Thermogelation of methylcellulose from solution in N,N‐dimethylformamide and characterization of the transparent gels

Abstract

A transparent gel was prepared through the cooling of a methylcellulose (MC) solution in N,Ndimethylformamide (DMF) at 808C to a lower temperature. The temperature at which gelation occurred was dependent on the concentration of the solution. The gel temperature increased with an increase in the concentration of MC. The gelation of MC in DMF was studied by means of optical microscopy (OM), differential scanning calorimetry, and dynamic mechanical analysis (DMA). The OM studies revealed the presence of loosely bound beads of MC with DMF at a lower concentration. These beads became interconnected to rods, and subsequently, a continuous, thick gel was formed as the concentration increased. From DMA studies, it was observed that the loss modulus of the gel crossed over the storage modulus at two different frequencies. This indicated the presence of two types of network structures generated from the weak and strong associations of MC with the organic solvent DMF.

Studies on rheological, thermal, and morphological properties of methylcellulose gel in aqueous medium

“…Figure is the optical image, showing an amalgamation of two beads to form a single bead (10 m). On the other hand, the amalgamation of beads to form larger bead was not observed in MC‐DMF gels under optical microscope and SEM . In comparison to MC aqueous system, the gelation of MC‐DMF is due to polymer conformational changes during cooling.…”

“…Therefore, the internal energy is decreased resulting in the drop in entropy, and thus, the kinetic energy of beads may not be sufficient to collide to form the larger bead. So, the combination of beads manifests the formation of rods, leading to the formation of further strong gel network .…”

“…This shift in the peak toward higher frequency shows the greater tendency of gel to absorb vibrational energy (the reheating was done in a closed container to avoid evaporation losses). The reheating may induce the permanent association among MC helixes, which are irreversible . Thus, it is assumed that the weakly associated beads may already present in the reheated MC‐4000 before the second run of the experiment.…”

“…The inverse‐gelation phenomenon is rather considered to be hydrophobic and hydrophilic associations . During heating, the MC molecules get aggregated to form junction zones, micelles, helixes, beads, rods, core‑shell, and cage‐like structures . However, these conformations are schematically represented by Tanaka.…”

Rheological properties of methylcellulose aqueous gels under dynamic compression: Frequency sweep and validity of scaling law

“…The strength of the gel is derived from two different types of gel structures. The first type of structure of gel consists of the weakly associated molecules of MC separated apart and the second type is composed of the highly associated lumps of MC 12, 13. In Figure 1(g), a small increase in E ′ is initially observed, followed by the steep increase.…”