McAllister John W, Lott Joseph R, Schmidt Peter W, Sammler Robert L, Bates Frank S, Lodge Timothy P
Materials Science and Engineering, The Dow Chemical Company, Midland, Michigan 48674, United States.
ACS Macro Lett. 2015 May 19;4(5):538-542. doi: 10.1021/acsmacrolett.5b00150. Epub 2015 Apr 21.
Cryogenic transmission electron microscopy and small-angle neutron scattering recently have revealed that the well-known thermoreversible gelation of methylcellulose (MC) in water is due to the formation of fibrils, with a diameter of 15 ± 2 nm. Here we report that both the linear and nonlinear viscoelastic response of MC solutions and gels can be described by a filament-based mechanical model. In particular, large-amplitude oscillatory shear experiments show that aqueous MC materials transition from shear thinning to shear thickening behavior at the gelation temperature. The critical stress at which MC gels depart from the linear viscoelastic regime and begin to stiffen is well predicted from the filament model over a concentration range of 0.18-2.0 wt %. These predictions are based on fibril densities and persistence lengths obtained experimentally from neutron scattering, combined with cross-link spacings inferred from the gel modulus via the same model.
低温透射电子显微镜和小角中子散射最近揭示，甲基纤维素（MC）在水中众所周知的热可逆凝胶化是由于形成了直径为15±2 nm的原纤维。在此我们报告，MC溶液和凝胶的线性和非线性粘弹性响应都可以用基于细丝的力学模型来描述。特别是，大振幅振荡剪切实验表明，水性MC材料在凝胶化温度下从剪切稀化转变为剪切增稠行为。在0.18 - 2.0 wt%的浓度范围内，细丝模型能很好地预测MC凝胶偏离线性粘弹性区域并开始变硬时的临界应力。这些预测基于通过中子散射实验获得的原纤维密度和持久长度，以及通过同一模型从凝胶模量推断出的交联间距。
