Microsystems in Physical Review Applied

Work from our group was published in Physical Review Applied. In the article, Mechanics from Calorimetry: Probing the elasticity Elasticity for Responsive Hydrogels, we illustrate and exploit the inherent thermodynamic link between thermal and mechanical properties by showing that the compressive elastic modulus of a thermosensitive PNIPAM hydrogel can be probed using differential scanning calorimetry.

In our paper, we perform calorimetric measurements on PNIPAM hydrogels at different levels of compression and show that the change in internal energy required to heat a sample at starting temperature T0 to a final temperature Tf above its LCST is lower than that for an uncompressed sample that undergoes the same heat treatment. The difference between these two changes in internal energy must be equal to the difference in internal energy between the initially compressed and the uncompressed states, respectively. We approximate this difference in internal energy ΔU as the work W required to compress the gels at a constant temperature T0, which in turn yields the compressive (bulk) modulus

As our method does not require mechanically loading the sample it could be particularly valuable for determining the mechanical response of thermosensitive submicron-sized and/or oddly shaped particles, to which standard methods are not readily applicable.