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Very excited to share this work! Please note, ALL the data for the project is available online on Figshare ( https://doi.org/10.6084/m9.figshare.c.5010869.v4) More notes in the thread https://twitter.com/NPeppas/status/1360385699057442820
We independently confirmed via buoyancy measurements that for PVA and PEGDA hydrogels, calculating polymer volume fraction from polymer mass fraction is valid. This is not true for all hydrogels!
When in doubt, directly measure polymer volume fraction using the buoyancy method! You will conveniently also get the data you need for the mass fraction to compare. You can 3D print your own density kit: https://www.thingiverse.com/thing:3972888
Fig. 2 is what convinced me we need to publish this. Initial polymer volume fraction equals relaxed polymer volume fraction. That part's easy and unsurprising. BUT...
The reference ratio (new term for the swelling from the relaxed state, more clear than the swelling ratio) INDEPENDENTLY responds to degree of polymerization between crosslinks. This sort of ideal behavior was entirely unexpected.
The two independent relationships draw clear, predictable connections between hydrogel synthesis conditions and swelling that were previously "hidden" by an emphasis on the swollen polymer volume fraction.
The meta-analysis confirms that our reference ratio result is not an artifact of our experiments and that it is broadly applicable among hydrogel systems.
