Contribution of the fluorescence spectroscopy to the determination of binary phase diagrams of mesomorphic mixtures. I. Investigation of a system-alkylcyanobiphenyl/phenyl-cyclohexanecarboxylate

The study of the spectral distribution and intensity of the fluorescence of binary mesomorphic mixtures as a function of the temperature is presented as a convenient method for obtaining phase diagrams. For a mixture of a given composition, the fluorescence intensity measured in the frequency range of the monomer and of the excimer emission, shows two types of discontinuities at the phase transitions. Ratio IM/ID ranging from 0 to ∞ can be obtained as a function of the composition, of the temperature, and of the nature of the phase. Monomer fluorescence (IM) is characteristic of the crystalline and of the S B phases while in the SA1, N and the I phases, excimer fluorescence (ID) is predominantly observed. The emission spectra can detect simultaneously the presence of molecular association, the degree of order and the molecular mobility of the phase involved.L' étude de la distribution spectrale et de l'intensité de fluorescence en fonction de la température d'un mélange mésomorphe binaire est présentée comme une méthode commode pour établir des diagrammes de phase. Pour un mélange de composition donnée, on peut montrer que la mesure de l'intensité de fluorescence dans le domaine de fréquences d'émission du monomère et de l'excimère présente deux types de discontinuités aux transitions de phase. Des valeurs I M/ID variant entre 0 et ∞ peuvent être obtenues en fonction de la composition, de la température, et de la nature de la phase. La fluorescence du monomère (IM) est obtenue dans la phase cristalline et dans la phase SB. La fluorescence d'excimère ( ID) s'observe préférentiellement dans les phases SA1 , N et isotrope. Les spectres de fluorescence peuvent révéler simultanément l'existence ou non d'associations moléculaires, le degré d'ordre et la mobilité moléculaire dans la phase considérée

Investigation of polymer miscibility by spectroscopic methods V. Effect of molecular weight and block copolymerization of syndiotactic poly(methyl methacrylate) on its miscibility with poly(vinyl chloride)

peer reviewedaudience: researcherInvestigated by nonradiative energy transfer (NRET), the state of mixing of PVC and s.PMMA which is on the dimensional scale of a few nanometers is significantly affected by the chain length. When PVC is blended with s.PMMA of increasing molecular weight (MW), the longest chains of s.PMMA are likely to segregate from a homogeneous blend formed by PVC and low‐MW s.PMMA. The phase separation should therefore be of purely entropic origin and strongly dependent on both the relative percentage and the chain length of each component. These results are in qualitative agreement with conclusions previously drawn from DSC and transmission electron microscopy. NRET is a more powerful tool in probing heterogeneities compared to DSC and the thermally stimulated depolarization current method; it provides evidence against the previously suggested model of a 1:1 PVC/s.PMMA aggregate. Copyright © 1986 John Wiley & Sons, Inc

N-Substituted Aldonamides V X-Ray Diffraction Study of the Crystal and Thermotropic and Lyotropic Mesophases of N-Alkylribonamides

The structure of two N-alkylribonamides both in the anhydrous state and in concentrated water solution has been studied by X-ray diffraction. A Lamellar Crystalline, a Lamellar Liquid-Crystalline and a Cylindrical Hexagonal Liquid-Crystalline Structures have been found. The influence of temperature and of water concentration on the geometrical parameters of the mesophases has been established. The organization of the molecules in the three structures is described and a step by step melting behavior is proposed for the N-alkylaldonamides. © 1992, Taylor & Francis Group, LLC. All rights reserved.SCOPUS: ar.jinfo:eu-repo/semantics/publishe