Phase transition kinetics in Langmuir and spin-coated polydiacetylene films
Yevgeniy Lifshitz, Alexander Upcher, Olga
Shusterman, Baruch Horovitz, Amir Berman and Yuval Golan
Phys. Chem.
Chem. Phys., 2010,
12, 713-722
Received 3rd August 2009, Accepted 21st October 2009
First published as an Advance Article on the web 19th November 2009
DOI: 10.1039/B915527A
AbstractThin
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. Several reaction kinetics models were
applied in order to describe the phase transitions in the films. The
results present the phase evolution in PDA and compare the kinetics for
Langmuir films vs. spin-coated films. Polymerization directly at the
air–water interface was found to be two-to-three orders of magnitude
faster compared to solid-supported films of the same material.
Moreover, we show that the data of the solid supported films is
considerably better fitted when a reversible intermediate phase between
the blue and the red phases is considered. Furthermore, a shift of the
Raman active triple bond supports the presence of the intermediate
phase.