The Flory-Rehner equation does give the relation between cross-linking density and the swelling ratio. But will there arise a difference in the swelling ratio if a polymer is immersed in a solvent for 48 hours as against, say, 72 hours. How will that be accounted for, since, the ratio is used to calculate the cross linking density?
The swelling behaviour of polymer can be attributed to the degree to which solvent diffuses into the intermingled and entangled polymeric chain molecules which in turn depends upon the structure of polymer. It is the amount of access polymers offer depends more upon the voids or empty spaces in the entangled polymers than time. More crosslinking density will reduce swelling tendency.
Thank you very much, Mr. Kulkarni and Mr. Tsanov for your informative answers.
The Flory-Rehner model describes the swelling of polymer networks under equilibrium conditions, i.e. at long times, when the swelling degree is no longer a function of the swelling time.
In practice, if you wait too long, the network may start rupturing. Choosing the correct swelling time is therefore not a trivial question as you need to allow for enough time for the gel to equilibrate but short enough for it to not degrade. The following article (see Figure 2) provides some useful information on this topic:
Article Uncertainties in the Determination of Cross-Link Density by ...
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