Interplay of Phase Separation and Thermoreversible Gelation in Aqueous Methylcellulose Solutions

Abstract

Rheology and turbidity measurements were performed under similar thermal histories to probe the relationship between thermoreversible gelation and phase separation for a set of three methylcellulose (MC) materials with similar degrees of substitution (DS) and contrasting molecular weights after hydration in cold water. Frequency-independent loss tangents were used to identify the gel point (T gel ) in MC solutions well over the chain overlap concentration (c ≥ 10c*). Transmittance of 633 nm laser light through the solutions revealed that all MC solutions cloud upon gelling, with a relative transmittance of 86% closely associated with the gel point. The gelation temperature of MC solutions was found to decrease with increasing MC concentration and the results for all molecular weights superposed. Using gel and cloud points, a phase diagram was constructed which reveals that clear MC solutions transition directly into turbid gels. Frequency-independent storage moduli of fully developed MC gels scaled with φ 2.3 , consistent with theory and experiment of entangled systems. Gelation of MC has strong dependence on heating rate while the melting of the gel has little dependence on cooling rate, suggesting that thermogelation of MC proceeded by a nucleation and growth mechanism rather than spinodal decomposition.

Thermal inverse phase transition of azobenzene hydroxypropylcellulose in aqueous solutions

“…Through another methodology, most researchers focus on using instrumental techniques to elucidate the thermodynamic mechanisms involved in the sol-gel transition and/or phase separation. These techniques include turbidity, laser light scattering, viscometry, rheology, differential scanning calorimetry (Arvidson et al 2012;Fairclough et al 2012;Lu et al 2002;Xu et al 2004), and recently by mid/near infrared spectroscopy (Jing and Wu 2013), small-angle neutron scattering combined with cryogenic transmission electron microscopy (cryo-TEM) (Lott et al 2013a, b;McAllister et al 2015). These studies demonstrate that the sol-gel transition is a spinodal process (Takeshita et al 2010) or a nucleation and growth mechanism (Arvidson et al 2012).…”

“…These techniques include turbidity, laser light scattering, viscometry, rheology, differential scanning calorimetry (Arvidson et al 2012;Fairclough et al 2012;Lu et al 2002;Xu et al 2004), and recently by mid/near infrared spectroscopy (Jing and Wu 2013), small-angle neutron scattering combined with cryogenic transmission electron microscopy (cryo-TEM) (Lott et al 2013a, b;McAllister et al 2015). These studies demonstrate that the sol-gel transition is a spinodal process (Takeshita et al 2010) or a nucleation and growth mechanism (Arvidson et al 2012). The cryo-TEM even revealed that MC chains associate into nanofibrils with uniform diameter of 15 ± 2 nm in the MC gels, which clearly explains the formation of optically turbid gel or precipitation (Lott et al 2013a, b;McAllister et al 2015).…”

Cellulose-Derivatives-Based Hydrogels as Vehicles for Dermal and Transdermal Drug Delivery

“…Recently, it was confirmed experimentally by rheological measurements that a nucleation and growth mechanism is also involved in the gelation of MC, as the gelation temperature depends on the heating rate [65].…”

Analysis of Water State and Gelation of Methylcellulose Thermo-reversible Hydrogels by Thermal Analysis and NMR

“…Because the gelation of MC hydrogels is a rate-dependent process, 18,19 simultaneous measurement is essential. Raman spectroscopy is a non-contact technique.…”

“…The development of a fibrillar structure with increasing temperature correlates with the rheological and turbidity behavior. 18,19 The MC-PEG-water system forms a thermo-reversible gel during heating. We have investigated the water state and dynamic mechanical property of an MC-PEG-water system and reported that the memory of the gel state was maintained for three days after gelation at 277 K. The period of maintaining the memory of the gel state after gelation is in agreement with the strength of the PEG-water interaction.…”