Abstract
The phenomenon of thermoreversible gelation of methylcellulose (MC) in N, N-dimethyl formamide (DMF) is studied with respect to the earlier reported coil-Helix model. The proposed model in the MC-DMF system includes beads and rods in the existing coil helix model for gelation. In this new coil-helix-bead-rod system, the random coils are first converted to helixes on cooling, and these helixes may be the further aggregated into beads and rods. As observed under the SEM, the actual rod length is always greater than the size of a bead (2.5 μm). As observed from the modeling of gelation, the minimum number of helixes and beads in a chain has to be 14 × 109 and 5.6, respectively for gelation to occur. The process of gel-sol transition in the MC-DMF system (for 3 wt.% MC-88000) as studied through a differential scanning calorimeter (DSC) is divided into two parts, ranging from 71 to 92.9 °C and 91.9 to 107.5 °C. The primary peak at 75.6 °C indicates the disintegration of strongly associated rods into weakly associated beads, whereas the secondary peak at 91.9 °C indicates the disintegration of beads into a solution.
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