Sommaire:

Water and alcohol are well known to form mixtures with properties that are not just a linear
combination of the properties of the two components. Remarkably, such anomaly in the
solvent properties is also reflected in the solvation behaviour of poly‐N‐isopropyl acrylamide
(PNiPAM) in water/alcohol mixtures. At room‐temperature PNiPAM is perfectly soluble in
pure water and pure alcohol, but not in certain mixtures of both.
In this contribution we show that this 'co‐nonsolvency' phenomenon has to be understood
as that the phase behaviour of PNiPAM is governed by two distinct contributions. While the
phase behaviour is governed by classical mixing contributions in the alcohol‐rich regime, in
the water‐rich regime the phase behaviour of PNiPAM is determined by the solvent state.
This denotes that solvation of PNiPAM in water is primarily governed by hydrophobic
hydration, while the PNiPAM‐alcohol interactions are largely unspecific.

I. Bischofberger, D. C. E. Calzolari, P. De Los Rios, I. Jelezarov and V. Trappe, Hydrophobic
hydration of poly‐N‐isopropyl acrylamide: a matter of the mean energetic state of water,
Scientific Report 4 (2014) 4377

I. Bischofberger, D. C. E. Calzolari and V. Trappe, Co‐nonsolvency of PNiPAM at the transition between solvation mechanisms, Soft Matter (2014) accepted DOI: 10.1039/c4sm01345j

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