot at the bottom of the IUPAC page, which is reproduced here:

This plot shows how range of atomic masses for carbons strongly depends on the source. The largest range is in marine sediments, while other sources of carbon, such as crude oil, have significantly smaller ranges. But ironically, rather than providing justification for a range, this plot completely undermines the efforts.

I completely understand the importance for knowing these variations for fields where extremely high accuracy is needed, and I would imagine that any researcher needing to know these variations would be made aware of them very early on in their research efforts. But very few if any researchers are going to be working with carbon sources that cover this vast range. Most organic chemists are going to be working with carbon supplied from crude oil and nowhere else.

So this then begs the question of whether the ranges supplied by IUPAC are of any value. If you are like most chemists, 12.011 amu, the previous standard atomic mass for carbon is likely to be adequate enough. But if it isn't, then the new range of 12.0096 - 12.0116 amu is unlikely to be of any value either. Yes, the range is large enough to cover all the various carbon sources, but is it really necessary to have a range when a single value is sufficient for most work? And for researchers that need to understand to consider a range within their samples, any of the individual ranges in the figure above would be more helpful than to use the entire range of values supplied by IUPAC which is all inclusive.

A good chemist is going to use the range of atomic masses that makes the most sense for them. The IUPAC range is not clarifying the matter, only muddying the waters.

Previous Years

January 6, 2015 - Weeding-out Engineering Students

January 6, 2014 - How Cold Is It???

January 6, 2012 - Free Access to Articles in the Polymer Literature

January 6, 2010 - Polycarbonate (and BPA and Phosgene)

Another overhyped polymer to start the New Year

It's been a year-and-one-half since the science press last went gaga about a new wonder polymer from IBM researchers that does everything, including making us all better looking, more intelligent and with naturally wavy hair. So we are overdue for a new such polymer.

Esteemed fellow blogger Chemjobber first made me aware of this wonder polymer back in December. I hoped that the hype would have quickly died down, but was disappointed to find that it is alive and kicking a month later.

The research report was published in Nature Chemistry (subscription required), and describes the ring-opening polymerization of ?-butyrolactone (GBL) to form a type of polyester, as well as the depolymerization of the polymer, accomplished via heating.

That the researchers were complicit in hyping this research is what I find most upsetting.

"Textbooks and scientific literature had described these small molecules as too happy and thermally stable in their monomeric chemical states to polymerize. 'Don�t even bother with this monomer,' Chen summarized the conventional wisdom. 'You cannot make a polymer out of it because the measured reaction thermodynamics told you so.'"

Wow. A textbook is wrong? How can that be? (Maybe someone should read yesterday's post about textbook mistakes.) What is more disingenuous about this is that the authors are well aware of previously reports on the polymerization of GBL, since they cited many of these reports and even the review article on the topic. So is this polymerization really that novel?

But the hype continues as the authors give us the illustration on the right. Not only can they polymerize the GBL, but with heat, they can depolymerize it too. It's a neat trick, but hardly novel. It's so well established a concept that there is a term for it: ceiling temperature, and it even has its own Wikipedia page. That's right, there are LOTS of polymers that depolymerize upon heating to reform their monomers. So why call this "hot breaking" as if it is something new? (Worse yet, why call the polymerization route "cold fusion"? Who wants to be associated with that?)

That the hype over new wonder polymers is created by people drinking the same Koolaid, look at the term the researchers use to call the thermal depolymerization: "recycling". That is the exact same word used by the researchers at IBM behind last year's wonder polymer (linked to at the beginning) who also claim that reverting their polymer back to its source monomers is "recycling".

Maybe from a very broad viewpoint, it can be viewed as recycling, but this "recycling" takes far more energy, materials and equipment than conventional recycling does. The polymer first has to be heated (far hotter than the melt point) and held at temperature to form the monomers, then the monomers have to be purified (you really don't expect 100% yield, do you?) and then the monomers, with a catalyst have to polymerized. Only then can the polymer pellets be melted and processed. Compare that to conventional recycling: heat the polymers and process them.

If a commercial entity was using this verbiage in advertising, they should expect a Cease and Desist letter in short order from their competitors and/or the government. So how come academia can get away with it?

Previous Years

January 5, 2015 - Time's "Person of the Year" - and Plastics

January 5, 2011 - ANTEC Bound

January 5, 2010 - Amusing Names for Rheology Models

What is the motion of one molecule diffusing?

I survived my first semester as a professor. I really enjoyed it and am looking forward to the next semester.

The only complaint that I had was with the text. We are using "Chemistry - The Central Science" by Brown, LeMay et al. and it drives me nuts at times. Such how it only mentions 3 states of matter - solid, liquid and gas - and overlooks plasmas. Plasmas are not some exotic state of matter completely void of chemistry. Light a Bunsen burner and you have a plasma. It's possible that one or more the students has seen a plasma TV as well. To not mention plasmas is really surprising, especially since the text has no problem in mentioning more esoteric topics, such as Noble gas compounds and ionic compounds.

The section on polymers has too many mistakes to even list, but I think I did a good job of keeping those thoughts to myself.

But what really had me livid (and my students will verify this since it was I spent time in lecture on it, covered it again in the chapter synopsis and even asked about it on the final exam) is this illustration:

The expression "throwing out the baby with the bathwater" has never been more aptly applied.

This figure is a snippet of a random walk and as such, the molecule pictured is most likely to end up right where it started. The molecule is bouncing around at random - there are no signs to indicate which way it is suppose to diffuse and so a single molecule by itself won't diffuse. To call a random walk "diffusion" is a horrible misrepresentation of diffusion. A single molecule won't diffuse anywhere. It will just wander around at random and go nowhere.

So then how do we get diffusion from a collection of random walking molecules? Diffusion is the result of concentration gradients - differences in concentration over a distance. If there is a higher concentration of molecule A on the left and a smaller concentration of molecule A on the right, the odds are better (and yes, diffusion is the result of statistical phenomena) that more molecules from the left will move to the right than from the right to the left since there are more A molecules on the left. There is nothing special about this. The molecules on the left have no clue that they should go to the right - it's just that since there are more of them on the left than the right, they are more likely to overwhelm the molecules on the right moving to the left. But at all times, molecules on the left are each moving to the right and even further to the left while molecules on the right are moving to the left and even further to the right. They have to move in both directions since they are moving randomly without any guidance. The diffusion we observe is based on the statistical outcome of this game of chance and nothing more.

Over time, diffusion lessens the gradient which means that diffusion will lessen over time until eventually the gradient is gone and so is the diffusion. No gradient, no diffusion.

So how can Figure 10.18 above illustrate diffusion when there is only a single molecule in it? It can't. It's not possible. Even if the other molecules were added to the picture, there would still be no diffusion without a concentration gradient. The Zen koan asks "what is the sound of one hand clapping?" to which there is no answer. This picture asks "what is the motion of one molecule diffusing" to which there is no answer, despite the authors claiming to have one.

Previous Years

January 4, 2021 - How will the Law and Chemistry Interact? - The Sheri Sangji Case

January 4, 2011 - Extruder Philosophy

Janaury 4, 2010 - A new year, a change to the comments

1,000,000 Pageviews

Sometime in the last few minutes, the all-time number of pageviews for this blog made the quantum leap to 7 figures.

(Ok Mom, you can stop clicking on random internal links now). If I only had a nickel...

Since it took just over 9 years to get this far, I project it will take about 90 years to get to 8 figures. Looks like I ought to seriously start exploring life extension options.

If you were perchance on of that 1,000,000, I express my sincere thanks to you. I'm deeply honored that anyone wants to read what I write.

Reinventing the Wheel (only this time it's a biodegradable plastic!)

While I've always been of the opinion that biodegradable plastics will be limited to very specialized niches, others don't always feel that way. Take Marieke Havermans of the Netherlands. A former packaging designer for Heinz (as in ketchup), she recently discovered an unrecognized application for biodegradable plastics. As reported last month by Plastics Today:

"When Marieke Havermans� mother-in-law died, the family was given a catalog to browse through by the funeral home from which to choose the casket they wanted. 'Each and every one of them was basically dark, ugly and too expensive. For the most part, they were made of particleboard that was lined with leak-proof paper�which was not what we were looking for,' she said. 'Particleboard is a cheap construction material that emits formaldehyde. There�s no dignity in particleboard.'

Havermans was convinced that there had to be a better way. Her idea was simple: 'Why not design a sustainable casket made of a natural bioplastic that would, in time, simply biodegrade? A casket that would not only impact less on the environment, but that would also be an attractive and affordable option for everyone,� she explained.'

So she got together some polylactic acid (PLA) and some reinforcing fibers and voila! created a biodegradable plastic casket.

I'm not sure that I see any "dignity" in PLA, but maybe others do. Further, PLA is only considered biodegradable in an industrial compost site, which is not the same thing as a cemetery.

Another sticking point is that here in the US, the use of concrete burial vaults is very common. The bottom of the vault is placed in the ground first, the casket is placed inside the vault and then the concrete lid is placed on top. The reasons for use of burial vaults aren't exactly clear. Possible reasons are to prevent the ground from sinking over time as the casket degrades. Or because it slows the degradation of the body in case it needs to be exhumed for a criminal investigation. Or (cynically), because someone wanted to make more money than just selling caskets and burial lots.

Regardless of the reason, the near ubiquitous use of vaults will probably prevent these caskets selling well here in the US. But there is one other reason that I don't see them selling well (and why I have to laugh at the idea of this casket): it's because biodegradable burial caskets have already been in use for hundreds/thousands of years. They are called "pine boxes":

Reinventing the wheel I say. That the wheel is justified by marking it as "biodegradable" when other traditional options are too is scamming people when they are emotionally vulnerable.

Previous Years

(Nothing)

Time for a Cage Match

Apologies to the fans fan of this blog (Hi Mom!) for not posting in such a long time. Between Thanksgiving and winding up the school term, it's been pretty haywire. But the final exam has been written, (not proctored - that comes Wednesday) and then it's just a matter of final grades, although I am taking advantage of the break to start working on lecture notes for next semester.

But I have a great welcome back item - the announced merger of Dow and DuPont. Both of these companies have a lot in common. They are both huge. Their names both start with the letter "D". And they both have had to put up with activist investors in the last year or two.

Dow was the first to be attacked from "within", in this case by Daniel Loeb (1, 2, 3, 4, 5 and 6). That all ended when Dow and Loeb and declared a truce just over a year-ago. In a classic case of monkey-see, monkey-do (a phrase that in this case insults monkeys, even really dumb monkeys), Dupont was then attacked from within by Nelson Peltz (1, 2, 3 and 4) before finally losing his proxy battle.

But both of these guys are still hanging around the picture, which then raises the biggest question in my mind about the merger: which activist investor will be the top dog afterwards? Everyone is far more concerned concerned about government approval for the deal, but what about the undercard: Loeb vs. Peltz? As big as this new company will be, it still will not be big enough for these two mega-egos. One of them will have to go.

My proposal: a cage match!

Which company had the better activist investor? This would be the once-in-a-lifetime chance to find out. Imagine the pay-per-view revenue. Wall Street bankers, financiers and countless C-Executives (especially ones previously harassed by these two) would pay thousands to watch this. Mayweather vs. Pacquiaou pulled in $410 millions - this could double that and give me enough cash that I could become an activist investor! The bookies would have Loeb as the early favorite as he is a sprite 53 years (turning 54 later this week) while Peltz is almost 20 years his senior, but when big money like this is at stake, these guys would be as ferocious as 2 emaciated tigers fighting over a fattened lamb.

"Grace, get me Loeb on the phone right away. Oh, and start dialing up that Peltz guy too. We're going to do lunch..."

Previous Years

December 14, 2012 - Changes. Big Changes.

December 14, 2011 - Isolating Thixotropy from Shear Thinning

December 14, 2010 - Will the Supreme Court become Probabilistic?

December 14, 2010 - Epoxy Resin Drop as Art - and Rheology Puzzler

December 14, 2009 - LyondellBasell to go East?

December 14, 2009 - Thermal Hystersis