Thermal microscopy cross polarization

The characterization of liquid crystals by polarized light microscopy is the most straightforward method available and, whenever possible, it should be carried out in the initial stages of an investigation on new polymers. Thermal analyses alone can be misleading. In this procedure, a thin layer of the melt is kept at constant temperature on a hot-sta and obsawed between crossed polars. The appearance or texture of the melt is dependent on the structure of the mesophase, and, therefore, it is often possible to directly identify the type of mesophase present by this method. A good review of the microscopy of liquid crj b ajqjears in the books by Hartshome and by Demus and Richter... 

In many cases unique optical textures are observed for the various orientations and structures of the three classes of liquid crystals. Thin films of nematic crystals, for example, can be identified by the pattern of dark tlueads (isogyres) which can appear in the optical microscope in transmission with crossed polarizers. Hot stage polarizing optical nucroscopy is often used to identify the phases and the transition temperatures. In some cases, the optical texture is not uniquely identifiable and x-ray diffraction and thermal analysis by DSC are used to complement the microscopy. 

In terms of beam delivery, the DLW method is based on optical microscopy, confocal microscopy [4,6,13] and laser tweezers [14] (for reviews on laser tweezers see [ 15,16]). These techniques allow for a high spatial 3D resolution of a tightly focused laser beam with optical exposure of micrometric-sized volumes via linear and nonlinear absorption. In addition, mechanical and thermal forces can be exerted upon objects as small as 10 nm molecular dipolar alignment can be controlled by polarization of light in volumes of with submicrometric cross-sections. This circumstance widens the field of applications for laser nano- and microfabrication in liquid and solid materials [17-22]. 

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