Rheological properties of the methylcellulose gels in N,N-dimethyl formamide: Validity of scaling laws

Abstract

The rheological behavior of the methylcellulose (MC) gels in N,N-dimethylformamide (DMF) was studied under dynamic compression with respect to the presence of various concentrations c (1, 2, 2.5 and 3 wt %) and different molecular weight M (4.1 × 104, 6.3 × 104 and 8.8 × 104) of MC in the gels. The temperature scan for the 1 wt % MC gel (M = 8.8 × 104) in DMF shows double crossover of the storage modulus E′ with the loss modulus E″. This indicates that two types of transitions namely the phase separated MC-DMF mixture to MC-DMF gel and MC-DMF gel to solution are present. The plot of storage modulus E′ with temperature shows almost plateau like behavior. This plateau like behavior may reflect the equilibrium between the core formation and core disintegration. In the frequency scan of MC gels, the modulus increases with an increase in the concentration. This can be explained by the increase in core structure of the gel. The core formation in the MC-DMF gel is a concentration dependent parameter. While comparing the different molecular weight grades of MC, it is observed that the storage modulus increases with an increase in the molecular weight of the MC. The validity of three scaling laws is also investigated with respect to various concentration of MC-88.000. The modified scaling law in terms of relative frequency and modulus \(\left( {\eta '_r = \frac{{\left| {\frac{{E''}} {\omega } - \left( {\frac{{E''}} {\omega }} \right)_c } \right|}} {{\left( {\frac{{E''}} {\omega }} \right)_c }}andE'_r = \frac{{\left| {E' - E'_c } \right|}} {{E'_c }}} \right) \) is seemed to be applicable.