Phase diagrams of liquid-crystal binary systems of lanthanum(III) laurate with some divalent metal laurates

Article abstract of DOI:10.1134/S003602360604022X

Phase equilibria in binary systems of lanthanum(III) laurate with laurates of divalent metals (lead, cadmium, zinc, and cobalt) are studied at temperatures from 0 to 350°C using differential thermal analysis (DTA) and polythermal polarized-light microscopy. Continuous or terminal smectic A liquid-crystal (LC) solutions are found to form in all systems. The temperature-concentration fields of formation of ionic LCs and glasses are determined. Pleiades Publishing, Inc., 2006.

Full text of DOI:10.1134/S003602360604022X

ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2006, Vol. 51, No. 4, pp. 639–641. © Pleiades Publishing, Inc., 2006.
Original Russian Text © D.V. Bylina, T.A. Mirnaya, S.V. Volkov, 2006, published in Zhurnal Neorganicheskoi Khimii, 2006, Vol. 51, No. 4, pp. 695–697.
PHYSICOCHEMICAL ANALYSIS
OF INORGANIC SYSTEMS
Phase Diagrams of Liquid-Crystal Binary Systems
of Lanthanum(III) Laurate
with Some Divalent Metal Laurates
D. V. Bylina, T. A. Mirnaya, and S. V. Volkov
Vernadsky Institute of General and Inorganic Chemistry, National Academy of Sciences of Ukraine,
pr. Palladina 32/34, Kiev,252601 Ukraine
Received June 6, 2005
Abstract—Phase equilibria in binary systems of lanthanum(III) laurate with laurates of divalent metals (lead,
cadmium, zinc, and cobalt) are studied at temperatures from 0 to 350°C using differential thermal analysis
(DTA) and polythermal polarized-light microscopy. Continuous or terminal smectic A liquid-crystal (LC) solu-
tions are found to form in all systems. The temperature–concentration fields of formation of ionic LCs and
glasses are determined.
DOI: 10.1134/S003602360604022X
Metal alkanoates are capable of forming ionic liq- recrystallized from hot toluene and vacuum dried at
uid-crystal (LC) phases [1], mainly, with smectic order- 80°C for 48 h.
ing. Ionic mesophases and glasses of alkanoates show
promise for design of novel materials with special opti-
cal and physical properties [2, 3]. Unfortunately, we
have found scarce information on the mesomorphic
behavior of binary or more complex systems containing
rare-earth alkanoates. Only phase equilibria in the
binary systems of lanthanum laurate with some univa-
lent metal laurates have been studied to date [4]; ther-
motropic LCs and optically anisotropic mesomorphic
glasses were found in these systems.
Cobalt(II) laurate was prepared by metathesis of
cadmium nitrate and sodium laurate. The product was
washed with isopropanol and water; then it was vacuum
dried at 50°C for 48 h.
IR spectra show that all the salts are free of water
and acid.
Phase-equilibrium temperatures were studied using
differential thermal analysis (DTA) and polythermal
polarized-light microscopy. A Paulik-Paulik-Erdey
Q-1500D derivatograph was used with a Pt/Pt–Rh ther-
mocouple; Al2O3 was the reference. The heating rate in
We have studied phase equilibria in the binary sys-
tems of lanthanum laurate with laurates of some diva- all experiments was 2.5 K/min; an argon atmosphere
lent metals (lead, cadmium, zinc, and cobalt) in order to was used.
determine the temperature and concentration ranges of
formation for the LC phase and mesomorphic glasses.
These systems are interesting and useful in the context
of manufacturing anisotropic materials with special
optical and nonlinear optical characteristics.
AnAmplival polarizing microscope equipped with a
heating stage was used to identify the mesophase and to
estimate phase equilibria between an isotropic liquid
and a crystal (Tm) and between an isotropic liquid and a
mesophase (Tcl).
The phase-transition temperatures of the individual
salts synthesized correlate with the literature data [5–8].
Lanthanum laurate melts at 110°C into a smectic
mesophase whose clearing temperature is 160°C. Lead
laurate experiences a solid-phase transition at 94°C,
melts into a smectic mesophase at 104°C, and trans-
forms into an isotropic liquid at 111°C. Cadmium lau-
rate melts at 95°C into a smectic mesophase, which
clears at 97°C. Zinc laurate undergoes a solid-phase
transition at 99°C and melts at 134°C into a viscous iso-
tropic melt. Phase-transition temperatures for cobalt
EXPERIMENTAL
Lanthanum laurate was prepared, according to [5, 6],
by metathesis of sodium laurate and lanthanum nitrate
in water. Crystals were collected on a filter and recrys-
tallized from a n-pentanol and ethanol mixture (5 : 1);
then, they were dried in a vacuum drier at 85°C. The
lanthanum laurate was fused under dry argon to remove
remnant water.
Cadmium, lead, and zinc laurates were prepared by laurate are not found in the literature. We found cobalt
metathesis of lead and cadmium nitrates and sodium laurate to melt at 67°C into a mesophase, a birefringent
laurate, according to [7, 8], combining the water–alco- liquid with poorly defined microscopic texture, appar-
holic solutions of the reagents. The products were ently, because of its strong tendency toward homeotro-
639

640
T, °ë
BYLINA et al.
All the salts, except for nonmesomorphous zinc lau-
rate and cobalt laurate (for which the LC order has not
been determined uniquely), form an enantiotropic
smectic A phase [10].
200
IL
RESULTS AND DISCUSSION
150
1
Figures 1–4 display the phase diagrams for the
binary systems investigated.
System {x(C11H23COO)3La
+
(100
–
x)-
LC
(C11H23COO)2êb}. Continuous solid solutions with a
minimum at 75°C, x = 32 mol % are formed in the sys-
tem (Fig. 1). A continuous LC solution (smectic A) is
formed upon melting of the solid solution. The melts in
the range 20 < x ≤ 100 mol % are undercooled to form
LC glasses.
100
50
S
2
System {x(C11H23COO)3La
+
(100
–
x)-
0
50
100
(C11H23COO)2Cd}. Continuous LC solutions (smectic
A) are formed by a eutectic reaction between the termi-
nal components (Fig. 2). The liquidus curve has a
eutectic point at 80°C, x = 32 mol %. The two-phase
domain in which the mesophase coexists with an isotro-
pic liquid is less than 2°C in our experiments; it is not
indicated in the diagram.
ı, mol %
Fig. 1. Phase diagram for the {x(C
H COO) La + (100 –
11 23 3
x)(C
H COO) Pb} binary system. Here and in Figs. 2–4,
11 23 2
IL and LC are single-phase domains of isotropic melts and
LC solutions (smectic A), S is solid solution, and figures
indicate two-phase domains: (1) IL + LC and (2) LC + S.
Undercooling of the mesophase and the formation
of LC glasses were observed in range 30 < x ≤
100 mol %.
pic orientation of LC domains, as in the cobalt
decanoate mesophase [9]. We failed to determine the
clearing temperature of the cobalt laurate mesophase.
System {x(C11H23COO)3La
+
(100
–
x)-
(C11H23COO)2Zn}. The phase diagram of the system
T, °ë
200
T, °ë
200
IL
IL
150
150
LC
LC
1
1
2
SZn
100
50
100
3
3
4
SLa
SLa
2
4
5
SCd
50
0
50
100
0
50
100
ı, mol %
ı, mol %
Fig. 3. Phase diagram for the {x(C
H COO) La + (100 –
Fig. 2. Phase diagram for the {x(C
H
COO) La + (100 –
11 23 3
11 23
3
x)(C
H COO) Zn} binary system: (1) IL + LC, (2) IL +
x)(C
H COO) Cd} binary system: (1) IL + LC, (2) LC +
11 23 2
11 23 2
S
S
, (3) LC + S , (4) LC + S , and (5) S + S , where
S
, (3) LC + S , and (4) S + S , where S and S are
Zn
Zn La Zn La
Cd
La Cd La La Cd
and S are solid solutions based on lanthanum and zinc
solid solutions based on lanthanum and cadmium laurate,
respectively.
La
Zn
laurate, respectively.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 51 No. 4 2006

PHASE DIAGRAMS OF LIQUID-CRYSTAL BINARY SYSTEMS
641
an incongruently melting compound is formed; its sug-
gested composition is (C11H23COO)3La
4(C11H23COO)2Co. The clearing temperature curve has
not been drawn completely, since cobalt-laurate-rich
compositions form a mesophase whose texture was
pseudoisotropic when observed in a polarized light.
T, °ë
·
200
IL
150
100
Mesomorphic glasses were observed over the entire
concentration range of the system.
In summary, our investigation shows that the LC
phases of mesogenic laurates of divalent metals are
fully soluble in the lanthanum laurate LC phase. Non-
mesogenic zinc laurate is incompletely soluble in the
lanthanum laurate mesophase. In addition, terminal or
complete solid solutions are formed in the systems of
lanthanum laurate with laurates of divalent metals
whose d shell is fully filled (Pb, Cd, Zn). Binary mix-
tures in the systems of lanthanum laurate with divalent
metal laurates form mesomorphic glasses over a wide
concentration range.
LC
1
3
5
2
4
50
0
50
100
ı, mol %
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Fig. 4. Phase diagram for the {x(C
H COO) La + (100 –
11 23 3
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(100
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x)-
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RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 51 No. 4 2006