Microcalorimetric Study of the Effects of a Chaotropic Salt, KSCN, on the Lower Critical Solution Temperature (LCST) of Aqueous Poly(N-isopropylacrylamide) (PNIPA) Solutions
| Autor: | Inna Shechter, Irina Portnaya, Yoav D. Livney, Ory Ramon, Yaron Paz |
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| Rok vydání: | 2009 |
| Předmět: |
Aqueous solution
Chromatography Polymers and Plastics Organic Chemistry Cooperativity Lower critical solution temperature Endothermic process Inorganic Chemistry chemistry.chemical_compound Chaotropic agent chemistry Chemical engineering Ionic strength Potassium thiocyanate Materials Chemistry Poly(N-isopropylacrylamide) |
| Zdroj: | Macromolecules. 43:480-487 |
| ISSN: | 1520-5835 0024-9297 |
| Popis: | The LCST phase-transition of aqueous PNIPA solutions in rising concentrations of the strong chaotropic salt KSCN was studied microcalorimetrically by DSC and apparently for the first time by ITC. An endothermic (entropy driven) binding of KSCN onto PNIPA was observed, explained by electrostatic perturbation of hydrophobic hydration by adsorbed ions. A good fit was found for the one-type-of-sites binding model, and the binding affinity increased with rising temperature from 15 to 20 °C but decreased at 25 °C. DSC measurements emphasized the lowering and broadening of the endothermic peak of PNIPA phase-transition with rising KSCN concentration, explained by reduced cooperativity of coil-to-globule collapse with increased heterogeneity along the polymer chain, caused by salt adsorption. A hysteresis was observed between heating and cooling DSC peaks, which decreased asymptotically with rising KSCN concentration, further supporting that binding occurs. This work provides new insights into the mechanisms of c... |
| Databáze: | OpenAIRE |
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