In vitro chiral nematic ordering of chitin crystallites.

Microfibrillar fragments of purified crab and shrimp chitin were prepared by hydrolysis in 3 M HCl at its boiling point (104 degrees C). After removal of the acid by centrifugal washing and dialysis, an ultrasound treatment converts the residual product to a colloidal suspension stabilized by NH3+ charges. When dewatered to a critical concentration, spontaneous formation of a two-phase equilibrium system system occurs. The upper phase (lower concentration) is isotropic and the lower phase is anisotropic. The latter displays chiral nematic order and dries to a solid film which mimics the helicoid organization characteristic of the chitin microfibrils in the cuticle of arthropods.