Russian Journal of Applied Chemistry, 2009, Vol. 82, No. 4, pp. 563−568.
Pleiades Publishing, Ltd., 2009.
Original Russian Text
E.P. Sokolova, T.G. Churyusova, 2009, published in Zhurnal Prikladnoi Khimii, 2009, Vol. 82, No. 4, pp. 570−575.
OF SYSTEMS AND PROCESSES
Phase Equilibrium in Binary Liquid-Crystal Mixtures
of 4-n-Pentyl-4'-Cyanobiphenyl and Phenyl Benzoates
E. P. Sokolova and T. G. Churyusova
St. Petersburg State University, St. Petersburg, Russia
Received November 12, 2008
Abstract—Differential scanning calorimetry and polarization microscopy were used to study the phase diagram
of a mixture of nematic liquid crystals, 4-n-pentyl-4'-cyanobiphenyl and 4-n-octyloxyphenyl-4'-hexylbenzoate.
The wide use of liquid crystals in systems for
information display and processing, visualization of
radiation, ﬂ aw detection, and other ﬁ elds of technology
necessitates development of liquid crystal materials
(LCM) —mesomorphic mixtures whose physicochemical
parameters are determined by a particular technological
device [1–3]. An important role in the development
of LCMs is played by phase diagrams of binary and
multicomponent systems and by the possibility of
using these diagrams to vary the temperature ranges of
mesophase existence by choosing the appropriate regions
of mixture compositions.
Most widely used in display technologies are mixtures
based on nematic (N) liquid crystals (NLCs), which
include both strongly and weakly polar compounds.
However, smectic liquid crystals are also used in
devices for optical information processing . These
mesophases have a layered structure in which, in addition
to the nematic orientation ordering, centers of mass of
molecules are lying, on average, in equidistant planes.
Spatial light modulators use the effect of preservation of
a structure appearing under the action of an external ﬁ eld
in a smectic layer (long-term memory). The electric ﬁ eld
most easily orients smectic A (SA) liquid crystals; in these
mesophases, the axis of the preferred orientation of the
long axes of molecules is perpendicular to the layer plane.
LCMs are also developed using smectic phases formed
(induced) in mixing of strongly and weakly polar NLCs
in certain temperature and concentration intervals. By
varying the relative concentrations of components, the
optimal combination of the required LCM parameters
can be obtained, of which the most important are low
values of the enthalpies of N–I and SA–N transitions
and narrows ranges of coexistence of the components (I
is the isotropic phase). Thus, systems formed by NLCs
with molecules of different polarities are of interest both
as regards technical applications and in the context of
studying the stabilization of intermediate smectic phases
and the nature of transformations between phases with
different symmetries [4–11].
This study is concerned with the phase diagram of
a mixture of two diaryl nematic mesogens: 4-n-pentyl-
4''-cyanobiphenyl (5CB) and 4-n-octyloxyphenyl-
4'-hexylbenzoate (I); the chemical formulas of these
compounds are H
–C≡N and H
, respectively. The individual
components of the system under study have no smectic
phases. The primary experimental goal consisted in
conﬁ rming that an induced smectic is formed on mixing
the components and determining its stability ﬁ eld. The
strongly polar 5CB (dipole moment of the terminal –C≡N
group is 13.4 × 10
C m ) belongs to the class of
cyanoderivative liquid crystals, which are among the
most important components for LCM development.
These compounds possess a large optical anisotropy
and are highly chemically and photochemically stable.
4-n-Octyloxyphenyl-4'-hexylbenzoate is a weakly polar
mesogen, with the dipole moment of the –C(O)O– group
equal to 6.3 × 10
C m. The properties of substituted aryl
benzoates depend on the position of terminal substituents