SWELLING OF SCLEROGLUCAN GELS IN BINARY DMSO WATER SOLVENTS/

The aim of the present study is to investigate the correspondence betw een volume transitions of scleroglucan gels and the reported conformat ional properties of the uncrosslinked polymer chains. The swelling beh aviour of scleroglucan gels in binary solvent consisting of water and dimethylsulphoxide (DMSO) was investigated by first crosslinking aqueo us scleroglucan in cylindrical tubes. The resulting cylindrical gels w ere cut into small pieces and subsequently equilibrated for several da ys in the DMSO/H2O mixtures with weight fraction of water, W-H, rangin g from 0.0 to 1.0. The diameters of the gel pieces were observed using a calibrated phase contrast microscope. The experimental results obta ined at T = 20 degrees C show one volume transition at W-H = 0.1-0.15, and another at W-H = 0.8-0.9. The volume transition at W-H = 0.1-0.15 correlates with the reported dissociation of the scleroglucan tripler into random coils in mixed DMSO/water solvents at the same value of W -H. The reduction in gel volume for W-H < 0.1 is caused by the decreas ed mean-square end-to-end distance of the elastic segments in the diss ociated random coil compared to the tripler state. The second gel volu me transition at W-H = 0.8-0.9 occurs at the same value of W-H as the intra-triple helical transition in DMSO/water mixtures. This transitio n arises because of differences in the molecular interaction between p olymer and solvents. We found that the location of the second volume t ransition shifted towards smaller W-H with increasing temperature. Thi s is consistent with the reported stabilisation effect of DMSO on the low-temperature intra-triple-helical transition. The present study ind icates that the two macroscopic volume transitions of scleroglucan gel s reflect the conformational properties of the non-crosslinked polysac charide chains.