The absorption spectra of 4f electron transitions of the neodymium complex with 8-hydroxyquinoline and octylphenol poly(ethy1ene glyco1)ether have been studied by conventional and third-derivative spectrophotometry. The absorption spectrum for neodymium at 575 nm is resolved into three bands centring at 572,580 and 584 nm, respectively. The use of third-derivative spectra both eliminates the interference from other rare earth elements and enhances the sensitivity for neodymium. Beer's law is obeyed for 0-14 pg cm-3 of neodymium. The corresponding value of Sandell's sensitivity is 0.29 pg cm-2. The relative standard deviations evaluated from 11 independent determinations of 2.0 pg of neodymium are 0.87% for neodymium alone and 1.6% in the presence of 80 pg of lanthanum. The detection limit (signal-to-noise ratio = 2) is 0.12 pg cm-3 of neodymium. A method for the direct determination of neodymium in mixtures of rare earth elements with good accuracy and selectivity, is described.
Two-dimensional (2-D) phase transitions of three low-mass-weight liquid crystals (LMWLC) with different mesogens have been studied by π-A isotherms at different temperatures, UV-spectroscopy, and Brewster angle microscopy (BAM). The effects of mesogenic unit structures, which are biphenyl or benzoate phenyl ester or ether bonds at various locations in the mesogenic unit, on the bulk phases and the monolayer behaviors have been discussed. The molecules with benzoate phenyl mesogens have existed in the liquid expanded (L-E) monolayer structure phase in which the molecules lie flat on the surface of water because of the strong anchoring effect of the ester group on the water surface, whereas the liquid condensed (L-C) phase is the form in which the molecules are close-packed and oriented perpendicular to the film plane. 2-D phase changes from the L-E to the L-C phase were characterized by UV spectra and observed in situ by using BAM. The experimental results of surface pressure dependence on the area per molecule were in good agreement with the theoretical results which involved the formation of L-C domains dispersed as a superlattice in the continuous L-E phase. The adjustable parameter ωf used for the best fit of the theoretical results and experimental data is close to both the vertical sections of the molecules in L-E phase and the cross sections of the mesogens in the L-C phase for the molecules. The effect of the functional group in the mesogens on the monolayer behavior is essential for the orientation and spreading behavior of the molecules.
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