We are able to generate a 200 micrometer layer on the bottom of a glass bottom dish using a spin coater. However, for our purposes, is it possible to put another layer of PDMS atop of the bottom layer without the two layers of PDMS bonding to one another?
If I were you, I would deposit firstly that "basic" coating, and then add a second layer by film on liquid method for example (Langmuir-Blodgett technique). Will work.
Hi, Travis.
I encountered a similar problem in my work, and have two solutions.
Solution1: Cure the two layers at different temperatures.
Cure the first layer at room temperature and second layer at 100 deg C. The difference in temperature gives rise to difference in the stiffness of the two layers. I have experienced that with some effort, it is possible to separate the two layers. If they separate, it means that they do not bond. However, in your case, it may be very challenging as the thickness of the layers is only 200 microns and the layers may tear. Another drawback of this method is that I have seen debris on the second layer.
Solution2: Silanization
This works very well for me.
1.Take the first layer of PDMS. Activate its surface by plasma - you can use the same setting as the one that you would use to bond PDMS and glass.
2.Then, take a few drops of APTES or dichlorodimethysilane or HMDS or any silanizing agent that you know. From my experience, the first three work for sure. Place the silanizing agent and the activated PDMS in a closed chamber (a closed petri-dish or a vacuum desiccator depending on the size of the sample) and leave it for about 30 minutes. Now open the chamber under a fumehood. The surface of first layer of PDMS is silanized.
3.Now, pour or spin the PDMS mixture to form the second layer without much time delay. Cure. The two layers of PDMS will be separable.
I hope this helps.
Regards,
Bhuvana.
I agree with Bhuvana, however, silanation can both increase or decrease bond strength, so agent selection will be important. Is the second layer the same PDMS composition? Perhaps adding an incompatible PDMS fluid to the 2nd PDMS prior to application to reduce bond strength between layers, and adding a "pure" boundary of the 2nd PDMS to the edges to maintain discrete points of contact after curing, and allow formation of the pocket.
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