Fig. 1: Schematic of PE lamellar structures.
From: Reassessing chain tilt in the lamellar crystals of polyethylene
a Crystal structure of orthorhombic polyethylene (PE)11. Two types of planar-zigzag-structured PE chains—shown as a light-green central chain and dark-green corner ones—occupy the unit cell with different setting angles (the angle between the bc and zigzag planes). b, c Schematics of the molecular-chain orientation in a lamellar crystal with a b, perpendicular and c, non-perpendicular (tilting) c-axis. The crystalline region is shown in yellow, and the flat faces of the lamellar crystals are highlighted in red. The angle between the red dashed line (normal to the flat face of the crystal) and green arrow (molecular chain axis; c-axis) is the chain tilt angle φ. The flat-face area increases by a factor of 1/cosφ. d Ordered-folding model featuring adjacent re-entry of regular sharp folds. e Density-anomaly-free modified-folding model14, in which the crystalline region, flat faces, lamellar thickness (lc), and chain ends are represented by a yellow area, dotted lines, a black arrow, and triangles, respectively. Diverse chains are coloured differently.
