How are Molecules in Liquid Crystals Spatially Arranged?

Liquid crystalline substances have physical properties similar to both solids and liquids. The materials flow like a liquid but possess the optical properties of some solids - directional dependent.  These behaviors are due to the orientational, but not positional, long-ranged ordering of their molecules. 

Crystalline Solid:

The positions and orientations of atoms and molecules relative to one another, within a crystalline solid, are fixed and repeats after a periodic distance.  The atoms and molecules within a crytalline solid are rigidly held in it position by strong intermolecular or ionic forces and chemical bonding.  Small amounts of motion are present due to thermal vibrations.  A schematic of this arrangement is illustrated in the picture immediately below. 
 

Liquid Crystal:

Smectic - 

Smectic liquid crystals are turbid and viscous substances.  Their molecules are arranged into eqidistant two-dimensional sheets.  The long axis of the molecules is perpendicular to or tilted by a certain angle to the face of the layers.  The lateral spacing between the molecules within a layer may be regular or random. Hydrogen-bonding between the polar groups link the molecules laterally and cooperatively to form head-to-head tail-to-tail bilayers. This class is further separated into several subclass, due to subtle differences.  A schematic of this arrangement is illustrated by the picture immediately below. 
 

Nematic - 

Nematic liquid crystals are so-named because of the thread-like optical patterns seen in thin-films of these substances.  These substances are less turbid and more mobile than the smectic liquid crystals.  They exhibit long-ranged orientational ordering in a preferred direction, with the long axis of their molecules aligned.   The molecules are randamly positioned, much like an ordinary liquid.  Usually formed by molecules that have no hydrogen- bonding functional groups and do not have both a polar and non-polar end.  A schematic of this arrangement is illustrated by the picture immediately below. 
 

Cholesteric - 

Cholesteric liquid crystals are also sometimes referred to as twisted- nematics.  These liquid crystals exhibit selective reflection and polarization of light.  The molecules are organized to form a stack of two-dimensional, equidistant sheets, like the smectic phase. However, through cooperative intermolecular interactions between the sheets, the orientation of molecules in each layer change by a fixed angle relative to each other to form a helical structure.  A characteric distance, peripendicular to the layers, such that the orientations of molecules within the layer completes a 360 degrees turn is known as the pitch of the liquid crystal.  This pitch is frequently similar to the wavelength of visible light, thus results in the diffraction of light.  This pitch is also sensitive to temperature and pressure changes       

Isotropic Liquid:

The molecules within a liquid are constant moving within the volume exhibiting a large degree of disorder and rapid fluctuations of position and orientation with time. Unlike a gas, whose volume contains a large amount of void space, the molecules of a liquid are not separated by long distances. As a consequence of this, a liquid have low compressibility. Unlike a crystalline solid, the molecules within a liquid do not occupy fixed positions or possess fixed orientations. The intermolecular forces acting between the molecules are also relatively strong. These forces are not strong enough to give the liquid rigidity, so that the liquid will conform to the shape of its container. They are of sufficient strength to give a liquid resistance to increase it surface area (surface tension) and resistance to flow (viscosity). Surface tension is caused by a balance between cohesive forces between the molecules within the liquid and adhesive forces between these molecules and other types of molecules at the liquid's interface, increasing with the strength of the attractive intermolecular forces. Viscosity also increases with the strength of the cohesive intermolecular forces. It is also affected by the size and length of the liquid's constituent molecules, where large and long molecules can entangle each other.  A schematic of this arrangement is illustrated by the picture immediately below.