A robust method to calculate the volume phase transition temperature (VPTT) for hydrogels and hybrids

Abstract

Here, we report three different methods to determine the volume phase transition temperature (VPTT) of various systems including poly(N-isopropylacrylamide) (pNIPAm) based nanogels, Au nanoclusters and a combination of inorganic and polymeric systems. Although all the methods reveal close VPTT values, we suggest that method III is the least computation dependent and most reliable. In an attempt to define the overall system reversibility, a predictive reversibility parameter (RP) was defined that explains the system behavior at each state point. RP takes into consideration all the system states during both heating and cooling cycles. Reversible systems were found to have RP values less than 1, while irreversible systems were observed to have RP values of 2. We predict that real systems will show RP values between 1 and 2. Thus, by knowing both the system's VPTT and its reversibility, a particular application can be designed or upgraded.