8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

Tue 611:23-14:00P2.77How the liquid-liquid transition affects hydrophobichydration of a polymer chain in supercooled waterTomonari Sumi, 1 Hideo Sekino, 1 and Tomonari Sumi 11 Toyohashi University of Technology, 1-1 Hibarigaoka, Tempaku-cho, 441-8580,Toyohashi, JapanA density-functional theory (DFT)-based multiscale simulation of a hydrophobic polymer chainin deeply surepcoolded water is presented. First, we determine the phase diagram of supercooledwater by performing molecular dynamics (MD) simulations with the TIP4P/2005 model of water.The second critical point is estimated at a temperature of 182K, a density of 1.02 gcm −3 , and apressure between 1580 and 1620 bar. Second, we determine a free-energy functional for water usingstructure factor of bulk water that is calculated with high precision from the hypernetted chainintegral equation combined with the reference MD data. The multiscale simulation reproduces hydrophobiccollapse of the polymer chain at room temperature and low pressures. We also observethat a globule-coil transition of the hydrophobic polymer chain occurs at lower pressures than thesecond critical point with supercooling toward a low-density liquid. The swelling reduces partialmolar volume of the polymer chain in the low-density liquid. We find that a length of the period ofhydration shell surrounding the unfolded polymer chain is larger than that surrounding the foldedone. The observation suggests that the swelling of the hydrophobic polymer chain enhances anice-like tetrahedral structure in the hydration shell. A decrease in entropy due to the swelling canbe attributed to both the decrease in volume and the formation of the ice-like tetrahedral structure.The swelling behavior of the polymer chain is consistent with an increase in solubility of a hydrophobicsolute with the transformation of water into the low-density liquid. Moreover, our DFTresult qualitatively agrees with that obtained from a MD simulation of a polymer chain in the Jaglamodel of water that is a hard spherical fluid with penetrative week repulsion. This observation suggeststhat the Jagla fluid can reproduce water-like solvation thermodynamics near the liquid-liquidtransition.77