--- trunk/tengDissertation/LiquidCrystal.tex 2006/06/02 21:31:49 2785 +++ trunk/tengDissertation/LiquidCrystal.tex 2006/06/09 02:41:58 2839 @@ -7,37 +7,38 @@ exploited in great detail in the last two decades. Typ 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. +exploited in great detail in the last two decades\cite{Huh2004}. +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. 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 +supramolecular chemistry\cite{Niori1996, Link1997, Pelzl1999}. +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 $\text{SmCP}$\cite{Link1997}. 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}). +Fig.~\ref{LCFig:SMCP}). \begin{figure} \centering @@ -49,9 +50,9 @@ molecular structure and intermolecular interaction. Fr 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 +molecular structure and intermolecular interaction\cite{Reddy2006}. +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, @@ -62,22 +63,20 @@ limitation of time scale required for phase 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 direct transition to the -biaxial nematic, as well as some possible liquid crystal -phases\cite{Lansac2003}. Other anisotropic models using -Gay-Berne(GB) potential, which produce interactions that favor local -alignment, give the evidence of the novel packing arrangements of -bent-core molecules\cite{Memmer2002,Orlandi2006}. +limitation of time scale required for phase transition and the +length scale required for representing bulk behavior, +models\cite{Perram1985, Gay1981}, which are based on the observation +that liquid crystal order is exhibited by a range of non-molecular +bodies with high shape anisotropies, became the dominant models in +the field of liquid crystal phase behavior. 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 direct transition to the biaxial nematic, as well as some possible +liquid crystal phases\cite{Lansac2003}. Other anisotropic models +using Gay-Berne(GB) potential, which produce interactions that favor +local alignment, give the evidence of the novel packing arrangements +of bent-core molecules\cite{Memmer2002,Orlandi2006}. Experimental studies by Levelut {\it et al.}~\cite{Levelut1981} revealed that terminal cyano or nitro groups usually induce @@ -185,11 +184,11 @@ ratio between \textit{end-to-end} well depth $\epsilon \caption[]{} \label{LCFig:BananaMolecule} \end{figure} -\begin{figure} -\centering -\includegraphics[width=\linewidth]{bananGB.eps} -\caption[]{} \label{LCFigure:BananaGB} -\end{figure} +%\begin{figure} +%\centering +%\includegraphics[width=\linewidth]{bananGB.eps} +%\caption[]{} \label{LCFigure:BananaGB} +%\end{figure} \begin{figure} \centering