Tailoring PNIPAM hydrogels for large temperature-triggered changes in mechanical properties
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N-isopropylacrylamide (NIPAM)-based hydrogel films are used for touch-controlled applications, where the temperature-induced change in the mechanical properties is utilized to create tactile feedback. N,N′-methylenebisacrylamide (BIS) and poly(ethylene glycol)diacrylate (PEGDA) are used as cross-linkers to study the influence of their size and concentration on the viscoelastic properties in a temperature-controlled rheology setup. The changes in water content between swollen and collapsed state of the hydrogel samples increase with decreasing cross-linking density and increasing size of the cross-linker resulting in bigger meshes in the network. The difference in the viscoelastic properties of the hydrogels increases with increasing deswelling ratio and is highest for the P(NIPAM-PEGDA) hydrogels with low cross-linking density with a 50-fold increase in the storage modulus. The deswelling ratio of these P(NIPAM-PEGDA) hydrogels is up to five times higher compared to the P(NIPAM-BIS) hydrogels of the same cross-linking density. The mesh sizes are estimated from the mechanical properties.
KeywordsPNIPAM hydrogel film BIS PEGDA Elasticity Swelling behaviour
Benjamin von Lospichl and Sarah Schatte are thanked for support with the rheology measurements, and Marc Griffel from the mass spectrometry analytic centre of the Institute of Chemistry at TU Berlin is acknowledged for his service.
The authors thank the Deutsche Forschungsgemeinschaft (KL1165/15-1) for financial support.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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