Dilatometric Studies Across the Isotropic to Smectic-F Transition

1997 ◽  
Vol 52 (10) ◽  
pp. 713-716
Author(s):  
M. Srinivasulu ◽  
D. M. Potukuchi ◽  
V. G. K. M. Pisipati
Keyword(s):  
Liquid Crystalline ◽  
Density Fluctuations ◽  
Scanning Calorimetry ◽  
Isotropic Liquid ◽  
Crystalline Phases ◽  
First Order ◽  
Thermal Range ◽  
Liquid Crystalline Phases ◽  
Non Linear ◽  
Dilatometric Studies

Abstract Thermal Microscopy (TM), Differential Scanning Calorimetry (DSC) and dilatometric studies were carried out to characterise the liquid crystalline phases and mesomorphic transitions exhibited by three higher homologues of N-(p-n-dodecyloxy benzylidene)p-n-alkyl anilines, viz., N-(p-n-dodecyloxy benzylidene)p-n-dodecyl aniline, (12O.12), N-(p-n-dodecyloxy benzylidene)p-n-tetradecyl aniline, (12O.14) and (N-(p-n-dodecyloxy benzylidene)p-n-hexadecyl aniline, (12O.16). The three com-pounds exhibit enantiotropic smectic-F and smectic-G liquid crystalline phases between the isotropic liquid and the solid crystal. The change in density across the phase transformations and the thermal expansion coefficient confirm the first order nature of the isotropic to smectic-F (I-SmF) and smectic-F to smectic-G (SmF-SmG) transitions. The dilatometric studies infer strong pre-transitional fluctuations in a relatively large thermal range. The pre-transitional effects are estimated by αeff in the vicinity of the mesomorphic fluctuation-dominated non-linear region (FDNLR) of the I-SmF transition. The strength of non linear growth of density fluctuations is discussed in the wake of reports at the I-N, I-SmA and I-SmC transitions.

Liquid Crystalline Compounds in the Thiophene Series, Part 11+ Liquid Crystalline Thiophene Carboxylic Esters

1995 ◽  
Vol 50 (8) ◽  
pp. 1265-1274 ◽  
Author(s):  
Gerhard Koßmehl ◽  
Barbara Hirsch
Keyword(s):  
Liquid Crystalline ◽  
Polarized Light ◽  
Scanning Calorimetry ◽  
Crystalline Phases ◽  
H Nmr ◽  
Smectic Phases ◽  
Liquid Crystalline Phases ◽  
Nematic Phases ◽  
Optical Textures ◽  
Carboxylic Esters

The new series of ten 4,4'-bis(5-alkyl-2-thienylcarbonyloxy)azobenzenes (2a -2j) and ten 2,5-bis(5-alkyl-2-thienylcarbonyloxy)toluenes (3a -3j) were prepared. These, as yet unknown esters were characterized in relation to their structures by elemental analyses, IR, UV, 1H NMR spectra and MS. The azobenzene-esters 2a -2j which form liquid crystalline phases were studied by microscopy under polarized light and DSC (differential scanning calorimetry). Through the observation of the optical textures nematic phases were monitored. Only 2j has an additional smectic phase; 2h and 2i form monotropic smectic phases during cooling. The toluene-esters 3a -3j do not form liquid crystalline phases.

Thermal and X-Ray Studies of 1,6-Bis-[4-(trans-4-n-propylcyclohexyl) phenyl]-hexane and 3,5-Bis-[4-(trans-4-n-propylcyclohexyl) phenyl]-1,2,4-thiadiazol

1987 ◽  
Vol 42 (7) ◽  
pp. 774-776
Author(s):  
I. H. Ibrahim ◽  
W. Haase
Keyword(s):  
Nematic Phase ◽  
Liquid Crystalline ◽  
Layer Structure ◽  
Mass Density ◽  
Density Fluctuations ◽  
Smectic Layer ◽  
Scanning Calorimetry ◽  
X Ray ◽  
Liquid Crystalline Phases ◽  
Diffraction Patterns

The liquid crystalline phases of the title compounds have been investigated by differential scanning calorimetry, optical microscopy and X -ray diffraction methods. Transition temperatures and transition enthalpies of these compounds have been determined. The diffraction photographs in the nematic phase of the first compound showed diffraction patterns corresponding to two coexisting mass density fluctuations with commensurate wavelengths, whereas a single diffraction pattern was observed in the nematic phase of the second compound. The thermal and X -ray data showed that the first compound has a quasi-smectic layer structure.

Higher Homologues of Mesomorphic Benzylidene Anilines. Manifestation of Smectic Polymorphism

2003 ◽  
Vol 58 (9-10) ◽  
pp. 573-580 ◽  
Author(s):  
S. Padmaja ◽  
M. Srinivasulu ◽  
Venkata G. K. M. Pisipati
Keyword(s):  
Differential Scanning Calorimetry ◽  
Phase Transitions ◽  
Liquid Crystalline ◽  
Scanning Calorimetry ◽  
Crystalline Phases ◽  
Temperature Controller ◽  
Liquid Crystalline Phases

The synthesis and characterisation of higher homologues of the well-known benzylidene anilines, viz. N-(p-n-tridecyloxy, tetradecyloxy, and hexadecyloxy benzylidene)-p-n-alkylanilines, 13O.m, 14O.m and 16O.m liquid crystalline compounds have exhibited mono, bi and tri phase variant smectic polymorphism. The different liquid crystalline phases are characterized by an optical polarising microscope equipped with a PC based temperature controller. The phase transitions are studied by using differential scanning calorimetry. The results are discussed in the light of the data available on other nO.m compounds.

Electron microscopy and diffraction of crystalline dendrimers and macrocycles

1993 ◽  
Vol 51 ◽  
pp. 1218-1219
Author(s):  
C. J. Buchko ◽  
P. M. Wilson ◽  
Z. Xu ◽  
J. Zhang ◽  
S. Lee ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Liquid Crystalline ◽  
Structural Information ◽  
High Resolution Electron Microscopy ◽  
Scanning Calorimetry ◽  
Tertiary Butyl ◽  
Phenyl Acetylene ◽  
Selected Area Electron Diffraction ◽  
Liquid Crystalline Phases ◽  
Resolution Electron

The synthesis of well-defined organic molecules with unique geometries opens new opportunities for understanding and controlling the organization of condensed matter. Here, we study dendrimers and macrocycles which are synthesized from rigid phenyl-acetylene spacer units, Both units are solubilized by the presence of tertiary butyl groups located at the periphery of the molecule. These hydrocarbon materials form crystalline and liquid crystalline phases which have been studied by differential scanning calorimetry, hot stage optical microscopy, and wide-angle x-ray scattering (WAXS).The precisely defined architecture of these molecules makes it possible to investigate systematic variations in chemical architecture on the nature of microstructural organization. Here we report on the transmission electron microscopy (TEM), selected area electron diffraction (SAED), and high resolution electron microscopy (HREM) studies of crystalline thin films formed by deposition of these materials onto carbon substrates from dilute solution. Electron microscopy is very attractive for gaining structural information on new molecules due to the scarcity of material to grow single crystals suitable for conventional crystallography.

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