This paper presents
the liquid crystal (LC) properties of poly(
l
-lactide) (PLLA).
Mesophase behavior is investigated using
polarized optical microscopy, X-ray diffraction, and differential
scanning calorimetry. The performed analyses confirm that pressed
PLLA films exhibit the unique capability of self-assembling into a
nematic mesophase under the influence of mechanical pressure, temperature,
and time. It was originally demonstrated that the chiral nematic mesophase
can be obtained by introducing fine powders into the polymer. Based
on the research conducted, it was proved that the pressed PLLA films
have a chiral nematic mesophase with a nematic-to-isotropic phase
transition and a large mesophase stability range overlapping the temperature
of the human body, which can persist for years at ambient temperature.
The obtained films show tailor-made properties toward a nematic mesophase
with a specific texture, including colored planar texture of the chiral
nematic mesophase and blue-phase (BP) LC texture. The BP, described
for the first time in plain PLLA, occurred over a wider than usual
temperature range of stability between isotropic and chiral nematic
thermotropic phases (Δ
T
≈ 9 °C),
which is an advantage of the obtained polymer material, in addition
to ease of preparation. This opens up new prospects for advanced photonic
green applications.
Optical and structural properties of a blend thin film of (1:1 wt.) of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) doped with iodine (I2) and then exposed to a stepwise heating were reported and compared with the properties of doped P3HT films. The UV-Vis(T) absorption measurements were performed in situ during annealing runs, at the precisely defined temperatures, in a range of 20–210 °C. It was demonstrated that this new method allows one to observe the changes of absorption spectra, connected with the iodine release and other structural processes upon annealing. In addition, the thermally-induced changes of the exciton bandwidth (W) and the absorption edge parameters, i.e., the energy gap (EG) and the Urbach energy (EU) were discussed in the context of different length of conjugation and the structural disorder in polymers and blends films. During annealing, several stages were distinguished and related to the following processes as: the iodine escape and an increase in P3HT crystallinity, the orderly stacking of polymer chains, the thermally inducted structural defects and the phase separation caused by an aggregation of PCBM in the polymer matrix. Moreover, the detailed X-ray diffraction studies, performed for P3HT and P3HT:PCBM films, before and after doping and then after their thermal treatment, allowed us to consider the structural changes of polymer and blend films. The effect of iodine content and the annealing process on the bulk heterojunction (BHJ) solar cells parameters was checked, by the impedance spectroscopy (IS) measurements and the J-V characteristics registration. All of the investigated P3HT:PCBM blend films showed the photovoltaic effect; the increase in power conversion efficiency (PCE) upon iodine doping was demonstrated.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.