| 7 |
|
anisotropy of the macroscopic phases originates in the shape |
| 8 |
|
anisotropy of the constituent molecules. Among these anisotropy |
| 9 |
|
mesogens, rod-like (calamitic) and disk-like molecules have been |
| 10 |
< |
exploited in great detail in the last two decades. Typically, these |
| 11 |
< |
mesogens consist of a rigid aromatic core and one or more attached |
| 12 |
< |
aliphatic chains. For short chain molecules, only nematic phases, in |
| 13 |
< |
which positional order is limited or absent, can be observed, |
| 14 |
< |
because the entropy of mixing different parts of the mesogens is |
| 15 |
< |
paramount to the dispersion interaction. In contrast, formation of |
| 16 |
< |
the one dimension lamellar sematic phase in rod-like molecules with |
| 17 |
< |
sufficiently long aliphatic chains has been reported, as well as the |
| 18 |
< |
segregation phenomena in disk-like molecules. |
| 10 |
> |
exploited in great detail in the last two decades\cite{Huh2004}. |
| 11 |
> |
Typically, these mesogens consist of a rigid aromatic core and one |
| 12 |
> |
or more attached aliphatic chains. For short chain molecules, only |
| 13 |
> |
nematic phases, in which positional order is limited or absent, can |
| 14 |
> |
be observed, because the entropy of mixing different parts of the |
| 15 |
> |
mesogens is paramount to the dispersion interaction. In contrast, |
| 16 |
> |
formation of the one dimension lamellar sematic phase in rod-like |
| 17 |
> |
molecules with sufficiently long aliphatic chains has been reported, |
| 18 |
> |
as well as the segregation phenomena in disk-like molecules. |
| 19 |
|
|
| 20 |
|
Recently, the banana-shaped or bent-core liquid crystal have became |
| 21 |
|
one of the most active research areas in mesogenic materials and |
| 22 |
< |
supramolecular chemistry. Unlike rods and disks, the polarity and |
| 23 |
< |
biaxiality of the banana-shaped molecules allow the molecules |
| 24 |
< |
organize into a variety of novel liquid crystalline phases which |
| 25 |
< |
show interesting material properties. Of particular interest is the |
| 26 |
< |
spontaneous formation of macroscopic chiral layers from achiral |
| 27 |
< |
banana-shaped molecules, where polar molecule orientational ordering |
| 28 |
< |
is shown within the layer plane as well as the tilted arrangement of |
| 29 |
< |
the molecules relative to the polar axis. As a consequence of |
| 30 |
< |
supramolecular chirality, the spontaneous polarization arises in |
| 31 |
< |
ferroelectric (FE) and antiferroelectic (AF) switching of smectic |
| 32 |
< |
liquid crystal phases, demonstrating some promising applications in |
| 33 |
< |
second-order nonlinear optical devices. The most widely investigated |
| 34 |
< |
mesophase formed by banana-shaped moleculed is the $\text{B}_2$ |
| 35 |
< |
phase, which is also referred to as $\text{SmCP}$. Of the most |
| 22 |
> |
supramolecular chemistry\cite{Niori1996, Link1997, Pelzl1999}. |
| 23 |
> |
Unlike rods and disks, the polarity and biaxiality of the |
| 24 |
> |
banana-shaped molecules allow the molecules organize into a variety |
| 25 |
> |
of novel liquid crystalline phases which show interesting material |
| 26 |
> |
properties. Of particular interest is the spontaneous formation of |
| 27 |
> |
macroscopic chiral layers from achiral banana-shaped molecules, |
| 28 |
> |
where polar molecule orientational ordering is shown within the |
| 29 |
> |
layer plane as well as the tilted arrangement of the molecules |
| 30 |
> |
relative to the polar axis. As a consequence of supramolecular |
| 31 |
> |
chirality, the spontaneous polarization arises in ferroelectric (FE) |
| 32 |
> |
and antiferroelectic (AF) switching of smectic liquid crystal |
| 33 |
> |
phases, demonstrating some promising applications in second-order |
| 34 |
> |
nonlinear optical devices. The most widely investigated mesophase |
| 35 |
> |
formed by banana-shaped moleculed is the $\text{B}_2$ phase, which |
| 36 |
> |
is also referred to as $\text{SmCP}$\cite{Link1997}. Of the most |
| 37 |
|
important discover in this tilt lamellar phase is the four distinct |
| 38 |
|
packing arrangements (two conglomerates and two macroscopic |
| 39 |
|
racemates), which depend on the tilt direction and the polar |
| 50 |
|
|
| 51 |
|
Many liquid crystal synthesis experiments suggest that the |
| 52 |
|
occurrence of polarity and chirality strongly relies on the |
| 53 |
< |
molecular structure and intermolecular interaction. From a |
| 54 |
< |
theoretical point of view, it is of fundamental interest to study |
| 55 |
< |
the structural properties of liquid crystal phases formed by |
| 53 |
> |
molecular structure and intermolecular interaction\cite{Reddy2006}. |
| 54 |
> |
From a theoretical point of view, it is of fundamental interest to |
| 55 |
> |
study the structural properties of liquid crystal phases formed by |
| 56 |
|
banana-shaped molecules and understand their connection to the |
| 57 |
|
molecular structure, especially with respect to the spontaneous |
| 58 |
|
achiral symmetry breaking. As a complementary tool to experiment, |
| 63 |
|
smectic arrangements\cite{Cook2000, Lansac2001}, as well as other |
| 64 |
|
bulk properties, such as rotational viscosity and flexoelectric |
| 65 |
|
coefficients\cite{Cheung2002, Cheung2004}. However, due to the |
| 66 |
< |
limitation of time scale required for phase |
| 67 |
< |
transition\cite{Wilson1999} and the length scale required for |
| 68 |
< |
representing bulk behavior, the dominant models in the field of |
| 69 |
< |
liquid crystal phase behavior are generic |
| 70 |
< |
models\cite{Lebwohl1972,Perram1984, Gay1981}, which are based on the |
| 71 |
< |
observation that liquid crystal order is exhibited by a range of |
| 72 |
< |
non-molecular bodies with high shape anisotropies. Previous |
| 73 |
< |
simulation studies using hard spherocylinder dimer |
| 74 |
< |
model\cite{Camp1999} produce nematic phases, while hard rod |
| 75 |
< |
simulation studies identified a Landau point\cite{Bates2005}, at |
| 76 |
< |
which the isotropic phase undergoes a direct transition to the |
| 77 |
< |
biaxial nematic, as well as some possible liquid crystal |
| 78 |
< |
phases\cite{Lansac2003}. Other anisotropic models using |
| 79 |
< |
Gay-Berne(GB) potential, which produce interactions that favor local |
| 79 |
< |
alignment, give the evidence of the novel packing arrangements of |
| 80 |
< |
bent-core molecules\cite{Memmer2002,Orlandi2006}. |
| 66 |
> |
limitation of time scale required for phase transition and the |
| 67 |
> |
length scale required for representing bulk behavior, |
| 68 |
> |
models\cite{Perram1985, Gay1981}, which are based on the observation |
| 69 |
> |
that liquid crystal order is exhibited by a range of non-molecular |
| 70 |
> |
bodies with high shape anisotropies, became the dominant models in |
| 71 |
> |
the field of liquid crystal phase behavior. Previous simulation |
| 72 |
> |
studies using hard spherocylinder dimer model\cite{Camp1999} produce |
| 73 |
> |
nematic phases, while hard rod simulation studies identified a |
| 74 |
> |
Landau point\cite{Bates2005}, at which the isotropic phase undergoes |
| 75 |
> |
a direct transition to the biaxial nematic, as well as some possible |
| 76 |
> |
liquid crystal phases\cite{Lansac2003}. Other anisotropic models |
| 77 |
> |
using Gay-Berne(GB) potential, which produce interactions that favor |
| 78 |
> |
local alignment, give the evidence of the novel packing arrangements |
| 79 |
> |
of bent-core molecules\cite{Memmer2002,Orlandi2006}. |
| 80 |
|
|
| 81 |
|
Experimental studies by Levelut {\it et al.}~\cite{Levelut1981} |
| 82 |
|
revealed that terminal cyano or nitro groups usually induce |
