MOLECULAR ARRANGEMENTS OF PENTACOSADIYNOIC ACID LANGMUIR-BLODGETT-FILMS BEFORE AND AFTER ELECTRON-BEAM IRRADIATIONS

Electron beam (EB) induced polymerization of 10,12-pentacosadiynoic acid (PDA) Langmuir-Blodgett (LB) films has been studied in relation to a molecular density or molecular arrangement of the films by using X-ray diffraction analysis and infrared (IR) spectroscopy. The molecular arrangement or density of the PDA LB films was controlled by subphase conditions when the films were built up, such as pH, temperature of the subphase, or salt concentration in the subphase. It was revealed by the X-ray diffraction analysis that, in the low-density (A-type) PDA LB film, the PDA molecules were bent to a larger extent than those in the high-density (B-type) PDA LB film and that the polymerization proceeded topochemically; that is, the thickness decreased little after the EB irradiation in a helium atmosphere. On the other hand, in the B-type PDA film, the thickness decreased about 10% by the EB irradiation. By IR reflection-absorption (RA) measurements, it was confirmed that conjugated diacetylenic bonds disappeared and conjugated double bonds appeared after the EB irradiation. These results support my previous conclusions1 that 1,4-polymerization, i.e., polydiacetylene-type polymerization, occurs easily in the A-type PDA LB films and 1,2- or 3,4-polymerization, i.e., polyacetylene-type polymerization, occurs in the B-type PDA LB films.