Keiko Katsuta

Rheology of schizophyllan solutions in isotropic and anisotropic phase regions

In this paper, we discuss the rheological properties of aqueous solutions of a rigid triple-helical polysaccharide, schizophyllan (SPG), in isotropic, biphasic, and fully anisotropic phases. Both steady shear and dynamic rheological behaviors reveal remarkable changes when SPG solutions pass through the three phases. The steady shear flow exhibits shear thickening at low shear rates for anisotropic SPG liquid crystalline samples, which is attributed to the shear-induced cholesteric to nematic transformation. The first normal stress difference and transient rheological experiments demonstrate that director tumbling is absent or negligible in SPG liquid crystals in the range of examined shear rates. Additionally, the stress relaxation of SPG liquid crystals after flow cessation shows an inverse relation between the relaxation time and preshear rate, as expected by Larson and Mead’s theory [Larson and Mead (1989)]. Small amplitude oscillation measurements following flow cessation show decreasing complex modulus with time for SPG liquid crystals, which is probably related to an increase of molecular orientation after flow cessation. The evolutions of complex modulus after flow cessation are discussed in terms of chain persistence length.

Effects of sugars on stability of egg foam and their rheological properties

Publisher Summary This chapter studies the rheological property of foams and describes the effects of saccharides on the stability of foam systems. The linear viscoelastic region for foam systems under uniaxial compression is very narrow. The creep behavior for foam systems can be divided into three parts: elastic, viscoelastic, and steady flow part. The creep compliance and steady flow part of the foam systems decreases with increases in sugar concentration. The amounts of draining from the foam systems increase and the protein contents in drainage liquid decrease with standing time. The rate of draining is impeded when sucrose is added to albumen. Furthermore, the density of the foam systems becomes larger on addition of saccharides because the particle size of the gas cells becomes smaller and more homogeneous in the presence of sugar. The spin-spin relaxation times of foam systems, obtained by the Carr-Purcell-Meiboom-Gill (CPMG) method, becomes shorter on addition of sugar. It might be considered that saccharides prevent the mobility of water between the films of foam, therefore foam systems might be stabilized.

Application of the raised cosine pulse method to the systems having yield stress

Dynamic viscoelasticity of the systems having yield stress was measured using the raised cosine pulse (RCP) method by means of a cone‐plate type rheometer. The systems employed were mayonnaise and ketchup which are typical plastic materials. Influence of the amplitude of RCP strain on the convergence of the response stress was investigated. The response stress for a large RCP strain does not converge to zero. That is, the stress has a finite negative value still after a long time. In this case, the Fourier transformation of the response stress cannot be performed with a satisfied accuracy. On the other hand, the response stress converges to zero within a very short time for a small RCP stain and the frequency dependences of the dynamic moduli can be obtained, which are sufficiently congruent to them by the usual dynamic measurement.