Meaning
Molecular transport frameworks explain the relationship between the empty space between molecules and the mobility of a polymer system. The principles of free volume theory state that a material can only flow or react if there is enough room for the molecules to shift. This concept is fundamental to understanding how resins behave as they cool or cure.
Void Distribution
Gaps between polymer chains provide the paths needed for molecular rotation. According to free volume theory these gaps shrink as the temperature drops or the density of the network increases. The loss of this space is what causes a liquid to turn into a glass.
Mobility Gradient
Movement speed within the resin is directly proportional to the amount of unoccupied space. Calculations based on free volume theory show why viscosity increases so rapidly during the late stages of a reaction. This data is used to set the limits for molding and shaping operations.
Saturation Threshold
Processing becomes impossible once the free volume reaches a critical minimum. If a manufacturer attempts to form a part below this limit the material will crack or fail to fill the mold. Free volume theory provides the theoretical basis for determining the minimum processing temperature.
This framework allows engineers to predict the service life of a polymer by understanding how it will stiffen over time.
