The colloidal and liquid crystal properties of surface modified chitin crystallites

Chitin crystallites were prepared from crab chitin using HCl hydrolysis. On avenge, the surface charge density of the chitin crystallites was calculated to be 0.5 e/nm2 based on conductimetric titration data. The formation of a chiral nematic phase in aqueous suspensions of chitin crystallites and the in situ texture of the crystallite suspensions were investigated using polarised optical microscopy and freeze-fracture transmission electron microscopy. The effect of the interparticle electrostatic interaction on phase separation has been explored through phase diagrams and the interaction energy was calculated based on experimental zeta potentials. The flow properties of the liquid crystalline phases of chitin crystallites have been studied rheologically. Shear thinning behaviour and a two-regime flow curve were observed for isotropic suspensions and biphasic suspensions respectively. A typical three-regime flow curve for liquid crystalline polymers was found for the anisotropic suspension of chitin crystallites. The maximum in the viscosity-concentration curve was found at the phase transition concentration: isotropic to biphasic. Chitin crystallites were systematically deacetylated using NaOH hydrolysis. It was found dud the reaction was pseudo first order. These modified crystallites are highly charged. Their phase behaviour contradicts the theoretical prediction by Stroobants et al. in addition, crystallites with a different extent of N-sulfonation were obtained in an aqueous medium using triethylamine/sulfur trioxide (TEA/SO3) by controlling the TEA/SO3 concentration used in the reaction. The colloidal behaviour of the suspension of the N-sulfonated crystallites was studied by plotting the zeta potential of the suspension as a function of the pH. Once the extent of N-sulfonation reached a certain level (80% or above), the chiral nematic; phase formed while below this level only the nematic phase was observed. TEM studies showed that the crystallites were well dispersed when the extent of N-sulfonation was above 80%.