Water‐Like Anomalies of Core‐Softened Fluids: Dependence on the Trajectories in ( PρT ) Space

Abstract

In the present article we carry out a molecular dynamics study of the core-softened system and show that the existence of the water-like anomalies in this system depends on the trajectory in P − ρ − T space along which the behavior of the system is studied. For example, diffusion and structural anomalies are visible along isotherms, but disappears along the isochores and isobars, while density anomaly exists along isochors. We analyze the applicability of the Rosenfeld entropy scaling relations to this system in the regions with the water-like anomalies. It is shown that the validity of the of Rosenfeld scaling relation for the diffusion coefficient also depends on the trajectory in the P − ρ − T space along which the kinetic coefficients and the excess entropy are calculated.

Viscosity anomaly in core-softened liquids

“…This confirms the idea of different behavior of a system along different trajectories in ρ−T −P space which is discussed in details in Ref. [14,15].…”

“…5 (a)). Here we observe a self crossing loop like the one observed for diffusion in our previous works [13][14][15]18]. Fig.…”

“…with a = 5.0, r 0 /σ = 0.7 and c = 1.0. The diffusivity of this system was studied in several papers [11][12][13][14][15]. Note that the parameters of the potential are chosen in such a way that the effect of attraction becomes negligibly small and one can consider this system as a purely repulsive core-softened one.…”

“…One can see that the scaling relations break down in case of isotherms. The reason for this breakdown is that while viscosity is monotonous function of density the excess entropy demonstrates anomalous behavior [14,15]. As a result viscosity as function of S ex demonstrates nonlinear behavior.…”

Experimental tests for a liquid-liquid critical point in water

“…It relates the density anomaly to the negative thermal expansion coefficient, and the structural anomaly-a decrease in the system structural order-to an increase in pressure. The diffusion anomaly is caused by the increase in the self-diffusivity upon compression [92,136,223]. Figure 37 also shows how the bulk water data indicate this diffusion anomaly that arises at low pressures for T < 320 K and that the D S behavior at fixed temperature has a slight maximum.…”