Wednesday, October 31, 2012

Shaken, not Stirred

Given the free access from Springer until the end of November for Rheologica Acta [*], I've been scanning some of the journals to see if there are any interesting articles. One article caught my eye in particular, but I was disappointed after reading the article. First, the research and the results:

The authors dissolved various molecular weights of polyethylene oxide (PEO) in water, either by shaking the containers or by stirring them, in both cases over a period of 4 days. Surprise, surprise, the shaken samples had a higher viscosity than the stirred ones due to the mechanical breakdown in molecular weight of the more aggressive process. This only happened with higher molecular weight materials with 35,000 g/mole being the cut off.

As I said, I was pretty disappointed with the article. This is one of those cases where the results were pretty much expected even if they had never been published. Much like those data on the nonlinear rheology of polystyrene that I posted here a couple of weeks ago. It might not be a completely worthless effort to publish them somewhere but a 12-page article is overkill.

But it is pretty apparent that the referees never looked at the article. Consider this blooper on page 1 of the article:
"The specific chemical structure of PEO, HO − [(CH2)n − O]x −H with n = 2, confers to this polymer very unusual interactions with water. Indeed, while poly(methylene oxide) with n = 1 and poly(butylenes oxide) with n = 3 are both hydrophobic and insoluble in water..."
Psst! For n = 3, these would be poly(PROPYL-ene oxides). Oh brother...Thankfully, the quality of the other articles that I am reading is higher.


[*] You are taking advantage of this access, right? It also includes Colloid and Polymer Science,Polymer Bulletin, and Polymer Science Series A

Monday, October 29, 2012

More Open Access articles in Polymers and Rheology

Here's a couple of rather significant chances to access the literature, but these are limited time offers, so act fast.

First up, the AIP is offering access to their publications for the time period 1999 to present. Unfortunately, the access is only until October 31, so move fast. The complete list of journal titles is available here. There are a good number of rheology and polymers articles in Applied Physics Letters and others - you just have to search around a little bit.

Springer is being a quite bit more generous with not only the time range of article available, but also the access window. It seems that for select journals, the entire archive is available until November 30. The list of available journal titles is here. Some of the more relevant journals for readers of this blog are So get reading! [*] This journal goes back to 1907 when it was originally published in German under the name Zeitschift fuer Chemie und Industrie der Kolloid. Gradually over the decades it not only started publishing articles in English, but also even articles about polymers, becoming Kolloid Zeitschrift, Zeitschrift fuer Polymere somewhere along the line, a journal title that I can still type in my sleep as "Kolloid-Z. u. Z. Polymere", having done it endless times in my dissertation.

Friday, October 26, 2012

Pronouncing and Mispronouncing "Thixotropy"

O.k., I get it. People love to use the word "thixotropy" whenever they can. It's a very unusual word and can sound rather impressive. It's pretty much impossible to figure out the meaning just from the word itself and even from the context in most cases. If you use it incorrectly, I will track you down and correct it, but what I cannot do is make sure that at every watercooler conversation around the world the term is pronounced correctly. So let me do what I can to help. Merriam-Webster has the proper pronunciation while Forvo does not

That's right, just like "kilometer" is not "kilo-meter" but "ki-lom-meter", "thixotrpy" is not "thixo-tropy" but "thix-ot-tropy". You've been warned.

Thursday, October 25, 2012

Chem Coach Carnival Entry

SeeArrOh is organizing a Chem Coach Carnival this week through his "Just Like Cooking" Blog. Here's my rundown on his questions

Your current job
The company that I work for is quite small, so short and sweet, I'm the polymer guy. Polymer chemist, polymer physicist, polymer engineer and rheologist. I get to do it all. Even if I'm not formally assigned to a project, I can still be brought in as a consultant to other projects.

What you do in a standard "work day"
While it is quite common for people to say that there no standard work day where they are employed, this place, with its emphasis on contract R & D guarantees that no day is like any other. Over the years I've worked for clients in flooring, construction, telecommunications, automotive, sports and leisure, oil production, medical devices, aerospace, food, packaging and biotechnology. There aren't too many industries that I haven't done something in. With that variety of clients, there is an equivalent variety in my work days. Sometimes I'm running rheology tests, sometimes I'm formulating polymers, sometimes I'm prepping to be an expert witness, sometimes I'm reading papers or patents...

What kind of schooling / training / experience helped you get there?
Finally an easy question with a formulaic answer. All my education (B.S, M.S. and Ph. D.) was in chemical engineering, but I also took as much chemistry as I could fit in too. As my colleagues would say, I am a "Big C" chemical engineer, while most of them are "Big E" chemical engineers. What I find most interesting is that, while there certainly are times when my graduate education is needed, the variety of problems I face forces me to rely my undergraduate education far more often than I ever imagined. In any new situation, I always reduce the problem to the fundamental science principles and not get hung up on the views and jargon of the industry. Those principles were learned as an undergrad.

How does chemistry inform your work?
Even when I am working on the physical side of a polymer problem, I am always thinking of the chemical side. For instance, the chemistry of pendant groups hanging off the polymer backbone greatly impacts the properties of it such as
  • the glass transition temperature
  • how the polymer interacts with fillers and other additives
  • how temperature, UV light, solvents and other environmental conditions will affect the polymer
Also, being able to work intelligently with reactive polymers such as urethanes, epoxies or thermosets requires knowledge of the chemistry that is occurring. (I love it when clients say they tried a urethane, it didn't work and so we shouldn't waste our time trying a urethane.)

Finally, a unique, interesting, or funny anecdote about your career
For my first job, I worked in the R & D section of a large company. The company wanted their R & D people to have some practical experience so a group of us were located at a polypropylene film plant in Terre Haute, Indiana. I had just gotten my Ph.D., and my supervisor was also a Ph.D., but no one else at the plant was.

The plant had a number of large ovens that heated the film so it could be stretch thin. These ovens also had access points where you could go in the oven. One day, I went into the oven to show my supervisor something and the door shut behind us. I kicked and kicked and could't get the door open. After a few seconds, one of the smart-aleck engineers opened the door from the outside and loudly yelled so everyone else could hear, "How many Ph.D.'s does it take to lock themselves in the oven???"









Wednesday, October 24, 2012

Different Chemistries for a Different World

With each passing day, more and more progress is being made in bio-sourcing polymers that have been traditionally based on petroleum products. While the end polymer will have the same generic name (polyethylene, polypropylene,...) the chemistry involved in getting to the starting monomer will be completely foreign to a traditionally trained chemist or chemical engineer. Currently, ethylene, propylene, butadiene,... are made from hydrocarbon feedstocks that are "cracked', dehydrogenated or otherwise processed to form the desired product. It's simply a matter of selectively removing a few hydrogen atoms from each molecule.

Preparing these same monomers from bio-based feedstocks however, is an entirely different matter. For starters, the feedstocks are not just C & H hydrocarbons, but instead have oxygen in them, which one way or another has to be removed. This illustration shows the differences in the two approaches:
Source: Hydrocarbon Processing, February 2012, p. 19

Ethylene for instance, is made by the dehydration of ethanol, while PX (para-xylene, which ends up becoming p-terephthalic acid, a monomer used to make PET) starts out from isobutanol, which like ethanol, is dehydrated to become isobutylene, but then is dimerized to become isooctene and then cyclinized (?) to become PX. That's quite a bit different than the standard route of physically separating the PX from the BTX (benzene-toluene-xylene) mix. Or who would think that propylene would be made from plant oils? The fatty acids are removed to leave glycerin, which is then reduced to the monomer.

Once the monomers are made, they can be polymerized as before. This is significant as it means not only that the capital investments already made in polymerization plants will endure, but also that the final products will be virtually indistinguishable from their petroleum-base equivalents. While long-time readers know that I loathe calling anything a drop-in replacement, this might be one of the few exceptions I would consider using the term with. The only difference would be that the bio-based polymers would have a few extra neutrons - biobased feedstocks have a small but measurable amount of carbon-14, whereas petroleum based feedstocks have long ago lost all traces of this radioactive component. This difference ensures that it will be difficult for someone to greenwash a petroleum-based polymer and sell it as bio-based.

This is the future of commodity chemistry. It is very different from that which our forefathers had and it will replace the knowledge that they passed on to us.




Monday, October 22, 2012

White Isn't Always White

Today's post isn't about polymers per se but about additives for polymers. With the exceptions of pigments and dyes, the manufacturers of most additives strive for a lack of color in the their products, with Nirvana being "water white". This has always struck me as a strange term, and newcomers to the industry need to have it explained to them the first time they hear it, but "water white" does not refer in any way, shape or form to "white", but rather to the "water" aspect - they are as clear as water.

The term is most commonly used for petroleum-based products, and often the "water" is dropped so that we are left with such liquids as "white oils", "white mineral oils" and "white gas". There are many hydrocarbon-based resins (polymerized olefinic materials of low molecular weight, often used as tackifiers) that are sold as "water white", but the term is even used to sell modified rosin compounds that are nearly colorless when molten.

I'm not having any luck finding the origin of the term, but given that it came from the petroleum industry that is used to working with liquids that are as black as anything you can find, I can imagine that liquids that are purified as much as possible could be "white". Any other ideas?

Friday, October 19, 2012

Linear and Non-Linear Rheology - Doing it Wrong and Right

Today's post features original rheology data. I can't really call it origianl research, as it is something that is not surprising in the least, but at the same time too, it is something that I have never seen formally documented. It's been nagging at me for a while, so I thought I would give it a run on some polystyrene sitting around the lab and see what happens.

Whenever I get a new sample in for rheological characterization, the first screen that I run is a strain sweep, such as you see here.
At low strains, the storage modulus, G', stays constant, but at higher strains, G' begins to drop. (Need a primer on G'? You can get it right here.) The flat section is the linear deformation region and is very important to many rheological measurements. Typically, once a sample is put into the rheometer, you expose it to multiple measurements (various strains or strain rates and all at one or more temperatures). But at the same time, polymers have a "memory" of how they have been previously deformed. They do not relax instantaneously, but can need seconds, minutes, hours or even in extreme cases, days and years to relax. So how can we resolve this dilemma of a polymer that remembers with multiple measurements on the same sample? By working in the linear region. In the linear region, the deformations are small enough that what happens in one measurement will not influence what occurs in the next. So by looking at the plot above, you can see that for this particular polymer, a strain of about 50% or less will still be in the linear region.

Rheometers, like pretty much any analytical equipment these days, are computer controlled. The plot above was made using the strain sweep program which starts at the lowest strain measurements and increases the strain over time automatically. A sweep like this is done in about 2 minutes depending on how much the strain is increased between measurements.

The problem with the output above is that it is wrong. Or at least, the nonlinear region is wrong. Why? For the reasons I gave above. Once the strains are high enough to result in nonlinear deformations, then the sample still has memory of that deformation while the next measurement is being started.

The plot below shows the same data as before, but also shows additional data in the nonlinear region.
Each of those samples was taken by putting a new sample into the rheometer for each measurement. (A big hassle, let me tell you.) As expected, there is a difference. With the continuous sweep, the deformed polymer is already shear-thinning does not recover from that state before the next measurement begins. Hence the next measurements show more shear-thinning than actually is present.

One last plot. This is the same as before, but has a third set of data that is a combination of the two measurement options.
It was made with a single sample, but each measurement was made 60 seconds after the previous one. At the lower strains, G' tracks what happened with the individual samples, but at the highest strains, it begins to drop below that curve, just as the continuous sweep data does. This says to me that the 60 second interval is enough time for the polymer to relax from small nonlinear deformations, but not the large ones.

All in all, this is what I expected to see, but as I said initially, I've never seen these actual plots - just an admonition to work in the linear region. If you ever wanted proof for that guidance, now you have it. That said, LAOS (Large Amplitude Oscillatory Spectroscopy) is a very active research area that is in fact making measurements in the nonlinear region. From what I've read of it, I'm not even sure that the single point measurements that I made are that correct either.

Thursday, October 18, 2012

3 Views on 3-D Printing

  1. The cover story for the October 2012 issue of Design News is "3D Printing Takes Off".
  2. Plastic News is reporting that the future of 3D printing "is not so rosy."
  3. Coincidentally, print versions of both items 1 and 2 were in my mailbox this morning.
  4. So which is it? Probably somewhere in the middle. 3D-printing will continue to grow and impact us in new ways (good and bad), but it's not as if my mom is going to have a printer anytime soon.

Wednesday, October 17, 2012

Overlooking the Obvious: Self-Healing PVOH Hydrogels

While polymer research is typically done with ever more advanced technology, every once in a while I run across something amazingly simple that makes me wonder how many other what other simplicities are so readily available.

This new research (free access for a very short time period) is about a rather mundane subject - polyvinyl alcohol (PVOH) [1] hydrogels. I say mundane as PVOH hydrogels are more commonly known to school children as "slime" - the result of mixing white glue with borax. The borax crosslinks the chains using their pendant alcohol groups.

The researchers took a slightly different approach to making their gels, one that did not require the addition of any crosslinking agent. They made a very concentrated (35 wt%) PVOH hydrogel by first dispersing it in 95 oC water [2], froze it for an hour, and then warmed it to room temperature, a process that is well-known for forming crystallites that serve as crosslinks for the gel. What is surprising is that these very stiff gels could self-heal upon being cut, but only under certain circumstances. The plot below shows the stress-strain curves for the original material and also how the repaired gels improve their properties over time.
If you've ever played with slime, you are probably wondering what all the fuss is about. Slime will self-repair very quickly as it is not only very soft, but also crosslinks are rather fluid and prone to breaking and reforming. Those are not characteristics of these gels however, as not only are they stiffer, but the crystallites are pretty well frozen into place. What is surprising about these gels is that in fact, higher concentrations of PVOH are necessary for the self-repair features to be present as this figure shows.
What is not as surprising is that the separation time affects the ability to self-repair. The results above were for gels that were rejoined after 5 seconds of separation, but as the plot below shows, leaving the parts separated for an hour reduces the gel's strength by about 20%, and leaving them apart for a day pretty much eliminates all the self-repair characteristics.
This strongly suggests that the surface of the gels is rearranging itself over time, a rearrangement that then prevents the necessary interdiffusion of the PVOH chains. A similar trend, also not surprising is seen as the number of freeze/thaw cycles increases, steps that are well known for increasing the crystallinity of the hydrogels.
Gels with increase crystallinity will also have a harder time interdiffusing their chains after being cut.

Being that these gels are made only from PVOH and water - no crosslinking agents are needed or used - these materials and their simple chemical makeup have an appeal for biomedical applications. But that such unexpected behavior can be found in such simple formulations and processes is what is intriguing. Making these gels is no more complicate than making slime and could be done by college students (or high schoolers if they can handle the long cooling/freezing times and the boiling water.) How many other simple systems with such surprising properties are out there?

[1] I prefer to use PVOH as the abbreviation for this polymer rather than PVA, as PVA could stand for either polyvinyl alcohol or polyvinyl acetate. And it's all the more confusing as polyvinyl alcohol is made from polyvinyl acetate. You can't polymerize vinyl alcohol as vinyl alcohol doesn't exist. Even if you could make it, it would undergo a keto-enol rearrangement to form acetaldehyde. So instead, polyvinyl acetate is hydrolyzed to form PVOH. If you've ever look into ordering PVOH, you will find that the various grades are not only the result of differences in molecular weight, but also differences in degrees of hydrolysis.

[2] PVOH readily dissolve in water at room temperature - too readily - so much so that making a solution with more than a percent or two is a really problem. If you aren't adding the powder very slowly and with large amounts of mixing, you will end up with lumpy snots of undissolved material. Two options to avoid this are to 1) cool the water (adding ice directly is best), or 2) use extremely hot water as the researchers did here. The former option works because it slows down the dissolution rate so that you can evenly disperse the powder and then dissolution occurs as the water slowly heats up, while the second option works because PVOH is insoluble in the extremely hot water, so that again, it can be dispersed first and then slowly dissolved as the water cools. The ice option can work for solutions of about 10 wt% max. I have no idea what the maximum concentration is for the second option. The researchers here were able to make 40 wt% solutions.

Friday, October 12, 2012

Biobased Polypropylene

In the past, most if not all commercial polymers were based on petroleum. That is changing as bio-based polymers are becoming more common. Polylactic acid (PLA) is clearly the leading commercial polymer with a volume of probably about 500 millions lbs. annually. Other polymers are available, polyhydroxy alkanoates (PHA's) for one, but these polymers have yet to achieve the volumes to be deemed a commercial success.

Further up the development pipeline are other biobased polymers that are, at least from a chemical structure viewpoint, drop-in replacements. [*] Dow/Braskem are working on biobased polyethylene, and Coke has a supplier for biobased PET. Now comes an announcement that a biobased polypropylene is being worked on. Making propylene monomer without petroleum feedstocks is pretty challenging:
"Since there are no known natural pathways leading to propylene in microorganisms, creating a process for the direct bio-production of propylene required the design of an artificial metabolic pathway based on previously unknown enzymatic reactions and on novel metabolic intermediates."
As I said yesterday, we are beginning to see the future of chemistry and chemical engineering and it will not be anything like the organic reactions that we all learned as sophomores. We can either embrace these changes or let them run us over.

[*] I've discussed a time or two or three in the past that "drop-in" replacements are never that. Ask any engineer who has been on the job for more than 2-years and they will agree.






Thursday, October 11, 2012

Yes, This Year's Nobel Prize Chemistry Prize was given for Chemistry

The 2012 Nobel Prize in Chemistry was announced yesterday and the reaction from many chemists in the various social media outlets was of outrage that the prize was again awarded for work in biochemistry and not "true" chemistry.

I am not sympathetic to the arguments in the least.
  1. I've yet to see anyone in social media complaining who actually stood a chance to win the prize. The uproar is all caused by bystanders who are never ever going to be considered for the prize. As such, this no different than sports fan complaining about a call in the big match that went against their team. And the end result is the same in both cases. The sun will rise tomorrow and life goes on and years from now no one except the complainers themselves will remember their complaints and their bitterness.
  2. Look at what is being published in leading journals that qualifies as "chemistry". Here's what the most recent issue of Nature Chemistry has for research articles:
    • Use of the interior cavity of the P22 capsid for site-specific initiation of atom-transfer radical polymerization with high-density cargo loading
    • Selective transformations of complex molecules are enabled by aptameric protective groups
    • Electrode-assisted catalytic water oxidation by a flavin derivative
    • Rapid point-of-care detection of the tuberculosis pathogen using a BlaC-specific fluorogenic probe
    • Ab initio carbon capture in open-site metal–organic frameworks
    • Thiourea-catalysed ring opening of episulfonium ions with indole derivatives by means of stabilizing non-covalent interactions
    • Visualization of hierarchically structured zeolite bodies from macro to nano length scales
    • Submicrometre geometrically encoded fluorescent barcodes self-assembled from DNA
    • The energy barrier in singlet fission can be overcome through coherent coupling and entropic gain
    • Label-free measuring and mapping of binding kinetics of membrane proteins in single living cells
    • Engaging unactivated alkyl, alkenyl and aryl iodides in visible-light-mediated free radical reactions
    That's pretty heavy on the bio side of things, isn't it? Well, how about another major chemistry journal such as The Journal of the American Chemical Society?(I bolded the articles that are clearly bio-oriented, and I arguably could have bolded even more)
    • Direct Stereospecific Amination of Alkyl and Aryl Pinacol Boronates
    • Photoinduced Dynamics of Oxyluciferin Analogues: Unusual Enol “Super”photoacidity and Evidence for Keto–Enol Isomerization
    • Tuning the Thermoelectric Properties of Conducting Polymers in an Electrochemical Transistor
    • Femtosecond Conical Intersection Dynamics of Tryptophan in Proteins and Validation of Slowdown of Hydration Layer Dynamics
    • Porphyrin Shell Microbubbles with Intrinsic Ultrasound and Photoacoustic Properties
    • Ruthenium-Catalyzed Aldehyde Functionality Reshuffle: Selective Synthesis of E-2-Arylcinnamaldehydes from E-β-Bromostyrenes and Aryl Aldehydes
    • Photodriven Charge Separation Dynamics in CdSe/ZnS Core/Shell Quantum Dot/Cobaloxime Hybrid for Efficient Hydrogen Production
    • Pt5Gd as a Highly Active and Stable Catalyst for Oxygen Electroreduction<
    • Light-Inducible Spatiotemporal Control of Gene Activation by Customizable Zinc Finger Transcription Factors
    • Coherent Picosecond Exciton Dynamics in a Photosynthetic Reaction Center
    • Antibody-Linked Spherical Nucleic Acids for Cellular Targeting
    • Efficient Medium Ring Size Bromolactonization Using a Sulfur-Based Zwitterionic Organocatalyst
    • Catalyst-Controlled Regioselectivity in the Synthesis of Branched Conjugated Dienes via Aerobic Oxidative Heck Reactions
    • Direct-Write Patterning of Bacterial Cells by Dip-Pen Nanolithography
    • Bulk Superconductivity in Bismuth Oxysulfide Bi4O4S3
    • Tryptophan Switch for a Photoactivated Platinum Anticancer Complex
    • Predictions for Cholesterol Interaction Sites on the A2A Adenosine Receptor
    • Transition-Metal-Free Oxyarylation of Alkenes with Aryl Diazonium Salts and TEMPONa
    • Ba1–xNaxTi2Sb2O (0.0 ≤ x ≤ 0.33): A Layered Titanium-Based Pnictide Oxide Superconductor
    • Facile “Modular Assembly” for Fast Construction of a Highly Oriented Crystalline MOF Nanofilm
    • Nanofluidic Ion Transport through Reconstructed Layered Materials
    • Diketopyrrolopyrrole–Diketopyrrolopyrrole-Based Conjugated Copolymer for High-Mobility Organic Field-Effect Transistors
    • Glycine Rescue of β-Sheets from cis-Proline
    • Synthesis of Thieno-Bridged Porphyrins: Changing the Antiaromatic Contribution by the Direction of the Thiophene Ring
    • Chain-Walking Strategy for Organic Synthesis: Catalytic Cycloisomerization of 1,n-Dienes
    • Low-Voltage Organic Field Effect Transistors with a 2-Tridecyl[1]benzothieno[3,2-b][1]benzothiophene Semiconductor Layer
    • Cyclization Cascades Initiated by 1,6-Conjugate Addition
    • Neuron-Targeted Copolymers with Sheddable Shielding Blocks Synthesized Using a Reducible, RAFT-ATRP Double-Head Agent
    • Near Infrared Light Triggered Release of Biomacromolecules from Hydrogels Loaded with Upconversion Nanoparticles
    • Modulation of a Pre-existing Conformational Equilibrium Tunes Adenylate Kinase Activity
    • Catalysis through Temporary Intramolecularity: Mechanistic Investigations on Aldehyde-Catalyzed Cope-type Hydroamination Lead to the Discovery of a More Efficient Tethering Catalyst
    • Multiprotein Heme Shuttle Pathway in Staphylococcus aureus: Iron-Regulated Surface Determinant Cog-Wheel Kinetics
    • Kinetic Stability of the Streptavidin–Biotin Interaction Enhanced in the Gas Phase
    • Solar Cell Efficiency, Self-Assembly, and Dipole–Dipole Interactions of Isomorphic Narrow-Band-Gap Molecules
    • Identification of an Aggregation-Prone Structure of Tau
    • Macromolecular Crowding and Protein Stability
    • Detection of the Water-Binding Sites of the Oxygen-Evolving Complex of Photosystem II Using W-Band 17O Electron–Electron Double Resonance-Detected NMR Spectroscopy
    • Multiple-Site Concerted Proton–Electron Transfer Reactions of Hydrogen-Bonded Phenols Are Nonadiabatic and Well Described by Semiclassical Marcus Theory
    • A New Direction in Dye-Sensitized Solar Cells Redox Mediator Development: In Situ Fine-Tuning of the Cobalt(II)/(III) Redox Potential through Lewis Base Interactions
    • Fe/N/C Composite in Li–O2 Battery: Studies of Catalytic Structure and Activity toward Oxygen Evolution Reaction
    • From Aggregation-Induced Emission of Au(I)–Thiolate Complexes to Ultrabright Au(0)@Au(I)–Thiolate Core–Shell Nanoclusters
    • Ruthenium Stilbenyl and Diruthenium Distyrylethene Complexes: Aspects of Electron Delocalization and Electrocatalyzed Isomerization of the Z-Isomer
    • Photoelectrochemical and Impedance Spectroscopic Investigation of Water Oxidation with “Co–Pi”-Coated Hematite Electrodes
    • Spectroscopic and DFT Studies of Second-Sphere Variants of the Type 1 Copper Site in Azurin: Covalent and Nonlocal Electrostatic Contributions to Reduction Potentials
    • General Acid–Base Catalysis Mediated by Nucleobases in the Hairpin Ribozyme
    • Nanoscale Graphene Oxide (nGO) as Artificial Receptors: Implications for Biomolecular Interactions and Sensing
    • Mechanistic Studies on Histone Catalyzed Cleavage of Apyrimidinic/Apurinic Sites in Experimental Verification of the Homoaromaticity of 1,3,5-Cycloheptatriene and Evaluation of the Aromaticity of Tropone and the Tropylium Cation by Use of the Dimethyldihydropyrene Probe
    • Exploiting the π-Acceptor Properties of Carbene-Stabilized Phosphorus Centered Trications [L3P] 3+: Applications in Pt(II) Catalysis
    • Self-Assembly and Photopolymerization of Sub-2 nm One-Dimensional Organic Nanostructures on Graphene
    • Total Syntheses of HMP-Y1, Hibarimicinone, and HMP-P1
    • Superoxide Reaction with Tyrosyl Radicals Generates para-Hydroperoxy and para-Hydroxy Derivatives of Tyrosine
    • Identification and Characterization of the Echinocandin B Biosynthetic Gene Cluster from Emericella rugulosa NRRL 11440
    • Lateral Distribution of Charged Species along a Polyelectrolyte Probed with a Fluorescence Blob Model
    • Crystal Structure of a Preacylation Complex of the β-Lactamase Inhibitor Sulbactam Bound to a Sulfenamide Bond-Containing Thiol-β-lactamase
    • Mechanism of Metal-Free Hydrogen Transfer between Amine–Boranes and Aminoboranes
    • Single-Molecule Electrochemical Gating in Ionic Liquids
    • Tailoring Bimetallic Alloy Surface Properties by Kinetic Control of Self-Diffusion Processes at the Nanoscale
    • Populated Intermediates in the Thermal Unfolding of the Human Telomeric Quadruplex
    • Dynamics of Catalytic Resolution of 2-Lithio-N-Boc-piperidine by Ligand Exchange
    • Stereospecific Cross-Coupling of Secondary Organotrifluoroborates: Potassium 1-(Benzyloxy)alkyltrifluoroborates
    • Mechanism of Amination of β-Keto Esters by Azadicarboxylates Catalyzed by an Axially Chiral Guanidine: Acyclic Keto Esters React through an E Enolate
    • Reactivity of U–E–U (E = S, Se) Toward CO2, CS2, and COS: New Mixed-Carbonate Complexes of the Types U–CO2E–U (E = S, Se), U–CS2E–U (E = O, Se), and U–COSSe–U
    • Theoretical Investigation into the Mechanism of Au(I)-Catalyzed Reaction of Alcohols with 1,5 Enynes
    • Site-Selective Chemistry and the Attachment of Peptides to the Surface of a Microelectrode Array
    • Dynamic Nuclear Polarization NMR Spectroscopy of Microcrystalline Solids
    • Are MXenes Promising Anode Materials for Li Ion Batteries? Computational Studies on Electronic Properties and Li Storage Capability of Ti3C2 and Ti3C2X2 (X = F, OH) Monolayer
    While not as bio-bent as Nature Chemistry, there still are a lot of those awful biochemical names that end in -ase and all those protein code names... It's just horrible to think that someone would let that soil the pages of a pure chemistry journal like JACS. I could go one with other journals, but you get the point. Chemistry journals long ago decided that chemistry could have a strong bio-base orientation and still qualify as chemistry.
  3. The underlying foundation for much of chemistry is changing from its traditional petroleum-basis to a biological basis. This is most apparent in the areas of polymers and fuels, but it will soon spread to the rest of organic chemistry and beyond. But more to the point, the reactions that are creating these materials ARE NOT in many cases, the classic reactions that we all learned as sophomores, but are different and will require that synthetic chemists of the future become familiar with these bio-based reaction options as well.
  4. What I find most laughable about this whole situation is that I'm the guy that is on the backside of my career and yet I'm the one that is both applauding this new breadth of "chemistry" and having to tell younger people to adjust to the new paradigm. Shouldn't I be the old curmudgeon who grinds my teeth and complains about those upstart bio people who are coming on my yard ("Get off my grass or I'll get my shotgun...")? I don't get it.
While I'm not going to predict specific individuals who are going to the Nobel Prize in the future, I will say that an ever increasing number of the awards are going to go to "bio" chemistry in all it's many forms. That's the way research and industry are heading. If you don't like it, that's too bad. You can do no more to change this than you can stop the tide from coming in.

Update: Stuart Cantrill, the Chief Editor of Nature Chemistry pointed out that the articles I originally had posted were incorrect. And that I still wasn't right when I corrected it.




Tuesday, October 09, 2012

Some Open Access Articles from Wiley

For the month of October, Wiley has taken down their pay-per-view firewall for a number of "Special Issues" related to polymers. These cover a wide range of topics, so their should be something to interest everyone.

The issues:
And if you think this is a good thing and would like to see more of it, it might not hurt to drop Wiley a quick thank-you note. You can find your regional contact on this page.

Monday, October 08, 2012

A World-Wide Diaper Shortage? Yeah, but that's just for Starters

There was a fire last week at a chemical plant in Japan that was poorly covered. While there was coverage that the plant made superabsorbant polymers (SAP) used in (disposable) diapers (nappies for the readers using Commonwealth English), what was not mentioned (shame on C & E News) was that the plant also made acrylic acid.

It is potentially understandable that that linkage could be missed. Superabsorbant polymers are made by copolymerizing sodium acrylic acid and a crosslinker, SAP manufacturers are not required to be manufacturers of acrylic acid - you can simply by it from a manufacturer and you are good to go. But while the plant is a major manufacturer of SAPs (20% of the world market), the fact that it also makes 10% of the world's acrylic acid is a potentially larger concern. Why? Well acrylic acid is an extremely versatile and important chemical feedstock. While it is of little or no value by itself, it is used either as itself or after esterification with various alcohols as the base for endless acrylic polymers, such as
  • Paints of all manners, such as
    • House paints
    • Car Paints
    • Spray Paints (for tagging the 'hood)
    • Marine paints, and
    • Artist Paints
  • Sealants
  • Adhesives, particularly pressure-sensitive adhesives
  • Thickeners
  • Dispersing agents
  • Suspending agents
  • Emulsifying agents
  • Coatings, such as
    • Floor coatings
    • Glass coatings
    • Window coatings, and
    • Architectural Coatings
and of course,
  • Plexiglas
The bottom line is that we need to be concerned about more than just a shortage/price increase in disposable diapers, but also in a plethora of other products that play a big part of our modern lives. As an aside, acrylic acid is a petroleum based products with no bio-based alternatives available - yet. That will change. When you have the biggies such as Dow/OPX, BASF/Cargill/Novozymes, and others working towards a bio-based production, something will certainly pan out.

Thursday, October 04, 2012

Rheology of a Bacterial Culture

The Physics Arxiv has a new preprint which I find...interesting. It's pretty simple to describe the setup - the researchers simply put a actively growing bacterial culture in an standard dynamic mechanical analyzer and looked at what happened over time as the colony multiplied via division [*]. I say that this is "interesting" because while the rheology details aren't quite right, the overall results are still pretty fascinating. Here's the primary finding:
with the blue/black curves showing how the viscosity rises and falls over time in a steady-state shear condition. It's a pretty dramatic climb and fall, but if you look at the magnitudes of the viscosities, you can still see that these are pretty thin liquids (water has a viscosity of about 0.001 Pa s). The inset shows how the optical density (shown by the dots) and the number of colony forming units (CFUs) (shown by the bars) changed over time. Obviously there is something more going on here than just say that the viscosity is proportional to the number of bacteria.

The researchers had expected such non-linear results as they were working with Staphylococcus aureus, a microbe known to produce adhesins (yes, adhesins, not adhesions). These are proteins on their cell walls that allow them to adhere to surfaces and each other. Adhesin production is greatest when the growth of the CFU's is the greatest. After the cell density is high enough that a more-or-less continuous network of cells is formed, the adhesin production then drops off (I suspect that this is to allow cells to move off and infect new areas, much like when cancer cell metastasizes).

The researchers are proposing that it is largely the adhesin production cycle that is being shown in the rheological data. During the initial production stages, the viscosity rises are the cells stick to each other and the rheometer's plates. Later, once the adhesin production falls, the shear in the rheometer is able to break apart the cell-cell and cell-wall interactions and destroy the network. Getting both shear-thickening and shear-thinning behavior from a single sample is pretty difficult with the inert materials that a rheologist commonly faces, but for biological samples, it's all in a day's work.



[*] More proof that microbiologists are bad at math - they think multiplication and division are one and the same.

Wednesday, October 03, 2012

3D Printing a Gun

3D-printing - the controlled deposition of tiny blobs of plastic which can be built up to form 3D-objects - continues to grow at a nice clip. This is not only as because of falling prices for the printers, but also because of the creativity that people are showing in what they can and do make. I've talked in the past of an extreme example - medical organs - but that is still a ways off. In the mean time, we'll have to be happy with jewelry, artwork, and other common items.

But now there is news that someone has attempted to make an all-plastic gun with a 3-D printer. In this case, they didn't succeed as they were leasing the printer and as soon as the leasing company found out about it, they immediately took back their printer and ended the lease.

The concerns here are rather obvious: that someone could make and then own a gun without any permits and background checks, meaning that felons could easily acquire them. Such a gun could also not be detected by a metal detector (although the ammunition would), meaning that the gun could be brought through security in airports, courthouses and other building with security concerns.

And while these are legitimate concerns, a plastic gun is much less of a concern than a metal one. A gun made of plastic such as this would obviously only be good for one shot, and I would question if that would even work very well. Unless the gun is heavily reinforced in the back of the barrel, I would think there is a good chance that some part of it could come flying back at the shooter.
This would then mean that some gangster punk not only be holding the gun sideways (a great way to reduce the accuracy of the aim), but also to the side in order to avoid the exploding parts (leading to a further reduction in the aim accuracy). In short, such a gun would pretty much require that it be shot a point-blank range or even direct contact. And thinking about it further, if there is any recoil from the gun, that would then be stressing the shooters wrist and arm at a very bad angle leading to a sprained wrist at the very least. I think someone may think it's cool to shoot a polymer gun once, but they would think long and hard about shooting another one.