Two-Dimensional Arrangements of Adsorbed Alkylammonium Halides on Cleaved Mica Surface

The adsorbed films of alkylammonium halides, 1C n TAX and 2C n DAX with alkyl chain lengths of n = 1, 6, 8, 10, 12, 14, 16, and 18, on cleaved mica surfaces was analyzed by atomic force microscopy for their two-dimensional arrangement and molecular area. The stable hydrophobic surface was obtained by cleaving mica in an adsorption bath and stands for prolonged adsorption time of 72 h at 5 °C. The adsorbed molecules are stable and do not desorb easily when put in distilled water. The occupied area of double-chained alkylammonium bromides, 2C n DAB, on a mica surface was found to range from 0.45 to 0.47 nm 2, which is equivalent to the density of a potassium ion (1/0.47 nm -2 ), while the single-chained alkylammonium halides, 1C n TAX, showed the area ranging from 0.23 to 0.24 nm 2 per molecule, which is half the density of a potassium ion (1/0.47 nm -2 ) on a mica surface. The symmetry of the two-dimensional arrangement of adsorbed molecules agreed with the lattice structure of a cleaved mica surface despite the numbers and the lengths of alkyl chains.