Synthesis and liquid crystalline properties of some esters of 4-ferrocenyl-4'-hydroxyazobenzene.

The paper describes synthesis and mesogenic behavior of a new class of ferrocenomesogens obtained by esterification of 4-ferrocenyl-4'-hydroxyazobenzene with some 4-n-alkyloxybenzoic acids / 4-n-alkanoyloxy or 4-n-alkenoyloxybenzoic acids in the presence of N,N'-dicyclohexylcarbodiimide and 4-dimethylaminopyridine. Based on differential scanning calorimetry and polarized optical microscopy investigations, it was established that 12 from the 15 synthesized compounds presented liquid crystalline properties, mainly monotropic nematic. All the investigated compounds were thermally stable in the existence range of the mesophases. Molecular modeling studies have been performed in order to establish correlations between structure and liquid crystalline properties. Parameters as lengths, diameters, dipole moments and molecular asymmetry coefficients and geometries of minimum energy have been obtained. A model of a cell of minimum energy for systems containing eight molecules of type 4-((4-ferrocenyl-phenylazo)phenyl) 4-alkyloxybenzoate has been proposed.

An atomic force microscopy statistical analysis of laser-induced azo-polyimide periodic tridimensional nanogrooves.

The surface morphology of azo-polyimide films was investigated after 355 nm Nd: YAG laser irradiation with two different incident fluencies. Atomic force microscopy (AFM) was employed to correlate the laser-induced tridimensional nanogrooved surface relief with the incident fluence and the number of irradiation pulses. The height images revealed that the grooves depth increased even tens of times by increasing the incident fluence, using the same numbers of irradiation pulses. For low incident fluence, the films were uniformly patterned till 100 pulses of irradiation. Instead, when using higher fluence, after 15 pulses of irradiation the accuracy of the surface relief definition was reduced. This behavior could be explained by means of two different mechanisms, one that suppose the film photo-fluidization due to the cis-trans isomerization processes of the azo-groups and the second one responsible for the directional mass displacement. The dominant surface direction and parameters like isotropy, periodicity, and period were evaluated from the polar representation for texture analysis, revealing the appearance of ordered and directionated nanostructures for most of the experimental conditions. Also, the graphical studies of the functional volume parameters have evidenced the improvement of the relief structuration during surface nanostructuration. The correlation of these statistical texture parameters with the irradiation characteristics is important in controlling the alignment of either the liquid crystals or the cells/tissues on patterned azo-polyimide surfaces for optoelectronic devices and implantable biomaterials, respectively.