I guess this is a chemistry question.
I cant find the answer online, all I see online is that u should keep chocolate in an airtight container.

my question however is, is a a chocolate layer itself an airtight seal ?

I am wondering this because I am experimenting in making my own chocolates with dried fruits and other fillings, but the expiration date that I would use for them depends on if the filling inside the chocolate is coming in contact with oxygen.

Hope you guys can help me out.

Kind regards,
Gee

I don't know of any measurements of the actual values of the constants involved though doubtless the confectionery industry has measured this, but here is a case for invoking Fick's Law.

 

At any given temperature gaseous molecules such as oxygen will have a mobility through chocolate (which can be called a semisolid).

 

The rate of diffusion through a barrier of chocolate will depend upon the diffusion coefficient, the thickness of the barrier, the partial pressure difference of the diffusing gas on each side of the barrier.

 

https://www.google.co.uk/search?hl=en-GB&source=hp&biw=&bih=&q=Fick%27s+Law&gbv=2&oq=Fick%27s+Law&gs_l=heirloom-hp.3..0l10.1329.3750.0.4282.10.6.0.4.4.0.203.765.0j4j1.5.0....0...1ac.1.34.heirloom-hp..1.9.923.PJYwtUz7Tzs

 

This should be enough to to research the subject further.