NORMALIZED FLUCTUATIONS, H2O VS N-HEXANE - SITE-CORRELATED PERCOLATION

Entropy, volume and the cross fluctuations were normalized to the aver age volume of a coarse grain with a fixed number of molecules, within which the local and instantaneous value of interest is evaluated. Comp arisons were made between liquid H2O and n-hexane in the range from -1 0 degrees C to 120 degrees C and from 0.1 MPa to 500 MPa. The differen ce between H2O and n-hexane in temperature and pressure dependencies o f these normalized fluctuations was explained in terms of the site-cor related percolation theory for H2O. In particular, the temperature inc rease was confirmed to reduce the hydrogen bond probability, while the pressure appeared to have little effect on the hydrogen bond probabil ity. According to the Le Chatelier principle, however, the putative fo rmation of ''ice-like'' patches at low temperatures due to the site-co rrelated percolation requirement is retarded by pressure increases. Th us, only in the limited region of low pressure (<300 MPa) and temperat ure (<60 degrees C), the fluctuating ice-like patches are considered t o persist. (C) 1996 American Institute of Physics.