Journal of Polymer Science Part B: Polymer Physics, Vol.32, No.16, 2653-2659, 1994
Surface Studies of Tetraalkylammonium Bromides and Iodides Using Atomic-Force Microscopy
The surface structures of two series of tetra-n-alkylammonium halides, N(CxH2x+1)(4)I and N(CxH2x+1)(4)Br have been investigated with atomic force microscopy (AFM) and compared to hexatriacontane (C36H74) The surfaces could be imaged with atomic resolution. The observed primitive, square surface-patterns of tetra-n-butyl chloride and bromide are in good accord with x-ray single-crystal structure. For n > 4, x-ray powder diffraction showed that increasing the alkyl chain-length leads mainly to an appropriate increase of the unit cell along the c-axis, which suggests similar layer structures for all long-chain salts beyond the butyl homologue. Within the centers of the molecular layers of these crystals reside the halide anions and the quaternary nitrogens. The surfaces accessible for AFM consist of methyl end-groups. As the number of carbon atoms increases beyond four, the surface symmetry changes to the face-centered square patterns characteristic of many paraffins. The chains of the tetraalkyl ammonium salts pack, however, less dense than paraffins.
Keywords:STATE C-13 NMR;X = BR;ALKYLAMMONIUM SALTS;CONDIS CRYSTALS;SMALL MOLECULES;MESOPHASES;DISORDER;HOMOLOGS;MOTION;POLYETHYLENE