ABSTRACT Thermally induced variations in the strain and stress for poly(N‐isopropylacrylamide) (PNIPAm) hydrogels were investigated by strain gauges for the first time. The strain gauges revealed microscale contraction strains above the thermoresponsive temperatures. The micro‐scale strain of PNIPAm aggregates could reach ∼10 2 µɛ, resulting in local stress around ~10 2 mPa, and the contraction state is not recovered even after the hydrogel turns transparent again. These mechanical values are crucial for specific applications, such as in biomedical fields. Moreover, the present measuring method directly captured the thermoresponsive microscale strains induced by thermoresponsive aggregations of the PNIPAm, thereby elucidating the polymeric movements in amorphous hydrogels. This approach successfully characterizes the thermally induced strain and stress properties of PNIPAm gels.
Qin et al. (Wed,) studied this question.