An isochronous decoration method for measuring linear growth rates in polymer crystals

Abstract

The long spacing l of lamellar crystals of linear polyethylene increases with the crystallization temperature T_c. For low degrees of supercooling, the ratio Δl/ΔT is around 0.5 nm K⁻¹ for PE single crystals obtained from solution in xylene. In the restricted situation where only conduction in the crystallization vessel is involved, a heat transfer analysis shows that about 20 s is needed to change by 5 K the crystallization temperature T_c in a cylindrical vessel of 1.5 mm radius. Such rapid change of the crystallization temperature induces a sharp increase or decrease of the thickness of the single crystals. After conventional shadowing with palladium–gold alloy, the steps on the crystals are observed by conventional bright‐field electron microscopy. A pioneering work was performed in this way by Bassett and Keller in 1962. Our technique allows one to determine both the shape and the dimensions of single crystals or twinned crystals of polyethylene as a function of the time of crystallization, and therefore give the quasi‐instantaneous growth rates at various times.