How big is the surface-area?

If it's possible to make it larger, it would lessen the effects of the surface-tension, in the interface.

Only 1cm^2 at this point, but going larger is definitely an option.

I think you are very close to an optical flat, if you increase it to app. 5 cm in diameter. Of course depending on the beam spot size.

I am somewhat confined to a square cell! I have a 3 cm x 3 cm cell that I can try. Thx.

Dear Palash,

at my Institute we are working with light guides and we have Teflon trough (Accurion GmbH) and we uses water and a transparent oil and look at the interfaces with imaging ellipsometry.

Best regards

Christian

Dear Christian,  

Thanks for your input.  We solved this issue as well.  We make hydrophilic -hydrophobic coating on the glass cell wall on the water and dodecane sides respectively.  A sharp interface on that, can be achieved simply by i) first coating the inside with a photoresist and expose it from outside, lets say the top half, ii) then clean the bottom half of unexposed resist and coat it with a hydrophobic silane, iii) now clean the top part and repeat the process with a hydrophobic silane.  We get best results with this.  However, another easier way to do this, is to have a smaller (say covering half the height) teflon cell constructed that will fit inside the larger glass cell, by placing it upside down.  The smaller teflon cell should have a circular hole on top cover.  Now build the water layer inside the teflon cell until it reaches the hole height and then gently build the dodecane layer on top.  The flatness of the interface obviously depend on the size of the hole and smoothness of the wall surrounding the hole in the teflon cell. 

Thanks,

Palash