Porous hybrid poly(N-isopropylacrylamide) hydrogels with very fast volume response to temperature and pH

0508103 - ÚMCH 2020 RIV GB eng J - Journal Article
Strachota, Beata - Oleksyuk, Khrystyna - Strachota, Adam - Šlouf, Miroslav
Porous hybrid poly(N-isopropylacrylamide) hydrogels with very fast volume response to temperature and pH.
European Polymer Journal. Roč. 120, November (2019), s. 1-14, č. článku 109213. ISSN 0014-3057. E-ISSN 1873-1945
R&D Projects: GA ČR(CZ) GA19-04925S
Institutional support: RVO:61389013
Keywords : polymeric hydrogels * smart materials * nanocomposites
OECD category: Polymer science
Impact factor: 3.862, year: 2019
Method of publishing: Limited access
https://www.sciencedirect.com/science/article/pii/S0014305719313965?via%3Dihub

Super-porous hydrogels were prepared, which are able of fast to ultra-fast volume response to temperature and to pH, and thus show a promise as soft actuators. The hydrogels are based on the poly(N-isopropylacrylamide) (PNIPAm)/silica nanocomposite, in which the filler strongly raises the modulus and also stabilizes the pore walls against collapse during deswelling. The well-interconnected sub-millimetre-sized porosity was generated via solvent freezing during synthesis. The gels morphology makes possible both ultra-fast deswelling and re-swelling (5.5 s for 70% in both directions, in response to T). This work focused on introducing pH-responsiveness into the gels. To this end, 1–10 mol% of sodium methacrylate (SMA) were incorporated as co-monomer. Distinct pH-responsiveness was achieved already at 1 mol% of SMA. Increase of SMA content markedly expands the temperature range of the pH-responsiveness and raises its amplitude. At the same time the increase of SMA content reduces the amplitude of the T-responsiveness, which is only moderate at 10 mol% SMA. The rate of pH-response was found to be always slower than in case of the T-response: 75 s are needed for 70% of de-swelling, and 90 min for 70% of re-swelling. The vast difference in the rates of pH- and T- response can be explained by different mechanisms of stimulus propagation (momentum transfer for T, vs. diffusion for pH) and by the mechanical effect of a contracting stiff and porous surface layer (much faster pH-deswelling than re-swelling). More generally, in case of the pH-stimulus, the mechanistic limits of its propagation in ‘simple’ porous gels become evident.
Permanent Link: http://hdl.handle.net/11104/0299318