Three-dimensional director fields studied by fluorescence confocal polarizing microscopy

We develop the technique of fluorescence confocal polarizing microscopy (FCPM) to image the three-dimensional (3D) director fields in soft matter. As compared to traditional Fluorescence Confocal Microscopy, the new features of FCPM are: (a) the light probe is polarized and (b) the dye is aligned by the liquid crystal (LC) host. The fluorescence signal depends on the angle a between the dye transition dipole (parallel to the local director) and polarizer, usually as I_FCPM∼cos4α. The resolution worsening due to the defocusing in a birefringent medium is proportional to zΔn, where z is the depth of scanning and Δn is the birefringence of LC. Therefore, we use LCs with low birefringence Δn ∼ 0.05. We illustrate the capabilities of FCPM on the examples of Frederiks transition in a nematic LC and focal conic domains in SmA. We prove the validity of the FCPM imaging by comparing the experimental and computer generated FCPM textures.; Using FCPM, we establish the 3D director patterns associated with dislocations in cholesteric LC. We demonstrate for the first time that the kinks along the b = p/2 dislocations are confined to the glide plane and are long, extending for length (5–10)p, where p is the pitch. The kinks along the b = p dislocation are of a typical size ∼p in all directions and form cusps pointed perpendicularly to the glide plane. At the cusp, the λ-disclinations of opposite sign interchange their ends. The edge dislocation in a confined lamellar system can glide towards or away from a rigid boundary, depending on the surface anchoring and bulk elasticity. We develop the coarse-grained model of cholesteric anchoring that explains the experimental results.; We employ FCPM to study the shape of meniscus and 31) director structures in the free-standing films of twist grain boundary (TGB) phases. We observe the radial pattern characteristic only for the meniscus of the TGB phases and attribute it to the layer undulations.; To conclude, we develop a new technique that is capable of 31) imaging of orientational order in LCs and explore the director structures that would be difficult to decipher by other techniques.