free volume model

The free volume model describes how molecules move within a material based on the tiny gaps or spaces—called free volume—around them. These gaps allow molecules to wiggle and flow, which affects properties like viscosity and melting point. As temperature increases, these free volumes expand, making movement easier and reducing viscosity. Conversely, at lower temperatures, free volumes shrink, restricting movement and making the material more solid-like. This model helps scientists understand and predict how materials behave under different conditions, especially in polymers, glasses, and other complex substances.