Three dimension Liesegang rings of calcium hydrophosphate in gelatin

Abstract

Three dimensional Liesegang spherical layers of CaHPO4 in gelatin ball were performed by employing CaCl2 and Na2HPO4 as the inner and outer electrolyte, respectively. Effects of concentrations of inner and outer electrolyte as well as pH on the morphologies of Liesegang rings (LRs) were investigated. As a result, it was observed that the time law, spacing law and width law found in 1D/2D gel systems were obeyed in this 3D gelatin system. The interaction of Ca2+ and HPO4 2− with gelatin matrix played a key role to the formation of LRs due to the existence of carboxylic groups on the gelatin chains. Using Ca2+ as the inner electrolyte, LRs were prepared. However, employing HPO4 2− as inner electrolyte, LRs were not obtained. Moreover, pH of gelatin solution greatly impacted on the formation of LRs. The number of LRs increased with the decrease of pH, whereas the width inversely decreased. pH 4.40 was a turn point, from which the spacing coefficient abruptly increased as pH increased. All these results indicated that the network was created by the interaction of Ca2+ and –COO− of gelatin chains, which dominated the formation of CaHPO4 LRs in gelatin.