Berlin 2018 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 69: Focus: Polymers in Multi-Component and Aqueous Solutions I - organized by Jens-Uwe Sommer and Debashish Mukherji
CPP 69.11: Vortrag
Donnerstag, 15. März 2018, 18:15–18:30, C 130
Detailed calorimetric study on the collapse of poly(N-isopropylacrylamide) in aqueous sodium and guanidinium salts solutions — •Daniel Ondo, Adam Kovalčík, Jakub Polák, Vladimír Palivec, and Jan Heyda — University of Chemistry and Technology, Prague, Czech Republic
Poly(N-isopropylacrylamide) (pNIPAM) is a thermoresponsive polymer with a lower critical solution temperature (LCST) in pure water at 33 C. Addition of electrolytes, protein denaturants or organic cosolvents as a third component into aqueous pNIPAM mixtures, may change its solvation and balance between a collapsed hydrophobic and a swollen hydrophilic states hence alter the LCST and related thermodynamic quantities. In this work, employing the isothermal titration (ITC) and differential scanning (DSC) calorimetry, the LCST and total enthalpy of the collapse process of pNIPAM as a function of polymer and salt concentration (NaCl, Na2SO4, NaClO4, NaSCN, GndCl, Gnd2SO4, GndSCN) were measured. Any effort to fit the calorimetric data by mass-action chemical binding or kinetic models failed. Nevertheless, the solvation of the collapsed polymer at 35 C is well described by Schellman’s solvation model. The experimentally observed trends in LCST and total collapse transition enthalpy are in agreement with literature, verify the salt-polymer solvation model and are consistent with specifically designed dialysis measurements. Moreover, the microscopic details derived from the calorimetric measurements are in accord with performed µ-long atomistic simulations in the explicit solvent.