Micro-mechanics of Polymer Crystallization

Dr Lucia Scotti, Dr Mike Jenkins, Dr Hector Basoalto

University of Birmingham

Introduction 

  • Polymers crystallise in spherulites composed by  lamellae of semi crystalline material alternating with amorphous regions;
  • The size, morphology and crystallinity of the spherulites influence the polymer properties;
  • The radius of spherulites range from lateral μm to cm;
  • The lamellae are very thin compared to the fully extended chain: usually 10 nm.
  • A fully extended chain requires an enormous decrease of entropy, so it can be obtained only under particular conditions;
  • The folding back and forth of polymer chains requires a release of a part of the entropy;
  • The folded chains are metastable phases: the free energy of the folded-surfaces is much higher than the lateral surface;
  • These crystals are stabilised by spontaneous thickening processes

 

 

 

 

 

 

Fig.1: Schematic representation of lamellae composed of folded chains and amorphous regions in spherulite.

Fig.2: Schematic representation of a polymer  chain phase