Supercritical synthesis and studies on non-isothermal kinetics and thermodynamics of solid state decomposition of nanoferrogels

Abstract

Poly-N-isopropyl acrylamide (PNIPAM) and related nanoferrogels (NFG) were synthesized in supercritical carbon dioxide and investigated for their non-isothermal kinetic and thermodynamics of solidstate decomposition in oxidative media. Ferrite nanoparticles (FNPs, 10.5 nm) were prepared for NFG through chemical method. Thermal stability, along with kinetic and thermodynamic evaluationsof NFG has been shownthrough simultaneous thermogravimetric (TG) - differential thermal analysis (DTA) - differential thermogravimetry (DTG) in air.Thermal, non-isothermal kinetic and thermodynamic data of NFG was compared with FNP and PNIPAM. NFG have shown two step decompositions with reduction in their TG onset by 10 °C over FNPs and PNIPAM. This was associated with simultaneous increase in heat of fusion (mJ/mg) of NFG (2.88) over PNIPAM (2.55). Horowitz- Metzger (HM) and Coats-Redfern (CR) at reaction orders (n) ranging 0 to 3 reveals consistency in order of solid-state decomposition for FNPs (n = 1), PNIPAM and NFG (n = 3) with negative values of changes in entropy and enthalpy. HM methods reveals greater values of energy of activation (Ea) with respect to CR methods. Applied methods provide large differences in the values of Ea of solidstate degradations with marginal changes in thermodynamic parameters of NFG over PNIPAM. Kinetic and thermodynamic calculations reveal enhanced thermal stability of NFG over PNIPAM followed by FNPs. High thermal stability of NFG makes them possible for agricultural and biomedical applications.