trunk/tengDissertation/LiquidCrystal.tex

\chapter{\label{chapt:liquidcrystal}LIQUID CRYSTAL}

\section{\label{liquidCrystalSection:introduction}Introduction}
% liquid crystal

Long range orientational order is one of the most fundamental
properties of liquid crystal mesophases. This orientational
anisotropy of the macroscopic phases originates in the shape
anisotropy of the constituent molecules. Among these anisotropy
mesogens, rod-like (calamitic) and disk-like molecules have been
exploited in great detail in the last two decades. Typically, these
mesogens consist of a rigid aromatic core and one or more attached
aliphatic chains. For short chain molecules, only nematic phases, in
which positional order is limited or absent, can be observed,
because the entropy of mixing different parts of the mesogens is
paramount to the dispersion interaction. In contrast, formation of
the one dimension lamellar sematic phase in rod-like molecules with
sufficiently long aliphatic chains has been reported, as well as the
segregation phenomena in disk-like molecules.

% banana shaped
Recently, the banana-shaped or bent-core liquid crystal have became
one of the most active research areas in mesogenic materials and
supramolecular chemistry. Unlike rods and disks, the polarity and
biaxiality of the banana-shaped molecules allow the molecules
organize into a variety of novel liquid crystalline phases which
show interesting material properties. Of particular interest is the
spontaneous formation of macroscopic chiral layers from achiral
banana-shaped molecules, where polar molecule orientational ordering
is shown within the layer plane as well as the tilted arrangement of
the molecules relative to the polar axis. As a consequence of
supramolecular chirality, the spontaneous polarization arises in
ferroelectric (FE) and antiferroelectic (AF) switching of smectic
liquid crystal phases, demonstrating some promising applications in
second-order nonlinear optical devices. The most widely investigated
mesophase formed by banana-shaped moleculed is the $\text{B}_2$
phase, which is also referred to as $\text{SmCP}$. Of the most
important discover in this tilt lamellar phase is the four distinct
packing arrangements (two conglomerates and two macroscopic
racemates), which depend on the tilt direction and the polar
direction of the molecule in adjacent layer (see
Fig.~\cite{LCFig:SMCP}).

%general banana-shaped molecule modeling
Many liquid crystal synthesis experiments suggest that the
occurrence of polarity and chirality strongly relies on the
molecular structure and intermolecular interaction. From a
theoretical point of view, it is of fundamental interest to study
the structural properties of liquid crystal phases formed by
banana-shaped molecules and understand their connection to the
molecular structure, especially with respect to the spontaneous
achiral symmetry breaking. As a complementary tool to experiment,
computer simulation can provide unique insight into molecular
ordering and phase behavior, and hence improve the development of
new experiments and theories. In the last two decades, all-atom
models have been adopted to investigate the structural properties of
smectic arrangements\cite{Cook2000, Lansac2001}, as well as other
bulk properties, such as rotational viscosity and flexoelectric
coefficients\cite{Cheung2002, Cheung2004}. However, due to the
limitation of time scale required for phase
transition\cite{Wilson1999} and the length scale required for
representing bulk behavior, the dominant models in the field of
liquid crystal phase behavior are generic
models\cite{Lebwohl1972,Perram1984, Gay1981}, which are based on the
observation that liquid crystal order is exhibited by a range of
non-molecular bodies with high shape anisotropies. Previous
simulation studies using hard spherocylinder dimer
model\cite{Camp1999} produce nematic phases, while hard rod
simulation studies identified a Landau point\cite{Bates2005}, at
which the isotropic phase undergoes a transition directly to the
biaxial nematic, as well as some possible liquid crystal
phases\cite{Lansac2003}. Other anisotropic models using Gay-Berne
potential give the evidence of the novel packing arrangement of
bent-core molecules\cite{Memmer2002,Orlandi2006}.

\section{\label{liquidCrystalSection:model}Model}

\section{\label{liquidCrystalSection:methods}Methods}

\section{\label{liquidCrystalSection:resultDiscussion}Results and Discussion}
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#	User	Rev	Content
1	tim	2685	\chapter{\label{chapt:liquidcrystal}LIQUID CRYSTAL}
2
3			\section{\label{liquidCrystalSection:introduction}Introduction}
4	tim	2781	% liquid crystal
5	tim	2685
6	tim	2781	Long range orientational order is one of the most fundamental
7			properties of liquid crystal mesophases. This orientational
8			anisotropy of the macroscopic phases originates in the shape
9			anisotropy of the constituent molecules. Among these anisotropy
10			mesogens, rod-like (calamitic) and disk-like molecules have been
11			exploited in great detail in the last two decades. Typically, these
12			mesogens consist of a rigid aromatic core and one or more attached
13			aliphatic chains. For short chain molecules, only nematic phases, in
14			which positional order is limited or absent, can be observed,
15			because the entropy of mixing different parts of the mesogens is
16			paramount to the dispersion interaction. In contrast, formation of
17			the one dimension lamellar sematic phase in rod-like molecules with
18			sufficiently long aliphatic chains has been reported, as well as the
19			segregation phenomena in disk-like molecules.
20
21			% banana shaped
22			Recently, the banana-shaped or bent-core liquid crystal have became
23			one of the most active research areas in mesogenic materials and
24			supramolecular chemistry. Unlike rods and disks, the polarity and
25			biaxiality of the banana-shaped molecules allow the molecules
26			organize into a variety of novel liquid crystalline phases which
27			show interesting material properties. Of particular interest is the
28			spontaneous formation of macroscopic chiral layers from achiral
29			banana-shaped molecules, where polar molecule orientational ordering
30			is shown within the layer plane as well as the tilted arrangement of
31			the molecules relative to the polar axis. As a consequence of
32			supramolecular chirality, the spontaneous polarization arises in
33			ferroelectric (FE) and antiferroelectic (AF) switching of smectic
34			liquid crystal phases, demonstrating some promising applications in
35	tim	2782	second-order nonlinear optical devices. The most widely investigated
36			mesophase formed by banana-shaped moleculed is the $\text{B}_2$
37			phase, which is also referred to as $\text{SmCP}$. Of the most
38			important discover in this tilt lamellar phase is the four distinct
39			packing arrangements (two conglomerates and two macroscopic
40			racemates), which depend on the tilt direction and the polar
41			direction of the molecule in adjacent layer (see
42			Fig.~\cite{LCFig:SMCP}).
43	tim	2781
44	tim	2782	%general banana-shaped molecule modeling
45			Many liquid crystal synthesis experiments suggest that the
46			occurrence of polarity and chirality strongly relies on the
47			molecular structure and intermolecular interaction. From a
48			theoretical point of view, it is of fundamental interest to study
49			the structural properties of liquid crystal phases formed by
50			banana-shaped molecules and understand their connection to the
51			molecular structure, especially with respect to the spontaneous
52			achiral symmetry breaking. As a complementary tool to experiment,
53			computer simulation can provide unique insight into molecular
54			ordering and phase behavior, and hence improve the development of
55			new experiments and theories. In the last two decades, all-atom
56			models have been adopted to investigate the structural properties of
57			smectic arrangements\cite{Cook2000, Lansac2001}, as well as other
58			bulk properties, such as rotational viscosity and flexoelectric
59			coefficients\cite{Cheung2002, Cheung2004}. However, due to the
60			limitation of time scale required for phase
61			transition\cite{Wilson1999} and the length scale required for
62			representing bulk behavior, the dominant models in the field of
63			liquid crystal phase behavior are generic
64			models\cite{Lebwohl1972,Perram1984, Gay1981}, which are based on the
65			observation that liquid crystal order is exhibited by a range of
66			non-molecular bodies with high shape anisotropies. Previous
67			simulation studies using hard spherocylinder dimer
68			model\cite{Camp1999} produce nematic phases, while hard rod
69			simulation studies identified a Landau point\cite{Bates2005}, at
70			which the isotropic phase undergoes a transition directly to the
71			biaxial nematic, as well as some possible liquid crystal
72			phases\cite{Lansac2003}. Other anisotropic models using Gay-Berne
73			potential give the evidence of the novel packing arrangement of
74			bent-core molecules\cite{Memmer2002,Orlandi2006}.
75	tim	2781
76	tim	2685	\section{\label{liquidCrystalSection:model}Model}
77
78			\section{\label{liquidCrystalSection:methods}Methods}
79
80			\section{\label{liquidCrystalSection:resultDiscussion}Results and Discussion}