The shear rheology of thin compressed liquid films

Abstract

Thin liquid films at elevated pressures have a unique property. A sufficiently high shear stress can be generated in steady shear without encountering the thermal softening limit or interfacial slip that it is possible to observe, in low molecular weight liquids, various non-Newtonian effects ordinarily thought to be reserved for high polymers. These include shear thinning, viscoelasticity and cohesive failure. The relevant rheology literature is reviewed. Only the properties of the continuum are addressed here, omitting near-surface effects. Within the last 10 years in particular, both experiment and molecular simulation have shown that many analogies may be made between lubricants and liquid polymers when allowance is made for the much shorter relaxation time of the low molecular weight liquid. Shear thinning, elasticity and liquid failure are all aspects of the shear response of thin films of low molecular weight liquids at elevated pressures.