Advanced two-step cryopolymerization to form superporous thermosensitive PNIPA/clay gels with unique mechanical properties and ultrafast swelling-deswelling kinetics

• Published in: Colloid and polymer science 2018-04, Vol.296 (4), p.753-769
• Main Authors: Strachota, Beata, Šlouf, Miroslav, Hodan, Jiří, Matějka, Libor
• Format: Article
• Language: English
• Subjects: Characterization and Evaluation of Materials; Chemistry; Chemistry and Materials Science; Complex Fluids and Microfluidics; Cooling rate; Evolution; Food Science; Freezing; Gels; Hydrogels; Mechanical properties; Morphology; Nanotechnology and Microengineering; NMR; Nuclear magnetic resonance; Original Contribution; Physical Chemistry; Polymer Sciences; Polymerization; Porosity; Reaction kinetics; Soft and Granular Matter; Swelling
• ISSN: 0303-402X; 1435-1536
• DOI: 10.1007/s00396-018-4289-8

The superporous thermosensitive PNIPA/clay hydrogels were prepared by the advanced two-step freezing polymerization. The formation and properties of the cryogels were controlled by freezing conditions, such as time of freezing during the two-step polymerization and the rate of cooling. The freezing of the reaction mixture in different well-defined stages of structure evolution during polymerization made it possible to fine tune the structure, morphology, and properties of cryogels. The development of structure during polymerization was followed by NMR and chemorheology, and moreover, the morphology, porosity, swelling behavior, and mechanical properties of the cryogels were determined. The results contribute to the basic understanding of the structure evolution under freezing conditions and to the knowledge of the mechanism of a cryogel formation. The smart thermoresponsive gels with a wide variety of properties were prepared, ranging from the weak ultrafast responding cryogels (deswelling in 30 s, reswelling in 8 min), prepared by the early freezing, up to the porous gel with extraordinary mechanical properties ( σ b  = 320 kPa, ε b  = 900%) still displaying a relatively fast thermal volume transition. The advanced two-step freezing polymerization is shown to be a suitable general approach to controlling and tuning porosity, as well as swelling and mechanical properties of porous gels.