INVESTIGATION OF GELLAN NETWORKS AND GELS BY ATOMIC-FORCE MICROSCOPY

Methods previously developed for the atomic force microscopy (AFM) ima ging of individual polysaccharides (Kirby, A. R.; Gunning, A. P.; Morr is, V. J. Biopolymers 1996, 38, 355-366) have been extended in order t o image networks and gels formed by the bacterial polysaccharide gella n gum. Networks were formed by air-drying solutions of K+ gellan onto freshly cleaved mica. AFM images were obtained in the direct current c ontact mode at constant force under butanol. Network formation can be inhibited by diluting the stock gellan solution or by converting K+ ge llan into the tetramethylammonium salt form. Inhibition of network for mation led to AFM images of heterogeneous populations of gellan aggreg ates (gel precursors). Attempts have been made to image the surface of bulk aqueous gellan gels under butanol. The quality of the images obt ained improved with increasing gel modulus. For rigid acid-set gellan gels, molecular resolution was achieved, revealing a bifurcated branch ed fibrous network.