The role of pH, temperature and nucleation in the formation of cholesteric liquid crystal spherulites from chitin and chitosan

Abstract

The alpha chitin and chitosan used in the experiments came from crab shell waste (Sigma). This was treated to form a colloidal suspension of chitin or chitosan crystallites. The electrostatic 'charge coat' surrounding the chitin was then manipulated. This was achieved by alteration of the pH of the chitin or chitosan colloid (Chitin pKa = 6.1). This allowed the charge density on the crystalline rod of chitin or chitosan to be altered. The effect of this treatment was ascertained by measuring the diameter of spherulites formed in vitro. The results were analysed to see if the experimental optimal pH agreed with theoretical approximations. Further investigations were carried out on the initiation of the spherulites and the effect of temperature on spherulite formation. The spherulites form via self assembly through a liquid crystalline cholesteric phase. Manipulation of the electrostatic coat of the chitin could be a method of cellular remote control for formation of the helicoid in arthropod cuticle. This would allow the arthropods to set up conditions that aid the self assembly process.