Entropic effects on the rheological behaviour of n-eicosane and comparison with n-heptadecane

摘要

Alkanes are among the main components of crude oil, and heptadecane and eicosane are often among those with alkanes of average molar fraction. It is known that their rheological behaviour is directly related to the microphases these compounds can form. Their shear steady viscosity follows the pattern of a shear thinning region with a subsequent plateau. However, mixtures rich in eicosane or pure eicosane exhibit a viscosity increment with temperature at low shear rates, briefly named 'temperature thickening' in this study. This unusual behaviour can be explained through the formation of ordered structures, probably similar to those of liquid crystals, at low temperatures near the melting point, which disappear at higher temperatures provoking a significant entropy arising.