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Hofmeister Effect of Sodium Halides on the Switching Energetics of Thermoresponsive Polymer Brushes
Author(s) -
Naini Crispin Amiri,
Thomas Marc,
Franzka Steffen,
Frost Sven,
Ulbricht Mathias,
Hartmann Nils
Publication year - 2013
Publication title -
macromolecular rapid communications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.348
H-Index - 154
eISSN - 1521-3927
pISSN - 1022-1336
DOI - 10.1002/marc.201200681
Subject(s) - hofmeister series , halide , chemistry , enthalpy , polymer , thermodynamics , energetics , kinetics , sodium , entropy (arrow of time) , chemical physics , polymer chemistry , ion , inorganic chemistry , organic chemistry , physics , quantum mechanics
A laser temperature‐jump technique is used to probe the impact of sodium halides on the temperature‐dependent switching kinetics and thermodynamics of poly(N‐isopropylacrylamide) brushes. An analysis on the basis of a two‐state model reveals van't Hoff enthalpy and entropy changes. Sodium halides increase the endothermicity and the entropic gain of the switching process below and above T c following the Hofmeister series: NaCl > NaBr > NaI. In contrast, enthalpic and entropic changes at T c remain virtually unaffected. This provides an unprecedented insight into the underlying switching energetics of this classic stimuli‐responsive polymer. Because of its model character, these results represent an essential reference on the way to unpuzzle the molecular driving forces of the Hofmeister effect.