# Why is the critical seperation distance between two plates for capillary condenstation to occur negative?

I am currently reading this paper: Auto-adhesion model for MEMS surfaces taking into account the effect of surface roughness

In their numeric example, they find a critical distance for capillary condensation to occur as being -3.5nm. Why negative ?

Here is the extract from the paper:

EDIT:

I know that log(0.5) is −log(2), hence negative, but I am rather interested in the physical meaning of this ? There is no negative distance between two plates ! So... what does this mean ? Is it maybe measured in a inverted reference ??

• because $\log(0.5)=-\log(2)$... but something tells me you want a physical not mathematical explanation. – nluigi May 28 '18 at 8:35
• @nluigi Yes, exactley. My question was maybe not clear. I have updated it. – james May 28 '18 at 8:52