Meaning
Mathematical relationship used to describe the temperature dependence of the relaxation time and viscosity in amorphous polymer materials. This formula is particularly relevant for predicting the mechanical behavior of battery separators and adhesives near their glass transition temperature. The Williams-Landel-Ferry equation allows researchers to translate data measured at one temperature to another by using a shift factor.
It holds true for a wide range of polymers from approximately the glass transition point to one hundred degrees above it.
Time Temperature Superposition
Experimental data collected over a short timeframe at high temperatures can be used to predict long term behavior at lower temperatures. Applying the Williams-Landel-Ferry equation enables the creation of a master curve that describes the viscoelastic properties of a polymer across several decades of time. This is critical for understanding the creep resistance of battery seals and gaskets over years of operation.
Structural Constants
Equation relies on two empirical parameters that are specific to the material being analyzed. While the Williams-Landel-Ferry equation often uses standard values for many polymers, precise battery modeling requires measuring these constants for the specific electrolyte-soaked membranes used in the cell. These values dictate how the polymer will respond to the rapid mechanical shocks of a vehicle impact.
Processing Application
Manufacturing of thin film separators involves high speed stretching and cooling where the viscosity must be tightly controlled. The Williams-Landel-Ferry equation guides the setting of extrusion temperatures and line speeds to ensure the final product has the correct porosity and strength. It provides the physical basis for maintaining consistency in the polymer morphology during mass production.
