Subcell-matched epitaxy of normal long chain compounds on polyethylene. I. on the (110) plane

Polyethylene films with surfaces bounded by {110} planes were prepared. On the film surfaces, various normal long chain compounds, such as normal paraffins (n-C_nG_2n+2) with n of 23 through 50, alcohols (n-C_nH_2n+1OH) and carboxylic aci ds (_-Cn-1H_2n-1COOH) were epitaxially crystallized from solution, melt, and vapor phase. The molecular chains are lying down parallel to the chain axis of polyethylene when crystallized at low temperatures, exhibiting different crystalline modifications. Irrespective of the nature of the compound, the epitaxial relationships were explained in terms of a common lattice coincidence between orthorhombic subcells of the compounds and the unit cell of polyethylene: (110)_sc∥(110)_PE, [001]_sc∥[001]_PE, where sc a nd PE denote the subcells of the compounds and the polyethylene, respectively. By contrast, when crystallized at high temperatures from the vapor phase and the melt, the molecules stood normal on or tilted to the substrate, keeping the relations of (001) basal plane of the unit cell of the compounds parallel to (110)_PE and the [110] direction parallel to the [001] direction of polyethylene.