Scleroglucan gel volume changes in dimethylsulphoxide/water and alkaline solutions are partly caused by polymer chain conformational transitions

The relative equilibrium volume, V/V0, of swollen scleroglucan gels was determined at temperatures T from 4 to 40°C in aqueous alkaline solutions and binary solvents containing water and dimethylsulphoxide (DMSO), respectively. In some of the experiments scleroglucan was crosslinked using sodium-meta-periodate. In others the crosslinks were Schiff bases between the polyaldehyde of scleroglucan and primary amines on small amounts of added chitosan. The V/V0 showed discontinuous changes at a water weight fraction WH=0.13, independent of the temperature from 4 to 40°C in DMSO/water solvents. The V/V0 of the gels decreased when the pH in aqueous solvents was raised above 13. Both these findings coincide with the known strand separation of the triple-helical structure occurring under these solvent conditions. An additional abrupt change in V/V0 occurred at WH=0.84 and T=20°C for the binary DMSO/water solvents. This transition was shifted towards lower WH for increasing temperatures, at T=40°C it occurred at WH=0.56, which is similar to the temperature effect of the intratriple-helical conformational transition of scleroglucan. This study indicates that the conformational transitions of the elastically active chains of the polymer network can affect the equilibrium volume of swollen polymer gels.