Viscosity - It's only half the story

Most people's introduction to rheology is via fluid mechanics, which certainly is a fine place to start. In the texts, the material property of the fluid that exhibits itself throughout the equation is the viscosity. For simplicity's sake (again, this is quite fine for starters), the viscosity is taken as a constant - an idealization known as a Newtonian fluid. As one's studies advance into more advanced cases, non-Newtonian fluids are studied. In most cases, the viscosity is then allowed to depend on the shear rate. A simple example is the power-law fluid, a strictly empirical and therefore potentially DANGEROUS model (another topic for another day), where the viscosity is proportional to the shear rate raised to a exponential value, h = g^n-1 (Yes, it should be g with a dot over it, but coding that is beyond my HTML ability - any pointers?)

Again, all this is fine and nice. But at some point, it needs to be understood that viscosity is a SECONDARY material property, meaning that there are underlying properties that are even more valuable to understand. These are the storage and loss moduli, commonly denoted as G' and G". These properties can be measured in a dynamic state, one where a time dependent strain (such as a harmonic oscillation)is applied to the sample. If your material is a perfect solid, then it should deform in phase with the deformation, while if it is a perfect fluid, it should be 90 degrees behind the deformation (viscosity is proportional to the shear rate, not the shear). Non-Newtonian materials will generally show both of these characteristics to some degree, meaning that by performing dynamic measurements, you can generate curves for G' and G". In other words, viscosity is only half the story. Interpreting these curves is not simple and that is a big part of the reason that rheology is not taught to undergraduates, but there is considerably more information in the curves than a simple viscosity curve can ever show (in most cases being limited to a zero-shear viscosity region and a power-law region.)

As a rheologist, I am often asked for viscosity curves which might be what the client needs, but in most cases, going the extra step and preparing the moduli provides far more information on what is important to the client. Since most of them are not aware of rheology or the power of it, they don't know to ask for it, but are always happy with the results.

You might be curious if you can keep this going and look for even more fundamental properties than the dynamic moduli noted above. In fact you can. Further work shows that the relaxation spectrum, but devising this from the moduli is an ill-posed inverse problem that is difficult to complete. You ultimately end up with a distribution and thereby even more information than you find from just 2 modulus curves.

Lance Armstrong

In an earlier part of my life, I used to race bicycles. Any attempts to state how good I was would undoubtedly cause laughing-induced-cardiac failure in those that I raced against, so let's just say this: being a racer, I was faster than any non-racer (the types that go on long century rides or down to the store for an ice cream). This may sound like a tautology, but there is more to it. I knew plenty of people that put in long hours but never got their liscence to race, and consequently never got very fast. There is something about getting that liscence that forces you to either get serious enough so that you don't embarrass yourself or to quit and never mention that you raced at all. Keep in mind that bicycle racing is totaly different than running, where finishing a marathon dead last is still considered a good thing. In bicycling, you need to stay with (or ahead of) the pack or you are pulled from the race. After spending $20 on an entry fee and money and time getting to the race to have your visions of fame and glory end in less than five minute will motivate you one way or the other.

I still follow the sport and am quite curious about how well Lance Armstrong will do in his comeback. Elizabeth Kreutz has quite a few behind-the-scenes pictures of this (search through the index for "Lance's Comeback"), and what struck me were the number of distractions that Lance has to face. Given what I have to face in my professional career, I can barely find an hour to focus on reading a journal article or two. It's always done in smippets here and there. How this guy can deal with these distractions and THEN put 100% concentration into his bike is beyond me - regardless of whatever results he will ultimately achieve. Yes, it is his job to train, but I still wonder how he can set everything of modern life aside for so long.

Adieu Hercules

Hercules is no more. It's recent acquisition by Ashland Chemical brought to an end a tale (and trail) of tears and death by a thousand cuts. I had a front row seat for a short period (more about this below), as my first job after school was with Hercules in the Packaging Films Group (which was really only a polypropylene film group).

Hercules started back in 1912 as part of the anti-monopolistic breakup of DuPont. Originally making only black powder, the company expanded so that by the 1980's, it was in pulp and paper chemical, polypropylene resin and film, and even had an aerospace division. And then things started to fall apart. They sold off their share of the PP joint venture (Himont, with Montedison of Italy as the partner), followed by the PP film business which was rapidly becoming a commodity requiring ever bigger investments in larger machines, followed by the aerospace division, followed by the tackifying business... There just wasn't much left.

Regarding my first job: I started in late 1989 as a newly minted Ph.D. I was part of the R & D organization, but management decided that the researchers needed more practical experience so they had some of the people located at the manufacturing sites. In my case, this was Terre Haute. This wasn't a bad situation, as we were called in often to help with manufacturing problems, but we had no responsibility for any of the problems, which was a good thing, as there were plenty of problems. In one case, we came within 6 hours of shutting down a customer. To say this was a major customer was an understatement. This customer was (and still is) so large that pretty much everyone on the face of the planet has heard of them. There was yelling and screaming in meetings that I've not heard since. Once the crisis was over, things were never the same due to the internal shufflings that followed. But to my young eyes, the writing was clear: I left for greener pastures within a year.

And so it is adieu Hercules, not au revoir, but adieu.

Where are the acorns?

Not even remotely related to anything polymeric, we also have an extreme shortage of acorns this year at our house in Minnesota and a corresponding increase of squirrels below the bird feeder. No one is complaining, as in more normal years the deluge was hazardous to everyone. As for causes, I would chalk it up to the plentiful rain here during the pollination period (despite the contrary claim of the expert in the article.)

The oak pollen was excessively heavy on the ground this year. We do pay attention to the oak pollen as it is a yearly milestone in the late spring. After the snow has melted, we start bringing out the patio furniture, sweep the deck, blow the grit off the driveway... Only after oak pollination do we bring out the fabrics - umbrellas and chair cushions. We didn't know any better when we first moved into the area, and found out the our ignorance turned everything a bright yellow. As it is, we still have to reclean the porch screens and the tile floor in it, but it is a relief to be down with the pollination as then we can really enjoy the outdoors. And we really did notice that the pollen on screens and floor was unusually heavy. Since there was more pollen on the ground, it doesn't surprise me that there was less in the trees to pollinate.

This year we also have a black coating on everything under the oak trees. It's weird stuff. Water won't touch it, as is the case with a wide range of other solvents: turpentine, limonene, IPA. 409 works (quats). I'm wondering if there is any connection. This coating didn't appear until mid July or so. It wasn't a one-time event eiher as I had to clean some of the deck tables multiple times. Does anyone have any ideas?

Together at Last!

Exciting times in Akron. This photo (courtesy of Rubber and Plastics News - Nov. 17, 2008) features two of the longest living coporate icons together in one spot for the first time, despite the blimps being around since 1925 and the Weinermobile being around since 1936.

Speaking of Goodyear and Akron, their former crosstown rival Firestone, is rapidly fading into the history books. Bridgestone/Firestone has decided to drop the Firestone name entirely. (Bridgestone bought Firestone back in 1988 and moved the headquarters to Nashville.)

Concrete and Cement Rheology

The rheology of concrete and cements is always fun (i.e., a nightmare) to study. You have a reacting system made up of solid and liquid phases, giving off some heat for extra fun. Nowadays you can also find some polymer reinforcements too. To simplify the work, you get exposure to all the other rheological behaviors that you miss when spending most of your day on shear-thinning plastics. The exact ratio of water/solids is often not as precise as one use to lab procedures would expect, so this leads to measuring the rheology in the field.

UT Austin has a department devoted to just this subject - the International Center for Aggregates Research (ICAR). The have a number of publications available, some of them quite lengthy. The summary of 61(!) different workability test methods is great , but there is also a lengthy report (321 pages) on a new simple and portable rheometer.

I've done some work with cements here, and also installed some tile at home, so I know how much black magic and artistry there is to the area. Fortunately, cement has some fairly broad latitude in its working ranges and it can be foregiving. Unfortunately, that can also lead to disaster for the same reasons.

Natta's still waging a patent war

This one blows my mind. Maybe the LHC has created some timewarp in Europe, as this battle has been going on for over fifty years!

Giulio Natta, of "Ziegler-Natta catalyst" fame, has still been fighting for patents on those cataylsts. And yes, he originally filed for the patents back in 1955. The Court of Appeals of the Federal Circuit just decided that the last patent, US 6,365,687, issued in 2002, was obvious. Keep that in mind next time you see Nobel-prize winning research.

Natta himself died back in 1979, and as the patent was assigned to Basell, he has no skin the game. Additionally, this technology is now so commonplace that it is in undergraduate textbooks and has moved on to second, third, fourth... generation constrained-geometry catalysts/cocatlyst systems. I'm not sure that there is much value to the patent any more. If a company is still using this 50-year old technology, it won't be doing so much longer.

Logical Conclusions

Following up on last week’s post, there is more to say with the “scientific method”. The last step – drawing a conclusion - is the linchpin where you and your experiment will succeed or fail.

Unfortunately, I am not aware of any ironclad method to draw good conclusions. Even Nobel-winning scientists have made boneheaded conclusions. Possible logical failures are immense.

If there is ever a controversy in science, it is because of the conclusions that people have drawn. As I stated last week, drawing a conclusion is where failing humans really stick themselves in the middle of the picture.

I’ve seen a ton of erroneous conclusions over the years, (including my own), but the most common ones that are more difficult to see are these:

1) Reaching one conclusion and stopping. This is especially true if the conclusion was what was desired or predicted.

2) Reaching the conclusion based on a single piece of evidence. Sometimes 1 piece is all you can get, but that is honestly very seldom the case. Additional evidence from different perspectives makes it more unlikely that the conclusion is wrong.

3) Believing that repeatability of the experiment is additional evidence of the conclusion. All that repeatability shows is that the result is repeatable and that someone should be able to reproduce your result. It doesn’t mean that someone else will reproduce your conclusion. You see this in the drug tests on professional athletes. Their initial urine is divided into an A and B sample. If the A tests positive, the same lab, using the same procedure, retests the B sample. Is it ever surprising that the B test comes back positive as well?

Maybe it’s summed up best by Richard Feynman: “The first principle is that you must not fool yourself -- and you are the easiest person to fool.”

Melendez-Dias v. Massachusetts

Let's get the legal issue out of the way first, then I can tie some science into this.

The US Supreme Court took a case this week regarding the right of a defendent to question the scientist/techniciam who prepared a scientific report used by the prosecution.

You can read the summary of the case and the oral arguments online.

The US Constitution guarentees the right to confront one's accuser's, but certain documents have been found over time to be exempt from this - such as ordinary business records, accounting books,... The question here is whether the lab report is such a record.

I certainly do not think that it is one for a number of reasons, some of which were raised: lab tests are not 100% reliable, the standard procedure(s) may not have been followed... All true, but I think they missed a crucial distinction.

Despite the reputation, science is very much a human effort frought with errors. The scientific method which everyone is taught is "hypothesis --> experiment --> data --> resuts --> conclusion(s), but no one is ever taught that the last link is the weakest. Drawing a conclusion is where a human being enters the picture.

As such, the lab reports at issue in this case are not just a business record, but actually have a conclusion in them and that conlusion is subject to error. Accounting books do not have a conclusion in them - both side are free to argue whatever they desire of them. That is the distinction, and this basis was dissappointingly not used in the oral arguements.

Viscoelasticity Movies

The upcoming APS Fluid Dynamcis meeting has some interesting videos out. This paper has a couple of them showing the interaction between a hard surface and a viscoelastic drop. Lots of elasticity.

Water - That's Different

While it is not something I use every day, this site is extremely useful and well referenced with technical literature. It is the site to get good information on water and why it is so different from any other solvent in some many ways, some that you are not aware of.

P.S., "That's different" is a common phrase in the Minnesotan language, used to express doubt about something without being overtly critical. An example:

Lena: "Say Sven, what do you tink about dose new electic hybrid cars?"
Sven: "That's different"

Certainly not the meaning I take here.

So when are they going to ban Scotch Tape?

Triboluminescence is nothing new - it's been known for decades that if you quickly pull some tape off a roll, you can see sparks. (HINT: if you are trying this a home, do it in a dark room with you eyes adjusted to the darkness.) But now some researchers have found that you can even generate x-rays from this simple act.

Since they correlated it to the stick-slip phenomenon, this would predict that masking tape (tan, not blue) and even duct tape would be a stronger source. (Stick-slip is an uneveness in the peeling. As you pull on the tape, it doesn't peel until a critical amount of energy is stored in the system and then it lets go suddenly, starting the cycle all over again. This also produces noise. Noisy tapes have lots of stick-slip.)

Another Unusual Water Soluble LCST System

A family of block copolymers known as poloxomers (or by the BASF tradename Pluronics) can also act "funny". These polymers are made of two blocks of polyethylene oxide (which is readily water soluble at all temperatures) and a mid-block of polypropylene oxide (which isn't water soluble). You can get the blocks in varying lengths and the relative amounts, so it really is a family of copolymers. There's even a scheme to numbering and lettering the various grades, but I've never worried about it too much. In water, the propylene oxide blocks try to isolate themselves from teh water by hooking up with other PPG blocks from other molecules. As a result, weak crosslinks form.

F127 is a great example of some of the unusual behavior you can find. A 20 wt% solution makes a great gel at room temperature, but cool it down just a few degrees and it thins down to a very thin liquid. (You can also get the same viscosity if you heat it up to about 80 ^oC. Note that this is an example of LCST or UCST as the polymer is soluble in all cases. It is instead a matter of balancing the interaction energies of the two blocks and the water.

A polymer that has is all backwards

Poly(N-isopropylacrylamide), often abreviated as PNIPAM or similarly, is a water soluble polymer that doesn't act the way most polymers do. As backed up by your everyday experiences, solubility generally increases as the temperature increases. That is not so with PNIPAM. It is readily soluble at room temperature, but increase the mix to about 33 ^oC will cause the polymer to settle out. This is called a lower solution critical temperature (LCST). I suppose that having a name for this implies that it is something that is not so uncommon, or at least something that could be theorized. And yes, upper solution critical temperatures exist. They are very common, as that is the lowest temperature at which a material is soluble in a solvent.

Polymer solutions are not very useful in that state. You can remove the solvent (in this case water) and work with the dried polymer, but to do so would leave you without that neat LCST. So the way to have your polymer solution and play with it too is to crosslink the polymer. When this is done, the PNIPAM soaks up water like a sponge. Or at least until the temperature is raised. Once it hits the LCST, the water is expelled.

This is more a lab curiosity than anything important.

Magnets and Mileage

I'm undecided about this one. It's a modern upgrade of the "cow magnets on your gas line can dive you 200 mpg!" hype. On the up side, the researchers are from a reputable research institution (Temple University), but on the down side, the information provided is quite sparse and unclear. It also seems to have more than a few errors. Is is right that a Mercedes 300D engine is only producing 0.4 +/- 0.04 hp? Equation 1 is for a suspension, but it doesn't appear that anything is being suspended in the fuel.

Perhaps a patent is being filed, which could explain the lack of detail. Good luck in enforcing such a patent in the aftermarket. It would be an easy retrofit for existing cars, and only enforceable on new production.

BASF buys Ciba...

BASF is taking in Ciba for a big chunk of change ($5.5 billion). This could work out well, as BASF, a resin manufacturer. To paraphrase BASF's tagline from the recent past, Ciba's doesn't make the things you buy from BASF, they make them better. So having internal access to antioxidants, UV absorbers, ... certainly can work out well, plus there are certainly advantages in seeing what additives their competitors are buying as well.

I've always loved Ciba's products and especially the technical knowledge that they have so readily supplied with them. I can't think of any other company that compares. But all that free knowledge might be beginning to bite them. Lower cost suppliers of equivalent products - even using the same product numbers - are present and growing, although the quality is not there.

To the extent that Ciba has more goodies in development, the sale will likely work out well.

Accelerated Aging - Getting Bad Data Even Faster, Part 3

UV light is a very common culprit in degradation of plastics as these photons have enough energy to cause problems if they are absorbed by the polymer. E = h c/l so shorter wavelengths have higher energy. So the shorter the wavelength, the better, right?

Unfortunately this is also not correct for two reasons. First, the shorter wavelengths become increasingly rarer on the surface of the earth thanks to all the ozone up high. So going with lots of really short wavelength is unrealistic. But secondly, different plastics react differently to the spectra. A plot of degradation rate vs. wavelength will show a peak and it is seldom at the shortest wavelengths. This plot is known as the activation spectra (see Andrady's article for a good review) and is key to running good tests. Polypropylene for example, has a peak at about 350 nm, much higher than other plastics.

UPDATE: The formula for energy has been corrected. I was so excited to get the HTML right that I ignored the content.

My only political comment and it's not political at all

Flat out, politics will not be a topic of discussion on this blog, but there is one blog that I want to mention for having an unusually rational look at the daily polling results and predicting the Electoral College Results that decide the election, not nationwide polling.

The site is FiveThirtyEight.com. It can be a little confusing at first to look at, but here is the idea in a nutshell. Various groups publish polling data for each state, resulting in an average and a standard deviation, from which the distribution can be worked out. Using these input distributions, 10,000 Monte Carlo simulations are run for all 50 states with the output being another distribution. As of today, 8/13/08, Obama wins 65.4% of the simulations with the most likely outcome being 299.2 to 238.8, and the most likely outcome of the popular vote being 49.7% to 47.7%. The results change daily (or less frequently if there are no new polls for a given day). Watching the site over the last few weeks, the numbers reported above haven't been changing much: Obama is getting about 300 Electoral votes, winning about 60 - 65% of the simulations and getting about a couple of percentage points more than McCain in the popular vote. There are far more details to get into (older polls are weighted for less), but this is it in a nutshell.

While Monte Carlo simulations are just a tool that can be misused just like any other tool (scientific or otherwise - ever seen a bolt on a bike rounded off by a kid using pliers?), this is a far more rational approach that just looking at the "average" reported by a poll. However, this is the first national election for which the technique has been used, so the connection to "reality" has not be firmly established. I am certainly looking forward to seeing how well this model does in the actual election. And I have to expect that the "reality" will be used to refine the model for future elections.

The operator of the site is Nate Silver, a baseball statistician of renown. He is openly an Obama supporter, but believes that this effort is party-neutral.

Accelerated Aging - Getting Bad Data Even Faster - 2nd in a Series

A very common mistake in accelerated aging is to assume that "more is better", the the "more" applying to the stressing variable such as the lamp intensity. Such approaches can have numerous pitfalls. Accelerated UV aging already has advantages over natural aging since the lamp can be run 24/7 while old Sol runs (for most latitudes) at most about 16 hours, with most of this being at less than maximum intensity. But just like the endless pursuit of faster CPU speed (so that people can make stupid mistakes even faster than ever before!), the need for speed is also relentless in accelerated aging. Lamp intensity can be increased ever further (normal maximum intensity for Miami is 0.34 W/m² and this is commonly increased to 0.55 W/m² - all these measurements are most commonly done at 340 nm) but excessive increases lead to other problems. Increased lamp output increases the sample temperature which can lead to increases of reactions that are not of interest.

Oh No! Harold and Kumar...

I'm not going to make reviews of movies a regular entry here, but I was captured by one scene near the very end of "Harold and Kumar Escape from Guantanamo Bay". It was an all around bad movie, but this poem, attributed to David Feinberg, that only a geek could love, made it worthwhile: (BTW, the first two words of the original poem were "I'm sure". I changed it to "I fear", as that what was used in the movie and I thought it was much better.)

I fear that I will always be
A lonely number like root three

The three is all that’s good and right,
Why must my three keep out of sight
Beneath the vicious square root sign,
I wish instead I were a nine

For nine could thwart this evil trick,
with just some quick arithmetic

I know I’ll never see the sun, as 1.7321
Such is my reality, a sad irrationality

When hark! What is this I see,
Another square root of a three

As quietly co-waltzing by,
Together now we multiply
To form a number we prefer,
Rejoicing as an integer

We break free from our mortal bonds
With the wave of magic wands

Our square root signs become unglued
Your love for me has been renewed

Getting Violent over Glass

The New York Times has a decent article on some of the latest research on the glassy state. It's more than the old does-glass-flow arguements and hints at some of the difficulties.

What I really liked is that it captures the intensity of the argument, or more properly, the people involved. Only twice in my life have I ever seen a technical argument get to the point where I thought fists would fly - both times have been over the glass transition. And I've heard similar experiences from others. So when the Times article states: 1)"Thirteen years later, scientists still disagree, with some vehemence, about the nature of glass." and 2)“Many people tell me this is very contentious. I disagree violently with them.” (emphasis added), I can tell the author got it right.

Chemical Obviousness in Patents

To receive a US patent, the "invention" must pass three tests: 1) usefulness, 2) novelty and 3) non-obviousness. The first is easy to pass, the 2nd can take more effort to determine (and the determination is always subject to later reviews) but is doable while the last is the most difficult due to this question: When is an invention obvious?" Attempts to define obviousness have been going on for over 200 years and are not settled.

The SCOTUS recently came down with a landmark decision in the area KSR v. Teleflex which concluded that if you take two or more mechanical parts and combine them in such a way that they do no more than the sum of the parts, the invention is obvious. i.e., 1 + 1 = 2 is obvious, 1 + 1 = 3 is not, ditto for 1 + 1 = 0. In the second (and third) case, you found an unexpected result. Prior to this, the standard for obviousness was that an invention was obvious ONLY if there was literature stating that you should combine 1 + 1 to get 2. If no one had said 1 + 1 = 2, it was considered non-obvious.

KSR however only applies to mechanical devices. A new appeals court decision Eisai v. Dr. Reddy's Laboratory and Teva Pharmaceuticals has begun to address this issue, and I'm not sure that I agree with the outcome. The case involved a pharmaceutical.

But first some background. With patents on pharmaceuticals and in general, chemicals, the "heart" of the invented molecule is clearly and usually narrowly defined, but is the patents will always claim one or more moieties, "sidearms", for which the exact chemical composition is not critical. The moities only need to have certain characteristics such as water solubility, inertness,... After reading just a few patents, any good chemist would get the idea and be able to see what is going on with the moieties. In fact, these moieties are such a popular idea that they have their own name: "Markush claims" named after the first case that included them nearly 100 years ago. It is commonly understood that the inventor does not actually prepare all of the examples, but just uses his knowledge and experience to claim that they would work.

In this case, molecule with a trifluorethoxy moiety was known in the published literature to work. Eisai filed a patent with Markush claims that dropped the terminal trifluorocarbon and replaced with with (amongst others) a monofluorcarbon. The stated opinion of the judges was "To the extent an art is unpredictable, as the chemical arts often are, KSR’s focus on these "identified, predictable solutions" may present a difficult hurdle because potential solutions are less likely to be genuinely predictable.”

So here we have it both ways: broad Markush claims are predictable, but narrow examples nearly similar to them are not predictible. I'd even be willing to bet that there are multiple patents were the Markush claims would list both the mono- and trifluorocarbons.

Markush claims have been getting broader over the years, now they will really spread their wings and soar.

Learning by Writing and not by Reading

In the Pipeline mentions backtracking in experimentation - going back and repeating what was done and checking all the details. While I have backtracked in cases such as this, I more often do so to fill in gaps that I didn't see in the original eperimental layout. In most cases, these gaps don't become apparent until the final report (or a progress report) is being written.

What is it about writing that causes such clarity? Certainly being able to express yourself clearly can only happen if you understand the concepts and results at hand, think about this: This whole concept is backwards, isn't it? How much writing is done in order to teach (textbooks, research articles), or if not teach, convince/persuade/sway (editorials and blogs)? In these cases, the "knowledge" is in the author and is passed on to the reader (yeah, this is the ideal case). But when learning occurs during the writing process, the conveyed knowledge loops around to the author again before eventually ending up with the final readers.

I recall an old bicycling racing teammate back at UIUC that was getting his master's degree in education that was writing his thesis on this area, so I've been kicking this idea around for a couple of decades. I've always wondered what would happen if I were to pre-write the final report before starting the experiment. It would require using fictictional number with reasonable values, but it might be interesting to try sometime.

Playing the Building

I always like David Byrne (of Talking Heads fame). He has enough of a unique viewpoint but not so much that he has lost it. He latest creation is a new instrument in Lower Manhattan - the Battery Maritime Building - an empty 9000 square foot space with exposed beams, pipes, rafters... By adding various actuators (vibrating motors, air blowers and percussion strikers) which are wired into the back of an old pump organ, you can now "play the building". Some of the parts were actually "tuned" so that a chromatic scale of sorts exists. While the building doesn't have the subtle nuances of Rachmaninoff's Second Concerto played by Jean-Yves Thibaudet, it still is a neat idea that such potential exists in an otherwise vacant building.

Apparently I am well behind the times as this site has been open since May and will be closing next month. So what else is new? I found out about this from Design News (July 14, 2008, Supplemental), a trade mag that I really enjoy. It's somewhat geeky (the Gadget Freak files is way too much) but I always make time for this mag much more so than any of the dozens of others that are on my desk.

Accelerated Aging - Getting Bad Data Even Faster - 1st in a Series

Accelerated aging is a laboratory technique for simulating long periods of outdoor exposure in a much shorter time period. This is typically done by exposing samples to various UV lights with or without occasional water sprays, and even some dark periods where the light is shut off. Since the UV lights can run 24/7 while the sun shines for considerably less time (most of which is not a peak intenisty) just running a sample under a bulb as luminous as the sun could give faster results, while having an even more luminous bulb could give even faster results.

I say "could" for good reason. This testing is far more complicated than it appears (my employer does lots work for people that don't do their accelerate aging properly). All the pitfalls are too numerous to mention, but one for starters:

1) Acceleration of the wrong failure mechanism When a part fails in the outdoors, there is a specific chemical or physical mechanism that leds to this result. It is critical that this specific mechanism is accelerated in the testing more than any other mechanism. If this isn't done, your results will be meaningless as you've accelerated a mechanism that is not of interest.

Mixed feelings on PVC

My post the other day could give you the impression that I am in love with PVC. I am certainly not. Considering all the additives (plasticizers, UV and thermal stabilizers, internal/external lubricants, ...) that are needed (I did mention colorants as they are needed in all plastics) and the high levels of their addition, I've always felt that if PVC had been invented only last week, it would have been tossed aside as an academic curiosity.

It certainly is cheap. ~ 35 wt% of the polymer is tied up in chlorine atoms that are not a product of the petroleum industry so it is better able to weather price increases in crude oil. (Chlorinated PVC is even better situated with nearly twice the chlorine.) But I've always just found it a pain to work with, (the rheology of it is a nightmare compared to most thermoplastics or even thermosets) so that I have mixed feelings about the move away from it. I tepidly appreciate the move, but it is mostly being done for the wrong reasons such as the paranoia discussed previously. I find this disturbing as it rewards bad science, further encouraging more of it.

The Big get BIGGER

Dow is buying Rohm and Haas for 15.3 billion in cash at a 74% premium on the stock. It's a nice deal for R & H, but I'm not sure that Dow is getting much from the merger. Sure, the margins will be better than in many of the commodity plastics that Dow is already trying to move away from, but I don't see much of the valuable "synergy" that is desired in mergers. It almost comes down to Dow thinking that they can manage the business better than the the current management can. I've never yet met a manager who thinks that someone does a better job than they do (which is strange in comparison to scientists and engineers who for the most part will accept and state that someone else is a better scientist/engineer than they are), so time will tell. Dow's stock took a bit of a hit after the news was announced, so Wall Street seems to have doubts as well.

Don't drink the water

The last few weeks were doubly bad on the plastics-are-going-to-kill-us-all front. First, there was the your-shower-curtain-is-gassing-you-to-death-as-if-you-were-at-Auschwitz report that found lots (too much) media attention, but this is an easy target as the vinylphobes have been out and about for a couple of decades. It doesn't take too much effort to destroy the poor quality of the science in that report, but the Vinyl Institute has some points for starters.

But that's not all. It was also highlighted by the American Chemical Society that PVC water supply lines can lead to higher levels of lead in the water. It's not an obvious route to get from point A to point B, but it goes like this: Brass fitting often contain lead which can leach out at acid conditions which can occur more easily in PVC pipes than in copper pipes since the copper will inhibit the bacterial growth that lowers the pH.

So I guess the conclusions from all of this are:
1) Don't take a shower
2) Don't drink the water

Or maybe go with option 3) Relax and don't worry about it all so much.

Physical Aging - How Avoiding Jargon Leads to Confusion

In a recent discussion with a colleague, I mentioned "physical aging", and it quickly became apparent that the coworker thought they knew what I was talking about, but really didn't. "Physical aging" is one of those terms that is not unique enough to set itself off from everyday English and thus, in an (inadvertent ?) effort to avoid jargonese and provide clarity does quite the opposite and just causes confusion. It's similar with "Good Laboratory Practices", a term with a well-defined meaning courtesy of the US FDA, but if you ask chemist who has not worked for a pharma/medical device company "Do you follow good laboratory practices?", they will certainly say "yes!" with a good deal of pride and enthusiasm, despite their total ignorance of the documentation and process requirements.

So what is it? Physical aging occurs in polymers when they are below their glass transition temperature and are not at their equilibrium density. Despite the prohibition on flow that is implied by the glass transition, polymers will become denser over time leading to all sorts of unexpected results. Dr. Croll at North Dakota State (Fargo) has a number of publications on how this behavior can exasperate weathering and other degradation phenomenon.

Now that we have that out of the way

To my millions and billions of devoted readers, I am hoping to be back to a more consistent posting routine. I won't go into all the details of the absence, other than to say this: Cancer sucks. Or better yet, metastatic cancer sucks. Free- loading parasitic cells dance in the circulation looking for new homes to colonize, multiply and grow. The growth puts unnatural pressure on the other internal organs causing additional problems. Doctors say "sure we can treat that too" with additional drugs, with additional side effects that cause additional problems that might call for more drugs. Slowly you get backed into a corner without an escape route.

And less you try and read too much into this, no, the cancer didn't strike me (or a relative). Just a dear friend. I've lost people to cancer before, but this was different in that I had a front row seat. We could see the future and it was miserable.

And then a miracle occurred. Truly a miracle. For without any medical intervention the metastatic tumors are gone. The oncologist is at a loss for words, other than to say that no rational explanation exists. Too many tests would have to have been consistently wrong for there to be an error. It would have been several errors. I teased him by joking that I had been synthesizing cis-platin in the lab in evenings and using that. He said that was as plausible as any explanation he could provide. It was a miracle. Truly a miracle.

And so I face this paradox. As a scientist, miracles are not part of the job. Miracles are not repeatable - why it happened here and not to another person of similar faith is impossible to explain - and science is all about repeatability. That's why scientific journals exist. You report what you did and what you found so that others can repeat it. If they can't repeat it, then something is wrong. So needless to say, miracles are not part of the scientific literature. They can't be consistently reproduced.

My way out is the thought provided by Freeman Dyson: "Science and religion are two windows that people look through, trying to understand the big universe outside, trying to understand why we are here. The two windows give different views, but they look out at the same universe. Both views are one-sided, neither is complete. Both leave out essential features of the real world. And both are worthy of respect."

Each year, I grow professionally and feel I have a much better grasp of science and technology. My current job is extemely helpful in this regards as I am exposed to so many different problems in such a vast range of industry in an very short period of time. It would have been impossible to acheive this growth in any of my previous jobs. But each year my personal growth also occurs and this episode, as well as many of pains in the last 7 years have quickly left me with a with different perspective: that we really have little control over our lives and that there will be twists and turns that cannot be foreseen. Helping each other in these times is essential, as it can easily happen to you. It might hit you as a sudden blow or as a slow creeping, but life is not linear. Kinetics can outrun thermodynamics for the short term, but eventually it loses out.

So that is my article of faith. Another paradox for the pile. Add it to particle-wave duality, the twins paradox and the rest. Paradoxes make the world so much more interesting.