Novel Liquid Crystalline Cinnamoyloxy Cinnamates
21
in the same series. Geometrically, the arrangement of atoms in space of the molecules
of series 1 and X appreciably differs in respect of the extent of their molecular width.
Therefore, net molecular polarity and polarizability vary according to molecular width and
length to breadth ratio. Greater molecular width (i) increase intermolecular distance and
reduces the magnitude of intermolecular anisotropic forces of attractions on one hand,
while on the other hand, (ii) increases the magnitude of intermolecular anisotropic forces
of attractions due to increased molecular breadth or polarizability. Thus, two opposing
effects, viz., (i) and (ii) are operating at a time. Therefore, net resultant effect observed is,
that of predominating effect out of two opposing effects (i) and (ii) operating at a time.
In case of lower value of average nematic-isotropic thermal stability or total mesophase
length of series 1 as compared to series X is attributed to the predominancy of factor (i),
which resists the thermal vibrations to cause statistically parallel orientational order of
molecules in floating condition a little bit less in series 1 as compared to series X. The
absence of smectogenic character in series X and appearance of smectogenic character
in addition to nematic mesophase in series 1 is attributed to the absence and presence of
lamellar packing in the crystal lattices, respectively, depending upon net result effect, out
of two opposing effects (i) and (ii). The commencement of smectic phase occurance from
octyloxyhomologue in series 1, which does not occur until the last hexadecyl homologue
in series X. This observation is attributed to the extent of noncoplanarity caused by the
molecule due to electron–electron interactions and steric interactions [3,6]. This effect,
i.e., difference in magnitude of noncoplanarity of molecule of series 1 and series X is
responsible to cause early or late commencement of smectic phase. Thus, lamellar packing
in crystal lattices of molecules of series 1 is possible while it lacks in case of molecules of
series X. Hence, smectogenic character in series X is absent till the last hexadecyl derivative
and it appears from the octyloxy homologue of series 1. The stable state of a substance is
associated with definite quantity of energy stored by the molecule at room temperature and
one atmospheric pressure. That is, thermodynamically it is called enthalpy change (H) of
a substance at normal temperature and pressure. As heat is supplied to a sample substance
(system) from a surrounding to system; supplied heat energy from surroundings operates
against the intermolecular anisotropic forces of attractions and molecules tend from sta-
bilized state to destabilized state at a temperature T1. Under this condition, molecules of
a sample substance under investigation are disaligned at an angle less than 90◦ with the
plane of a surface resisting exposed thermal vibrations and acquire mesophase formation
at T1. Mesophase formation continues till a higher temperature T2 and then mesophase
disappears for anisotropic liquid crystal. As temperature rises beyond T2, molecules are
randomly oriented in all possible directions in an irregular manner, such randomness or
molecular disorder or entropy increases with a rise of temperature and decreases with a
fall of temperature. Similarly, for monotropic liquid crystal T2 < T1, where T1 is isotropic
temperature or higher temperature. Difference of T1 and T2 is called a phase length or a
range of liquid crystallinity. Thus, S value is calculated for any transition state from DSC
scans using H value of corresponding transition temperature value. Thus, thermal stability
values are related with a H value of a sample substance. The variation in mesomorphic
properties from homologue to homologue in the same series and from series to series for
the same homologue are due to the sequentially added methylene unit and laterally or ter-
minally present functional group of fixed polarity, respectively. Thus, according to Gray’s
view [3,6] that, presence of anaphthyl unit in a molecular moiety induces nematogenic
character relatively more and increase in molecular breadth reduces smectogenic character
and smectic–nematic thermal stability. This statement is well supported by present inves-
tigation. Hence, the smectic and nematic group efficiency order derived on the bases of