Eutectic solidification and oriented growth in mixtures of polyethylene and 1,3,5-tribromobenzene

The melting and crystallization behaviour of mixtures of linear polyethylene and 1,3,5-tribromobenzene has been investigated by differential scanning calorimetry, optical and electron microscopy. The phase diagram reveals the existence of a pseudo-binary eutectic (polymer volume fraction of about 58%; T_m=116°C). The experimental observations are compared with the predictions of the Flory-Huggins theory of melting point depression. The polyethylene component of the eutectic assumes a habit in which lamellae are highly oriented with the chains in the 110] contact plane parallel to the tribromobenzene needle axes. This well defined orientation is most probably based on an epitaxial relation between polymer and substrate.