Stephen J. Ebbens
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.
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
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
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
Catalyst: Glucose oxidase and Biliruben oxidase
Propulsion: Self electrophoresis
Terrain: Aqueous meniscus
Max Speed: 1 cm/s
Mitch’s Name: The Komatsu Truck (because it is huge)
Article: Bioelectrochemical Propulsion
Catalyst: Synthetic catalse
Terrain: Acetonitrile solution
Max Speed: 35 um/s
That is the highly controversial claim made by Kate Ovchinnikova and Gerald Pollack in Langmuir earlier this year.[Langmuir] Electroneutrality is a guiding principal in electrochemistry and is a method to understanding electrolytic cells (Pt electrodes in dilute aqueous NaCl solutions). It stipulates that any charge imbalance across an electrochemical system is quickly (~ns) balanced by the salt present in the water being driven by the electric field in such a way to neutralize that charge imbalance. Thus the need for salt bridges and all that wonderful G-chem stuff we have learned. There is even a cool little applet you can play with electroneutrality by the Harvey Project. When I tried to sit down with electrochemists to discuss the claims by O&P they quickly dismissed them out of hand after reading the beginning of their paper. So the big question is, did O&P stumble across something amazing or did they spectacularly overstate the results of their experiment.
I can summarize their paper succinctly:
Insert electrodes into electrolytic cell
Turn on power supply
Disconnect the electrodes from the circuit
Remove the bridge between beakers
Reconnect electrodes to measure residual charge in the two beakers.
The design seems thoughtful enough, but before I get into the merits of their results I need to take time to mention a few gems in their paper. Here is a quote from them.
Bubble formation occurred in all experiments (n > 20), although position and...
When you look into the nanoparticles, the nanoparticles also look into you.
Graphic abstract from: Stabilization of Superparamagnetic Iron Oxide Core−Gold Shell Nanoparticles in High Ionic Strength Media
Pun From: Play on the famous quote by Friedrich Nietzsche
If I wanted to add colors to SEM pictures how would I do it? Let’s also add the stipulation that I don’t have access to PhotoShop or anything that would cost money. Illegal downloading isn’t an option. This has been on my mind for quite some time, but yesterday I sat down after dinner and developed my solution. This is my logic through the process.
I need a way to analyze the RGB of every pixel in an image.
I need to develop a simple algorithm to manipulate the RGB for every pixel.
Apply the algorithm and generate the colored picture.
RGB is the value for Red, Green, and Blue coded for each pixel. They run from 0 to 255. So, I wrote a script that will analyze this pixel information using php. My canvas was Yow et al.‘s recent image of colloidosomes, shown below.
A gray scale picture will have the same value for RGB. The simplest manipulations will be to hold either R, G, or B to zero and let the others retain their original value. This yields teal for R=0, violet for G=0, and yellow for B=0.
To generate blue (R=0, G=0), green (R=0, B=0), and red (G=0, B=0) you’ll need to set two values to zero.
Primary colors are nice, but if you want to have softer gentler colors you’ll need to apply an algorithm to your RGBs. For a light blue, I use the following R=(0.2 * B), G=(0.6 * B), B=B.
An orange I like is R=R, G= (0.5 * R), B=0.
If someone knows a simpler way of SEM color manipulation please share. Also, if someone would like me to make a script...