(The) in situ photopolymerization and LB film preparation of 2,4-hexadecadienoic acid monolayer at the air/water interface

Abstract

The in situ photopolymerization of 2,4-Hexadecadienoic acid(2,4-HDDA) for the film stabilization and the film deposition characteristics of 2,4-Hexadecadienoic acid were investigated. The photopolymerization of 2,4-HDDA monolayer was performed at the air/water interface by UV-irradiation, and the polymerization rate at a given surface pressure and temperature was obtained from the area change of the monolayer during the polymerization. It is found that the photopolymerization rate is proportional to the three halves power of monomer surface concentration and the activation energy for the photopolymerization is ca. 7.7 kJ/mole. For the 2,4-HDDA monolayer mixed with stearic acid, the trends of area change during the photopolymerization was different from that of pure 2,4-HDDA monolayer-the area contracts or expands according to the mixing compositions, thre surface pressure and temperature. It may be, therefore, suggested that the molecular orientation of 2,4-HDDA molecules be changed by the presence of stearic acid. 2,4-HDDA multilayer and mixed multilayer(equimolar compostion) were prepared by the conventional Langmuir-Boldgett film technique. The polymerized mixed monolayer on the $Cd^{2+}$ ion-contaning water subphase could be easily transferred to Cr-coated silicone substrate. Polymerized mixed multilayers of 2,4-HDDA and stearic acid(equimolar composition) were characterized by the use X-ray diffraction, FTIR and UV spectroscopy, and their electrical properties were measured using the metal-LB film-metal (MIM) structure. The lattice spacing was found to be ca. $50.3 \mbox{\AA}$ by X-ray diffraction method. No detection of the conjugated double bond in Infrared ATR spectrum indicated that the diene groups are almost disrupted during the UV-polymerization. From the measurement of electrical properties, the order of magnitude of the perpendicular conductivity was foumd to be ca. $10^{-9} s/cm$.