Meaning
Thermodynamic kinetic models describe secondary nucleation and crystal growth rates in semi-crystalline polymer melts as a function of supercooling. Under the Hoffman Lauritzen theory, linear growth velocity depends on the competition between chain segment deposition and thermal surface detachment. Datasheet melting points represent theoretical equilibrium states, whereas actual injection molding kinetics occur at substantial undercooling.
Polymer processors use these kinetic parameters to model spherulite formation in molding simulations.
Kinetic Mechanism
Secondary nucleation initiates on existing crystal faces through the attachment of stem segments from coiled polymer chains. The rate of chain detachment decreases as undercooling increases, accelerating overall crystal growth until mass transport becomes diffusion-limited. Surface free energy parameters dictate the work required to form a stable nucleus on a growing crystal face.
High melt temperatures reduce nucleation rates, yielding larger spherulitic structures with distinct boundary lines.
Nucleation Regime
Crystallization kinetics transition across three distinct regimes based on the relative rates of substrate completion and secondary nucleation. Low undercooling defines the first regime where single nucleations complete entire crystal layers before new steps form. High nucleation density characterizes the second regime where multiple nucleation sites compete across the fold surface simultaneously.
Severe undercooling marks the third regime where molecular mobility restricts chain folding efficiency.
Crystallite Geometry
Lamellar thickness correlates directly with supercooling magnitude during crystallization. Higher crystallization temperatures produce thicker lamellae with higher melting points and increased stiffness. Control over kinetic growth parameters governs final part density and optical clarity in semi-crystalline molded components.
