We investigated the structure and viscoelastic properties of ternary gels of curdlan in mixed solvents of dimethyl sulfoxide (DMSO) and water as a function of the weight fraction of water φw to reveal the gelation mechanism. Dynamic viscoelasticity measurements demonstrated that the gelation begins to be induced by the addition of 1 wt % of water (i.e., φw = 0.01) and that the plateau modulus increases with increasing φw in the φw range up to 0.15. Spinlattice relaxation time T1 measurements using 1H-NMR technique revealed that there exist at least two different types of water with different T1 values in the ternary gel. By comparing those T1 values with that of the water proton in the mixed solvent, the water with shorter T1 (Water-1) was ascribed to the water molecules dispersed in the mixed solvent contained in the ternary gel. On the other hand, the water with the longer T1 (Water-2) was presumed to exist under the situation where water-water interaction is dominant. We hypothesized that Water-2 is localized around the vicinity of cross-linking points and is more relevant to the formation of cross-linking points. Almost a linear relation was observed between the plateau modulus Gc and the weight fraction of Water-2 φWater-2, indicating that the number of crosslinking points increases in proportion to φWater-2 in a constant volume of the ternary gel. Further, the distance between neighboring cross-linking points and the size of the region of Water-2 (i.e., equivalent spherical radius) was estimated at 15-9.3 nm and 2.1-2.5 nm depending on φWater-2, respectively. All these results support the validity of our hypothesis about Water-2.
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Condensed Matter Physics
- Mechanics of Materials
- Mechanical Engineering