Determination of latent transition temperatures of nonmesomorphs by extrapolation method in binary systems

Article abstract of DOI:10.1080/15421406.2011.591663

Eight binary systems consisting of mesomorphs and nonmesomorphs (A ₁ or A₂ + B₁ B₂, B₇, B₈) were studied with a view to determine the latent transition temperature (LTT) for the nonmesomorp

Full text of DOI:10.1080/15421406.2011.591663

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Determination of Latent Transition
Temperatures of Nonmesomorphs by
Extrapolation Method in Binary Systems
A. V. Doshi a , U. C. Bhoya b & J. J. Travadi c
a Matushri Virbaima Mahila Science and Home Science College ,
Rajkot , Gujarat , India
b Department of Chemistry , Saurashtra University , Rajkot ,
Gujarat , India
c Kamani Science and Prataprai Arts College , Amreli , Gujarat ,
India
Published online: 27 Dec 2011.
To cite this article: A. V. Doshi , U. C. Bhoya & J. J. Travadi (2012) Determination of Latent Transition
Temperatures of Nonmesomorphs by Extrapolation Method in Binary Systems, Molecular Crystals and
Liquid Crystals, 552:1, 10-15, DOI: 10.1080/15421406.2011.591663
To link to this article: http://dx.doi.org/10.1080/15421406.2011.591663
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Mol. Cryst. Liq. Cryst., Vol. 552: pp. 10–15, 2012
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2011.591663
Determination of Latent Transition Temperatures
of Nonmesomorphs by Extrapolation Method
in Binary Systems
A. V. DOSHI,1 U. C. BHOYA,2 AND J. J. TRAVADI3,∗
1Matushri Virbaima Mahila Science and Home Science College, Rajkot,
Gujarat, India
2Department of Chemistry, Saurashtra University, Rajkot, Gujarat, India
3Kamani Science and Prataprai Arts College, Amreli, Gujarat, India
Eight binary systems consisting of mesomorphs and nonmesomorphs (A1 or A2, + B1,
B2, . . . B7, B8) were studied with a view to determine the latent transition temperature
(LTT) for the nonmesomorphic component (B) of a binary system by an extrapolation
method. Encouraging results supporting earlier views and LTT values were obtained
for seven binary systems. Instead of reporting a single value of LTT, the range of
temperature or two or three values are reported herewith depending upon the possible
paths of extrapolation. LTT reported earlier for nonmesomorphs lie within the range
of temperature determined presently. Though the “group slope value” differs from the
earlier reported value, the group efficiency order remains the same. Thus, the present
investigation raises the credibility of an extrapolation method to determine LTT and
group efficiency order for nematic mesophase. Component A1 and A2 are nematogenic,
namely, p-(pꢀ-n-propyloxy benzoyloxy) anisole (A1) (90.0 to 116.0) and p-(pꢀ-n-butyloxy
benzoyloxy) anisole (A2) (116.0 to 105.5). B1 to B8 are Schiff’s bases. Transition and
melting temperatures are observed through hot stage polarizing microscope for binary
mixtures and pure components.
Keywords mixed mesomorphism, mixed melt, nematic, smectic, liquid crystal
1. Introduction
The melting point and transition points are depressed by mixing two like components of a
binary system following a law of mixtures. Such binary systems are studied with a view to
understand the effect of molecular structure on mesophase formation and to determine latent
transition temperature (LTT) of nonmesomorph by extrapolation method for obtaining low
temperature liquid crystal material applicable and useful for the devices to be operated at
room temperature or desired temperature at economical cost.
∗Address correspondence to J. J. Travadi, Jyotirav Nagar, Opp. Radhika Hospital, Chittal Road,
Amreli, Gujarat 365601, India. E-mail: j.travadi72@gmail.com
10

Latent Transition Temperatures of Nonmesomorphs
2. Experimental
2.1 Synthesis of Component A1 and A2
11
Mesogenic components of a binary system, namely, p-(pꢀ-n-propyloxy benzoyloxy) anisole
(A1) and p-(pꢀ-n-butyloxy benzoyloxy) anisole (A2), were synthesized and purified by the
usual method [1].
2.2 Synthesis of Component B1–B8
Components B of the binary mixtures are Schiff’s bases. Schiff’s bases are prepared
[3] by refluxing equimolar proportion of corresponding Aldehyde and aromatic amine in
alcohol for about 1–2 hours. Products obtained were purified in alcohol until it gave constant
melting point.
2.3 Preparation of Binary Mixtures and Method of Study
Binary mixtures of binary systems were prepared by usual established standard method [3].
3. Results and Discussion
Nonmesomorphic substances without passing through anisotropic state of existence have
the potential to exhibit mesomorphic behavior. But mesophase does not appear because
the transition temperature from amorphous liquid to mesophase lies below normal melting
point. Such substances in their binary mixtures with mesomorphic or nonmesomophic
substances can give rise to “mixed liquid crystal” formation over a range of composition
and temperature. Thus search for virtual transition temperature is important.
More than eight binary systems were studied presently; among those, results of seven
binary systems (A1 + B1, A1 + B2, A2 + B3, A2 + B4, A2 + B5, A2 + B6, and A2 + B7)
are considered here for discussion.
Temperatures are plotted versus the mole percent of component A1/A2. Smooth curves
are drawn through like and related points. Mesomorphic–isotropic (or vice versa) transition
curve is extrapolated to zero mole percent of A1/A2 by selecting possible reliable paths
of extrapolation. The transition temperatures of pure components and binary mixtures, as
derived from phase diagrams, are recorded in Table 1. The representative phase diagrams
are given separately in this manuscript (see Fig. 1).

12

Latent Transition Temperatures of Nonmesomorphs
13
Figure 1. Phase behavior of representative binary systems of sets i and ii.
A careful examination of the phase diagrams reveals the fact that the nematic–isotropic
(or vice versa) transition curve in set 1 (binary systems A1 + B1 and A1 + B2) meets the
solid-isotropic (or nematic–isotropic) liquid curve to the right of the corresponding eutectic
points, i.e., the triple points are to the right of the eutectic point. In set 2, where first
component A2 is monotropic nematic, a triple point is absent in phase diagram.
The formation of mixed liquid crystals in the binary systems (see Table 1) is clearly
understood as the molecules are being aligned in a typical manner in their mixed melts. In
the mixed melts, a set of molecules belonging to mesomorph (A1 or A2) get mixed with
another set of molecules belonging to nonmesogen (Schiff’s bases). The nonmesomorphs
differ from the mesomorphic molecules in two respects, namely, magnitude of the polar
nature of the terminal groups and central bridge linking two phenyl rings. But the effect of
central bridge being negligibly small, the former effect of the polarity of terminal end groups
is considerably more. The mesomorphic components A1 and A2 has terminal groups with
sufficient polar nature, which give rise to terminal attractions in ample measure. Therefore,
on heating the binary mixtures, they form mesophase of the nematic variety for all the
binary systems under discussion. Only a binary system (A2 + B7) form smectic variety of
mesophase in addition to nematic mesophase.
Thus, formation of nematic variety of mesophase occurs due to terminal attractions,
which offer resistance to thermal vibrations maintaining an end-to-end alignment over
a range of temperature. As mesomorphic molecules get mixed with nonmesomorphic
molecules (B1, B2 . . . B7), they acquire an environment of considerably less terminal

14
A. V. Doshi et al.
attractions. Naturally, the forces operative in the direction of maintaining an end-to-end
orientations of molecules get interrupted by the entry of such nonmesomorphic molecules
causing a kind of disturbance.
Obviously, the mesomorphic molecules of the mixed melt are not able to offer enough
resistance to the thermal vibrations on heating to higher temperature and, hence, converted to
isotropic liquid somewhat, earlier than their usual transition temperature. Hence depression
in transition curve is caused. The disturbance offered by the nonmesomorphic molecules
is limited and increases with increasing proportion of their composition. The minimum
proportion of composition needed to disrupt completely; the mesomorphic alignment of
the mesogenic melts in turn depends upon the polar nature of its own terminal groups.
In the case of a majority of nonmesomorphic Schiff’s base, the component required
to disruption is 50% or more. Thus, mesophase is prolonged as monotropic mesophase,
which helps in setting a smooth trend to the transition curve and allows real curvature
or a proper bend characteristics of component B up to 24 to 50 mol% of mesomorphic
component A1/A2. The mesomorphic–isotropic (or vice versa) transition curves of all
the binary systems have been extrapolated through possible paths in keeping with the
smoothness of the transition curves as set in by their mesomophic–isotropic (or vice versa)
transition versus their concentration in mole percent of the liquid crystalline component at
constant atmospheric pressure. The range of LTT or different values of LTT determined
from phase diagrams for nonmesomorphic components are reported in Table 2.
Careful examination of LTT range or different two or three values of LTT for each
Schiff’s base under the present investigation are quite comparable with those reported
earlier.
Table 2. Relative comparison of LTT in ◦C reported earlier
Nonmesomorph
X C6H4 CH
LTT in ◦C present
investigation for
nematic/smectic
mesophase
LTT in ◦C reported earlier
N C6H4
X
Y
Schiff’s
base
Ref.- Ref.-
Ref.-
Ref.-
Y
AVD KJG JML/AVD CGJ
CH3
Cl
OCH3
CH3
CH3
Br
B1
B2
B3
70.5–77.0
77.0–100.0–105.0
81.5–105.0
64.0
—
82.0
86.0
72.5
—
—
73.0
82.0
—
—
100.0
(81.5–86.0–105.0)
49.0–80.0
(49.0–66.0–80.0)
45.0–118.0
(49.0–106.0–118.0)
70.0–102.0
(70.0–78.5–102.1)
Nm. 58.0–74.0
(58–67–74)
OCH3
Cl
Cl
COCH3
Cl
B4
B5
B6
B7
42.0
43.0
75.0
—
—
—
42.0
—
92.0
—
Cl
75.0
—
Cl
Br
72.5
—
—
—
—
—
—
—
Sm. (for A2) 86.0
Note: Nm, nematic mesophase; Sm, smectic mesophase. AVD = A.V. DOSHI; JML = J.M.
LOHAR; KJG = K.J. GANATRA; CGJ = C.G. JOSHI.

Latent Transition Temperatures of Nonmesomorphs
15
The binary systems consisting of nonmesomorphic Schiff’s bases having terminal end
groups of insufficient polarity are CH3, Cl, Br, and COCH3. The degree of meso-
morphism exhibited is much limited since the mesomorphic–isotropic transition curves cut
B1 and B2 (or do not cut B3 to B7) solid-isotropic curves at the point to the right of the
corresponding eutectics with prolonged monotropy, which leads to extrapolate a more real
curvature or proper bend causing variance of few ◦C. Thus, persistence of monotropy to a
large extent leads extrapolation to more accurate determination of LTT.
Polarity concept is further supported by initial slope values of the nematic–isotropic
liquid (or vice versa) transition curves. The group slope values are mutually differ for set
1 and set 2 as well as with previously reported values by earlier researchers. However the
order of polarity and hence the group efficiency order derived in the present investigation
very well matche with earlier work. The order of group efficiency for nematic derived is
OCH3 > Cl ≈ CH3 > COCH3 > Br.
Thus initial slope and hence group slope value may vary with the first component
(A1/A2) but finally the group efficiency order derived on the basis of polarity concept as
well as order of polarity remains unaltered with reference to earlier work2.
4. Conclusion
The extrapolation method to determine LTT of nonmesomorphs is quite dependable when
nonmesomorphic substances are structurally similar to mesomorphic substances and pos-
sess sufficiently polar terminal end groups, for homogeneous binary mixtures and melting
points of the constituent components do not differ to a large extent. For greater dependability
of the extrapolation method, the eutectic point should preferably be in equilibrium with the
anisotropic liquids. However, the evidence obtained by the present investigation raises the
reliability and credibility of the extrapolation method to determine LTT of nonmesomorphs.
Acknowledgment
The authors are thankful to the Head and members of the staff of Department of Ap-
plied Chemistry, Faculty of Technololgy and Engineering, Maharaja Sayajirao University,
Baroda, for their valuable cooperation in the work.
References
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[2] Gray, G. W., & Winsor, P. A. (1974). Liquid Crystals and Plastic Crystals, Ellis Horwood:
Chichester, Volume 1, Chapter 4, pp. 103–172.
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