Block Copolymers Containing Liquid Crystalline Segments

Photochromism of 4-cyanophenylazobenzene in liquid crystalline-coil AB diblock copolymers: the influence of microstructure

“…k max remained constant from 0 to 128 mJ N cm -2 and then showed minor decreases upon further irradiation to 365 nm at 8 200 mJ N cm -2 . It is also assumed that in the AB diblock copolymer, the polystyrene microdomain prevents the Az units from aggregation and any orientational change due to geometrical restriction from the microdomain [13,14] as observed in the annealing effects (Fig. 3).…”

“…[13,14] UV-visible absorption spectra were taken in the transmission mode using a Hewlett-Packard 8452A. Light irradiation was performed with a 150 W Hg-Xe lamp (San-ei UV Supercure-230S) combined with optical filters for wavelength selection (Toshiba optical filters UV-35/UV-D36, and Y-44/V-42, for 365 and 436 nm illumination, respectively).…”

“…The features of the spectral shape were essentially unchanged by annealing with a similar absorbance and an absorption maximum at 350 nm. This implies that the phase separated PS microdomain structure [13,14] severely hinders the aggregate formation and orientational change observed in the homopolymer. Detailed understanding requires further investigation, however, it is obvious that the discrepancy is unequivocally brought about by the existence of the polystyrene microdomain.…”

“…[12] This block copolymer adopts the cylindrical morphology of polystyrene (diameter of 20-30 nm) embedded in the liquid crystal matrix (separation distances between the cylinders are also in the range of 20-30 nm) in a cast film. [13,14] The cylinders have a close hexagonal packing. The mesogens adopt a homogeneous orientation, i. e., parallel to the intermaterial dividing surface (IMDS) as indicated by small angle X-ray diffraction studies (SAXS).…”

“…The mesogens adopt a homogeneous orientation, i. e., parallel to the intermaterial dividing surface (IMDS) as indicated by small angle X-ray diffraction studies (SAXS). [13,14] Because of a large v parameter, liquid crystalline block copolymers usually have a much higher order-disorder transition temperature (ODT) than their LC clearing transition temperatures (T c ) unless M -n of the block coplymer is too low. A large vN guarantees that a block copolymer falls into a strong segregation regime which is the case in this report.…”