Polymer Glass Transition: Free Volume & WLF Equation

Every amorphous polymer — from a rubber band to an acrylic sheet — switches between a hard, brittle glass and a soft, flowable rubber over a narrow temperature window centered on its glass transition temperature, T_g. This simulator renders a set of bead-spring polymer chains in 3D and drives their segmental motion directly from real free-volume theory: as temperature crosses T_g, the free volume between chain segments opens up and the Williams–Landel–Ferry equation predicts how fast segments can now hop past each other. Sweep temperature, pick a real polymer's T_g, adjust the free-volume constants, or run a live cooling ramp and watch the specific-volume curve kink exactly where the chains freeze from a wiggling melt into a rigid glass.