Archive for March, 2012
Today I read more about roughness and started a LaTeX document with my re-derivation of Hamaker’s constant. I also got a nice paper discussing theoretical models of adhesion using different roughness models.
- Eichenlaub S, Gelb A, Beaudoin S (2004) Roughness models for particle adhesion. Journal of Colloid and Interface Science 280:289–298. PMID:15533399. http://dx.doi.org/10.1016/j.jcis.2004.08.017.
I am still working on the complete derivation and once I am finished, I will post it in my notebook.
I spoke with Oli today about some high speed imaging techniques and experiments to do. I am engineering a chamber for the inhalers now.
I still have not gotten the sputter coater working. I am going to try vacuum greasing the chamber a lot and see if that does anything.
I was able to contact an engineer at nanoTherics today. Hopefully we can figure out what is wrong with our device. So far, my interactions with them indicate that they are an awesome company and anyone reading this should buy stuff from them.
Damian and I tried even more things. Including removing and cleaning all connections to the chamber. Nothing worked. We even globed on a bunch of vacuum grease every where to see if there were inadvertent leaks. Again, nothing worked.
Accelerometer power supply
Sarah and I completed the power supply modifications today. This is good news as we can now start looking at the accelerometer for the pendulum
Non ferrous stirrer.
Tommy needed a stirrer for magnetic nanoparticles. So, I ripped apart a hand drill that functioned off of a 6V battery pack. Unfortunately, the battery pack was dead and the charger didn’t work. So, I swapped out the battery pack for a 6V wall wart with not a lot of current. This is fine as the stirring doesn’t need to be fast. By removing the battery pack, the ability to change the speed went away. I’m guessing that there is some way to reinstate this. In the mean time, sorry Hugh for ripping apart your old hand drill. I will fix it when it is no longer needed. The stir bar is a glass pipet that was cleaved and the paddle is a microscope slide that is epoxied to the pipet. No metal!
The sputter coater has 2 valves that control the exhaust (for when you want the chamber to return to atmospheric pressure) and the other for filling the chamber with the gas of your choice. In order to determine if the release valve is the culprit for our leak, I did the following things.
- Removed the release valve and re-Teflon taped the filter and hose connected to it.
- Completely bypassed the release valve and rigged together a manual release valve.
Neither of these things worked. Rather than try to fuss with the valves, I am going to remove all connections to the chamber and try to find a way to test pressure inline with the vacuum pump. Perhaps the actual chamber is the problem.
- Plug all connections to the chamber and test.
If the chamber isn’t the problem, then it may be the pressure gauge. That, I can’t fix and will be an absolute bear if we need to replace it since the machine is out of production.
Continuing with my other interests in roughness, I obtained the original Hamaker publication which talks about the aptly “Hamaker coefficient” that I have been reading about. I plan to rederive the coefficient for two spherical bodies as it should be interesting.
I have been able to read Hamaker’s original article
Hamaker HC (1937) The London-van der Waals attraction between spherical particles. Physica 4:1058–1072. http://dx.doi.org/10.1016/S0031-8914(37)80203-7.
and I have worked through his calculations. I am getting a sign error for some reason and will have to investigate that later. In the very least, it feels good to do some math and flex my integrating muscles. I’ll post my calculations in a later post.
The sputter coater is down due to the device’s inability to pump the sample chamber to the required pressures to sputter. Damian and I have tried the following things to try and fix it.
- Cleaned the pump.
- Changed the hose.
Unfortunately, neither of those fixed the problem. I just now switched out the pump with a different one and the same problem is occurring. My next steps are:
- Change out the hose material.
- Re-teflon tape the other hose connectors that are connected to valves etc.
Changing the hose material did nothing for the pumping. Actually, it made it worse so it is most definitely not the hose, nor is it the pump. This leaves the following connections that need to be checked:
- Gas inlet hose.
- Pressure gauge.
- Gas mixing valves.
Drat…a lack of Teflon tape is preventing me from looking at the rest of the valves.
Another project that is related to fixing the sputter coater is to investigate roughness. I feel like I am spinning my wheels on this one a good amount as the paper I am reviewing:
- Rabinovich YI, Adler JJ, Ata A, Singh RK, Moudgil BM (2000) Adhesion between nanoscale rough surfaces: I. role of asperity geometry. Journal of Colloid and Interface Science 232:10–16. PMID:11071726. http://dx.doi.org/10.1006/jcis.2000.7167.
is not easy to follow as there seem to be missing steps with the RMS roughness calculations. Especially since I feel like equation 4 is coming out of left field with its coefficients. Of course, this is probably because I don’t know the field well enough…I am currently investigating other references but I am finding it difficult to find articles.