Characteristic nano thicknesses of pure heptane and hexadecane liquids: the boundary between the microscopic and macroscopic liquid worlds

How to find the boundary between microscopic and macroscopic worlds is always of great interest. Studies indicate that such a boundary may be in existence but has never been found so far. Here we find that there exists the smallest thickness of bulk layer at nano scale for pure heptane and hexadecane liquids. The characteristic nano thickness (CNT) defined as the sum of thickness of surface layer and the smallest thickness of bulk layer is thus the smallest thickness of macroscopic liquid. If their thicknesses are less than their CNTs, heptane and hexadecane liquids are no longer in the form of macroscopic liquid but in a state of microscopic world. Thus, the size of CNT defines the boundary between microscopic and macroscopic liquids. This is the most significant finding in present study. The CNTs of pure heptane and hexadecane liquids have been determined. We also find that the phase transition of heptane and hexadecane liquids from bulk to surface is exothermic. The transition heats per square meters are less than -0.017 J/m2.