Héctor here, your AFM expert at Nanosurf calling out for people to share their Friday afternoon experiments. Today I take a look at the humble pen. You will learn:
Behold a wonder of technology, the ball point pen, or birome as known in some parts of the world.
Did you knew that it takes an AFM to produce it?
The modern ball point pen dates back to a patent filled in 1938 by László Bíró. A previous version dates back about 50 years, but it was far more different to the ones we use nowadays.
Over the years, there have been many modifications to the original concept, some using springs, some using additional channels for the ink, and lately ones combining ink with the capability to write on electronic devices.
However, over the years one key factor has remained the same. The roughness of the steel (or ceramic in some cases) is critical for the performance of the pen, and nowadays the tolerances are smaller than ever because customers demand homogeneous products that work all the time. So, how AFM makes this possible?
Let's recap. Ball point pens have come a long distance since they where invented, and nowadays the tolerances are so tight that AFMs are required during production. This is something that Nanosurf knows well, because we have been providing instruments to automatize this task for the last 15+ years. Here I showed you how to mound pens to examine the ball that carries the ink, how to clean the ink, and how to analyze the data with Gwyddion and MountainsSPIP. In addition, we also look at how usage affects the roughness and how the surface of a new ball, which is "flat" with holes in it, turns into a surface covered in scratches.
I hope you find this useful, entertaining, and try it yourselves. Please let me know if you use some of this, and as usual, if you have suggestions or requests, don't hesitate to contact me.
Extra:
For those that prefer to skip the video, here are the key steps.
In order to measure roughness first we need to mount the sample somehow. Because I have no access to the steel ball itself, I need to find a way to secure the ball while it is still part of the pen. Thanks to the tip scanner on the DriveAFM this is not a problem, as the sample can have any size or weight.
Please have in mind the time constraints when reviewing my design.
For brand new pens the ink hasn't yet touched the ball, so they are clean, however, for pens that have been used, I need to figure out a way of cleaning the surface. Well, it turns out that if the pen has been used recently (within a few minutes), the ink is still liquid and can be cleaned by carefully touching the ball with a tissue (making sure the ball doesn't rotate).
So, in order to clean the ball and remove the ink I put the pen under an optical microscope and carefully touched the ball with a tissue.
Then it was time for AFM imaging.
First I imaged the brand new ball.
Then I simulating some real use...
... which took far longer than expected, hence I recruited Clemens to automatize this step...
... and eventually got us the ball from a completely used pen.
As you can see, there is a huge difference, and no wonder that eventually pens start leaking ink... basically the scratches are so many and so deep that they don't seal anymore.
Now, for the analysis, I showed how to calculate roughness both using Gwyddion and MountainsSPIP, because during the production of pens balls are regularly examined, and if they don't match the roughness tolerances they are discarded.
Gwyddion:
MountainsSPIP:
Hope you find the summary as useful as the main video.