A STUDY OF COLLOIDAL CRYSTAL MORPHOLOGY AND ORIENTATION VIA POLARIZING MICROSCOPY

We present microscopic observations of colloidal crystals grown in thin capillary cells. Observation between crossed polarizers reveals striations and polarization-dependent crystal colors. We employ dynamical diffraction theory to account for the depolarization of diffracted light in colloidal crystals and to correct Bragg diffraction wavelengths and intensities. Using Jones calculus, we predict crystal colors and intensities transmitted through crossed polarizers. We construct theoretical conoscopic images that provide a summary of the effect of crystal orientation on diffraction wavelength and intensity. Both striated and unstriated high volume fraction face-centered cubic (fcc) crystals often appear to orient with the (110) planes parallel to the cell walls. We show that striated crystals are twin fcc structures by determining the relative orientation between successive bands. We illustrate that as the volume fraction and cell thickness decrease, the tendency of the suspensions to crystallize with the (111) planes parallel to the cell walls increases while the number density of striated crystals decreases.