AFM studies on gelation mechanism of xanthan gum hydrogels

The effect of annealing on xanthan gum molecules was investigated using atomic force microscopy (AFM). The values of height and width of xanthan gum molecules in AFM images are ca. 1 nm, which strongly indicates that xanthan gum molecules extended on the mica surface are in mono- or double layers. When xanthan gum aqueous solution was annealed, a network structure was observed. In contrast, a network structure was not observed for non-annealed solution. AFM images provide direct information concerning oscillational change of the network structure. It is concluded that xanthan gum molecular chains in aqueous solution aggregate and dissociate in an oscillational manner with increasing annealing time and that a homogeneous network structure was formed by annealing at 40 °C for 24 h.