Hydrodynamic properties of aqueous solutions of galactomannans

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Abstract
Galactomannans were extracted from the seeds of seven different legumes to obtain samples which differed in average molecular weight, in polydispersity, and in average mannose‐to‐galactose ratio in the molecule. Measurements were made of the viscosities as a function of shear rate and of the sedimentation and diffusion coefficients of the aqueous solutions of all the galactomannans. Average molecular weights were calculated from the sedimentation and diffusion coefficients using the Svedberg equation. The Mark‐Houwink relationship between the intrinsic viscosity and the average molecular weights was found to hold for the series of galactomannans despite differences in the mannose‐to‐galactose ratios of the solutes. Estimates were made of the galactomannan polydispersities from both the sedimentation‐coeffient distributions and also from the diffusion‐coefficient ratios, Dm/DA. The two methods gave results in qualitative agreement. The hydrodynamic properties of the more homogeneous galactomannans were compared with the predictions of the Flory‐Fox hydro‐dynamic theory, with results very similar to those which were obtained for the water‐soluble synthetic cellulose derivatives, hydroxyethylcellulose and ethydroxycellulose.

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