Rheology of Melts and Solutions Part 2 – Viscoelasticity, Temperature, and Surface Flow

By Clifford K. Schoff

This article continues the discussion of rheological behavior of polymer melts and solutions that was begun in Part 1 (JCT COATINGSTECH, August 2007). It begins with a discussion of viscoelasticity of concentrated solutions, mainly in terms of qualitative ways to discern elastic behavior, but references for quantitative methods are also given. The coverage of viscosity-temperature effects includes both the Arrhenius relationship (Andrade’s equation) and the Williams-Landel-Ferry treatment.

The latter does a better job of relating viscosity and temperature for many coatings. The influence of solvents on rheology is mentioned. Surface flows and surface defects are discussed in terms of crater formation, crater edge velocity, surface tension gradients, and the rate of formation of craters. References are given for other defects and flows. This article deals with the rheological behavior of polymer melts and polymer solutions as related to organic coatings.

Part 1 discussed melt and solution viscosity and described methods of measurement.

Part 2 covers viscoelasticity of concentrated solutions, viscosity-temperature effects, influence of solvents on rheology, surface flows, and surface defects. The discussion is brief, but a number of references are given for additional study.