Index of content:
Volume 60, Issue 2, March 2016
60(2016); http://dx.doi.org/10.1122/1.4938525View Description Hide Description
The gelation behavior of κ-carrageenan in aqueous solution was studied by microdifferential scanning calorimetry and rheology. It was found that the formation and melting of κ-carrageenan hydrogels were thermally reversible and extremely sensitive to κ-carrageenan concentration. In comparison with the crossover of G′ and G″, the extrapolation method based on multiwave oscillation and Winter–Chambon criterion were able to give more accurate critical gel temperature Tc. At the gel point, the critical relaxation exponent n was almost constant whereas the critical gel strength Sg increased with κ-carrageenan concentration. In the stable gel state, the plateau modulus Ge depended on temperature according to a power-law scaling, Ge ∝ ε2.2, where ε is the relative distance (=|T − Tc|/Tc) and independent of κ-carrageenan concentration. The presence of potassium ions shifted the formation and melting temperatures of κ-carrageenan hydrogel to higher temperatures, and the temperatures for gel formation and melting increased with increasing potassium ions' content.
60(2016); http://dx.doi.org/10.1122/1.4939098View Description Hide Description
The improved anisotropic rotary diffusion (iARD) model was previously regarded as a suitable description of anisotropic orientation states for long fibers in concentrated suspensions. However, the iARD tensor does not pass the classic rheological rule of Euclidean objectivity, namely, material frame indifference. It is hard to ignore the nonobjective effect due to the fact that different coordinate systems may yield different answers. Such an issue can be attributed to the iARD tensor related to the nonobjective velocity-gradient tensor. We therefore proposed a new iARD tensor, which depends on the square of the objective rate-of-deformation tensor. It is important to differentiate between the original Phelps–Tucker anisotropic rotary diffusiontensor and the objective iARD tensor via computing their first invariants. Furthermore, we validated this new iARD model's accuracy in predicting a distinct, broader core-shell orientation structure of injection-molded long-fiber composites through careful experimental verification.
60(2016); http://dx.doi.org/10.1122/1.4938048View Description Hide Description
The present study develops an extension of the approach pioneered by Farris [Trans. Soc. Rheol. 12, 281–301 (1968)] to model the viscosity in polydisperse suspensions. Each smaller particle size class is assumed to contribute to the suspensionviscosity through a weighting function in two ways: first, indirectly, by altering the background viscosity, and second, directly, by increasing the contribution of the larger particles to the suspensionviscosity. The weighting functions are developed in a consistent fashion as a power law with the exponent, , a function of the relative volume fraction ratio and the base, , a function of the solid particle size ratio. The model is fit to available theoretical and experimental results for the viscosity of several binary suspensions and shows good to excellent agreement depending on the functions and chosen. Once parameterized using binary suspensionviscosity data, the predictive capability to model the viscosity of arbitrary continuous size distributions is realized by representing such distributions with equivalent ternary approximations selected to match the first six moments of the actual size distribution. Model predictions of the viscosity of polydisperse suspensions are presented and compared against experimental data.