Friday, July 31, 2015

Maybe this is why the Philae Probe didn't "Stick the Landing"

The Philae lander that made (multiple) contacts with the 67/P comet last November has finally reported back some data on the chemistry at the surface. And it appears that there is a polymer, polyoxlmethylene (POM) amongst the mix. The official report is behind a firewall (which means I haven't read it), but there is also extensive reporting by Carmen Drahl (formerly of C & E News) and C & E News itself.

Whenever I think of POM, two thing immediately come to mind. The first is that this polymer probably has more names associated with it than any other polymer. POM is also commonly referred to as acetal, polyacetal, and Delrin (the latter being a tradename that is well on its way to becoming generic). Most other polymers have only a couple of names associated with them.

But the other immediate thought is POM is well known for it's low coefficient of friction (COF) - it's excellent for making plastic gears and other parts that slide past each other. So is the low COF part of the reason that the probe had such a difficulty in landing and staying landed?

Don't laugh. There may be lots of polymer on the surface

"If the polymer covers much of the comet, it could explain the object’s dark colour..." For such a strong visual effect, the polymer is would have to be more than just a monolayer. Additionally, "The polymer may also be masking signals from other interesting compounds formed earlier in the comet's history...", again, indicative of a thicker layer. (And did you notice how junky polymers are already taking the blame polluting up the comet.)

Landing a probe on any comet will always be challenging since the gravitational attraction is so low. But having a slippery surface is only going to make matters worse. This is still mostly speculative, but if it turns out in the future that there actually is a slippery, thick layer of POM on the surface, well, you read it hear first.



Previous Years

July 31, 2014 - Polyprefixicide

July 31, 2012 - Accelerated Aging, Flash Photography and Museums

July 31, 2009 - "It's all about the Entanglements"

Thursday, July 30, 2015

Polydopamine

One of the more fascinating puzzles in contemporary polymer science is polydopamine. As you might guess, this is made from polymerizing dopamine, a fairly simple molecule:
Dopamine
Even though this monomer has been polymerized and extensively studied for 8 years, there still is disagreement on what the structure of the polymer is. And this has nothing to due with whether the polymerization proceeds through the 3- or 4- hydroxy group. The hydroxy groups are not part of the polymer's backbone (as far as anyone can tell!).

Look at this rogues gallery of structures that have been proposed:
Possible structures of polydopamine
Source ($) and Source (OA)

All from such a simple monomer. Heaven forbid someone would want to copolymerize something in along with it.

While polymer science is fairly advanced and the number of good mysteries is being reduced, I'm glad something like this can come along once in a while to keep us on our toes.


Previous Years

July 30, 2009 - Class Action Junk

July 30, 2008 - Getting Violent over Glass

Tuesday, July 28, 2015

Real World UV Degradation of PET

Long-time readers of this blog are well aware of my ongoing complaints (1, 2, 3, 4, 5, 6, 7, 8, 9 and 10) about researchers running poorly designed UV exposure tests on polymers. So when PlasticsNews yesterday highlighted a new report from Plastic Technologies, Inc., on how UV exposure leads to yellowing in recycled polyethylene terephthalate (PET), I figured it would make for some terrific blogging fodder for tomorrow.

I was wrong. Or at least my expectations were wrong. Here's what changed my mind completely:
"Two-liter PET bottles produced using a commercial grade of PET were used for this study. This resin did not contain any ultraviolet absorbing additives. These virgin bottles were crushed, stacked five to six deep, and placed in uncovered open sided crates to afford maximum exposure to the elements. These crates of bottles were then placed on the roof of Plastic Technologies, Inc. building in early January. Every three months, the bottles in the crates were agitated so that those on the bottom had a chance over time to move to the top or outside edges. Another set of bottles was stored indoors approximately 18-inches under a fluorescent light source. This light source was left on continuously, exposing the bottles for two months. A third set of bottles was stored and protected from light exposure for one year for use as a control."
I can't believe it. Sure, they ran the mandatory expose-it-to-a-continuous-UV-light-source-to-scorch-it-beyond-all-reason, but they also had material exposed to REAL WORLD CONDITIONS. Industrial researchers got right what so many academic researchers have gotten wrong!

The results of the testing were pretty interesting as well. While the sunlight did yellow the PET a little, putting the exposed PET through an extruder (once again, duplicating REAL WORLD CONDITIONS) drastically increase the amount of yellow. While the authors did not offer an explanation, I would guess that the sunlight initiated a degradation reaction (perhaps along the lines of a Photo-Fries reaction) and the additional thermal cycle really allowed for the reaction to run wild.

But this graph on the right is especially telling. The y-axis is the "b*" values from a Hunter L*a*b* spectrophotometer. I won't go into all the details, but positive b* values are a measure of yellowness. The plot is for test plaques, meaning the PET has already gone through the extruder. The blue diamond is the yellowness for the samples exposed to a fluorescent lamp for 2 continuous months. That point is well off the curve, and shows that sunlight is more more aggressive about degrading PET. This also re-emphasizes my point to ALWAYS run real world exposure controls. Accelerated aging is not just a matter of counting photons - it is far more complicated. Woe unto those who think otherwise.

My hats off to Dr. Schloss and Ms. Brown for getting the research right. You can simulate real world conditions all you want, but nothing beats using the real world conditions. Is it really that difficult of a concept?



Previous Years

July 28, 2014 - The Failed Dow Chemical/Kuwaiti JV: Is it finally over?

Monday, July 27, 2015

A Sweet Ring-Opening Polymerization Scheme

Before I get to today's polymers, let me ask you a few questions:
  • If you could see a movie for free or pay to get a review of the movie, which would you choose?
  • If you could eat a restaurant for free, or pay to get a review of the restaurant, which would you choose?
  • If you could go to a concert for free or pay to get a review of the concert, which would you choose?
Hold your answers until later when the motivation for them will become clearer.

There was a polymer chemistry paper published last month in the Journal of the American Chemical Society (JACS) that brings two separate ideas together to produce some novel polymers.
  1. Ring opening polymerizations proceed best when the ring is small in size and has some strain built in to help the reaction along. Epoxies, being a three-member ring are a great example of this, capable of reacting at room temperature or below. (Many epoxies are shipped on dry ice). But smaller rings offer only a small choice in what will end up in the back bone. Larger rings offer more options, but greatly reduced reactivity.
  2. A recently developed ring-opening methathesis polymerization (ROMP) is called relay polymerization and is illustrated here:
    Relay polymerization
    In the enyne starting material, the triple bond moves to the left to form the five-member ring found in the product and at the same time opens the six-member ring up for polymerization.

The authors combine both of these concepts to produce polymerizations such as this:
Trigger polymerization
While ROMP polymerizations are well known, they have always had restricted chemistries until now:
"For the first time, polymers with arbitrary functionality (ester, amide, sulfonamide, aliphatic, aromatic, heterocyclic, etc.) within the backbone can be produced while still providing control over molecular weight and molecular weight distribution."
Having esters in the backbone means that this material could be hydrolytically degraded. While such degradation is most often undesirable, at other times, it can be a blessing. Regardless, just having it as an option is helpful.

And this polymerization is extra sweet as the trigger is built using saccharin as a starting material. All in all, very clever.

I need to mention that the article is open access. Anyone can read it for free. But if you try and read a review of it at Nature Chemistry, you have to pay. So, one last question:
If you could read a research article for free or pay for a review of it, which would you choose?
(Shameless self-promotion: my article reviews have always been and always will be free.)


Previous Years

July 27, 2012 - The Most Overlooked Analytic Technique in Polymers - DSC

July 27, 2011 - Bad Management or Excellent Engineering?

July 27, 2010 - Gelators - Part I

Thursday, July 23, 2015

Ocean Plastic Greenwashing

While the concern over ocean plastic continues to grow, a new threat associated with it that needs our more immediate attention: greenwashing. There is an ever growing list of companies and publicity-seeking celebrities that are trying to leverage this problem into cash in their pockets by giving the illusion that they are solving or helping to solve the problem.

Adidas is the latest to join in this hoax with an ocean plastic shoe. The Huffington Post has a nice takedown on this scam so I won't go any further. Just last week there was a Dutch engineering group that proposed making roads out of ocean plastic. Last year Pharrell Williams proposed making blue jeans from ocean plastic. Before that there was also the Elexctrolux vacuum cleaners (a grand total of 5 were made and were never for sale to the public), surfboards and the Method hand soap bottle. These are all the items that I am aware of, so there could be more.

The common thread through all of these is that the "Ocean Plastic" that they are using is really "Beach Plastic", plastic gathered on beaches while it is still in large pieces that have suffered minimal degradation.
Method's comments::
"The framework that we're using is that there are a number of beach cleanup organizations that work here in California and that work in Hawaii that are regularly cleaning up this plastic..."
And Pharrell said
"The PET bottles are collected from the coastlines after washing in from the ocean."
(Bottles that haven't washed out into the ocean will apparently be overlooked for this project.)

The reason that all these efforts are using Beach Plastic and not Ocean Plastic is that collecting ocean plastic and doing anything with it is (other than burning it as fuel) is not going to happen. This is what plastic in a gyre looks like:
Ocean plastic - as it really is
A view of an ocean gyre - see any plastic?
Tiny, tiny pieces of degraded plastic. The degradation pretty much ensures that even if recovered (How? Filtration would simultaneously collect a tremendous amount of living creatures from the ocean, arguably "killing the wildlife in order to save them"), the plastic would not be strong enough to make anything useful. Additionally, the recovered plastic would be a mixture of many types which would need to be sorted prior to recycling, something that cannot be done economically with such small pieces.

Sorry, but ocean plastic is going to remain as ocean plastic, and no company or celebrity should give you any impression otherwise. That is why prevention is to key. Plastic has no business being in the ocean, so do your part to make sure it doesn't end up there. Supporting these businesses in their greenwashing efforts is not part of the solution.


Previous Years

July 23, 2012 - Wrap-Up on the Nylon-12 Shortage

July 23, 2010 - A New Nano-Clay for Polymer Reinforcemen

July 23, 2010 - Isn't this Obvious??



Wednesday, July 22, 2015

Fairlife Followup

Last week I wrote the bottle that contains Fairlife chocolate milk and in particular about how confusing the recycling code at the bottom is. It's the number 7, but instead of saying "other" as it should, it says "PETE" (which corresponds to the number 1 code). I contacted Fairlife about this and received the following email:
"Hi John!

Thanks so much for reaching out; we REALLY appreciate your taking the time to get in touch with us.

Our bottles are primarily made from PET, which is #1 plastic. We add a very small percentage of white colorant to protect the milk from UV and visible light (UV and visible light impact the integrity of the milk and the vitamins present in it). The addition of the white colorant is what makes the plastic bottle #7. PET plastic and the white colorant are both approved by the FDA as safe for packaging food products. There is no BPA in any of our packaging.

If you have any other questions or comments, please do not hesitate to give us a shout!

All the best,

Brooke
Consumer Affairs

fairlife® ultra-filtered milk"

(Glad to see that the exclamation point key on their computer works so well!)

This just doesn't add up. Adding white colorant to PET doesn't make it a number 7, just as adding any other pigment to any other plastic doesn't change the base polymer or its recyclability.

But I question the need for a pigment at all. While Brooke is correct that the white plastic will "protect the milk from UV and visible light", a white pigment isn't needed. The bottle is already mostly covered in a brown-colored overwrap film which will block light. Besides, "normal" milk is packed in high-density polyethylene (HDPE) which is a hazy white without any white additives. The whiteness arises from the crystals in the material scattering light (which coincidentally is also why milk appears white).

(As an aside, UV absorbers have been added to polyethylene milk bottles, but understandably, consumers are put off by the yellow color. This is hardly new technology, having been around since at least 1993.)

My guess: there is a barrier layer in the package which makes the whole mess incompatible with PET, and that the white pigment story is just a red herring.



Previous Years

July 22, 2011 - The Heat Index and Jenson's Inequality

July 22, 2010 - A Bio-based Acrylic

Thursday, July 16, 2015

Polymerization Dreaming

Chemists at the University of Arizona recently announced that they have experimental proof that ethylenedione, O=C=C=O, exists. It's basically two carbon monoxide molecules, C=O, butted together. The linked page will provide you more background about it; it's pretty interesting since the molecule has been theoretically proposed for quite some time, but since it falls apart in about half a nanosecond (literally) to two carbon monoxide molecules, you can't really plan on buying a gallon or two and doing something with it.

Too bad, as I would want to polymerize it. (No surprise there, huh?) All those double bonds are just screaming at me to be opened up and go chain forming. If you went for the C=C double bond, you would end up with what I am jokingly (or not) calling polydiacetyl:
poly diacetyl
Or maybe polypopcorn butter, since diactyl has been used for artificial popcorn butter flavoring. Polyketones - polymers with a carbon backbone and pendent ketones - do exist, but not like this. They are normally made by copolymerizing carbon monoxide and ethylene (and maybe some propylene), so there are far fewer ketones than what we would have here, hence the unique name to differentiate it.

But maybe having less ketones is a good thing.

The Wikipedia article on diacetyl states: "A distinctive feature of diacetyl (and other 1,2-diketones) is the long C-C bond linking the carbonyl centers. This bond distance is about 1.54 Å, compared to 1.45 Å for the corresponding C-C bond in 1,3-butadiene. The elongation is attributed to repulsion between the polarized carbonyl carbon centers." That's some intense repulsion to extend a C-C bond by 6%. But that repulsion then gives me a good idea of how the polymer would behave if it were ever made. Despite having a pure carbon backbone, the repulsion would force the chain into a fairly extended configuration, more like a liquid crystal than the random-walk globule so typical of most thermoplastics. So I would expect this to be pretty viscous when molten. While the polymer would have a pretty regular structure and could, at least on paper, seem amenable to crystallization, again, I think the repulsive centers would most likely resist such regular packing and so the material would likely be glassy as well.

Viscous and glassy and impossible to make. Not an ideal combination. I doubt I will ever have these guesses confirmed, but one can dream...


Previous Years

July 16, 2013 - The Added Dangers of A Fire at a Plastics Plant

July 16, 2012 - Rheology, Theology and Deborah

July 16, 2010 - No Death Knell for PVC


Wednesday, July 15, 2015

Plastic Roads

While I'm all in favor of plastics displacing traditional materials in most applications, I have some serious doubts about this one - a Dutch company, VolkerWessels, wants to replace traditional asphalt and concrete roads with plastic. And not just with a layer of plastic, but a construct that has a hollow inside so that pipes and other utilities can be run through it. Take a look at this concept drawing:
Plastic Road Concept Drawing
My immediate thoughts were how much this looks just like another picture that I recently discussed:
Morrison Bridge Cross Section
This is a cross-section of the infamous Morrison Bridge that was recently installed in Portland Oregon and has begun to fail very quickly.

Similarity in shape doesn't mean similarity in failure, but the article does little to allay my fears.
"VolkerWessels, is collaborating with the city of Rotterdam to start prototyping plastic-built roads in a “street lab” provided by the city...The idea is to recycle plastic from oceans into a tough aggregate that could be poured and molded into pre-fabricated “bricks” and installed on site quickly." (Emphasis added)
Ocean Plastic?!? Don't they know that nobody has an effective means to recover ocean plastic, certainly not on the scale that would be needed to make a road of any decent length? But since we are in the pre-prototype stage, you can dream all you want. Or at least until "the rubber meets the road" (sorry, couldn't resist) and the surfaces are tested. Somehow I think there will be lots of failures setbacks "learnings".
"VolkerWessels’...has years, even decades, of research and development ahead of it, if it survives."
Quite the understatement if you ask me.



Previous Years

July 15, 2014 - An Unlikely Combination: Thiol-Ene Chemistry and Isocyanate-Free Polyurethanes

July 15, 2013 - Closing the Door after the Horse has Gone Tilting at Windmills

July 15, 2011 - A New Polymer Blog

July 15, 2010 - Blow Molding on a Small Scale

Tuesday, July 14, 2015

Coincidences and Chicken Feathers

Coincidentally, I wrote just last week about how quickly the University of Illinois Alumni Association knew my new address. But yesterday, I got another piece of mail that also had not been forwarded, but instead had the new correct address. In this case, I was happy to see it, as it was from Patent Awards, announcing that a patent application of mine had issued. The company sells nice looking plaques for hanging on the wall with images of the first page of the issued patent. That's how it works in this country - the first time you find out about a patent issuing is not with an official government letter but when a company tries to sell you something. What was most shocking was that the patent had issued only last Tuesday. Was it possible that this company somehow in less than a week had seen the publication and also knew my new address? No, probably not. I looked at the file wrapper [*] on the USPTO Public PAIR website and saw that the notification for allowance was way back in early March, so they knew this was coming. Somehow they also knew my new address without me giving it to them, but I figure the Post Office probably sells that information.

The patent was from an application that I had filed back in 2012 when I was at Aspen Research. It involves the use of chicken feathers as a base for polymerizations. Chicken feathers are mostly a waste product that is largely ends up being buried. In the US alone, 4 - 5 billion pounds end up underground and so it represents a huge potential feedstock that is biobased and present around the world. That's at least 4 - 5 billion pounds of plastic that could be made, and more if the feathers are combined with other materials. We used to dream big and joke that the first 5 billions pounds would be free. After that:
Featherless chicken
"Eat more cowz!"
The feathers are about 90% keratin, a nasty crosslinked protein that, like most proteins, degrades upon heating before melting. The crosslinking is due to endless amounts of disulfide bonds. Attempts to plasticize them by solvating the disulfide bonds haven't worked out well in the past for a number of reasons. Being heavily involved in thiol-ene chemistry at the time, I was able to devise a scheme that worked with the disulfide bonds.

The Public PAIR website also showed that there was no office action - the patent sailed through unchallenged by the examiner. That's a first for me.

Coincidentally, I was just thinking about that chemistry yesterday before getting the letter. It's been a couple of years since I've worked with the stinky mercaptans, but it all came back when I read the latest installment of the Master Organic Chemistry blog on thiol reactions. James points out that mercaptans are analogous to alcohols in some ways (as would be expected), but not in others, particularly when undergoing oxidations. Alcohols are progressively oxidized to ketones/aldehydes and then carboxylic acids, while thiols are only oxidized to disulfides. I had never really given it much thought. Why aren't there -CSSH groups for instance? Apparently a C=S bond is rather unstable.

Update: As Joe Q. pointed out in the comments, dithiolcarboxylic acids (-CSSH) do in fact exist. A closer rereading of the James's post made it clear that thioketones and thiolaldehydes are what he was discussing, although they can be stabilized with an adjacent nitrogen or other functional groups, which was also mentioned by Joe Q.

[*] The file wrapper is an ancient term for all the paperwork associated with an patent application.



Previous Years

July 14, 2014 - A Novel Adhesive

July 14, 2010 - Chemistry and Music

July 14, 2010 - No RDA on BPA in the EU

July 14, 2008 - Accelerated Aging - Getting Bad Data Even Faster - 1st in a Series

July 14, 2008 - Playing the Building

Monday, July 13, 2015

Messing up on Recycling Codes

My wife and I had a bottle of Fairlife Chocolate Milk last week. After we finished if off, I looked at the bottom of the bottle to see if it was recyclable. It is. Or is it? You decide:
"PETE" or "Other"?
Yep. It's identified as both "PETE" and as a number 7.

The only problem is that PETE is a number 1, while a number 7 is "Other". So which is it? I can't tell just by looking at the bottle since it is colored white. If it was clear, then it would likely be PETE, but once a plastic has been pigmented white, it's a lot tougher to guess it's identity. At this point, I would have to say it is unrecyclable. I had no choice but to toss it in the trash.

My first thought is how can a major-league company like Coke (which owns Fairlife) screw up something so simple? But I have seen weird stuff in the past too, such as this one from 5 years ago where the bottle was labeled as both a 7 and a 5, but it clarified the matter by saying the 5 meant it was PP compatible.

I've always been unable to understand consumer confusion over the recycling codes, but company confusion seems to be common too.


Previous Years

July 13, 2012 - Open Access Polymer Journals and Other Links

July 13, 2011 - Just the same, only really different

July 13, 2010 - Physicists Can't Get Anything Right

July 13, 2010 - Betrayal by a Polymer Scientist


Thursday, July 09, 2015

Taxes, Death and Alumni Associations

Benjamin Franklin famously said "In this world nothing can be said to be certain, except death and taxes.". Benjamin Franklin never graduated from college or he would have added a third item: college alumni associations.

You may recall that the Rheothing household moved to a new house last month. Our mail is being forwarded. The way the US Postal Service (which coincidentally was founded by Mr. Franklin) handles this is to stick yellow labels with our new address stuck over the old address. Yesterday the mailbox was full of all manner of items, all with the yellow forwarding labels, but there was one and only one piece of mail without that label - it had the new address printed directly on it. It was the quarterly alumni bulletin from the University of Illinois Department of Chemical Engineering. It makes you wonder how far off the grid you would have to go to get away from them. I'm not complaining however, as I enjoy reading it (certainly much more than the one from Minnesota which goes right into the circular file).

I was saddened to see that Professor May had passed away. He had a wonderful personality and was well-liked by both students and staff. He was also a unique professor in that he had spent 35 years at Exxon before teaching at Illinois. As you might expect, he had a vast array of real-world examples that could make the mathematical-based engineering texts come alive. I was fortunate enough to TA his mass-transfer class one semester. After that I was convinced that all professors, and especially engineering professors, should work in industry for a few years before becoming professors.



Previous Years

July 9, 2014 - "Plastic Debris in the Open Ocean"

July 9, 2010 - Non-stick Chewing Gum

July 9, 2008 - Don't drink the water



Monday, July 06, 2015

Rheology and Memristors

Viscoselasticity in polymers is often modeled with mechanical elements, specifically springs and dashpots (think of a dashpot as a being like those cylinders that prevent doors from closing too quickly so as to not pinch fingers).
These elements can be connected in series such as in a Maxwell fluid shown on the left. This was proposed by James Maxwell of electromagnetic fame (more on that in a minute).
They can also be connected in parallel, such as in a Kelvin-Voight material.
Of course, there is no reason to limit any model to just two elements, and a Generalized Maxwell model will have a number of serially-connected springs and dashpots that are connected in parallel.

While knowing about these models is part of a good theoretical understanding of viscoelasticity (including knowing full well that these models, like all models, have limitations while still being useful), this can also be helpful when explaining viscoelasticity of people not trained in the subject. Mechanical/civil/aeronautical/... engineers and physicists catch on quickly, while electrical engineers can struggle. Fortunately, this struggle can easily be resolved by using mechanical-electrical analogies. A dashpot is analogous to a resister - energy is irrecoverably lost, while a spring is analogous to a capacitor as they both store energy. Viscoelasticity is simply an RC-circuit. I've made this analogy to electrical engineers many times and it works quite well.

But the analogy can be problematic at times. Electrical engineers also work with another basic circuit element, an inductor. Inductors resist the change of electrical flow by taking advantage of a nearby magnetic field. While mass/inertia/momentum can be considered analogs to inductance and we can describe a flowing polymer in unsteady conditions as an RCL circuit, the next element is where the analogy completely breaks down.

The next element? Beyond the resistor, capacitor and inductor? Maxwell (him again) first described those three as basic, circuit elements back in the 1800's, often using the electromechanical analogy described above. And for the longest time, those three elements were all that were known to exist, at least as passive devices. However, in 1971, Prof. Leon Chua, using symmetry arguments, proposed a forth basic circuit element - the memristor. This device, showing both a memory and resistance (hence the name), would show decreasing resistance as more current had flowed through the device, and it would also remember what its resistance was when the device was turned off. After restarting the element, the resistance would be the same as before. Changing the direction of current flow would reset the device to its initial resistance. As with the inductor, all of this is possible by a coupling the current to a nearby magnetic field.

Going from theory to practice took some 37 years. Or did it? Apparently a controversy exists. I'm not in any position to say who's right and who's wrong. Regardless of the physical existence of the device, it exists theoretically. But even trying to describe a mechanical analog of a memristor is complicated. HP Senior Fellow Stan Williams describes it as:
" An analogy for a memristor is an interesting kind of pipe that expands or shrinks when water flows through it. If water flows through the pipe in one direction, the diameter of the pipe increases, thus enabling the water to flow faster. If water flows through the pipe in the opposite direction, the diameter of the pipe decreases, thus slowing down the flow of water. If the water pressure is turned off, the pipe will retain it most recent diameter until the water is turned back on. Thus, the pipe does not store water like a bucket (or a capacitor) – it remembers how much water flowed through it."
And I further doubt that a polymeric analog of a memristor exists. While the whole idea of decreasing resistance with flow is quite analogous to shear thinning, the analogy fails on two fronts: polymers will lose the decreased viscosity upon cessation of flow (the rate of such loss being related to "the" relaxation time of the polymer), and switching flow directions will not reset the viscosity. Thank goodness, as dynamic mechanical analysis, where rheologists measure viscosity by imposing oscillatory shear on a sample, would not exist if it did.

Like all analogies, there are limits on their applications and if pushed too far, they break down. The analogy of a memristor to any part of a non-Newtonian fluid is just not going to happen, regardless of whether or not a memristor actually exists.

Previous Years

July 6, 2011 - "Scientists Develop Bioplastic"

July 6, 2010 - Ruminations on a Furnace Filter