Viewing Liquid Crystal Phases Under the Microscope

The molecules in liquid crystals usually have anisotropic optical properties – the response to light depends on the direction the light comes from relative to the molecule. Thus, by passing polarized light through a liquid crystal specimen one can detect the alignment of the molecules.

Using a drop of Top Crest Dishcleaning Detergent (Lemon Fresh) on a microscope slide we could observe the orientation of the molecules. At full hydration the soap is in a micelle phase so soap molecules are pointing in all different directions. Consequently, no alignment effect is observed. However, as the soap dries it goes into a lamellar liquid phase giving rise to long tubes (myelin figures) and spherical bubbles (lipid bilayers arranged like the layers of skin on an onion). These are anisotropic and give long tubes and spherical blobs that wiggle with thermal energy. Typical objects are 20-40 microns in size.

Figure One : A stolen diagram from David Weitz’s group at Harvard that looks a bit lik our thin films on a good day. I couldn’t get the camera to mate with the microscope this afternoon.