Effective rheology mapping for characterizing polymer solutions utilizing ultrasonic spinning rheometry

We propose a practical map representation termed rheology mapping for comprehensively evaluating the dependence of viscoelasticity on applied shear deformation and shear timescale represented by oscillation frequency, utilizing ultrasonic spinning rheometry, which has excellent applicability to a wide variety of polymer solutions. The rheology mapping was applied to two typical kinds of polymer solutions. One is carboxymethyl cellulose (CMC) aqueous solution, a well-known viscous and shear thinning fluid. The other is polyacrylamide (PAM) aqueous solution generally considered as a viscoelastic fluid while its viscoelasticity is difficult to be evaluated by a standard torque-type rheometer. The rheology mapping for the solutions showed notable rheological properties. The viscoelasticity of both the CMC and PAM solutions vary widely from elastic to viscous, depending on the applied shear rate, strain, and oscillation frequency. The mapping also revealed the clear dependence of the viscosity of the solutions: the CMC solutions on the shear rate and the PAM solutions on the shear strain. These results provide quantitative support of findings in other reports associating these macroscopic properties with the microscopic dynamics of polymer coils

Optical spinning rheometry test on viscosity curves of less viscous fluids at low shear rate range

We propose a method, named optical spinning rheometry (OSR), to acquire kinematic viscosity curves of Newtonian and non-Newtonian fluids in the same framework. The OSR is independent of torque measurements and utilizes velocity information measured by particle tracking velocimetry. This optical approach enables flexibility in velocity resolution, and benefits exploring the low shear rate region. In addition, the kinematic viscosity of less viscous fluids like water or dilute polymer solutions can be assessed as being free from the mechanical limitations of torque sensors. The applicable range of the OSR is discussed in detail, and its performance is verified in Newtonian fluids. Demonstrations in dilute xanthan gum solutions, concentrations of O(10 ppm), show the capability of measuring their shear-thinning behaviors and the kinematic viscosity curves even in the first Newtonian regime

A method for evaluating time-resolved rheological functionalities of fluid foods

We have developed an effective method for evaluating time-resolved rheological functionalities of swallowed foods using ultrasonic spinning rheometry (USR). USR can obtain variations over time in the rheological properties of fluids despite the fluids being in heterogeneous and nonequilibrium conditions. In addition, USR can evaluate time variations of shear-thinning property changing in a few seconds. Demonstrations were conducted with typical thickener solutions: starch, guar gum, and xanthan gum-based solutions, with alpha-amylase as a digestive enzyme. The flow curve of the starch-based solutions lowered with time, and a few minutes after addition of the amylase, the viscosity dropped to one-hundredth of the original value. In contrast, the guar gum- and xanthan gum-based solutions maintained the original viscosities as generally known. Applying the power law fitting to series of these flow curves, the time variation of the shear-thinning property is quantitatively characterized by the plots on typical K-n space, where K and n are parameters in the model, consistency index and power law exponent. The qualitative characteristics of the thickeners are successfully quantified in the K-n space, and this will be a practical tool for evaluating the time-resolved rheological properties of swallowed foods