Wednesday, June 9, 2010

I hardly think "Coffee-stain effect" is a scientific term

You know coffee nanoparticles is the name of this blog (with a much more apropos subtitle – which I will have to change once I return to the western world. Except for the steampunk romance part – that was pure clairvoyance), I haven’t actually spoken about coffee nanoparticles since my very first (and very brief) post. There I proposed the question: “Coffee – nanoparticle suspension or dissolved solution?”

Well now, my pretties, I feel I may have come to an answer. I do a lot of reading of recently published papers in a few of my favourite scientific journals (JACS, Nanoletters, Langmuir, Advanced Functional Materials, Nature Materials/Nano, etc) since I feel like this practice increases my chances of having a basic understanding of most problems or systems I’m likely to come across in work and at school.

Yesterday I was perusing Langmuir (a surface science paper, nanos can recall that this is the Langmuir of Langmuir isotherm/Blodgett films fame) and came across this paper: “Coffee-Ring Effect-Based Three Dimensional Patterning of Micro/Nanoparticle Assembly with a Single Droplet” by a group out of Berkeley. Obviously the first word caught my eye, the rest is just icing on the mocha, so to speak. The paper is pretty self explanatory, they just suspend some micro and nanoparticles in some solution, make a droplet, wait for it to evapourate, then watch the “coffee-ring effect” do its work in the form of a self-assembled circular microscructure composed of your particles. Take a looksee at the figure below.

Mmmm, coffee self assembly.

Anyway this isn’t what is important at all. This is just a new take on existing methods that exist to make such shapes and structures that we’ve looked into ad nauseum and inscribed in the tiniest of hands on our Nanofab cheat sheets. What’s important comes later:

And I quote: “Our technique is mainly grounded on the coffee-ring effect of solutes in an evaporating suspension. When a spilled drop of coffee dries on a solid surface, it leaves a dense, ring-like deposit along the perimeter. Such ring deposits are common wherever drops containing dispersed [nano]particulate solids evaporate on a surface.”
[Editor's node: I added a prefix I think the authors accidentally missed.]

There it is, spelled out in black and white in a peer reviewed journal. He even cites a reference for the last claim, so you know its legit. Coffee is a [nano]particulate solid dispersion. Just so we’re all clear now. I drank coffee nanoparticles this morning.



  2. Is addictiveness proportional to surface area?

  3. This comment has been removed by the author.

  4. Also, I still think it would have been appropriate (not to mention more eco-friendly!) if we had been forced to use nanolithography in order to make our nanolithography cheat sheets. Like, instead of giving us up to six 8.5" x 11" sheets, Bo Cui should've restricted us to a 1 mm x 1 mm square.

    Course, we'd each need our own SEM during the test in order to see what we wrote... that might get a little expensive.