Synthesis and thermotropic properties of novel double-chained quaternary ammonium chlorides with symmetric and asymmetric hydrocarbon chain length

Article abstract of DOI:10.1016/j.molstruc.2009.02.013

A series of novel double-chained quaternary ammonium chlorides with symmetrical and asymmetrical hydrocarbon chain length R₁-O-CH₂-CH(OH)-CH₂-N⁺(CH₃)₂-R₂·Cl^- (R₁, R₂: C₁₂H₂₅, C₁₄H₂₉, C₁₆H₃₃) have been synthesized by the reaction of 1-O-alkyl glycidyl ether with N,N-dimethylalkylamine and N,N-dimethylalkylamine hydrochloride. Their chemical structures have been characterized through FT-IR, ¹H NMR, MS and elementary analysis. Their thermotropic properties have been examined by differential scanning calorimetry (DSC), polarizing light microscopy (PLM) and X-ray diffraction (XRD). It has been found that the compounds with longer hydrocarbon chain length and being higher asymmetry in hydrocarbon chain length exhibit lower melting point (T_m)_, isotropization temperature (T_i) and narrower mesophase temperature range. However, the hydrocarbon chain length and the symmetry in the hydrocarbon chain length have little influence on the type of liquid crystals. All compounds form cholesteric liquid crystal.

Full text of DOI:10.1016/j.molstruc.2009.02.013

Journal of Molecular Structure 923 (2009) 127–131
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis and thermotropic properties of novel double-chained quaternary
ammonium chlorides with symmetric and asymmetric hydrocarbon chain length
Zhaoyun Ding a,*, Aiyou Hao b
a
School of Chemical Engineering, Shandong Institute of Light Industry, Jinan 250353, PR China
School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100, PR China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of novel double-chained quaternary ammonium chlorides with symmetrical and asymmetrical
Received 12 October 2008
Received in revised form 6 February 2009
Accepted 13 February 2009
Available online 24 February 2009
+
À
hydrocarbon chain length R
1
–O–CH
2
–CH(OH)–CH
2
–N (CH
3
)
2
–R
2
ÁCl (R
1 2
, R : C12H25, C14H29, C16H33) have
been synthesized by the reaction of 1-O-alkyl glycidyl ether with N,N-dimethylalkylamine and N,N-dim-
ethylalkylamine hydrochloride. Their chemical structures have been characterized through FT-IR, 1
H
NMR, MS and elementary analysis. Their thermotropic properties have been examined by differential
scanning calorimetry (DSC), polarizing light microscopy (PLM) and X-ray diffraction (XRD). It has been
found that the compounds with longer hydrocarbon chain length and being higher asymmetry in hydro-
carbon chain length exhibit lower melting point (T ) isotropization temperature (T ) and narrower meso-
m , i
phase temperature range. However, the hydrocarbon chain length and the symmetry in the hydrocarbon
Keywords:
Thermotropic phase behavior
Double-chained quaternary ammonium
chloride
Cholesteric liquid crystal
chain length have little influence on the type of liquid crystals. All compounds form cholesteric liquid
crystal.
Ó 2009 Elsevier B.V. All rights reserved.
1
. Introduction
stable bilayer structures, which further form vesicles and lamellae
[
17]. It can also form four microstructures such as an isotropic
micellar phase, a metastable L
sponge phase, a dispersion of pure
crystallites of lamellar phase in an isotropic phase, and a pure
lamellar phase L form upon increasing its concentration in water
[18]. Dioctadecyldimethylammonium chloride (DODAC) [19] and
Some double-chained quaternary ammonium bromides containing
acyl hydrophobic chains [20,21] can form vesicles in water.
Many amphiphilic molecules exhibit thermotropic liquid crys-
3
talline behavior upon heating from solids or cooling from liquid.
It has been known that certain ionic soaps, some cationic surfac-
tants, most carbohydrate derivatives, a few zwitterionic and
poly(oxyethylene) nonionic surfactant and some catanionic surfac-
tants exhibit thermotropic phase behavior [1–12]. The type of
liquid-crystalline phases exhibited by these compounds depends
on an interplay of the length and number of lipophilic chains, the
nature of the polar heads. Some single-chained quaternary ammo-
nium salts display thermotropic phase behavior. Some double-
chained quaternary ammonium salts also exhibit thermotropic
liquid crystalline behavior [13–16]. Arkas et al. [14] has reported
that N-cyanoalkyl(from methyl to hexyl)-N-alkyl(from dodecyl to
octadecyl)-N,N-dimethylammonium bromides display smectic A
phase. Alami et al. [15] has found that N,N-dialkyl-N,N-dimethyl-
ammonium bromides with alkyl chains from dodecyl to octadecyl
show smectic T phase. Everaars et al. [16] has investigated thermo-
tropic liquid crystalline behavior of a series of isomeric double-
chained quaternary ammonium salts. Some double-chained qua-
ternary ammonium salts tend to self-associate in water to form ves-
icles, and lyotropic liquid crystals. Didodecyldimethylammonium
bromide (DDAB) aggregates extensively in aqueous solutions into
a
Previous studies suggest that thermotropic properties of
double-chained quaternary ammonium salts strongly depend on
the structure and length of lipophilic chains, the nature of the
counter ions. More studies of these compounds will lead to better
understanding of their thermotropic phase behavior. In this
paper, a new series of double-chained quaternary ammonium
chlorides with symmetrical and asymmetrical hydrocarbon chain
length, N-(3-alkoxyl-2-hydroxy)propyl-N-alkyl dimethylammo-
+
À
nium chloride R
1
–O–CH
2
–CH(OH)–CH
2
–N (CH
3
)
2
–R
2
ÁCl (R
1 2
, R :
12
C H25, C14H29, C16H33), has been synthesized (see Scheme 1). In
previous studies, bromide has been chosen as counter-ion, mainly
because the bromides are easier to synthesize. In this study, chlo-
ride is chosen as counter-ion. The thermotropic properties of these
novel double-chained quaternary ammonium chlorides have been
investigated by DSC, PLM, and XRD. The purpose of this study is
to investigate the relationship between structure and property by
varying the hydrocarbon chain length and the symmetry in hydro-
carbon chain length. Based on the obtained results, some conclu-
sions as to the length of the hydrocarbon chain, the symmetry in
the hydrocarbon chain, and mesophase formation will be present.
*
Corresponding author. Tel.: +86 531 8963 1208.
E-mail address: zhaoyunding@gmail.com (Z. Ding).
0
022-2860/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2009.02.013

1
28
Z. Ding, A. Hao / Journal of Molecular Structure 923 (2009) 127–131
Scheme 1. Synthetic route of symmetrical and asymmetrical double-chained quaternary ammonium chlorides.
2
. Experimental and methods
for C37
H
78NO
2
Cl (604.47): C, 73.52; H, 13.00; N 2.32; found: C,
À +
7
3.66; H, 12.77; N, 2.21%. MS: signal at = 569.0 (m/z) [M–Cl ] .
1
2.1. Materials
14
G A
12C: H NMR (CDCl
3
, TMS, in ppm): 0.88 (t, 6H, 2CH
3
–),
+
1
CH
N –CH
N , O–CH
.26–1.36 [m, 40H, –(CH
2
)
9
–, –(CH
–CH –), 3.36–3.46 (m, 10H, 2CH
–), 3.55–3.59 [m, 4H, –CH(OH)–CH
–CH(OH)–], 4.44 [m, 1H, –CH(OH)–]. Elemental analysis:
calcd. (%) for C31 C (520.31): C, 71.56; H, 12.78; N, 2.69;
2
)11–], 1.51 (t, 2H, N –CH –
2
+
Dodecanol (>98%), tetradecanol (>98%) and hexadecanol (>98%)
2
–), 1.73 (t, 2H, O–CH
2
2
3
–N ,
+
were purchased from China Pharamactical Corporation (Shanghai,
China). N,N-dimethyldodecylamine (>98%), N,N-dimethyltetrade-
cylamine (>98%) and N,N-dimethylhexadecylamine (>98%) were
purchased from Shanghai Jingwei Chemical Company (Shanghai,
China). Epichlorohydrin, sodium hydroxide, hydrochloric acid,
chlorosulfonic acid and other solvents were all analytical grade.
2
–CH
2
–, O–CH
2
–CH
2
2
–
+
2
H66NO
2
found: C, 71.09; H, 12.54, N, 2.52%. MS: signal at = 484.9 (m/z)
À +
[MÀCl ] .
12C: 1H NMR (CDCl
, TMS, in ppm): 0.89 (t, 6H, 2CH
–),
16
G A
3
3
+
1
.27–1.37 [m, 44H, –(CH
2
)
9
–, –(CH
–CH –) 3.39–3.49 (m, 10H, 2CH
2
–) 3.55–3.61 [m, 4H, –CH(OH)–CH –
2
)13–], 1.52 (t, 2H, N –CH –
2
+
2.2. Synthesis of long-chain 1-O-alkyl glyceryl ethers
CH –), 1.75 (t, 2H, O–CH
2
2
2
3
–N ,
+
N –CH
2
–CH
N , O–CH
calcd. (%) for C33H70NO
2
2
–, O–CH
2
–CH
2
+
Long-chain 1-O-alkyl glycidyl ether was prepared by the reac-
2
–CH(OH)-], 4.48 [m, 1H, –CH(OH)–]. Elemental analysis:
Cl (548.36): C, 72.28; H, 12.87; N, 2.55;
tion of long-chained fatty alcohol with epichlorohydrin under
phase-transfer catalytic condition according to the literature [22].
found: C, 72.38; H, 12.61; N, 2.41%. MS: signal at = 513.0 (m/z)
À +
[
MÀCl ] .
G
12
A
14C: 1H NMR (CDCl
3
, TMS, in ppm): 0.88 (t, 6H, 2CH
3
–),
2.3. Synthesis of double-chained quaternary ammonium salts
+
1
CH
N –CH
N , O–CH
.26–1.34 [m, 40H, –(CH
–), 1.72 (t, 2H, O–CH
2
)
9
–, –(CH
–CH –), 3.35–3.46 (m, 10H, 2CH
–), 3.53–3.59 [m, 4H, –CH(OH)–CH
–CH(OH)–], 4.44 [m, 1H, –CH(OH)–]. Elemental analysis:
calcd. (%) for C31 Cl (520.31): C, 71.56; H, 12.78; N, 2.69;
2
)11–], 1.51 (t, 2H, N –CH –
2
+
A mixture of 1-O-alkyl glyceryl ether (0.1 mol), N,N-dim-
2
2
2
3
–N ,
+
ethylalkylamine (0.05 mol) and its hydrochloride (0.1 mol) [23] in
isopropanol (50 mL) was heated to reflux for 24 h. After the solvent
was evaporated under reduced pressure, the residue was recrystal-
lized several times from acetonitrile and dried under reduced pres-
sure to give the final products as white crystals. Their yields were
9
2
–CH
2
–, O–CH
2
–CH
2
2
–
+
2
H66NO
2
found: C, 71.56; H, 12.51; N, 2.54%. MS: signal at = 484.9 (m/z)
À +
[MÀCl ] .
1
16C: 1H NMR (CDCl
0%. Their chemical structures and purities were confirmed by H
12
G A
3
, TMS, in ppm): 0.87 (t, 6H, 2CH
3
–),
+
NMR (Advance 600, Bruker), MS (API 4000) and elemental analysis
1.24–1.33 [m, 44H, –(CH
CH –), 1.71 (t, 2H, O–CH
2
)
9
–, –(CH
–CH –) 3.36–3.45 (m, 10H, 2CH
–), 3.51–3.53 [m, 2H, –CH(OH)–CH
N ], 3.55–3.58 [m, 2H, O–CH –CH(OH)–], 4.42 [m, 1H, –CH(OH)–
]. Elemental analysis: calcd. (%) for C33 Cl (548.36): C,
2
)
13–], 1.50 (t, 2H, N –CH –
2
+
(
Perkin–Elmer 2400). These double-chained quaternary ammo-
2
2
2
3
–N ,
+
À
+
nium chlorides R
C
G
1
–O–CH
2
–CH(OH)–CH
2
–N (CH
12C (R
= C16
= C16
3
)
2
–R
2
ÁCl (R
1
, R
2
:
N –CH
2
–CH
2
–, O–CH
2
–CH
2
2
–
+
12
H
25, C14
H
29, C16
= C14
= C12
= C12
16C (R
H
33) are abbreviated as G12
A
1
, R
2
= C12
H
A
H
25),
2
A
14 14
C
(R
1
,
R
2
H
29),
G
G
16
A
A
16
C
C
(R
(R
G
1
,
R
2
H
33),
G
14
12
C
H70NO
2
(R
1
= C14
H
29
,
R
2
H25),
16
12
1
H
33
,
R
2
= C12
H
25),
72.28; H 12.87; N 2.55; found: C, 72.08; H, 12.67; N, 2.37%. MS: sig-
À +
G
C
R
12
A
14
33), G14
29).
12C: 1H NMR (CDCl
.23–1.32 (m, 36H, 2–(CH
t, 2H, O–CH –CH –), 3.33–3.43 (m, 10H, 2CH
–), 3.52–3.57 [m, 4H, –CH(OH)–CH
C
(R
1
H
25
,
R
2
= C14
H29),
12
A
16
C
(R
1
= C12
25
,
R
2
=
,
nal at = 513.1 (m/z) [MÀCl ] .
1
16
H
A
1
= C14H29, R
2
= C16
H
33), G16
A14C (R
1
= C16
H
33
14
G A
16C: H NMR (CDCl
3
, TMS, in ppm): 0.88 (t, 6H, 2CH
3
–),
+
= C14H
1.26–1.35 [m, 48H, –(CH
CH –), 1.73 (t, 2H, O–CH
2
)
11–, –(CH
–CH –), 3.38–3.47 (m, 10H, 2CH
–), 3.53–3.54 [m, 2H, –CH(OH)–CH
N ], 3.58–3.60 [m, 2H, O–CH –CH(OH)–], 4.44 [m, 1H, –CH(OH)–
]. Elemental analysis: calcd. (%) for C35 Cl (576.42): C,
2
)
13–], 1.51 (t, 2H, N –CH –
2
+
2
G
12
A
3
, TMS, in ppm): 0.86 (t, 6H, 2CH
3
–),
–), 1.70
–N , N –CH –CH –,
–N , O–CH
2
2
2
3
–N ,
+
+
1
(
2
)
9
–), 1.50 (t, 2H, N –CH
2
–CH
2
N –CH
2
–CH
2
–, O–CH
2
–CH
2
2
–
+
+
+
2
2
3
2
2
2
+
O–CH
2
–CH
2
2
2
–
H74NO
2
CH(OH)–], 4.38 [m, 1H, –CH(OH)–]. Elemental analysis: calcd. (%)
72.93; H, 12.94; N, 2.43; found: C, 72.72; H, 13.30; N, 2.32%. MS:
À +
for C29
H
62NO
2
Cl (492.26): C, 70.76; H, 12.69; N, 2.85; found: C,
signal at = 541.0 (m/z) [MÀCl ] .
À +
1
7
0.35; H, 12.44; N, 2.70%. MS: signal at = 456.9 (m/z) [MÀCl ] .
16
G A
14C: H NMR (CDCl
3
, TMS, in ppm): 0.88 (t, 6H, 2CH
3
–),
1
+
G
14
A
14C: H NMR (CDCl
.26–1.35 (m, 44H, 2–(CH
–CH –), 3.38–3.47 (m, 10H, 2CH
–), 3.54–3.55 [m, 2H, –CH(OH)–CH
–CH(OH)–], 4.46 [m, 1H, –CH(OH)–]. Elemental anal-
ysis: calcd. (%) for C33 Cl (548.36): C, 72.28; H, 12.87; N,
.55; found: C, 71.65; H, 12.64; N, 2.39%. MS: signal at = 513.0
3
, TMS, in ppm): 0.88 (t, 6H, 2CH
3
–),
–), 1.73
–N , N –CH –CH –,
–N ], 3.58–3.62
1.26–1.34 [m, 48H, –(CH
2
)
11–, –(CH
–CH –) 3.36–3.46 (m, 10H, 2CH
–), 3.52–3.55 [m, 2H, –CH(OH)–CH
N ], 3.57–3.60 [m, 2H, O–CH –CH(OH)–], 4.44 [m, 1H, –CH(OH)–
]. Elemental analysis: calcd. (%) for C35 Cl (576.42): C,
2
)
13–], 1.51 (t, 2H, N –CH –
2
+
+
1
2
)
11–), 1.52(t, 2H, N –CH
2
–CH
2
CH –), 1.73 (t, 2H, O–CH
2
2
2
3
–N ,
+
+
+
(
t, 2H, O–CH
2
2
3
2
2
N –CH
2
–CH
2
–, O–CH
2
–CH
2
2
–
+
+
O–CH
2
–CH
2
2
2
[
m, 2H, O–CH
2
H74NO
2
H70NO
2
72.93; H, 12.94; N, 2.43; found: C, 72.81; H, 13.27; N, 2.34%. MS:
À +
2
signal at = 541.0 l (m/z) [MÀCl ] .
À +
(
m/z) [MÀCl ] .
16C: 1H NMR (CDCl
.25–1.35 (m, 52H, 2–(CH
–CH –), 3.36 (s, 3H, CH
–N , N –CH –CH –, O–CH2/2–CH –), 3.47–3.53 [m, 3H,
–N , O–CH2/2–CH –], 3.58–3.64 [m, 2H, O–CH
G
16
A
3
, TMS, in ppm): 0.88 (t, 6H, 2CH
3
–),
–), 1.74
–N ), 3.39–3.43 (m, 6H,
2.4. Methods
+
1
2 2 2
)13–), 1.52 (t, 2H, N –CH –CH
+
(
t, 2H, O–CH
2
2
3
2.4.1. Thermogravimetry (TGA) and differential scanning calorimetry
(DSC)
The thermal stability was analyzed by SDT Q600 V8.0 Build 95
heating rate of 10 °C/min in nitrogen (50 mL/min). DSC measure-
+
+
CH
3
2
+
2
2
–
–
CH(OH)–CH
2
2
2
CH(OH)–], 4.48 [m, 1H, –CH(OH)–]. Elemental analysis: calcd. (%)

Z. Ding, A. Hao / Journal of Molecular Structure 923 (2009) 127–131
129
ments were carried out using a 822e DSC (Mettler Toleodo)
equipped with a cryostat cooling system. Heating–cooling cycles
were performed at a scanning rate of 5 °C/min. A flow rate of
5
0 mL of nitrogen was used in DSC cell.
2.4.2. Polarizing light microscopy (PLM)
A microscope (Olympus BX 51) equipped with a heating stage
(
Linkam THMSE 600) was used to observe the texture of samples
during the heating and cooling processes. The samples kept be-
tween coverslips were heated from room temperature to 150 °C
for double-chained quaternary ammonium salts, from room tem-
perature to 210 °C for novel zwitterionic geminis. The samples
were illuminated with linearly polarized light and analyzed
through a crossed polarizer. To capture images at different temper-
atures, a video camera (Qimage 5.0 RTV) was used.
Fig. 2. DSC thermogram of G12A12C during heating and cooling cycles.
2.4.3. X-ray diffraction (XRD)
X-ray measurements of these samples were performed using Cu
Ka (1.542 Å) radiation monochromatized with a Rigaku D/MAX-rA
X-ray diffractometer. The recording temperatures were chosen be-
tween points of phase transitions, in accordance with the DSC
curves. Scanning rates in small-angle and wide-angle range were
exhibit enantiotropic behavior. The phase transition parameters,
transition temperatures and changes in enthalpy, derived from
the DSC heating and cooling scans of these compounds are summa-
rized in Table 1.
Though the nine compounds show similar patterns of thermo-
tropic phase behavior, there are some differences in the details.
The increase in number of C-atoms in hydrocarbon chains of the
double-chained quaternary ammonium chlorides leads to the
4
and 2°/min, respectively.
3
. Results and discussions
m i d c
decrease of the T , T , T , and the increase of the T . The tempera-
3.1. TGA and DSC results
ture range for the occurrence of liquid-crystalline phase narrows
with hydrocarbon chain length increase. It can be seen from Table
Prior to study of thermotropic phase behaviors, the thermal sta-
1 that G16
m i d c
A16C exhibits lower T , T , T , higher T , and narrower
bilities of these double-chained quaternary ammonium chlorides
have been analyzed systematically by thermogravimetry. All these
compounds have similar thermal stability. They are found to
decompose above temperature of 175 °C upon heating. A typical
mesophase range than G12
A
12C and G14A
14C. On the other hand,
the symmetry in hydrocarbon chain length also influences the
phase transition temperatures. The double-chained quaternary
ammonium chlorides with higher degree of asymmetry in hydro-
thermogram recorded for G12
all these compounds are stable within the temperatures exhibiting
thermotropic phase behaviors.
A
12C is shown in Fig. 1. Upon heating,
carbon chain length such as G16
and T in comparison with the more symmetrical compound
14C bearing the same total carbon numbers with the two for-
A12C and G12A16C display lower
T
m
i
14
G A
DSC is a useful tool, which complements optical methods in the
study of liquid-crystalline phase transitions. To study the thermo-
tropic mesophase formation in more detail, DSC studies on the syn-
thesized compounds have been carried out. All transitions are
endothermic in the heating cycle and exothermic in the cooling cy-
mer compounds.
As shown in Fig. 3, hysteresis phenomenon occurs for all the
compounds when the clearing point is exceeded. The liquid crys-
talline crystal transition temperature shows more pronounced
supercooling during cooling scan when compared to isotropic
liquid crystalline transition temperature. For the nine double-
cle for the nine compounds. Typical thermogram of G12A12C is
illustrated in Fig. 2. On heating, these double-chained quaternary
ammonium salts show two endothermic peaks, they correspond
c
chained quaternary ammonium chlorides, the T is shifted down
to the crystal–liquid crystalline (T
pic (T ) transition temperatures, respectively. On cooling, all these
compounds show two exothermic peaks, they correspond to the
isotropic-liquid crystalline (T ) and liquid crystalline-crystal (T
transition temperatures, respectively [24,25]. All these compounds
m
) and liquid crystalline-isotro-
Table 1
i
Transition temperatures (T) and enthalpies
ammonium chlorides from DSC thermograms.
(
D
H) of double-chained quaternary
d
c
)
Compound
Heating
T °C
Cooling
À1
À1
D
H (kJ mol
)
T °C
D
H (kJ mol
)
G
12
G
14
G
16
G
14
G
16
G
12
G
12
G
14
G
16
A
A
A
A
A
A
A
A
A
12
C
14
C
16
C
12
C
12
C
14
C
16
C
16
C
14
C
120.4
59.8
2.3
68.1
1.9
80.9
1.7
58.1
2.1
56.9
1.9
64.4
2.4
63.9
1.9
62.6
1.4
141.8
85.5
139.2
89.7
129.3
92.2
139.6
83.8
135.7
81.6
143.1
94.8
137.5
84.9
133.9
93.1
2.3
53.7
1.6
65.6
1.2
80.8
2.0
54.6
1.7
58.6
2.0
67.6
1.8
62.0
1.3
62.2
1.9
1
45.5
120.0
44.0
119.1
36.0
118.0
44.1
113.3
41.0
120.7
1
1
1
1
1
46.7
15.3
42.6
1
116.3
39.7
117.4
39.8
1
72.3
1.8
134.0
88.7
1
71.8
Fig. 1. TGA trace of G12A12C registered in nitrogen upon heating at 10 °C/min.

1
30
Z. Ding, A. Hao / Journal of Molecular Structure 923 (2009) 127–131
for 34.9 (G12
2.2 (G16 12C), 25.9 (G12
and 28.7 °C (G16
A
12C), 30.3 (G14 16C), 34.2 (G14
A
14C), 26.9 (G16
A
A
A
12C),
16C),
3
A
A
14C), 30.4 (G12A16C), 23.2 (G14
A14C), respectively. This result shows that as
increasing the hydrocarbon chain length of these double-chained
quaternary ammonium chlorides, they display a less pronounced
thermal hysteresis in general.
As increasing hydrocarbon chain length for these double-
chained quaternary ammonium chlorides, the enthalpies of the
crystal–liquid crystalline phase transitions exhibits an increasing
tendency in general (see Table 1). The melting enthalpy of
16
G A16C is the highest among the nine compounds. This is expected
because the van der Waals interactions are stronger when the
number of aliphatic carbons increases [11,23,26]. However, the en-
thalpy change per methylene group is not constant (not shown),
but increases with hydrocarbon chain length, suggesting that mol-
ecules with longer hydrocarbon chain lengths give rise to more
favorable packing arrangement. On the other hand, the higher
asymmetry in hydrocarbon chain length induces lower melting en-
thalpy. The melting enthalpy of G16
A12C and G12A16C is lower than
that of G14 14C. It is also found from Table 1 that the enthalpy of
A
liquid-crystalline phase isotropic transition is at 1.4–2.3 kJ/mol,
which is relative small. Nematic and cholesteric liquid crystalline
compounds usually exhibit small enthalpies of liquid-crystalline
phase isotropic transition.
Fig. 4. Optical micrographs of double-chained quaternary ammonium chlorides
formed upon heating and cooling. (A) Oily-streak texture of G14 12C at 130 °C (upon
heating, 10Â); (B) schlieren texture of G16 12C at 132 °C (upon heating, 50Â); (C)
fan-shaped texture of G16
16C at 128 °C (upon cooling, 20Â); D maltese crosses of
12C at 128 °C (upon cooling, 10Â).
3
.2. Microscopy results
A
A
A
The thermal phase behaviors of the nine compounds have been
16
G A
observed under polarized light microscope, between slide and cov-
er slip. It has been found that all double-chain quaternary ammo-
nium chlorides display similar textures and seems independent of
the hydrocarbon chain length and symmetry. Thus, these pictures
shown in Fig. 4 are representative. The microphotographs of the
characteristic textures formed upon heating and cooling of these
double-chained quaternary ammonium chlorides are illustrated
in Fig. 4A–D. These characteristic textures observed for all the dou-
ble-chained quaternary ammonium chlorides include oily-streak,
schlieren, fan-shaped, and Maltese cross textures [12,27,28]. Oily
streak texture (Fig. 4A) is apparent during heating, and a schlieren
texture (Fig. 4B) is also observed in somewhere samples are rela-
tive thick.
imposed on the sample, such as slightly shearing, the fan-shaped
texture immediately transforms into oily-streak texture, which is
typical of cholesteric liquid crystals [29]. Maltese crosses are also
observed with thick samples during cooling. All the textures can
well recur for repeating observation. Optical changes occur at tem-
peratures in agreement with the DSC measurements for the nine
compounds.
3.3. X-ray results
When the isotropic state is cooled to deisotropic state, the fan-
shaped texture appears (see Fig. 4C). If a mechanical force is super-
Further insight into the structural properties of mesophase for
the double-chained quaternary ammonium chlorides is obtained
Fig. 3. Range of mesophase (shadow part) for double-chained quaternary ammonium chlorides upon heating (H) and cooling (C).

Z. Ding, A. Hao / Journal of Molecular Structure 923 (2009) 127–131
131
Maltese cross textures. XRD result shows that there is a sharp re-
flex in the small-angle region and a diffuse wide peak in the
wide-angle region for all compounds. All these confirm that these
compounds form cholesteric liquid crystal.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.molstruc.2009.02.013.
References
Fig. 5. XRD pattern of G12A12C at 130 °C upon heating.
[
[
1] I. Stella, A. Müller, Colloids Surf. A 147 (1999) 371.
2] M.C. Morán, A. Pinazo, P. Clapés, M.R. Infante, R. Pons, J. Phys. Chem. B 109
(
2005) 22899.
[
3] P.K. Bhowmik, H. Han, J.J. Cebe, R.A. Burchett, B. Acharya, S. Kumar, Liquid
Crystals 30 (2003) 1433.
4] D. Tsiourvas, C.M. Paleos, A. Skoulios, Liquid Crystals 26 (1999) 953.
by the examination of X-ray scattering data at mesophase transi-
tion temperature. It is found that all the double-chained quater-
nary ammonium salts exhibit similar packing arrangements of
liquid-crystalline phases. Typically, the XRD pattern of all the qua-
ternary ammonium chlorides in the liquid-crystalline phase con-
[
[5] A. Nikokavoura, D. Tsiourvas, M. Arkas, Z. Sideratou, C.M. Paleos, Liquid
Crystals 31 (2004) 207.
[
6] A. Mathis, M. Galin, J.C. Galin, B. Heinrich, C.G. Bazuin, Liquid Crystals 26
1999) 973.
[7] V. Vill, R. Hashim, Curr. Opin. Colloid Interface Sci. 7 (2002) 395.
(
sists of
a broad, high-angle diffraction peak near 2h = 20°
[
[
8] G. Milkereit, M. Morr, J. Tiem, V. Vill, Chem. Phys. Lipids 127 (2004) 47.
9] M. Arkas, D. Tsiourvas, C.M. Paleos, A. Skoulios, Chem. Eur. J. 15 (1999) 3202.
corresponding to the intralamellar spacing as shown in Fig. 5 But,
no diffraction peak is observed in small-angle region. Combining
the results of PLM with XRD, it can be concluded that the
double-chained quaternary ammonium chlorides form cholesteric
liquid crystal [29,30].
[
10] M.A. López-Quintela, A. Akahane, C. Rodríguez, H. Kunieda, J. Colloid Interface
Sci. 247 (2002) 186.
[11] E.F. Marques, R.O. Brito, Y. Wang, B.F.B. Silva, J. Colloid Interface Sci. 294 (2006)
40.
12] B.F.B. Silva, E.F. Marques, J. Colloid Interface Sci. 290 (2005) 267.
13] M. Arkas, K. Yannakopoulou, C.M. Paleos, P. Weber, A. Skoulios, Liquid Crystals
2
[
[
1
8 (1995) 563.
4
. Conclusion
[
[
14] M. Arkas, C.M. Paleos, A. Skoulios, Liquid Crystals 22 (1997) 735.
15] E. Alami, H. Levy, R. Zana, P. Weber, A. Skoulios, Liquid Crystals 13 (1993) 201.
Nine double-chained quaternary ammonium chlorides with
[16] M.D. Everaars, A.T.M. Marcelis, E.J.R. Sudhölter, Langmuir 16 (2000) 817.
[
[
[
17] T. Kunitake, Y. Okahata, J. Am. Chem. Soc. 99 (1977) 3860.
18] M. Dubois, T. Zemb, Langmuir 7 (1991) 1352.
19] C.D. Tran, P.L. Klahn, A. Romero, J.H. Fendler, J. Am. Chem. Soc. 100 (1978)
1622.
symmetric and asymmetric hydrocarbon chain length, N-(3-
alkoxyl-2-hydroxy)propyl-N-alkyl dimethylammonium chloride
+
À
R–O–CH
2
–CH(OH)–CH
2
–N (CH
3
)
2
–RÁCl (R: C12
H25, C14H29, C16H33),
1
[
[
20] S. Bhattacharya, M. Subramanian, U.S. Hiremath, Chem. Phys. Lipids 78 (1995)
have been synthesized and characterized by FT-IR, H NMR, MS
and elemental analysis. The thermotropic phase behaviors of these
compounds have been investigated by DSC, PLM and XRD. The ob-
tained results show that the hydrocarbon chain length and the
symmetry in the hydrocarbon chain length of these compounds
influence transition temperature, mesophase range, thermal hys-
tersis, and enthalpy changes in some degree, but exhibit little ef-
fect on the class of liquid crystal. The longer hydrocarbon chain
177.
21] S. Bhattacharya, S. Haldar, Langmuir 11 (1995) 4748.
[22] K. Urata, S. Yano, A. Kawamata, N. Takaishi, Y. Inamoto, J. Am. Oil Chem. Soc. 65
(1988) 1299.
[
[
23] A. Terreros, P.A.G. Gomez, E.L. Cabarcos, A. Müll, Colloids Surf. A 164 (2000) 47.
24] N. Filipovi c´ -Vincekovi c´ , I. Puci c´ , S. Popoci c´ , V. Tomaši c´ , D. Te zˇ ak, J. Colloid
Interface Sci. 188 (1997) 396.
[25] V. Tomaši c´ , J. Makarevi c´ , M. Joki c´ , Thermochim. Acta 444 (2006) 97.
[
[
26] Y. Wang, E.F. Marques, J. Phys. Chem. B 110 (2006) 1151.
27] D.J. Abdallah, A. Robertson, H. Hsu, R.G. Weiss, J. Am. Chem. Soc. 122 (2000)
m
length of these compounds leads to lower T , narrower mesophase
range, weaker thermal hystersis, and higher melting enthalpy, and
the higher asymmetry in the hydrocarbon chain length results in
3
053.
[28] V. Tomaši c´ , S. Popovi c´ , N. Filipovi c´ -Vincekovi c´ , J. Colloid Interface Sci. 215
1999) 280.
(
[
[
29] B.Y. Zhang, F.B. Meng, M. Tian, W.Q. Xiao, React. Funct. Polym. 60 (2006) 551.
30] Q.Z. Zhang, X. Sheng, X.Y. Yin, Y.P. Ji, G. Li, X.G. Zhao, Acta Chim. Sin. 61 (2003)
1478.
m
lower T and melting enthalpy. In the temperature of mesophase
range, all compounds show oily-streak, schlieren, fan-shaped and