Surface friction of gellan gels

The surface friction of three kinds of gellan gels, non-purified gellan gel, Ca2+ form gellan gel, and Na+ form gellan gel, has been investigated against a glass substrate in water and NaCl aqueous solution. The non-purified gellan gels exhibit the lowest friction in pure water, especially at a low sliding velocity, showing a frictional coefficient of 0.001. The frictional stresses of gellan gels increase with the increase of storage time in water or NaCl aqueous solution. Comparing with Ca2+-gellan gel and Na+-gellan gel, the non-purified gellan gel is more instable. Relatively low friction is observed in Na+-gellan gels in a salt concentration as high as 0.05 M. The low friction in a high ionic strength is attributed to the rigid double helical structure of the gel.