title: Hydrophobic hydration of poly-N-isopropyl acrylamide: a matter of the mean energetic state of water.
abstract: The enthalpically favoured hydration of hydrophobic entities, termed hydrophobic hydration, impacts the phase behaviour of numerous amphiphiles in water. Here, we show experimental evidence that hydrophobic hydration is strongly determined by the mean energetics of the aqueous medium. We investigate the aggregation and collapse of an amphiphilic polymer, poly-N-isopropyl acrylamide (PNiPAM), in aqueous solutions containing small amounts of alcohol and find that the thermodynamic characteristics defining the phase transitions of PNiPAM evolve relative to the solvent composition at which the excess mixing enthalpy of the water/alcohol mixtures becomes minimal. Such correlation between solvent energetics and solution thermodynamics extends to other mixtures containing neutral organic solutes that are considered as kosmotropes to induce a strengthening of the hydrogen bonded water network. This denotes the energetics of water as a key parameter controlling the phase behaviour of PNiPAM and identifies the excess mixing enthalpy of water/kosmotrope mixtures as a gauge of the kosmotropic effect on hydrophobic assemblies.
authors.affiliation: 1] University of Fribourg, Department of Physics, CH-1700 Fribourg [2].
authors.forename: I
authors.initials: I
authors.lastname: Bischofberger
authors.affiliation: University of Fribourg, Department of Physics, CH-1700 Fribourg.
authors.forename: D C E
authors.initials: DC
authors.lastname: Calzolari
authors.affiliation: Ecole Polytechnique Fédérale de Lausanne, Laboratory of Statistical Biophysics, CH-1015 Lausanne.
authors.forename: P
authors.initials: P
authors.lastname: De Los Rios
authors.affiliation: University of Zürich, Department of Biochemistry, CH-8057 Zürich.
authors.forename: I
authors.initials: I
authors.lastname: Jelezarov
authors.affiliation: University of Fribourg, Department of Physics, CH-1700 Fribourg.
authors.forename: V
authors.initials: V
authors.lastname: Trappe