Fast deswelling and highly extensible poly(N-isopropylacrylamide)-hectorite clay nanocomposite cryogels prepared by freezing polymerization

Poly(N-isopropylacrylamide) (PNIPAm)-hectorite clay nanocomposite cryogels (NC-C gels) were prepared by freezing polymerization at −18 °C of NIPAm monomer in the aqueous hectorite clay suspensions. The clay concentration CxLS was found to be a key factor determining the characters of the NC-C gels, because the average interparticle distance became smaller than the clay diameter when CxLS > 6 w/v%. The NC-C gels of CxLS ≤ 6.0 w/v% were heterogeneous at the nascent state and became homogeneous after 24 h thawing, which endowed the cryogels self-improved mechanical strength and elongation up to 900%. On the contrary, for the NC-C gels of CxLS > 6.0 w/v%, the extensibility was about half of the corresponding normal NC gels, suggesting that the heterogeneity cannot be homogenized after 24 h thawing. The deswelling and reswelling rate of the NC-C gels of CxLS > 6 w/v% was significantly accelerated due to the micropore structure formed by the molten ice crystals. The micro-pores were observed with SEM and CLSM from the cryogels with the clay content higher than 6 w/v%. The extensibility of the NC-C gels was much higher than other cryogels with high deswelling rate, promising some possible applications.