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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.

The reduced viscosity of polymer guar gum solutions containing a certain concentration of sodium dodecyl benzene sulfonate (SDBS) was measured. It has been found that the Huggins coefficient k_H of polymer solutions is very sensitive to the concentration of the surfactant, c_SDBS, in solutions. If c_SDBS is lower than CMC, the critical micelle concentration of SDBS, k_H increases rapidly with c_SDBS. On the other hand, if c_SDBS is larger than CMC, k_H decreases rapidly with c_SDBS. Comparatively, the intrinsic viscosity of polymer solution does not show a notable change with c_SDBS. The experimental results indicate that the interchain association of polymer guar gum in solution is greatly associated with SDBS interacted with polymer chains through hydrogen bonds. However, the effect of SDBS upon the intrachain association of polymer guar gum solution is negligible, presumably due to the fact that guar gum is a slightly stiffened random-coil chain polymer.