Monolayer properties and spontaneous Z-type Langmuir—Blodgett multilayers of 2-(heneicosa-2,4-diynoxycarbonyl)benzoic acid

Abstract

The monolayer properties of two diacetylene phthalates, — 2-(heneicosa-2,4-diynoxycarbonyl)benzoic acid and 2-(heptadeca-2,4-diynoxycarbonyl) benzoic acid — which are surfactants of different hydrocarbon chain lengths, at the air—aqueous solution interface have been examined using subphases containing CdCl 2 and a polyelectrolyte, poly(diallyldimethylammonium chloride). The headgroup on the longer chain phthalate appears to reorientate at a critical point as the monolayer is continuously compressed from high to low areas on a CdCl 2 subphase. This does not occur on the polyelectrolyte subphase. The apparent reorientation process was found to be highly sensitive to the monolayer compression rate and could be eliminated if a slow, stepwise compression was employed. The UV initiated polymerization of the phthalates was also examined at the air—aqueous solution interface at different compression areas and subphase conditions. At 20°C, polymerization was most extensive at high monolayer surface pressures (20 mN m −1) and on a CdCl 2 subphase. The longer chain phthalate formed spontaneous Z-type L-B multilayer films which could be readily polymerized. Polymerization in such films was greatest when the molecules were transferred from a monolayer on a CdCl 2 subphase at a surface pressure of 25 mN m −1, reflecting the topochemical nature of the polymerization process.