The tetrahedral borate ion can crosslink with polymer guar gum in aqueous solutions. If the concentration of guar gum is less than 0.045 g/dL

the intramolecular interaction between guar gum and borate ion increases due to the formation of crosslinks. As a result

the polymer chains of guar gum in solution shrink in size and the reduced viscosity of polymer solution decreases accordingly. On the other hand

if the concentration of guar gum is greater than 0.045 g/dL

the intermolecular interaction becomes apparent due to the same reason. The polymer chains

therefore

associate together and the reduced viscosity of polymer solution increases considerably. According to this technique

the critical concentration c*

presented by de-Gennes[1]

is determined successfully.