Sf. Yu et al., X-ray diffraction analysis of 10,12-pentacosadiynoic acid Langmuir-Blodgett films during polymerization, J MATER SCI, 34(13), 1999, pp. 3149-3154
10,12-pentacosadiynoic acid (PCDA) LB films were deposited on two different
subphases of CdCl2 and TbCl3 respectively and polymerized under UV-irradia
tion. It is found that the different subphase influenced the molecular pack
ing, and in turn, influenced the polymerization behavior in the LB films. T
he molecular arrangement structures of unpolymerized and photopolymerized L
B films were investigated by low angle X-ray diffraction. The periodic spac
ing of molecules in the LB films and the inclination angle of molecules on
the substrate were calculated from the X-ray diffraction profiles. The unpo
lymerized PCDA LB film had one set of diffraction peaks, however, two sets
of diffraction peaks were clearly observed in partly-polymerized PCDA LB fi
lms deposited on CdCl2 subphase and reduced to one set of diffraction peaks
corresponding to the polymerized LB films. On the other hand, the PCDA LB
films deposited on TbCl3 subphase had only one set of diffraction peaks thr
oughout. This is interpreted to correspond to different mechanisms of chain
propagation, i.e., heterogeneous chain propagation for the PCDA LB film de
posited on CdCl2 subphase and homogeneous polymerization for the LB film de
posited on TbCl3 subphase. A molecular arrangement model in LB film was emp
loyed to explain the phenomenon of the "even-odd intensity oscillation" qua
litatively. (C) 1999 Kluwer Academic Publishers.