Phase transition kinetics in Langmuir and spin-coated polydiacetylene films.

Thin films of 10,12-pentacosadiynoic acid were prepared using Langmuir and spin-coating techniques and polymerized using a controlled dosage of UV radiation. The radiation-induced phase transitions: from the colorless monomer, via the metastable blue phase, to the red polydiacetylene phase, and finally to degradation of the material, were monitored by optical absorbance spectroscopy. Deconvolution analysis of the absorbance curves allowed us to monitor quantitatively the dynamical changes in the chromatic properties of the films as a function of applied UV radiation dose.

Two-photon polymerization of polydiacetylene.

We show that visible light can polymerize diacetylene monomers into polydiacetylene (PDA) in a two-photon process. We monitor the process by measuring Raman intensities of PDA using a Raman laser at 633 nm with variable intensity I and show that the Raman cross section at short times increases as I3, corresponding to a two-photon process. The process generates a relatively stable blue phase PDA, in contrast with UV polymerization that leads to a fast blue to red phase transformation.