Microscopic theory of simple fluids

Abstract

Analyzing the basic details of a simple fluid, we developed its microscopic theory and discovered that (i) every fluid is a homogeneous mixture of two fluids, SUB1 and SUB2, respectively, composed of non-interacting quasi-particles (QP1) and interacting QP2, and (ii) its behavior is controlled by Pin(q)+Pin(K)=Pex+Pcoh as its equation of state (EOS) where Pin(q) and Pin(K) are two components of its internal pressure, while Pex and Pcoh, respectively, represent external and cohesive pressures. It further reveals the temperature (T) and pressure (P) dependence of compressibility factor (Z) of the fluid and its universal component Z(T)Vc=1+B2(T)/Vc (with B2(T) being its second virial coefficient), the reasons for the coexistence of liquid and vapor and the relation between their particle number densities ρl and ρg. It explains criticality and critical condensation/evaporation and, for the first time, unravels the microscopic origin of important empirical rules such as Trouton rule and Guldberg rule (discovered about 130years back) and several principles of corresponding states (PCS) discovered by Guggenheim. Our results have very good agreement with experiments. We hope our theory may emerge as an important means to (i) explain different properties of simple fluids, (ii) provide necessary foundation to develop similar theories of polar, strongly polar, ionic and complex fluids, and (iii) render useful direction for better understanding of widely different physico-chemical, bio-chemical and bio-physical processes and related aspects.