Microwave Grilling: How Does It Work?

Previous articles in the How Does It Work series:

• Homemade chloroform
• Coors Light cold-activated bottles
• Fruit ripening

If you have any topics where you'd like to know: How Does It Work, let me know in the comments

Today: how microwave grilling works. How does my Lean Cuisine Microwave Panini grill itself in my microwave? And how come when I microwave other things they just get soggy instead of crispy and grilled? It’s like using a toaster oven or George Forman, but not! What the heck is going on?

How'd you get so crispy?! Via Lean Cuisine

Read more »

Subscribe to the comments for this post

An Earth-Abundant Photoelectrochemical Cell: One Step Closer to a Hydrogen Economy?

In June I wrote a blog post titled “Artificial Leaf or Solar Powered Electrosynthesis?” about a photoelectrochemical cell (PEC) described in the Proceedings of the National Academy of Sciences (PNAS). The goal of this research was to create a PEC that can use sunlight to split water (H₂O) into oxygen (O₂) and hydrogen (H₂). The stored energy in hydrogen can then be used to generate electricity via a hydrogen fuel cell.

In that post I described the device and how it operates. It essentially has a water oxidation catalyst on top of a p-n junction silicon solar cell. It was a step toward a solar driven device, but unfortunately the solar cell alone did not provide the force (>1.23 V) necessary to drive water oxidation and proton reduction.  The cell had to be supplemented with an external power supply. The device marked a great step forward but not quite a standalone earth-abundant PEC. I concluded the post with the sentence “With further optimization, possibly involving a tandem solar cell architecture, I have no doubt we will see a fully functioning device within the next few years.” While I was technically right in my timeline (< a few years) my estimate was clearly too pessimistic.

A follow up paper to the PNAS publication was published last week in Science. The article “Wireless Solar Water Splitting Using Silicon-based Semiconductors and Earth-Abundant Catalysts”  by Daniel Nocera and the team at Sun Catalytix introduces a fully functional hydrogen and oxygen generating PEC. In fact two different architectures for the PEC were investigated and both can be seen below.

The article describes a triple junction amorphous silicon solar cell (3jn a-Si) as the light absorbing and charge separating component which creates the electricity necessary to run the electrolysis of H₂O. The 3jn a-Si is composed of alternating layers of amorphous silicon and amorphous silicon-germanium alloy on a stainless steel back plate. Unlike the devices described in the previous post, the 3jn a-Si can produce > 2 V of driving force and thus it does not require a power supply to run catalysis.

Read more »

Subscribe to the comments for this post

Coors Light Cold-Activated Bottles: How Does It Work?

If you're in the US, no doubt you've seen the commercials.  Coors Light's parodies of NFL coaches during post-game interviews was brilliant, but I'm talking about the one's for their cold-activated bottles:

So how does it work? The ability of something to change color with temperature is known as thermochromism, and the Coors Light bottles are printed with a thermochromic ink called a leuco dye.  A leuco dye is a coloring agent which can acquire two different forms: a colorless form and a colored form.  At warm temperatures, the thermochromic ink is colorless, and at cold temperatures, the thermochromic ink is (in this case) blue.  Put your beer in the fridge, when the ink cools below the color changing temperature, "the Rockies turn blue," and your beer is ready to drink.

So how do thermochromic inks work? Well, in general one aspect of a molecule that makes it colored at all is an extended conjugated pi-system.  A pi-bond absorbs light.  A single pi-bond absorbs light in the UV spectrum.  As the pi-system extends further and further, the wavelength of light absorbed becomes longer and longer, until extended pi-systems begin to absorb light in the visible spectrum - and the molecule becomes colored (see figure).  A molecule will typically absorb one wavelength of light better than others, and this wavelength of maximum absorption is designated λmax (read "lambda max").  Lycopene is red because its λmax is in the blue region.  It absorbs light in the blue region and reflects light in the red region and thus appears red.  If one were to disrupt an extended conjugated system in the middle of the pi-system, the extended pi-system would be severely shortened, and the molecule would (potentially) become colorless.  So most widely used thermochromic inks contain an extended conjugated pi-system that is easily interrupted.

The prototypical thermochromic ink is crystal violet lactone.  When the pH is high, the lactone interrupts the conjugation that would otherwise extend through all three aromatic rings.  When the pH is low, the lactone becomes protonated, and the lactone opens to the carboxylic acid, leaving a tertiary, benzylic carbocation behind.  This carbocation allows the conjugation to extend throughout all three aromatic rings.  With the conjugation extended, λmax increases into the visible region, and the leuco dye appears, well, violet colored.

For inks, the equilibrium is controlled in a very clever way.  We can't constantly be dousing our beer bottles with acid or base depending on which color we want.  For thermochromic inks, the manufacturers take the lecuo dye, some weak acid, and a high molecular weight solvent and encapsulate the components into a particle usually <50 μm in diameter.  The leuco dye chosen will depend on what color is desired. Weak acids typically chosen include bisphenol A (yes, that BPA), octyl or methyl p-hydroxybenzoate, 1,2,3-triazoles, or 4-hydroxycoumarin derivatives.  The solvent is typically an alcohol (laurel or cetyl alcohol), an ester (butyl stearate), a ketone, or an ether.  The melting point of the solvent is important.  The melting point of this solvent is the temperature at which color change will take place.

The paradox: It might seem at first glance that when the solvent is liquid, increased mixing should take place, and with more acid available in solution, the carbocation should be favored at elevated temperatures.  But if that were true, the thermochromic inks should be colored at high temperatures.  But almost invariably, all thermochromic inks are colored at cool temperatures and colorless at elevated temperatures.  It seems that in the solid state, the leuco dye and weak acid are in contact with each other and color change takes place.  In the liquid state, the two components disperse and the colorless form predominates.

Fun Facts: Note it's not actually temperature that's changing the form of the leuco dye.  The temperature changes the equilibrium point of the acid/base reaction which changes the form of the leuco dye.  So the dyes are not, technically, thermochromic... rather, they're halochromic.  The color actually changes with pH.  But the temperature controls the acid/base equilibrium, which controls the color, so these inks are generally referred to as thermochromic inks.  So when the color change occurs at the temperature of my refrigerator, I can use thermochromic inks to tell when my beer is cold (actually, it only tells me when my beer bottle is cold... not the actual liquid inside the bottle...) Phenolphthalein is another example of halochromicity.

On reading a few patents, it appears Coors Light utilizes thermochromic inks prepared by ChromaZone.  The actual structure of the blue dye appears to be either proprietary or a trade secret or I can't find it by browsing Google Patents or ChromaZone's webpage.  Maybe it's just crystal violet lactone!  ChromaZone's website has a lot of neat information on thermochromic inks.  Another popular manufacturer of thermochromic inks is Matsui.  Their thermochromic ink page has several headers with a lot more neat information to read.

Other Uses: • Other common uses of thermochromic inks are temperature probes for microwaveable foods.  Some maple syrup bottles have a black thermochromic ink which reveals the word HOT written in red when the syrup is warm enough to eat.  The ink doesn't actually change from black to red, though.  The thermochromic ink changes from black to colorless... to reveal the regular ink printed underneath which has the word HOT printed in red ink.

• The fad of on-the-battery testers utilizes thermochromic and conductive inks.  A three layer system is in use here.  The conductive ink is printed in a strip that gradually expands in width.  On top of that is printed (in regular rink) whatever design the company desires to show the battery is good.  On top of that is printed the thermochromic ink.  When the battery is tested, the resistance in the conductive ink causes the ink to warm.  A small current will heat the narrow parts of the testing strip, and more current is needed to heat the widest parts of the testing strip.  If there is enough current to heat the ink past the color-change temperature of the thermochromic ink, the ink will turn colorless and reveal the "good" indicator.  As the battery drains, less of the testing strip will turn colorless and the battery will show that it is less "good."

• A two-toned effect can be created by mixing a colored thermochromic ink with a colored regular ink.  Mixing a blue thermochromic ink with a yellow regular ink will result in a layer that appears green at low temperatures and yellow at elevated temperatures.

• As we said, leuco dyes are really halochromic inks dressed up as thermochromic inks.  The true thermochromic material is a thermochromic liquid crystals, with the most famous thermochromic liquid crystal being the old school mood ring.  Thermochromic liquid crystals are much more sensitive to temperature change than leuco dyes, but are more expensive to manufacture.  Liquid crystals appear in silly mood rings, practical LCD monitors, and more serious forehead thermometers where exact temperature is important.  In a liquid crystal, the molecules are oriented in a particular direction, but that orientation direction varies periodically with depth into the crystal.  The distance between repeating orientations is the pitch, and the pitch varies with temperature.  The value of the pitch is typically on the order of visible light, thus as the pitch changes, the colors reflected change, and the color of the mood ring changes.  See this paper for more information.

• Leaving thermochromicity for a second, transitions lenses for prescription eyeglasses also exhibit a similar effect - colorless indoors, colored (tinted) outdoors.  This is photochromicity, not thermochromicity, but the concept is the same.  When hit with ultraviolet light, the photochromic compound undergoes a chemical change which turns the molecule from colorless to black reversibly.  This interaction with UV light, but not visible light, is important so the lenses aren't tinted indoors.  The problem with many transitions lenses is they don't work well if there is UV tinted glass between the wearer and the sun... such as when driving a car.  Many windshields block UV light, thus the UV light can't interact with the photochromic molecules, and the wearer could experience no sunglasses effect when driving.  A product called Drivewear claims to combat this problem with a combination of UV-sensitive and visible light-sensitive molecules.

So now you know!  Next time you're enjoying a Coors Light (if that's your beer of choice), you can tell all your friends about thermochromic inks.  They'll either think you're real cool and buy your next beer... or they'll think you're real nerdy and buy your next beer because you need to be more drunk.  Either way, make sure you get a free beer out of it!

**Most of my information came from this awesome J. Chem. Ed. paper by Mary Anne White and Monique LeBlanc (insert joke about color chemistry paper written by White & The White here).

Subscribe to the comments for this post

Artificial Leaf or Solar Powered Electrosynthesis?

The tendency for sensationalism in science reporting is a problem. Phrases in a peer-reviewed article that say “this discovery could lead to applications such as x, y, and z” undergo a sensationalist spin when it’s reported that scientists have “discovered a cure for cancer,”  “found THE cause of schizophrenia," or “increased solar cell efficiency by 50%!” Sometimes the reporter facilitates the translation. Other times it is the researcher. The unfortunate result of this type of reporting is desensitization and, even worse, an increased skepticism of scientific claims. When a really important discovery comes along it is appropriately met with “AGAIN? Really?” and “well, then where is my flying car?”  For the sake of maintaining the public’s trust and support, scientists should do what they can to avoid sensationalism. To avoid sensationalism in the area of solar fuels research we should be more thoughtful and critical about the use of the term “artificial leaf.”

A leaf in nature uses the energy in sunlight to split water and convert carbon dioxide into energy-rich sugars, adenosine triphosphate, and other organic molecules in a process we know as photosynthesis. This complex process contains a number of stepwise events involving geometrically organized proteins and small molecules located in the chloroplast. I am not going to discuss the individual steps but I encourage everyone to read up on this incredible machinery. The question I now pose is this: how close to natural photosynthesis does a solar fuel cell have to be for us to reasonably consider it an artificial leaf? Is it enough that a device absorbs sunlight and makes chemical bonds? If that is the case then a bond forming reaction driven by a solar-powered hotplate could be considered an artificial leaf. Is it defined by the chemical bonds that are formed or is a well-defined molecular geometry for the photon absorption and electron transfer events sufficient? An official line between artificial photosynthesis and solar powered chemistry has not yet been drawn. I do not set out to define that line here but I do want to call attention to the differences in recent “artificial leaf” devices and describe how they fall short of their aspiring names while simultaneously indicating that a true artificial leaf may be imminent.

One “artificial leaf” receiving buzz at the moment is being publicized by MIT professor Daniel Nocera. The catalytic portion of this artificial leaf has a cobalt phosphate thin-film anode and a yet to be published nickel cathode.  When these electrodes are submerged in a pH 7 phosphate-buffered aqueous solution and a potential of 1.3 V vs NHE is applied, water is catalytically oxidized at the anode to give O₂. The remaining protons are reduced at the cathode to give hydrogen.  The hydrogen and oxygen can then be used for hydrogen fuel cells.

The applied potential to run the catalysts can come from any source: a water-wheel, a wind turbine, a person riding a bicycle equipped with a generator or any other device that generates electricity. In the case of Nocera’s artificial leaf the potential is created by hooking the electrocatalytic device described above to a silicon solar cell. By describing the device in this way I try to emphasize why I dislike its designation as an “artificial leaf.” It is only an artificial leaf in the most superficial sense in that it converts sunlight into molecular bonds. However, in a more logistical sense it is simply a solar cell (a more than 125 year old technology) attached by wires to a electrocatalytic cell (a more than 200 year old technology).

I am in no way trying to belittle the research of Professor Nocera but I am questioning the use of the descriptor “artificial leaf” rather than focusing on the device’s interesting and important materials. The water oxidation catalyst is not only composed of relatively inexpensive cobalt ions but it can also be electrodeposited on an electrode from a solution of Co²⁺ and phosphate. The importance of electrodeposition is twofold: 1) it makes production of the catalyst relatively easy and 2) it offers a mechanism for self-repair of the catalytic material.

When the line is drawn a true artificial leaf should, at the very least, integrate the two devices into one operational component that generates charges (ideally on a molecular level) and delivers oxidative/reductive equivalents to the catalysts. A simplified, one component system may also reduce the production and operational costs of such a device. Professor Nocera, his collaborator Professor Buonassisi and their colleagues have taken one step closer to a true artificial leaf in their recent publication in the Proceedings of the National Academy of Sciences. In this paper they describe a device where they combined the two component system into one by depositing the electrocatalytic cobalt material directly onto a silicon solar cell. The device can be seen below (not pictured are the Ag/AgCl reference and the platinum counter electrodes):

In this device’s architecture a standard p-n junction silicon solar cell  is coated on one side with metal contact and semi-transparent photoresist. The other side of the solar cell is coated with an indium tin oxide (ITO) layer and then the catalytic cobalt phosphate thin film. Under illumination the silicon absorbs photons to generate an exciton (a bound electron hole pair) which is separated at the p-n interface to give a free hole and an electron. The electron travels to the metal contact and then to the external circuit while the holes travel through the ITO layer to the cobalt film. The cobalt film then catalytically oxidizes H₂O to O₂.

When a silicon wafer is put under illumination in an aqueous solution an insulating layer of SiO₂ will form that kills the photocurrent. The key to using a silicon solar cell in this architecture is to passivate the surface of silicon with photoresist and ITO so the silicon will not get oxidized. Using this strategy they created a device that can generate oxygen from water consistently for at least 6 days.

Although the device is predominantly driven by photon energy, a single silicon solar cell unfortunately does not have the driving force to oxidize water. An external applied potential was still necessary to generate O₂. Despite this shortcoming, this is a great proof-of-concept device that, as the paper states, is “analogous to the wireless current in natural photosynthesis.” (It can be argued that the ITO in this case is acting as the wire but that is just more semantics). With further optimization, possibly involving a tandem solar cell architecture, I have no doubt we will see a fully functioning device within the next few years.

Although I do not think we have yet created a true “artificial leaf” and that we should be vigilant to avoid sensationalism, results like those described above as well as progress in other solar fuel strategies signal that man-made photosynthesis is on the horizon and a future powered by solar fuels is within our grasp.

Subscribe to the comments for this post

Separating the lanthanides: physical versus chemical methods?

Photo credit: Reuters**

There has been much talk about rare earth metals recently. In short, the People's Republic of China has become the dominant source of rare earth* elements in the world; the PRC government has used that fact to their strategic advantage. I don't really wish to get into the political debate; suffice it to say that I think there's more smoke than fire here and that predictions of war are probably overblown.

There are quite a number of articles on the subject, but only one talked about the chemistry. I was struck by a quote in an article on ForeignPolicy.com by Tim Worstall, a trader in scandium and other rare earths (now there's a job I didn't know about):

Another possibility is that we find a new and different way to separate rare earths, as we find new and different sources for the ores. The main difficulty is that chemistry is all about the electrons in the outer ring around an atom, and the lanthanides all have the same number of electrons in that outer ring. Thus we can't use chemistry to separate them. It's very like the uranium business: Separating the stuff that explodes from the stuff that doesn't is the difficult and expensive part of building an atomic bomb precisely because we cannot use chemistry to do it -- we have to use physics.

It's quite apparent that Mr. Worstall is referring to the unusual electronic configuration of the lanthanides, where the 4f orbitals are 'hidden' behind the 4d and 5d orbitals. This electronic configuration is also responsible for the lanthanide contraction, in which the atomic radii of the lanthanides are smaller than predictable by periodic trends.

However, I'm not quite sure what Mr. Worstall means when he draws a distinction between chemical and physical separation of the elements. Both this article (from Oxford) and the Wikipedia article on the lanthanides suggest that countercurrent exchange methods are used on industrial scale; it appears that separation is performed by means of ionic radii and size. While this certainly doesn't rely on the reaction chemistry of the lanthanides (because it appears they all act similar), I have a difficult time calling these techniques physics-based.

Readers, can you shed any more light on the issue? Do you agree with Mr. Worstall's distinction between chemical and physical means of purifying elements?

*It should be noted that the rare earths are, as they say, neither rare or nor earths.
**Photo from this International Business Times article.

Subscribe to the comments for this post

Puzzling polymorphs

Polymorphism is a common and sorta crazy issue in pharmaceutical process chemistry. Basically put, a drug molecule in the solid state can have multiple crystal forms. Different impurity profiles and different crystallization techniques (solvents, heating/cooling rates) can produce different polymorphs, which can have wildly different physical properties and bioavailabilities. A famous story of troublesome polymorphism is Abbott's ritonavir, where in the middle of manufacturing for sale (not during the R&D phase!), a new, much less soluble polymorph started showing up in batches. Moreover, once the new polymorph showed up, it was very difficult to generate the previous polymorph. Even crazier, a team of scientists went to another plant in Italy where the process was still working as desired, and soon after the team left, the new polymorph appeared. It took a crash program to understand which conditions were generating the new crystal form to get it under control.

A recent article by Pradash et al. in Organic Process Research and Development illustrates the problems of polymorphism similarly: once the authors determined that there was another crystal form ('Form A') than the original ('Form B'), they undertook a screening process (looking at varieties of solvent and crystallization techniques) to find other polymorphs. Interestingly, once they discovered a new polymorph ('Form C'), they found that it was impossible to generate Form B in their laboratories. They selected Form C for its physical properties and moved it into the pilot plant; lo, they then found Form D. This new crystal form began predominating and "those seeded crystallization processes that consistently produced Forms A and C started to produce predominately Form D in the laboratory." (Click on image to see pictures of the polymorphs and the structure itself.)

When I read these accounts, I am filled with admiration for pharmaceutical process chemists, the interesting science that they get to do and the vast reserves of patience and sangfroid they must have.  Chemistry (and manufacturing chemistry, especially!) is based on reproducibility and consistency; when issues arise, I suspect that there is a great deal of checking and double-checking to make sure that "this is really happening to us." Also, I can't help but wonder if those process chemists, when these issues are discovered, wonder if the laws of the physical universe are being temporarily suspended and some Loki-like diety is having its way with them.

Subscribe to the comments for this post

Eating Carbon Nanotubes

Fathi Moussa

Lon Wilson

Last year I covered Khodakovskaya et al.'s paper regarding the benefits of growing tomatoes in carbon nanotubes (CNT).^[CB] At the time I was concerned with the potential health risks associated from eating carbon nanotubes, but today in ACS Nano my concerns are alleviated. A paper from Lon Wilson's and Fathi Moussa's research groups discusses the effects from administering oral doses of carbon nanotubes (concentrations as high as 1g of CNT per kg body weight) to Swiss mice.^{[ACS Nano]} The authors summarize their work the best.

CNT materials did not induce any abnormalities in the pathological examination. Thus, under these conditions, the lowest lethal dose (LD_Lo) is greater than 1000 mg/kg b.w. in Swiss mice.

So feel free to eat all the CNTs you want in lab, assuming they are not functionalized, you do it only once, and you limit yourself to single walled carbon nanotubes. I think partly because the results of the oral administration of CNTs went without any interesting side effects to present, the authors also looked into what happens when you inject CNTs into the peritoneal cavity of mice.

The image on the left is the control while the image on the right is 14 days after injecting mice with CNTs at a concentration of 1g CNT per kg of mouse. Although it looks sickly, the mice injected with the high concentration of CNTs did not die. Well..., not from the CNTs anyways.

Link to paper: In Vivo Behavior of Large Doses of Ultrashort and Full-Length Single-Walled Carbon Nanotubes after Oral and Intraperitoneal Administration to Swiss Mice (ACS Nano)

Mitch

Subscribe to the comments for this post

This Message Will Self-Heal in 3, 2, 1...

Cassandra Fraser

Recently, Cassandra Fraser's group reported on a very cool property, reversible mechanochromic luminescence, observed in an easy to make material.^[JACS] The molecule of interest is the difluoroboron complex of avobenzone (BF₂AVB), that UV absorbing molecule in your sunscreen minus the boron and fluorines.

In broad general language, mechanochromic luminescence describes the ability of some materials to change colors after scratching under UV light. The image below shows BF₂AVB coated on weighing paper (A), a cotton swab is used to write "Light" (B), the surface is hit with a heat-gun (C), the surface is ready to be written on again with a cotton swab (D).

The image brings up all kinds of creative ways to write secret messages, especially as the letters will fade over time even without using a heat gun. But before the CIA intelligence wonks in the audience get ahead of themselves the material doesn't seem to be completely reversible at room temperature without annealing.

...even a small mechanical perturbation, such as a slight touch with the tip of a cotton swab, changed the green-blue BF2AVB film emission to yellow. The yellow emission gradually reverted back to green again at room temperature, with much faster recovery at elevated temperature. The written regions were no longer readable after annealing.

The field has, in short order, gotten tantalizingly close to a 100% reversible mechanochromic luminescent material at room temperature. Congrats!

Link to article: Polymorphism and Reversible Mechanochromic Luminescence for Solid-State Difluoroboron Avobenzone

Sam covered one of the first entrants to reversible mechanochromic luminescence a year ago: reversible mechanochromic luminescence is cool

Mitch

Update and Correction: Cassandra Fraser has corrected me, apparently the wording of the paper was just awkward to my ear, the material is fully reversible at room temperature!

Subscribe to the comments for this post

NanoPropulsion

Stephen J. Ebbens

Jonathan Howse

The current state of the art in nanopropulsion devices was recently reviewed by Ebbens and Howse in an article last Friday.^[SoftMatter] A short summary of the nano- systems is presented below with video action shots when I could find them.

The Whitesides

Catalyst: Pt
Fuel: H₂O₂
Propulsion: Bubble propulsion
Terrain: Aqueous meniscus
Max Speed: 2 cm/s
Mitch's Name: The Karl Benz (since it was the first)
Article: Autonomous Movement and Self-Assembly

The Sen-Mallouk-Crespi

Catalyst: Pt
Fuel: H₂O₂
Propulsion: Self electrophoresis/Interfacial tension
Terrain: Settled near boundary in aqueous solution
Max Speed: 6.6 um/s
Mitch's Names: The Ford Mustang of nanopropulsion. (It is a hot rod, get it?)
Article: Catalytic Nanomotors: Autonomous Movement of Striped Nanorods

The Jones-Golestanian

Catalyst: Pt
Fuel: H₂O₂
Propulsion: Pure self diffusiophoresis
Terrain: Free aqueous solution
Max Speed: 3um/s
Mitch's Name: The Volkswagen Beetle
Article: Self-Motile Colloidal Particles: From Directed Propulsion to Random Walk

The Mano-Heller

Catalyst: Glucose oxidase and Biliruben oxidase
Fuel: Glucose
Propulsion: Self electrophoresis
Terrain: Aqueous meniscus
Max Speed: 1 cm/s
Mitch's Name: The Komatsu Truck (because it is huge)
Article: Bioelectrochemical Propulsion

The Feringa

Catalyst: Synthetic catalse
Fuel: H₂O₂
Propulsion: Bubble/interfacial
Terrain: Acetonitrile solution
Max Speed: 35 um/s
Mitch's Name: The F150 (has some exhaust issues)
Article: Catalytic molecular motors: fuelling autonomous movement by a surface bound synthetic manganese catalase

The Sen-Mallouk

Catalyst: Pt (CNT) (+cathodic reactions at Au)
Fuel: H2O2/N2H4
Propulsion: Self electrophoresis
Terrain: Settled near boundary in aqueous solution
Max Speed: 200 um/s
Mitch’s Names: The Ford Mustang GT (has more kick than the regular version)
Article: Bipolar Electrochemical Mechanism for the Propulsion of Catalytic Nanomotors in Hydrogen Peroxide Solutions

The Feringa v2

Catalyst: Glucose oxidase and catalse
Fuel: Glucose
Propulsion: Local oxygen bubble formation
Terrain: Free aqueous buffer solution
Max Speed: 0.2–0.8 um/s
Mitch’s Name: The Chevrolet Nova (more hot rod action)
Article: Autonomous propulsion of carbon nanotubes powered by a multienzyme ensemble

The Gibbs-Zhao

Catalyst: Pt
Fuel: H₂O₂
Propulsion: Bubble release mechanism
Terrain: Aqueous solution
Max Speed: 6 um/s
Mitch's Name: The Rover
Article: Autonomously motile catalytic nanomotors by bubble propulsion

The Bibette

Engine: External magnetic field
Propulsion: Flagella
Terrain: Aqueous solution
Max Speed: unknown
Mitch's name: The BMW Mini E (because there is no such thing as a magnetic car)
Article: Microscopic artificial swimmers

The Sagués

Engine: External magnetic field
Propulsion: Doublet rotation coupling with boundary interactions
Terrain: Settled near boundary in aqueous solution
Max Speed: 3.2 um/s
Mitch's Name: The Smart ED
Article: Magnetically Actuated Colloidal Microswimmers

The Fischer

Engine: External magnetic field
Propulsion: Propeller drive
Terrain: Aqueous solution
Max Speed: 40 um/s
Mitch's Name:
Article: Controlled Propulsion of Artificial Magnetic Nanostructured Propellers

The Najafi-Golestanian

Engine: Conformation changes in linking units
Propulsion: Time irreversible translations
Terrain: Free solution
Max Speed: ?
Mitch's Name: The Eternal Concept Car
Article: Propulsion at low Reynolds number

Some devices that were not included by the authors of the review article, but should definitely be included in any list like this are below:

The Gracias

Engine: External magnetic field
Propulsion: Brute Force
Terrain: Aqueous solution
Max Speed: ?
Mitch's Name: The Truck Cranes
Article: Tetherless thermobiochemically actuated microgrippers

Tetherless Microgrippers Grabs Tissue Sample - Watch today’s top amazing videos here

The Nelson

Engine: External electromagnetic fields
Propulsion: Flagella
Terrain: ?
Max Speed: 18 um/s
Mitch's Name: The Tesla Roadster (simply awesome)
Article: Characterizing the Swimming Properties of Artificial Bacterial Flagella

Artificial Sperm - Watch more funny videos here

Link to Review Article: In pursuit of propulsion at the nanoscale

Mitch

Subscribe to the comments for this post