The thickness of ( 110) and ( 200) sectors in truncated single crystals of linear polyethylene grown from dilute n-octane solution at 95 °C was measured by atomic force microscopy (AFM) in tapping mode. The (110) sector was found to be 1.1 nm thicker than the (200) sector. This can be explained by a somewhat smaller tilt angle of the chains with respect to the basal plane of the crystal. The tilt of the chains in ( 110) and ( 200) sectors, obtained by electron diffraction, is 22°and 30°, respectively. This implies that the length of the stem, i.e., the length of the straight part of the chains between two consecutive folds, is identical in both sectors of the truncated single crystals. The melting of individual LPE truncated single crystals was revisited by AFM. The melting temperatures of the ( 200) and ( 110) sectors are 124.9 and 125.9 ( 0.3 °C, respectively. The lamellar thickness distribution calculated from AFM pictures clearly indicates that reorganization into thicker lamellae takes place during heating. The melting of mats of filtration of truncated LPE single crystals has also been investigated by time-resolved small-angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC). The melting curve of LPE single crystals generally exhibits two endotherms. The low and the high melting temperature endotherms are characteristic of single crystals formed from dilute solution and reorganized thicker lamellae during the heating ramp, respectively. Time-resolved SAXS measurements data indicate that two populations of lamellar crystals coexist between 122 and 128 °C. The maximum value observed for the lamellar thickness of the recrystallized material is 30 nm, i.e., twice the initial lamellar thickness of single crystals obtained from dilute solution. There is good agreement between the thicknesses of the crystalline layers obtained from the SAXS data and the values calculated from the Gibbs-Thomson relationship using experimental values of the peak temperature of the two endotherms.

The thermal dependence of the lamellar thickness (L p) and the thickness of crystalline layers (Lcryst) of linear polyethylene single crystals has been revisited. LPE fractions with different average molecular weights were crystallized at the same temperatures to avoid the delicate problem of an arbitrary choice of their equilibrium dissolution temperature to calculate their degree of supercooling. This procedure allows direct check of the thicknesses of the crystalline layers dependence on the degree of supercooling. Indeed, the equilibrium melting and dissolution temperatures depend on the average molecular weight. Mats of linear polyethylene single crystals of various narrow molecular weight fractions were obtained from dilute p-xylene solutions. Their lamellar thickness was determined from the SAXS intensity curve. The crystalline layers thickness was calculated from the linear correlation function of the SAXS intensity curves and from the LAM mode frequency of the Raman spectrum. It depends as expected on the crystallization temperature. However, at a given crystallization temperature, both the thicknesses of the lamellae and of the crystalline layers are nearly independent of molecular weight and therefore also of the degree of supercooling estimated from a well-known semiempirical relationship.