Miscibility between differently shaped mesogens: structural and morphological study of a phthalocyanine-perylene binary system.
The thermotropic, structural, and morphological properties of blends of a disk-like liquid crystalline phthalocyanine derivative and a lath-shaped perylenetetracarboxidiimide mesogen derivative have been studied by combining differential scanning calorimetry, thermal polarized optical microscopy, X-ray diffraction, solid-state nuclear magnetic resonance, and atomic force microscopy. The two compounds are fully miscible for blends containing at least 60 mol % of the disk-like molecule. In such composition range, the homogeneous blends form a columnar hexagonal (Col(h)) mesophase for which the thermal stability is enhanced compared to that of the corresponding mesophase of the pure phthalocyanine. The miscible blends self-align homeotropically between two glass slides. For blends containing between 55 and 40 mol % of the disk-shaped molecule, the two components are fully miscible at high temperature but the perylene derivative forms a separate crystalline phase when the temperature is decreased. Phase separation is systematically observed in blends containing less than 40 mol % of the discotic molecule. In this case, the resulting Col(h) mesophase is less stabilized compared to the blends containing a larger amount of the phthalocyanine derivative. These phase-separated blends do not show any homeotropic alignment. AFM investigations confirm the formation of a single columnar morphology in the phthalocyanine-rich blends, consistent with the full miscibility between the two compounds. Solid-state NMR measurements on the mixed phase show the influence of the presence of the perylene molecules on the molecular dynamics of the molecules; remarkably, the presence of the host molecules improves the local order parameter in the phthalocyanine columnar phase.
Zucchi
Gaël
G
Laboratoire de Chimie des Polymeres, Universite Libre de Bruxelles, Boulevard du Triomphe, B-1050 Bruxelles, Belgium. gael.zucchi@cea.fr
Viville
Pascal
P
Donnio
Bertrand
B
Vlad
Alexandru
A
Melinte
Sorin
S
Mondeshki
Mihail
M
Graf
Robert
R
Spiess
Hans Wolfgang
HW
Geerts
Yves H
YH
Lazzaroni
Roberto
R
D018360:Crystallography, X-Ray; D004583:Electrons; D007211:Indoles / Q000737:chemistry*; D054833:Isoindoles; D050866:Liquid Crystals / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D015394:Molecular Structure; D010316:Particle Size; D010569:Perylene / Q000737:chemistry*; D012995:Solubility; D013696:Temperature
D007211:Indoles; D054833:Isoindoles; D010569:Perylene; C013647:phthalocyanine