Fast temperature-responsive nanocomposite PNIPAM hydrogels with controlled pore wall thickness: Force and rate of T-response

Fast thermoresponsive porous hydrogels based on the PNIPAM–silica nanocomposite were prepared and optimized in order to obtain increased force (pressure) response to temperature stimuli. This was achieved by increasing pore wall thickness via changing the monomers concentration during the hydrogels’ cryogenic synthesis. The mechanically strong and compact pore structure of the best gel made it possible to increase the force (pressure) response 3 times and the shear modulus 4 times, while the volume ratio of swollen to deswollen state remained unchanged, and the kinetics of the T-response was only moderately slower than in the case of the analogous ultra-fast responsive soft gels. The porous structure of the hydrogels (SEM), the dispersion and particle size of the nanofiller in the pore walls (TEM), as well as the swelling behavior and time-resolved force response to T-change are discussed in this work.

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► Nanocomposite PNIPAM–SiO2 hydrogels with strong pore walls were prepared.
► The distinct thermo-responsivity including volume ratios was kept in the products.
► Force responses to T-jumps of up to 1 N were achieved.
► Force response was about 3 times faster than the swelling response.
► The SiO2 nanofiller was directly visualized by TEM.