Structure and Properties of Aqueous Methylcellulose Gels by Small-Angle Neutron Scattering

Abstract

Cold, semidilute, aqueous solutions of methylcellulose (MC) are known to undergo thermoreversible gelation when warmed. This study focuses on two MC materials with much different gelation performance (gel temperature and hot gel modulus) even though they have similar metrics of their coarse-grained chemical structure (degree-of-methylether substitution and molecular weight distribution). Small-angle neutron scattering (SANS) experiments were conducted to probe the structure of the aqueous MC materials at pre- and postgel temperatures. One material (MC1, higher gel temperature) exhibited a single almost temperature-insensitive gel characteristic length scale (ζ(c) = 1090 ± 50 Å) at postgelation temperatures. This length scale is thought to be the gel blob size between network junctions. It also coincides with the length scale between entanglement sites measured with rheology studies at pregel temperatures. The other material (MC2, lower gel temperature) exhibited two distinct length scales at all temperatures. The larger length scale decreased as temperature increased. Its value (ζ(c1) = 1046 ± 19 Å) at the lowest pregel temperature was indistinguishable from that measured for MC1, and reached a limiting value (ζ(c1) = 450 ± 19 Å) at high temperature. The smaller length scale (ζ(c2) = 120 to 240 Å) increased slightly as temperature increased, but remained on the order of the chain persistence length (130 Å) measured at pregel temperatures. The smaller blob size (ζ(c1)) of MC2 suggests a higher bond energy or a stiffer connectivity between network junctions. Moreover, the number density of these blobs, at the same reduced temperature with respect to the gel temperature, is orders of magnitude higher for the MC2 gels. Presumably, the smaller gel length scale and higher number density lead to higher hot gel modulus for the low gel temperature material.

Testing Classical Approach to Polymer Solutions on SAXS Data of λ-Carrageenan, κ-Carrageenan and Methylcellulose Systems

“…This approach was namely originally developed and then also successfully applied mainly to the SANS data. [7][8][9][10][11][12][13][14][15] Even though there are some similar studies available also on the SAXS data nowadays, we still miss thorough systematic reports on such analysis of experimental SAXS data. The lack of such studies could be reasoned by the necessity of some additional considerations that must be dealt with the SAXS data, i.e.…”

“…1,2 Although KC and MC are very similar in structure, their gelling mechanisms differ significantly and have been extensively studied in the case of both polymers. [3][4][5][6][7] It is namely generally accepted that the gelation of KC is a two-step process, where initially the transition from coils to double helices occurs with cooling and with further reduction of the temperature the double helices start to crosslink and form a three dimensional network. This results in the formation of an elastic gel.…”

Methylcellulose, a Cellulose Derivative with Original Physical Properties and Extended Applications

“…Chatterjee et al found by SANS (small angle neutron scattering) that Lp may be equal to even 13.6 nm [53]. It was also proven that chains associate into thin stiff fibrils when concentration increases (to 10 g/L) at 25 °C [52].…”

Magnetic field responsive methylcellulose-polycaprolactone nanocomposite gels for targeted and controlled release of 5-fluorouracil

“…MC is broadly used as a binder or thickener in pharmaceuticals, foods, ceramics, and emulsifier in food, hair shampoos, toothpastes, liquid soaps, and cosmetic applications. MC demonstrates a specific lower critical solution temperature (LCST) phase behavior and suffers a two-stage thermo reversible gelation in aqueous solution with increasing temperature when the concentration is above a critical solution temperature value [1,2]. Researchers worked on the effect of salts on the gelation temperature of MC [3][4][5].…”