Dynamic studies of polymerization in liquid crystal-polymer mixtures

This work studied the dynamic behavior of polymerization in films of liquid crystal (LC)-polymer mixtures by using the pump-probe technique. Chopped Ar+ laser pulses were used as pump beams, and probed by a cw He—Ne laser. The experimental results indicated that the transmission of the probe beam was modulated in response to the chopping frequency of the pump beam. The modulation was such that transmission during the on-time of the pump beam was initially smaller than, then equal to, and finally larger than that in the off-time. Analyzing the transparency difference between the films with and without the Ar+ laser pulse allows us to recognize the three stages of polymerization process, initiation, propagation, and termination. Moreover, both the LC content in the sample and the chopping on/off ratio of the pump beam significantly affected the turning point occurred and the modulation amplitude of the probe beam. A model is proposed to explain these observed results.