No abstract

It is known that the spreading rates of small liquid drops over a solid surface exhibit a strong dependence on the viscosity of the liquid. These observations have led us to study the spreading behavior of polymer solutions on high- and low-energy substrates to determine what role complex rheology plays in wetting kinetics. We did not observe any effects of non-Newtonian (nonlinear) behavior, nor were any obvious signs of viscoelasticity (memory) visible. Instead, we observed a most intriguing phenomenon that polymer solutions, despite having low surface energies, do not wet high-energy substrates. In addition, nonwetting drops spread to an equilibrium configuration by either one of two distinct mechanisms. In the first case, they spread as a wetting Newtonian liquid and then stopped, that is, equilibrated, abruptly. In the second, they equilibrated continuously. We offer some possible molecular and continuum arguments to explain the differences between these two mechanisms.

Drop shape dynamics of a Newtonian drop in a non-Newtonian matrix during transient and steady shear flow

No abstract

The onset of significant departure from isothermality caused by viscous energy dissipation in flow through a slit is determined for isothermal and adiabatic walls. A series solution of the energy equation enables calculation of dimensionless profiles for any power law fluid. Such solutions provide useful standards for judging performances of numerical schemes for solving complex nonisothermal flows.